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                                     Chapter 9. Nervous System

          Multicellular animals must monitor and maintain a constant internal environment as well as
monitor and respond to an external environment. In many animals, these two functions are coordinated by
two integrated and coordinated organ systems: the nervous system and the endocrine system. Three basic
functions are performed by nervous systems: (a) Receive sensory input from internal and external
environments (Sensory Function), (b) Integrate the input (Integrative Function), and (c) Respond to
stimuli (Motor Function).
 Sensory Input. Receptors are parts of the nervous system that sense changes in the internal or external
   environments. Sensory input can be in many forms, including pressure, taste, sound, light, blood pH, or
   hormone levels, that are converted to a signal and sent to the brain or spinal cord.
 Integration and Output. In the sensory centers of the brain or in the spinal cord, the barrage of input
   is integrated and a response is generated. The response, a motor output, is a signal transmitted to organs
   than can convert the signal into some form of action, such as movement, changes in heart rate, release
   of hormones, etc.

The Nervous System is divided into two major parts:
 The Central Nervous System (CNS) consists of the brain and the spinal cord. The spinal cord carries
  messages from the body to the brain, where they are analyzed and interpreted. Response messages are
  then passed from the brain through the spinal cord and to the rest of the body.
 The Peripheral Nervous System (PNS) consists of the neurons not included in the brain and spinal
  cord. Some peripheral neurons collect information from the body and transmit it towards the CNS.
  These are called afferent neurons. Other peripheral neurons transmit Information away from the
  CNS. These are called efferent neurons.

MENINGES OF CNS

         The central nervous system of humans is protected by three connective tissue membranes
collectively called as meninges. These are (a) Piamater, (b) Arachnoid, and (c) Duramater.




                      Fig. 9.1. C.S. of skull showing the three meninges of brain.


  (a) Piamater. It is the innermost covering lying in close contact with the brain. It is richly supplied
      with blood vessels. It is attached with the brain at two points forming choroid plexus for the
      secretion of CSF. These two points are epithalamus and roof of medulla oblongata.
  (b) Arachnoid. It is the middle layer and also vascular. The space present between piamater and
      arachnoid is termed as subarachnoid space where blood vessels are present.
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  (c) Duramater. It is the outermost, thick, double layered and non-vascular. The outer layer of
      duramater is fixed with the cranium inside. The space between arachnoid and duramater is termed
      as subdural space.

CENTRAL NERVOUS SYSTEM

         The Central Nervous System (CNS) is composed of the brain and spinal cord, which are
responsible for the most complicated functions of the human and other organisms. The CNS is composed
of the grey and white matter. The grey matter represents a collection of non-myelinated nerve fibres and
nerve cells (neurons) while the white matter consists of processes of these cells and white medullated
nerve fibres. Nerve cells or neurons are absent in the white matter. The neuroglia (glial cells) surrounds
the nerve cells (neurons). The part of CNS, i.e. the brain is lodged in the skull (or cranium) and the spinal
cord is protected by the vertebral column. Fluid and tissue also insulate the brain and spinal cord. The
brain is composed of three main parts: Forebrain, Midbrain and Hindbrain.

FOREBRAIN
         The forebrain is the largest and most complex part of the brain. It consists of the cerebrum (the
area with all the folds and grooves), diencephalon and the olfactory lobes.
(A) Cerebrum.
         It is the largest and most developed part of the brain divided into two parts by a prominent
longitudinal fissure known as Sylvian fissure. These two parts are called as left cerebral hemisphere and
right cerebral hemisphere, connected in the middle by a band known as corpus callosum made up of
large bundle of myelinated fibres. It enables the two hemispheres to communicate with each other. The
left side is considered the logical, analytical and objective side. The right side is thought to be more
intuitive, creative and subjective. Collectively, the cerebrum governs intelligence and reasoning, learning
and memory.
         Each cerebral hemisphere is highly folded into gyri (convolutions) and sulci (depressions). These
folding increase the surface area of the brain. The outer layer of cerebrum is the cerebral cortex made up
of grey matter. Information collected by the five senses comes into the brain from the spinal cord to the
cortex. This information is then directed to other parts of the nervous system for further processing. The
inner layer of the cerebrum is the cerebral medulla made up of white matter. Each cerebral hemisphere is
divided into four lobes known as frontal, parietal, temporal, and occipital.

  LOBES              FUNCTIONAL AREAS                                     FUNCTIONS
 Frontal      (i) Pre central (motor) area         (i) Controls voluntary muscular movements.
 lobes        (ii) Premotor Area                   (ii) Controls involuntary muscular movements.
              (iii) Motor speech centre (Broca’s   (iii) Controls delivery of speech.
                    area)
              (iv) Frontal association area        (iv) Most important part associated with memory,
                                                         learning and reasoning.
 Parietal     (i) Post central (sensory) area or   (i) Perceives sensation of pain, temperature,
 lobes             somesthetic area.                     pressure and touch.
              (ii) Gustatory (taste) area.         (ii) Interprets nerve impulses from the tongue.
                                                         Perceives sense of taste.
              (iii) Sensory speech area.           (iii) Perceives the spoken words.
              (iv) Parietal association area.      (iv) Same as frontal association area.
 Temporal     (i) Olfactory area.                  (i) Receives impulse from the nose, perceives sense
 lobes                                                   of smell.
              (ii) Auditory area.                  (ii) Centre of hearing.
              (iii) Wernicke’s area.               (iii) Responsible for understanding speech.
              (iv) Temporal association area.      (iv) Same as frontal association area.
 Occipital    (i) Visual area.                     (i) Centre for sight.
 lobes        (ii) Visual association area.        (ii) Same as frontal association area.

                    Table. 9.1. Four lobes of cerebrum with their functional areas.
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             Fig. 9.2. Lateral view of human brain showing important functional areas.


(B) Diencephalon.
        It is a part of the forebrain consisting of the thalamus (mid part), hypothalamus (floor) and
epithalamus (roof).
 (i) Thalamus is the largest paired structure constituting most of      Limbic system comprises parts of
the part of diencephalons. Messages from all receptors of the           cerebral cortex, corpus callosum,
body (except olfactory) are conveyed through the thalamus to the        hippocampus, amygdaloid nucleus
cerebral cortex; thus the thalamus acts as a relay centre. In           and parts of diencephalon. This
addition, the thalamus transmits nerve impulses to different            system plays an active role in the
structures of the brain stem. Multiple nuclei are present in the        control of autonomic functions,
thalamus, functionally divided into two categories: specific            control of behaviour, emotions and
nuclei and the non-specific nuclei.                                     establishment of memory patterns.
        The specific nuclei receives information from the
receptors and relay it to the specific areas of the cerebral cortex, where it is translated into sensations. The
non-specific nuclei have no direct connection with the receptors. They receive impulses from the
receptors indirectly through numerous synapses. Thalamus disorders in man may result in loss of emotion
associated facial muscle contraction, sleep disorders, hearing or vision impairment.

(ii) Hypothalamus forms the floor of diencephalon and is partially protected by the sella turcica of the
sphenoid bone. It participates in the control of protein, lipid, carbohydrate, salt and water metabolism,
heat production and loss (thermoregulation), appetite and satiety centre, sleep and waking states. The
anterior hypothalamic areas represent higher centers of the parasympathetic nervous system, while the
posterior areas represent centers of sympathetic nervous system. Numerous autonomic functions are
controlled by the hypothalamus. Besides the nervous functions, hypothalamus is also connected with the
pituitary gland for releasing various factors to activate or inhibit functions of other glands, through the
pituitary gland.

(iii) Epithalamus forms the roof of diencephalon and is not involved in any type of nerve response, i.e. is
non-nervous. It is fused with the piamater to form anterior choroid plexus for the secretion of
cerebrospinal fluid.
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MIDBRAIN

         The midbrain, located underneath the middle of the forebrain, acts as a master coordinator for all
the messages going in and out of the brain to the spinal cord. It is a very small, constricted part of the
brain. constituting the cerebral peduncles or crura cerebri and four optic lobes or quadrigeminal bodies
collectively called as corpora quadrigemina. In lower vertebrates, optic lobes are two in number, called
as corpora bigemina. The optic lobes are connected with the cerebellum through valves of Vieussens.
         The anterior quadrigeminal bodies or superior colliculi receive nerve impulses from the retina.
The response evoked by these signals is the alteration of the pupil lumen and accommodation.
Accommodation is adjustment of the eye to ensure clear vision of objects at different distances by
changing the convexity of the lens. The posterior quadrigeminal bodies or inferior colliculi receive
nerve impulses from the auditory nerve nuclei in the medulla oblongata. This causes reflex control of the
tonus of the middle ear muscles helps in sound oriented ear pricking.
         Destruction of quadrigeminal nuclei does not affect vision and hearing, but it disrupts orientation
responses to light and sound.




                    Fig. 9.3. The vital functions of body and its control by the brain.


HINDBRAIN

        The hindbrain is located at the back end of the cerebrum and consists of the cerebellum, pons and
medulla. The cerebellum is also called the ‘little brain’ because it looks like a small version of the
cerebrum. It is responsible for balance, movement, and coordination. The pons and the medulla, along
with the midbrain, are often called the brainstem. The brainstem takes in, sends out, and coordinates all
of the brain messages. It is also controls many of the body automatic functions like breathing, heart rate,
blood pressure, swallowing, digestion, and blinking. From an evolutionary viewpoint, the oldest and most
primitive part of the brain is the brainstem.

(A) Cerebellum.
        The cerebellum is the second largest part of the brain The first part of the brain to be
consisting of two cerebellar hemispheres and a central worm- affected by alcohol is the
shaped part, the median vermis. It is situated behind the medulla cerebellum. Therefore a drunk
oblongata and pons, covered with the occipital lobes of the person first loses his balance
cerebrum. The surface of the cerebellum consists of the grey matter, and is unable to walk properly.
which is defined as the cerebellar cortex and consists of the cell
bodies of the neurons. The white matter is composed of processes of these neurons and forms a branched
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tree like structure called as arbor vitae or tree of life. The main functions of the cerebellum are
coordination of movement, equilibrium of the body, maintenance of body posture, normal distribution of
muscle tone and regulation of autonomic functions.
         Disorders associated with the cerebellum are atonia (lack of impairment of muscle tone),
asthenia (loss of rapid onset of muscle fatigue), and astacia (loss of the capacity for sustained titanic
contractions). Motor disturbances associated with cerebellar injury are collectively defined as cerebellar
ataxia.

(B) Medulla Oblongata.
        The medulla oblongata is closest to the spinal cord, and is the most important part of the brain.
The anterior region of medulla has intermixed grey and white matter while the posterior region has grey
matter to the interior and white matter towards the exterior side, as is spinal cord. The roof of medulla is
attached to the piamater constituting the posterior choroid plexus for the secretion of cerebrospinal fluid
(CSF). The roof has three openings below the plexus providing the passage for CSF. These openings are
called as foramina of Luschka (laterally placed on either side) and foramen of Magendie (single,
median). Medulla oblongata is involved with the regulation of heartbeat, breathing, vasoconstriction
(blood pressure), and reflex centers for vomiting, coughing, sneezing, swallowing, hiccupping, etc.

(C) Pons Varolli.
        It is located in front of the cerebellum below the midbrain and above the medulla oblongata. It
consists mainly of nerve fibres which forms a bridge (pons = bridge) between the two cerebellar
hemispheres and of fibres which pass between the higher levels of the brain and the spinal cord. Pons also
contains the pneumotaxic and aponeustic area which helps in the control of respiration.

VENTRICLES OF THE BRAIN

                                                                                The ventricles consist of
                                                                       four hollow spaces inside the brain
                                                                       filled with the cerebrospinal fluid.
                                                                       The first two ventricles are present
                                                                       inside      the      two     cerebral
                                                                       hemispheres, collectively known as
                                                                       lateral ventricles or paracoel. The
                                                                       ventricle in the right cerebral
                                                                       hemisphere is the first ventricle,
                                                                       whereas left cerebral hemisphere
                                                                       contains the second ventricle. Each
                                                                       lateral ventricle is connected to the
                                                                       third      ventricle      by       an
                                                                       interventricular foramen (foramen
                                                                       of Monro). The third ventricle or
                                                                       diocoel is present in the
  Fig. 9.4. Schematic representation of ventricles of the brain.       diencephalons.        The     fourth
                                                                       ventricle or metacoel is present in
the pons and medulla oblongata and continues with the central canal of the spinal cord. Three openings in
the roof of medulla oblongata known as foramina of Luschka (laterally placed on either side) and
foramen of Magendie (single, median) allows the CSF to move upward to the subarachnoid space that
surrounds the brain and the spinal cord. The third and fourth ventricles are connected together by the
aqueduct of Sylvius or Iter in the midbrain portion of the brain stem.

CEREBROSPINAL FLUID (CSF)
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        Spaces under the brain meninges, ventricles and central canal of the spinal cord are filled with the
cerebrospinal fluid. An average amount of CSF in an adult is 100-150ml. It is a clear, colourless, slightly
alkaline fluid (7.33 pH). It contains small number of lymphocytes, 0.02% protein, 0.06% glucose, and
inorganic compounds in the amounts similar to those in the blood.
        The CSF is continuously produced from the blood plasma by the anterior and posterior choroid
plexus. It serves the internal environment of the brain, which maintains its stable mineral composition,
osmotic pressures and protects it against mechanical injury.

WHITE AND GREY MATTER

         The CNS is composed of the grey and white matter. The grey matter represents a collection of
nerve cells while the white matter consists of processes of these cells. In the brain (except medulla), the
white matter is internal and grey matter is external. In the anterior part of medulla the grey and white
matter are intermixed, and the posterior part of medulla has grey matter towards the inner side and white
matter towards the outer side. In the spinal cord the white matter is external and grey matter is external, as
that of posterior part of medulla.

SPINAL CORD

        The spinal cord acts as a communication link between the brain and the peripheral nervous
system. It is continuous with the brain and emerges from an opening at the base of the skull called as
foramen magnum. The spinal cord stretches downward for approx. 42 - 45 cm throughout the vertebral
column. At the first lumbar vertebra (13th vertebra) the spinal cord constricts to form conus medullaris,
and then continues as loose
filaments of connective tissue
called as filum terminale, up to
the coccyx.
        There are 31 pairs of
spinal nerves, called as cauda
equina, part of the peripheral
nervous system, that emerge from
the spinal cord for carrying
messages to and from the spinal
cord. The nerves are named
according to their respective
vertebrae. Each spinal nerve
consists of a dorsal root and a
ventral root. The dorsal roots
contain neurons that carry signals
to the CNS from various types of
sensory neurons. The ventral
roots contain the axons of motor
neurons, which are neurons that
contact and carry information to
the muscles and glands. Within the        Fig. 9.5. C.S. of spinal cord illustrating a typical reflex arc.
spinal cord and else where in the           Arrows indicate the direction of impulse transmission.
body are interneurons, which are
neurons that connect neurons to each other.
        In addition to carrying impulses to and from the brain, the spinal cord regulates reflexes. A reflex
is the simplest response to a stimulus, e.g. sneezing, blinking, etc. A reflex produces a rapid motor
response to a stimulus because the sensory neuron synapses directly with a motor neuron in the spinal
cord. Reflexes are very fast and most reflexes never reach the brain.
                                                                                                              7


PERIPHERAL NERVOUS SYSTEM

        The Peripheral Nervous System (PNS) contains only nerves and connects the brain and spinal
cord (CNS) to the rest of the body. The axons and dendrites are surrounded by a white myelin sheath.
Cell bodies are in the central nervous system (CNS) or ganglia. Ganglia are collections of nerve cell
bodies. Cranial nerves in the PNS take impulses to and from the brain (CNS). Spinal nerves take
impulses to and away from the spinal cord. There are two major subdivisions of the PNS motor pathways:
the somatic (voluntary) and the autonomic.

(A) Voluntary Nervous System.
        It constitutes the nerves arising from the brain (cranial nerves) and the spinal cord (spinal nerves).

(i) Cranial Nerves. There are twelve pairs of cranial nerves in man (amniotes) and ten pairs in frog
(anamniotes), mainly innervating the head region. In frog, the spinal accessory and hypoglossal are absent
thereby reducing the number to ten. In man, there are three pairs of sensory (1, 2, 8), five pairs of motor
(3, 4, 6, 11, 12) and four pairs of mixed (5, 7, 9, 10) cranial nerves. Of these, the trochlear is the smallest
cranial nerve, while vagus is the longest cranial nerve, having maximum branches, therefore also referred
to as wandering nerve. Trigeminal is the largest cranial nerve, divided into three parts namely,
opthalamic, maxillary and mandibular.

 No.   NAME               ORIGIN         LOCATION                  NATURE       FUNCTION
 1.    Olfactory          Olfactory      Nasal cavity              Sensory      Sense of smell
                          lobe
 2.    Optic              Optic lobe     Retina                    Sensory      Sense of sight
 3.    Oculomotor         Midbrain       Muscles of the eyeball    Motor        Movement of eye ball and
                                                                                constriction of pupil
 4.    Trochlear          Midbrain       Muscles of the eyeball    Motor        Rotation of eyeball
       (Pathetic)
 5.    Trigeminal         Pons varolli                             Mixed        Movement of tongue and
       (Mandibular)                                                             jaw muscles
        Opthalamic                       Eyelids, lacrimal
                                           glands, conjuctiva
        Maxillary                        Teeth and gums of
                                           upper jaw
        Mandibular                       Teeth and gums of
                                           lower jaw
 6.    Abducens           Medulla        Muscles of the eyeball    Motor        Rotation of eyeball
                          oblongata
 7.    Facial             Medulla        Taste buds, salivary      Mixed        Sense of taste, facial
                          oblongata      glands and facial                      expressions
                                         muscles
 8.    Auditory           Medulla        Internal ear (Organ of    Sensory      Sense of hearing and
                          oblongata      Corti and semicircular                 maintenance of equilibrium
                                         canals)
 9.    Glosso             Medulla        Tongue and muscles        Mixed        Sense of taste and touch,
       pharyngeal         oblongata      of pharynx                             swallowing
 10.   Vagus              Medulla        Pharyngeal muscles,       Mixed        Respiratory reflex,
       (Pneumo            oblongata      lungs, heart,                          peristalsis, heart beat,
       gastric)                          alimentary canal                       secretion of gastric glands
 11.   Spinal             Medulla        Palate, larynx, vocal     Motor        Pharyngeal muscles, Neck
       accessory          oblongata      cords, neck and                        and shoulder movements
                                         shoulder
 12.   Hypoglossal        Medulla        Muscles of tongue         Motor        Movement of tongue
                          oblongata

            Table. 9.2. Cranial nerves of human brain showing their nature and function.
                                                                                                         8




      Fig. 9.6. Diagrammatic representation of human cranial nerves with their site of action.

(ii) Spinal Nerves. These are 31 pairs in man divided into five groups, having the formula C8T12L5S5C1.
      Cervical nerves- 8 pairs.
      Thoracic nerves- 12 pairs.
      Lumbar nerves- 5 pairs.
      Sacral nerves- 5 pairs.
      Coccygeal nerves- 1 pair.
These arise from the spinal cord and formed by the union of dorsal and ventral roots. All the spinal nerves
are of mixed type, containing both sensory and mixed neurons. These leave the vertebral column through
                                                                                                            9


the intervertebral foramina. Each spinal nerve is divided into four branches, collectively known as
rami, having separate functions.
     Dorsal rami- Innervates the dorsal side of the body.
     Ventral rami- Innervates the ventral side of the body.
     Meningeal rami- Innervates the spinal cord by re-entering into it to supply nerves to vertebra,
        blood vessels and meninges.
     Communicans rami- Part of autonomic nervous system.

(B) Autonomic Nervous System.

         The autonomic nervous system is
an entire little brain and it regulates the
functions of our body without our
awareness or control. This system is
entirely motor having efferent fibres. It
innervates the internal organs, exocrine and
endocrine glands, blood and lymph vessels
and cardiac muscles. It is divided into two
systems which, when act together, often
oppose each other- the sympathetic and
parasympathetic systems. The sympathetic
system evokes responses characteristic of
the ‘fight-or-flight’ response such as pupils
dilate, muscle vasculature dilates, the heart
rate increases, and the digestive system is
put on hold. The parasympathetic system
has many specific functions, including
slowing the heart, constricting the pupils,
stimulating the gut and salivary glands, and
other responses that are not a priority. The
state of the body at any given time is
represented by a balance between these two
systems.
The best way to learn the functions and               Fig. 9.7. Spinal nerves and their functions.
structures of each system is by comparison.

    PARASYMPATHETIC NERVOUS SYSTEM                           SYMPATHETIC NERVOUS SYSTEM
  The cells of parasympathetic nervous system          The cells of the sympathetic nervous system
   are located in different nuclei throughout the        are located in the inter-medio-lateral column in
   brainstem, as well as a few in the sacral spinal      the thoracic spinal cord.
   cord.
  The pre ganglionic fibres (axons) originate from     The pre ganglionic fibres (axons) originate
   the brain and spinal cord and travel to the           from the thoracic spinal cord , and so are
   target organ, and so are longer.                      shorter.
  The pre ganglionic fibres branch before              The pre ganglionic fibres do not branch and
   entering the ganglia, therefore many organs are       enters singly in a ganglion, therefore only one
   affected by one fibre (multiple effect).              organ is affected by one fibre (single effect).
  The ganglia are near the target organs, so the       The sympathetic ganglia are often far from the
   post ganglionic fibres are short.                     target organs, so the post ganglionic fibres are
                                                         long.
  The post ganglionic fibres release the               The post ganglionic fibres release the
   neurotransmitter acetylcholine, therefore called      neurotransmitter noradrenaline, therefore
   as cholinergic.                                        called as adrenergic.
                                                                                                        10


 They have calming effect on the body and              They have excitatory effect on the body and
  operate during normal conditions of the body.          operate during stress activity or danger, i.e.
                                                         during emergency situations.
               Notable Structures                                      Notable Structures
 Edinger- Westphal nucleus - Axons from this           Superior cervical ganglion - supplies
  nucleus travel with cranial nerve III and helps in     sympathetic nerves to the head for dilating the
  pupil constriction and lens accommodation.             pupils, stimulating sweat glands and lifting of
                                                         the eyelids.
 Salivatory nuclei - These nuclei in the medulla       Celiac and mesenteric ganglia - These
  send axons to the salivary glands via the VIIth        ganglia distribute sympathetic nerves to the
  and IXth nerves.                                       gut. Functions include vasoconstriction and
                                                         inhibition of secretions.
 Dorsal nucleus of the vagus - This nucleus            Chain ganglia - running along the spinal cord
  gives rise to the secretomotor fibers of the           distribute sympathetic nerve to the thorax and
  vagus nerve (X). Its functions include                 periphery to increase heart rate, dilate bronchi,
  stimulating gastric secretion, gut motility and        selectively, vasoconstriction and vasodilation in
  respiratory secretion.                                 active muscles.
 Nucleus ambigus - Axons from these cells
  project via the vagus to the heart, lungs, and
  pharynx. It helps in decreasing the heart rate
  and bronchial constriction.

    Table 9.3. Comparison between the two components of the Autonomic Nervous System.




      Fig. 9.8. Sympathetic and parasympathetic nervous system showing their site of
                                   action in human body.
                                                                                                      11


NOTE: The sympathetic afferents mainly carry information about visceral pain. Since this information
converges with pain from the body surface, the pain is often perceived as originating at the body surface
instead of deep in the viscera. This phenomenon is called referred pain. For example, afferents from the
heart enter the spinal cord at the same level as those from the shoulder region. This is why pain in the
heart (heart attack) is often referred to the shoulder.

STRUCTURE OF NEURON

        The basic functional units that carry messages throughout the nervous system are called neurons.
Messages take the form of electrical signals, and are known as impulses. Neurons may have dozens or
even hundreds of dendrites but usually only one axon. The axons of most neurons are covered with a lipid
layer known as the myelin sheath. The myelin sheath both Insulates and speeds up transmission of action
potentials through the axon. In the peripheral nervous system, myelin is produced by Schwann cells,
which surround the axon. Gaps (nodes) in the myelin sheath along the length of the axon are known as the
nodes of Ranvier. Irrespective of their specific function, all neurons have the same physical parts: the
cell body, dendrites and axon.




                              Fig. 9.9. Basic structure of a neuron.

   Cell body – It is the largest part, contains the nucleus and much of the cytoplasm (area between the
    nucleus and the cell membrane). It is responsible for most of the metabolic activity of the cell,
    including the generation of ATP and synthesis of protein.
   Dendrites – These are short branch extensions spreading out from the cell body. Dendrites receive
    stimulus (action potentials) and carry impulses from the environment or from other neurons and carry
    them towards the cell body.
   Axon – It is a long fiber that carries impulses away from the cell body. Each neuron has only one
    axon. The axon ends in a series of small swellings called axon terminals.




                 Fig. 9.10. Schematic representation of transfer of nerve impulses.

Neurons can be classified into three types:
 Sensory neuron (afferent) - Carry impulses from the sense organs (receptors) to the brain and spinal
   cord. Receptors detect external or internal changes and send the information to the central nervous
                                                                                                         12


    system in the form of impulses by way of the afferent neurons.
   Motor neurons (efferent) - Carry impulses from the brain and spinal cord to muscles or glands.
    Muscles and glands are two types of effectors. In response to impulses, muscles contract and glands
    secrete enzymes or hormones, as the need of the body.
   Interneurons - Connect sensory and motor neurons and carry impulses between them. They are
    found entirely within the central nervous system.

CONDUCTION OF NERVE IMPULSES

         The Italian scientist Luigi Galvani found that nervous tissue (groups of cells that conduct
impulses) displays electrical activity in the form of a nerve impulse, which is a flow of electrical charges
along the cell membranes of a neuron. This electrical activity is due to movement of ions (charge
particles) across the cell membrane, namely sodium and potassium. The movement of these ions is
affected by their ability to pass through the cell membrane, their concentration inside and out of the cell,
and their charge. Neurons have an electrical charge different from the extracellular fluid that surrounds
them. A difference in electrical charge between two locations is called a potential.




             Fig. 9.11. Potential versus time graph showing action potential in a neuron.


(a) Resting Potential.
        A nerve cell has electric potential across its cell membrane because of a difference in the number
of positively and negatively charged ions on each side of the cell membrane, which carries a sodium
pump. During resting stage, the electrical potential is due to the poor permeability of the membrane
towards sodium and higher permeability towards potassium, which move sodium ions (Na +) out of the
cell and actively pump potassium ions (K+) into the cell. The result of this active transport of ions is the
cytoplasm of the neuron contains more K+ ions and fewer Na+ ions than the surrounding medium. The
concentration of sodium ions becomes about 14 times more in extracellular fluid and constitutionof
potassium ions will be 28-30 times more in axoplasm. This charge difference is known as the resting
potential (about 70mV) of the neuron's cell membrane. As a result of its resting potential, the neuron is
said to be polarized which means negatively charged on the inside of the cell membrane and positively
charged on the outside. A neuron maintains this polarization until it is stimulated. A stimulus is a change
                                                                                                           13


in the environment that may be of sufficient strength to initiate an impulse. The ability of a neuron to
respond to a stimulus and convert it into a nerve impulse is known as excitability.

(b) Action Potential.
         A Nerve Impulse causes a movement of ions across the cell membrane of a neuron. The cell
membrane of a neuron contains thousands of tiny molecules known as gates. These gates allow either
sodium or potassium ions to pass through. Generally the gates on a neuron are closed. A nerve impulse
starts when pressure or other sensory inputs, disturbs a neuron's plasma membrane, causing sodium gates
to open thereby changing the membrane permeability. At the beginning of an impulse, the sodium gates
open, allowing positively charged Na+ ions to flow inside the cell membrane. The inside of the membrane
temporarily becomes more positive than the outside. This is called depolarized, i.e. the charge inside the
axon changes from negative to positive as sodium ions enter the interior.
         As the impulse passes, the potassium gates open, allowing positively charged K + ions to flow
out. The membrane is now said to be repolarized. Once again negatively charged on the inside and
positively charged on the outside. The depolarization and repolarization of a neuron membrane is called
an action potential (20-30mV). Action potential is another name for a nerve impulse or simply an
impulse. After a nerve impulse is period when the neuron is unable to conduct a nerve impulse called the
refractory period. The refractory period is a very short period during which the sodium-potassium pump
continues to return sodium ions to the outside and potassium ions to the inside of the axon. Thus returning
the neuron to the resting potential. An impulse is not an electric current; it is a wave of depolarization and
repolarization. Or a nerve impulse is actually the movement of an action potential along a neuron as a
series of voltage-gated ions channels open and close. An impulse is much slower than an electric current.
Unlike an electric current, the strength of an impulse is always the same. There is either an impulse to a
stimulus or there in not (all or none law).

Saltatory Conduction.
         Myelin sheaths greatly increase the
speed of impulse along an axon. These are
composed of 80% lipid and 20% protein.
Myelin is made of special cells called
Schwann Cells that forms an insulated
sheath, or wrapping around the axon. There
are small nodes or gaps called the nodes of
Ranvier between adjacent myelin sheath
cells along the axon. As an impulse moves
down a myelinated (covered with myelin)
axon, the impulse jumps form node to node
instead of moving along the membrane,
known as saltatory conduction. This
jumping from node to node greatly increase
the speed of the impulse. Some myelinated
axons conduct impulses as rapid as 200
meters per second. The formation of myelin
around axons can be thought of as a crucial
event in evolution of vertebrates.
Destruction of large patches of myelin
characterize a disease called multiple
sclerosis. In multiple sclerosis, small, hard
plaques appear throughout the myelin.
Normal nerve function is impaired, causing
symptoms such as double vision, muscular            Fig. 9.12. Conduction of nerve impulse in (A)
weakness, loss of memory, and paralysis.           Myelinated; and (B) Non-myelinated nerve fibre.
                                                                                                      14


Threshold Stimulus.
        The strength of an impulse is always the same. Either there is an impulse in response to a
stimulus or not. A stimulus must be of adequate strength to cause a neuron to conduct an impulse. The
minimum level of a stimulus that is required to activate a neuron is called the threshold. Any stimulus
weaker than the threshold will produce no impulse. Any stimulus stronger than the threshold will produce
an impulse. A nerve impulse follows the all-or-none principle.

TRANSMISSION OF NERVE IMPULSES

        The axon ends with many small swellings called axon terminals. At these terminals the neuron
may make contact with the dendrites of another neuron, with a receptor or with an effector. Receptors are
special sensory neurons that receive stimuli from the external environment. Effectors are muscles or
glands that bring about a coordinate response. The point of contact at which impulses are passed from one
cell to another are known as the synaptic cleft or synapse. Neurons that transmit impulses to other
neurons do not actually touch one another. The small gap or space between the axon of one neuron and
the dendrites or cell body on the next neuron is called the synapse. One importance of the presence of
synapses is that they ensure one-way transmission of impulses in a living person. A nerve impulse cannot
go backward across a synapse. The axon terminals at a synapse contain tiny synaptic vesicles, or sacs.
These tiny vesicles are filled with chemicals known as neurotransmitters, usually acetylcholine.
Neurotransmitter is a chemical substance that is used by one neuron to signal another. The impulse is
changed from and electrical Impulse to a chemical impulse (electrochemical impulses).




                  Fig. 9.13. Transmission of nerve impulse through synapse.
                                                                                                         15



1. When an impulse reaches the axon terminal, increasing the permeability of presynaptic cell membrane
   towards calcium ions, which causes dozen of synaptic vesicles to fuse with the membrane and
   discharge the neurotransmitter into the synaptic cleft.
2. The molecules of the neurotransmitter diffuse across the gap and attach themselves to special
   receptors on the postsynaptic membrane of the neuron receiving the impulse.
3. When the neurotransmitter becomes attached to the cell membrane of the adjacent nerve cell, it
   changes the permeability of that membrane.
4. As a result, Na+ ions diffuse through the membrane into the cell. If enough neurotransmitter is
   released by the axon terminal, so many Na+ ions diffuse into the neuron that the neuron becomes
   depolarized. This causes a threshold to be reached and an impulse (action potential) begins in the
   second cell.
5. After the neurotransmitter relays it message it is rapidly removed or destroyed, thus halting its effect.
   The molecules of the neurotransmitter may be broken down by enzymes, particularly by
   cholinesterase. This enzyme hydrolyses acetylcholine to choline, which is taken up again by the axon
   terminal and recycled by using energy from ATP present in mitochondria.

        Synapses are the slowest part of the nervous system. The advantage to having many neurons,
with gaps between them, is that we can control and receive information from different parts of the body at
different times. They also ensure one-way transmission of impulses in a living person. Nerve gas
prevents enzymes from breaking down neurotransmitters, as a result muscles in the respiratory and
nervous system becomes paralyzed.

ELECTROENCEPHALOGRAM (EEG)

            The function of the brain can be evaluated by the pattern of its electric activity by recording
biopotentials from the exposed brain, called as electrocorticography (ECoG). In humans, cerebral
biopotentials are recorded using electrodes applied to the skin of the head. Since the potential difference
in the brain is negligible, biopotential amplifiers and oscillographs are required for recording the
biopotentials. This method of recording of electric potential fluctuations of the brain is named as
electroencephalography, and the tracing is called as electroencephalogram.
            Electroencephalography has found wide applications in clinical practice. Neurosurgeons,
neuropathologists, psychiatrists and other specialists use it. It allows for an objective evaluation of
lability, distribution and inter-relationships of excitatory and inhibitory processes in the brain.

EEG Rhythms. Electric waves registered on the EEG have different frequency, duration, amplitude and
shape, depending upon the mental activity of the organism. Four major rhythms are distinguished as
follows.
         The alpha rhythm is a regular sinusoid-shaped rhythm with a frequency of 8-13 waves/sec and
amplitude of 20-80 μV. These rhythms are registered in a resting man with his eyes closed and external
stimuli absent.
         The beta rhythm has the frequency of 14-35 waves/sec and amplitude of 10-30 μV. After
applying stimuli, when the eyes are opened or mental activity is performed, the alpha rhythm rapidly
vanishes and the beta rhythm appears. The replacement of the slow rhythm with a more rapid one is
termed burst response or desynchronization.
         The delta rhythm is characterized by slow potential fluctuation having frequency of 0.5-3
waves/sec and a high amplitude of 250-300 μV or even 1000 μV. It is detected during profound sleep and
general anaesthesia. In children under the age of 7 years, the delta rhythms can be registered in the
waking state.
         The theta rhythm has the frequency of 4-7 waves/sec and amplitude of 100-150 μV. It is
observed during light sleep, oxygen deficiency and moderate anaesthesia.
BRAIN AND DRUGS
                                                                                                       16


         Some neurotransmitters are excitatory, such as acetylcholine, norepinephrine, serotonin, and
dopamine. Some are associated with relaxation, such as dopamine and serotonin. Dopamine release
seems related to sensations of pleasure. Endorphins are natural opioids that produce elation and reduction
of pain, as do artificial chemicals such as opium and heroin. Neurological diseases, for example
Parkinson's disease and Huntington's disease, are due to imbalances of neurotransmitters. Parkinson's
is due to a dopamine deficiency. Huntington's disease is thought to be cause by malfunctioning of an
inhibitory neurotransmitter. Alzheimer's disease is associated with protein plaques in the brain. Drugs
are stimulants or depressants that block or enhance certain neurotransmitters. Dopamine is thought
involved with all forms of pleasure. Cocaine interferes with uptake of dopamine from the synaptic cleft.
Alcohol causes a euphoric "high" followed by a depression.
 Marijuana, material from the Indian hemp plant, Cannabis sativa has a potent chemical THC
   (tetrahydracannibinol) that in low concentrations causes a euphoric high (if inhaled, the most common
   form of action is smoke inhalation). High dosages may cause severe effects such as hallucinations,
   anxiety, depression and psychotic symptoms.
 Cocaine is derives from the plant Erthoxylon coca. It can be inhaled, smoked or injected. Cocaine
   users report a "rush" of euphoria following use. Following the rush is a short (5-30 minute) period of
   arousal followed by a depression. Repeated cycle of use terminate in a "crash" when the cocaine is
   gone. Prolonged used causes production of less dopamine, causing the user to need more of the drug.
 Heroin is a derivative of morphine, which in turn is obtained from opium poppy, Papaver somniferum.
   Heroin is usually injected intravenously, although snorting and smoking serve as alternative delivery
   methods. Heroin binds to ophioid receptors in the brain, where the natural chemical endorphins are
   involved in the cessation pain. Heroin is physically addictive, and prolonged use causes less endorphin
   production. Once this happens, the euphoria is no longer felt, only dependence and delay of withdrawal
   symptoms.

DISORDERS OF NERVOUS SYSTEM

 Brain tumors. A tumor is a swelling caused by overgrown tissue. A tumor in the brain may grow
  slowly and produce few symptoms until it becomes large, or it can grow and spread rapidly, causing
  severe and quickly worsening symptoms. Brain tumors in children can be benign or malignant.
  Benign tumors usually grow in one place and may be curable through surgery. A malignant tumor is
  cancerous and more likely to grow rapidly and spread.

 Cerebral palsy. Cerebral palsy is the result of a developmental defect or damage to the brain before
  or during birth. It affects the motor areas of the brain. A person with cerebral palsy may have average
  intelligence or can have severe developmental delays or mental retardation. Cerebral palsy can affect
  body movement in many different ways. In mild cases of cerebral palsy, there may be minor muscle
  weakness of the arms and legs. In other cases, there may be more severe motor impairment, a child
  may have trouble talking and performing basic movements like walking.

 Coma. It is a state of unconsciousness in which the person is unable to respond to a stimuli. It may
  occur due to injury in the brain, chemical imbalance or intake of poison. Its recovery may be followed
  by loss of memory (amnesia).

 Epilepsy. This condition is made up of a wide variety of seizure disorders. Partial seizures involve
  specific areas of the brain, and symptoms vary depending on the location of the seizure activity.
  Generalized seizures involve a larger portion of the brain and usually cause uncontrolled movements
  of the entire body and loss of consciousness when they occur. Although the specific cause is unknown
  in many cases, epilepsy can be related to brain injury, tumors, or infections. The tendency to develop
  epilepsy may be inherited in families.

 Headaches. Of the many different types of headaches, the most frequently occurring include tension
  headache, caused by muscle tension in the head, neck, and shoulders; migraine, an intense, recurring
                                                                                                         17


   headache with an unclear cause; and cluster headache, considered by some to be a form of migraine.
   Migraines occur with or without warning and may last for several hours or days. There seems to be an
   inherited predisposition to migraines as well as certain triggers that can lead to them. People with
   migraines may experience dizziness, numbness, sensitivity to light, and nausea, and may see flashing
   zigzag lines before their eyes.

 Meningitis and encephalitis. These are infections of the brain and spinal cord that are usually
  caused by bacteria viz. Streptococcus pnueumonie, Neisseria meningitides and Haemophilus
  influenza. Meningitis is an inflammation of the coverings of the brain and spinal cord, and
  encephalitis is an inflammation of the brain tissue. Both conditions may result in permanent injury to
  the brain.

 Mental illness. Mental illnesses are psychological and behavioral in nature and involve a wide range
  of problems in thought and function. Certain mental illnesses are now known to be linked to structural
  abnormalities or chemical dysfunction of the brain. Some mental illnesses are inherited, but often the
  cause is unknown. Injuries to the brain and chronic drug or alcohol abuse also can trigger some
  mental illnesses. Mental illnesses that can be seen in younger people include depression, eating
  disorders such as bulimia or anorexia nervosa and phobias.

 Head Injuries. Head injuries fall into two categories: external (usually scalp) injuries and internal
  head injuries. Internal injuries may involve the skull, the blood vessels within the skull, or the brain.
  An internal head injury could have more serious implications because the skull serves as the
  protective helmet for the delicate brain. Concussions are also a type of internal head injury. It is the
  temporary loss of normal brain function as a result of an injury. Repeated concussions can result in
  permanent injury to the brain.

 Stroke. It is a reversible or irreversible damage to the brain due to lack of oxygen, caused by
  interrupted blood flow, clotting of blood, etc.

REFLEX ACTION

         The cerebral cortex and sub-cortical centers represents higher divisions of the central nervous
system (CNS) in warm-blooded animals and man. They subserve the reflex responses underlying the
most complicated interactions of the animal and human organisms with the external environment. The
two mechanisms of the higher nervous activity are instincts and conditioned reflexes.
 Instincts or unconditioned reflexes are a complicate cascade of inborn, unconditioned reflexes
   resulting primarily from the activities of the subcortical and diencephalic nuclei. They remain after the
   removal of the cerebral cortex. Instincts are identical in all individuals of the same species; they are
   inherited and related to the vital activities of the body- nutrition, defense, reproduction, etc. The
   responses are relatively stable, stereotyped and unchangeable; due to this, unconditioned reflexes alone
   cannot ensure proper adaptations to changing environmental conditions.
 Conditioned reflexes are individual acquired reflexes based on the unconditioned ones. They are
   produced primarily due to the activity of the cerebral cortex. These reflexes vary in different
   individuals of a species. They are changeable and easily induced or lost depending upon the
   environmental conditions. Conditioned reflexes were categorized by Pavlov into natural and artificial.
1. Natural conditioned reflex arc induced by the natural properties of unconditioned stimuli, e.g.
   nutritional conditioned reflex is evoked by the odour or sight of the food.
2. Artificial conditioned reflex arises from a variety of artificial stimuli of a given unconditioned reflex
   (light, sound, odour, temperature, etc.). Any change in the external or internal environment of the body
   may become a conditioned stimulus.
                                                                                                           18


Mechanism of Reflex Action. The nerve impulse
travels through a path in a reflex action known as
reflex arc. It the reflex action is controlled by the
spinal cord, it is called as spinal reflex action and if
it is controlled by the brain, it is called as cerebral
reflex action. The components of a reflex arc,
mediating a reflex are:
(i) Receptor, which may be an organ, tissue or a
      cell receiving a stimulus.
(ii) Sensory (or afferent) nerve fibres, which passes
      the sensory impulses generated by the receptor
      to the CNS.                                              Fig. 9.14. Reflex action and reflex arc.
(iii) CNS (or integrating center), which may be
      spinal cord or brain, analyses the condition and decides specific action to be performed.
(iv) Motor (or efferent) nerve fibres, which carry the motor impulses generated in the CNS to the
      effector.
(v) Effector, which may be an organ, muscle or gland receives an order from the CNS via the motor
      neurons and works as ordered by the brain or spinal cord.

CONSCIOUSNESS

         Consciousness is the subjective experience of man varying from simple sensation to abstract
thinking. It emerged only at the highest developmental stages, in the humans. It is an active reflection of
objective reality. Although the spinal cord and other divisions of the central nervous system performs the
reflective function, this reflection is not psychic. Only the cerebral cortex is capable of perceiving psychic
qualities. Consciousness is the product of evolution. Labour and verbal communications led to the
development of consciousness in humans. It enables man to explore the properties and qualities of objects
and phenomena, to understand their laws, and to discriminate between the relevant and irrelevant.

PHYSIOLOGY OF SLEEP

        Sleep is a universal feature of the living nature; it is a physiological requirement of an organism.
Man spends one third of his lifetime in the stage of physiologically recurring sleep. During sleep, multiple
changes occur in the physiological systems of man; consciousness and responses to many environmental
stimuli are not operative, motor reflex responses are subdued, and conditioned activities are completely
inhibited. There are numerous changes in the autonomic functions: the heart and arterial pressure are
decreased, respiration is slower and shallow, metabolic rate and body temperature are slightly reduced,
and digestion and renal functions are attenuated. Profound sleep is associated with a decrease in muscle
tone and complete relaxation of most of the muscles.
        The sleeping-waking cycle in humans follows the diurnal day and night sequence. An adult
sleeps once a day, or has monophasic sleep. Children, especially infants, have multiphasic sleep. Sleep
requirements are age related. Daily sleep of newborns is 20-23 hours, 2-4 years old children sleep 16
hours, 4-8 years old sleep 12 hours, 8-12 years old 10 hours, 12-16 years old 9 hours, and adults 7-8
hours.

Mechanism of Sleep.
        Several concepts have been proposed to explain the physiology of sleep. These may be divided
into humoral and nervous. The most popular of the humoral concepts is the ‘sleep poisons’
(‘autointoxication’) hypothesis. It suggests that sleep is the product of brain autointoxication with
metabolites accumulated during the waking state (lactic acid, carbon dioxide, ammonium, etc.). During
the recent years, there has been an increasing focus on the chemical theories of sleep. This is related to
the identification and manufacturing of a hypogenic factor, a sleep inducing low-molecular weight
polypeptide. The naturally occurring hypogenic factors include serotonin.
                                                                                                            19


         Natural onset of normal physiological sleep is related to the activity of cortical neurons.
Functioning neurons gradually develop fatigue, which provides conditions for inhibition allowing for
restoration and rest of neurons. Inhibition initially occurs in a limited group of cortical cells. If it is not
counteracted by a strong excitation focus, inhibition irradiates over the entire cortex and reaches the
subcortical centers. Pavlov considered that sleep is ‘internal inhibition’ that had irradiated throughout the
hemispheres and to the lower-lying brain parts.
         Pavlov classified sleep into active and passive. Active sleep is induced by prolonged monotonous
stimuli like a lullaby or train-wheel rattle. Passive sleep is induced by a restriction of the impulse flow to
the cerebral cortex.
         The presence of a sleeping and waking center in the brain (thalamus and hypothalamus) has been
hypothesized on the basis of clinical and experimental findings. The current explanations of this
hypothesis relate it to the function of the reticular formation and its connections with the cerebral cortex.
Afferent impulses going through the reticular formation to the cerebral cortex activate the reticular
formation. Destruction or pharmacological suppression (aminazine) of the reticular formation induces
sleep. Therefore, the sleeping and waking center may be interpreted as structures, which modulate
cortical-subcortical communications, which act to induce sleep under some circumstances and maintain
wakefulness under the other. Therefore, the concept of sleeping and waking center may be accepted as
arbitrary. In brief, sleep should not be considered as the inactivity of the cortical neurons but as a change
in the activity of the cerebral cortex.


                                    COMPETITION DESK # 09

1. Ninth pair of cranial nerve in frog is (AFMC                 (c) hypothalamus     (d) medulla oblongata
   2005)
   (a) Hypoglossal      (b) Glossopharyngeal               6. Venom of cobra affects (AFMC 2001)
   (c) Vagus            (d) Trigeminal                        (a) circulatory system
                                                              (b) digestive system
2. Which cranial nerves show the maximum                      (c) nervous system
   branching? (AFMC 2003)                                     (d) respiratory system
   (a) Trigeminal    (b) Vagus
   (c) Optic         (d) Facial                            7. Which cranial nerve controls the heart
                                                              muscles? (AFMC 1998)
3. Which part of the brain is associated with                 (a) Facial       (b) Vagus
   smell? (AFMC 2003)                                         (c) Auditory     (d) Trochlear
   (a) Olfactory lobes
   (b) Cerebral hemispheres                                8. Mammalian brain differs from an amphibian
   (c) Medulla oblongata                                      brain in possessing (AFMC 1998)
   (d) Cerebrum                                               (a) olfactory lobe (b) cerebellum
                                                              (c) hypothalamus (d) corpus callosum
4. The impulses from the one neuron to
   another are send in the form of (AFMC                   9. Resting potential of a nerve is (AFMC
   2003)                                                      1998)
   (a) Mechanical impulses                                    (a) +70 millivolt  (b) +30 millivolt
   (b) Chemical impulses                                      (c) -30 millivolt  (d) -70 millivolt
   (c) Electrical impulses
   (d) Magnetic impulses                                   10. The number of spinal nerves in frog is
                                                               (AFMC 1995)
5. In homeotherm, the brain centre, which                      (a) 9 pair      (b) 10 pairs
   regulates body temperature, is situated in                  (c) 11 pairs    (d) 31 pairs
   (AFMC 2003)
   (a) cerebellum    (b) cerebral lobe                     11. Which of the following pair of ions play a
                                                                                                     20


    great role in nervous transmission and
    marinating potential difference? (AFMC           20. Preganglionic sympatheic fibers are (AIIMS
    1995)                                                1995)
    (a) Na+ and K+     (b) Na+ and Ca++                  (a) adrenergic    (b) cholinergic
    (c) Na+ and Cl‫־‬    (d) K+ and Ca++                   (c) synergic      (d) hypergonic

12. The transmission of nerve impulse, from one      21. Which of the following cranial nerve of man
    neuron to other, is facilitated by (AFMC             is both sensory and motor? (AIIMS 1994)
    1995)                                                (a) Optic           (b) Auditory
    (a) kinetin         (b) cholesterol                  (c) Olfactory       (d) Trigeminal
    (c) adrenaline      (d) acetylcholine
                                                     22. Node of Ranvier is a place where (CBSE
13. Respiration is controlled by (AFMC 1995)             2002)
    (a) cerebellum                                       (a) medulla sheath is discontinuous
    (b) medulla oblongata                                (b) medullary sheath and neurilemma is
    (c) olfactory lobes                                  discontinuous
    (d) hypothalamus                                     (c) axolemma is absent
                                                         (d) axolemma is discontinuous
14. True nervous system first of all originated in
    (AFMC 1995)                                      23. During activation of nerve the impulse is
    (a) Taenia         (b) Ascaria                       conducted in a fibre by (CBSE 2000)
    (c) Hydra          (d) Hirudinaria                   (a) more movement of sodium ions inside
                                                         and potassium ions outside
15. Earthworm and cockroach have which of the            (b) less sodium coming out and more
    following thing common? (AFMC 1995)                  potassium coming in
    (a) Ventral nerve chord                              (c) equal movement of both ions
    (b) Closed blood vascular system                     (d) more movement of potassium ions
    (c) Nephridia                                        towards inside and sodium ions outside
    (d) Cocoon
                                                     24. The vagus nerve is the cranial nerve
16. Nissl granules are rich in (AIIMS 2002)              numbering (CBSE 1997)
    (a) protein and lipids                               (a) 10           (b) 9
    (b) ribonucleoproteins                               (c) 7            (d) 5
    (c) fatty acids
    (d) nucleic acids                                25. By which nervous system and of what type,
                                                         the blood is supplied into visceral organ?
17. Secretion of which of the following is under         (CBSE 1996)
    neurosecretory nerve axons? (AIIMS 1998)             (a) Sympathetic nervous system, involuntary
    (a) Pineal gland                                     (b) Sympathetic nervous system, voluntary
    (b) Adrenal cortex                                   (c) Both SNS and PNS, involuntary
    (c) Anterior pituitary                               (d) Para-sympathetic nervous system,
    (d) Posterior pituitary                              involuntary

18. Sympathetic nerves in mammals arise from         26. The parasympathetic nerves in mammals
    (AIIMS 1998)                                         arise from (CBSE 1995)
    (a) sacral region                                    (a) thoraco-lumbar nerves
    (b) cervical region                                  (b) cervical nerves
    (c) thoraco-lumbar region                            (c) sacral nerves
    (d) 3rd, 7th and 9th and 10th cranial nerves         (d) 3rd, 7th, 9th, 10th cranial nerves and 2nd,
                                                         3rd, 4th sacral nerves
19. Arbor vitae is mainly composed by (AIIMS
    1998)                                            27. According to the accepted concept of
    (a) grey mater      (b) neuroglial cells             hormone action, if receptor molecules are
    (c) white mater     (d) all of these
                                                                                                    21


    removed from target organs, then (CBSE              (c) both
    1995)                                               (d) none of the above
    (a) the target organ will continue to respond
    to the hormone but will require higher          36. Saltatory conduction occurs in (CPMT
    concentration                                       1998)
    (b) the target organ will continue to respond       (a) myelinated nerve fibres
    to the hormone but in the opposite way              (b) non-mylenated nerve fibres
    (c) the target organ will continue to respond       (c) both
    to the hormone without any difference               (d) none of these
    (d) the target organs will not respond to the
    hormone                                         37. Which one of the following acts as slow
                                                        neurotransmiitter? (CPMT 1998)
28. The gilal cells that from the blood-brain           (a) GABA            (b) Adrenaline
    barrier by lining brain capillaries are the         (c) Epinephrine     (d) Acetylcholine
    (CPMT 2000)
    (a) Schwann cells                               38. Which of the following pairs of
    (b) astrocytes                                      elements/ions   required    for  nerve
    (c) oligodendrioglial cslls                         conduction? (CPMT 1998)
    (d) Raniver cells                                   (a) Ca, Na and K (b) Ca and Mg
                                                        (c) Mg and K       (d) Na and Mg
29. The neurotransmitter between a motor
    neuron and a muscle cell is (CPMT 2000)         39. Structures typically represented in every
    (a) endorphin      (b) serotonin                    segment of earthworm are (CPMT 1996)
    (c) dopamine       (d) acetylcholine                (a) ganglia         (b) lateral hearts
                                                        (c) genital ducts   (d) septal nephridia
30. Which of the following is a structure in the
    mesencephalon? (CPMT 2000)                      40. The autonomic nervous system has control
    (a) Inferior colliculi (b) Thalamus                 over (KPMT 2003)
    (c) Cerebellum          (d) Mammillare body         (a) Reflex action (b) Skeletal muscle
                                                        (c) Sense organs  (d) Internal organs
31. In earthworm neurons are (CPMT 2000)
    (a) motor         (b) sensory                   41. The most appropriate definition for
    (c) both above    (d) absent                        neuroglial cells are that they are (KPMT
                                                        2003)
32. Breathing is controlled by which part of the        (a) Nonsensory supporting cells
    brain? (CPMT 1998)                                  (b) Nonsensory supporting or secretory cells
    (a) lungs           (b) trachea                     (c) Sensory cells
    (c) medulla oblongata(d) hypothalamus               (d) Central nervous system

33. Which of the following is not essentially a     42. The energy transformation in the nervous
    part of nervous system? (CPMT 1998)                 system is (KPMT 2002)
    (a) Cyton            (b) Axon                       (a) chemical to radiant
    (c) Myelinated       (d) Intermedin                 (b) chemical to mechanical
                                                        (c) chemical to electrical
34. Which one of the following can act as spinal        (d) chemical to osmotic
    nerve? (CPMT 1998)
    (a) Hypolgossal    (b) Trigeminal               43. In the nerve cells, the reversal of the resting
    (c) Olfactory      (d) None of these                potential is known as depolarization. This
                                                        occurs due to (KPMT 2001)
35. Conditioned reflexes are different than             (a) influx of Sodium ions
    unconditioned reflexes in that (CPMT 1998)          (b) infux of Calcium and chloride ions
    (a) conditioned reflexes are limited to brain       (c) influx of Potassium ions
    (b) unconditioned reflexes are limited to           (d) influx of Sodium ions
    brain
                                                                                               22


44. Nissl granules could be seen in (KPMT
    2001)                                        54. Acetylcholine is a (KCET 1994)
    (a) bone cells    (b) gland cells                (a) enzyme           (b) chemical transmitter
    (c) myofibrils    (d) neurons                    (c) toxin            (d) vitamin

45. The first cranial nerve is (KPMT 2000)       55. Each spinal nerve in a mammal arises from
    (a) occulomotor       (b) auditory               the spinal cord by two roots, a dorsal and a
    (c) trigeminal        (d) olfactory              ventral. Of these the ventral root is
                                                     composed of (KCET 1994)
46. The parasympathetic nerve ending release         (a) somatic motor and visceral motor fibres
    (KPMT 2000)                                      (b) somatic sensory and visceral motor
    (a) acetylcholine (b) serotonin                  fibres
    (c) adrenaline    (d) dopamine                   (c) somatic sensory and visceral sensory
                                                     fibres
47. Pons connects the (KCET 2003)                    (d) somatic motor and visceral sensory
    (a) two lobes of cerebellum                      fibres
    (b) two cerebral hemisphere
    (c) spinal cord with the brain               56. In motor nerve fibers the impulse in the
    (d) cerebrum and cerebellum                      axon travels (CET 2003)
                                                     (a) towards the cell body
48. The correct sequence of meninges from            (b) away from the cell body
    inner to out side is (KCET 2003)                 (c) both a and b
    (a) duramater—piamater—arachnoid                 (d) cell body is not involved
    (b) duramater—archanoid—piamater
    (c) arachnoid—duramater—piamater             57. Synapse is proximity of (CET 2002)
    (d) piamater—arachnoid—duramater                 (a) two neurons    (b) two veins
                                                     (c) two arteries   (d) venules
49. Which of the following is a part of human
    brain? (KCET 2002)                           58. One of these is wrong statement
    (a) Corpora bigemina                             I. Neurotransmitter jumps from one junction
    (b) Corpora quadrigemina                         to another
    (c) Corpora allata                               II. After signal transmittance post synaptic
    (d) Corpora adiposa                              membrane is destroyed
                                                     III. Neurotransmitter is permanently
50. A bipolar neuron has (KCET 2002)                 destroyed after the transmission of nerve
    (a) 2 dendrites and 1 axon                       impulse has taken place (CET 2001)
    (b) 2 axons and 1 dendrite                       (a) I and II         (b) II and III
    (c) 1 dendrite and 1 axon                        (c) I andII          (d) none of these
    (d) 2 axons and 2 dendrites
                                                 59. Schwann cell is part of (CET 2000)
51. Corpus callosum is seen in the (KCET 2001)       (a) excretory system     (b)nervous system
    (a) pituitary       (b) ovary                    (c) respiratory system (d)muscular system
    (c) brain           (d) corpus luteum
                                                 60. ANS is not involved in (CET 2000)
52. The transmission of impulse in the axon is       (a) heart beat
    (KCET 2000)                                      (b) control of viscera
    (a) both away and towards cyton                  (c) mictuiration
    (b) not found                                    (d) learning and memory
    (c) away from cyton
    (d) towards cyton                            61. In a human being, the numbers of cranial
                                                     nerve are (CET 2000)
53. Cavities of brain are called (KCET 1998)         (a) 6 pairs       (b) 20 pairs
    (a) auricles         (b) coelom                  (c) 10 pairs      (d) 12 pairs
    (c) ventricles       (d) lumen
                                                                                                  23


62. Axon is characterized by (CET 2000)                  (a) adrenergic      (b) cholinergic
    (a) conduction of impulse                            (c) synergic        (d) hypergonic
    (b) transformation of energy
    (c) receiving the impulse                        72. Which nerve is exclusively            motor?
    (d) providing energy for impulse                     (Manipal 2000)
                                                         (a) Vagus           (b) Facial
63. Neurocyton is located (CET 2000)                     (c) Spinal accessory(d) Maxillary
    (a) cortex of the brain
    (b) outside the brain                            73. A disease occurring generally above 40s in
    (c) outside the spinal cord                          which person starts forgetting and hand
    (d) white matter                                     starts trembling, having poor CNS
                                                         coordination is (Manipal 2000)
64. The impulse for voluntary forced breathing           (a) Alzhiemer’s disease
    starts in (CET 1997)                                 (b) epilepsy
    (a) medulla oblongata                                (c) Parkinson’s disease
    (a) cerebral hemispheres                             (d) migration
    (c) vagus
    (d) spinal cord                                  74. One of these nerve is completely motor
                                                         (Wardha 2002)
65. Brain component regulating temperature of            (a) I            (b) VII
    body, the ectoderm is responsible for the            (c) X            (d) VI
    formation of (CET 1997)
    (a) hypothalamus (b) pituitary                   75. Route of reflex arc is (Wardha 2002)
    (c) medulla        (d) cerebellum                    (a) receptors, effectors, grey mater and
                                                         motor fibers
66. The impulse for voluntary forced breathing           (b) receptors, sensory fibers, grey mater,
    starts in (CET 1997)                                 motor fibers ad effectors
    (a) medulla         (b) vagus                        (c) sensory fibers, grey mater, motor,
    (c) spinal cord     (d) cerebral hemisphere          sensory fibres, receptors and effectors
                                                         (d) effectors, grey mater, motor, sensory
67. Cerebrum controls (Manipal 2003)                     fibers and receptors
    (a) vision         (b) speech
    (c) hearing        (d) all above                 76. Conduction of nerve impulse is connected
                                                         with (Wardha 2002)
68. Myelin sheath has which of the following?            (a) Ca and Mg     (b) Ca and K only
    (Manipal 2003)                                       (c) Na and K      (d) K and Mg
    (a) Carbohydrate (b) Starch
    (c) Protein       (d) Phospholipid               77. Which one of the following is not the reflex
                                                         action? (Wardha 2002)
69. The fluid which circulates in cerebrospinal          (a) Blinking of eye
    cavities is secreted by (Manipal 2002)               (b) Swallowing of food
    (a) Pons Varoili                                     (c) Removal of hand on pricking
    (b) Corpus callosum                                  (d) While hand is put on hot substance
    (c) Choriod plexi
    (d) Foramen of magendie                          78. Iter is (Wardha 2001)
                                                         (a) part of alimentary canal
70. Arbor vitae is (Manipal 2002)                        (b) connection between third and fourth
    (a) tree like structure in body                      ventricle
    (b) tree of life in cerebellum                       (c) lateral ventricle in cerebrum
    (c) tree of life in cerebrum                         (d) ear canal
    (d) ends part of spinal cord
                                                     79. CNS controls various body activities except
71. Preganglionic sympathetic         fibres   are       one of the following (AMU 2003)
    (Manipal 2001)                                       (a) heart beat
                                                                                                  24


    (b) reflex action                                   (c) axon            (d) both a and b
    (c) function of kidney
    (d) digestion of food                           89. In the development of the human body, the
                                                        ectoderm is responsible for the formation of
80. At the beginning of the start of nerve              (BHU 1997)
    impulse, the concentration of Na+ and K+            (a) sweat glands    (b) cutaneous glands
    are in the ratio (AMU 2003)                         (c) lens of the eye (d) all of these
    (a) 30 : 1          (b) 1 : 10
    (c) 10 : 30         (d) 1 : 20                  90. Which of the following is the part of mid
                                                        brain of rabbit? (BHU 1996)
81. Which cells cannot divide following birth in        (a) Diencephalon
    humans? (AMU 1997)                                  (b) Cerebrum
    (a) Muscle cells   (b) Erythroblasts                (c) Corpora quadrigemina
    (c) Osteoblasts    (d) Neuron                       (d) None of these

82. Salivation is mammal is under the control of    91. The 3rd, 6th and 11th cranial nerves are
    (AMU 1997)                                          (BHU 1995)
    (a) medulla oblongata                               (a) optic, facial and spinal nerves
    (b) mesencephalon                                   (b) occulomotor, trigeminal and spinal
    (c) hypothalamus                                    accessory
    (d) cerebellum                                      (c) occulomotor, abducens and spinal
                                                        accessory
83. Refractory period is during (BHU 2002)              (d) trochlear, abducens and vagus
    (a) polarization     (b) depolarization
    (c) repolarization (d) both b and c             92. Lateral ventricle and diocoel of brain (third
                                                        ventricle) are connected by (BHU 1995)
84. Nerve impulse conduction is unidirectional          (a) occipital foramen
    as (BHU 2002)                                       (b) foramen of Monro
    (a) axons combine with axon                         (c) foramen Magnum
    (b) neurotransmitters are site specific             (d) aqueduct of Sylvius
    (c) neurotransmitters can nerve be relapsed
    from dendrites                                  93. Which brain structure in rabbit is directly
    (d) Ca++ cannot be liberated at post synaptic       related to vision? (BHU 1994)
    junction                                            (a) Corpus callosum
                                                        (b) Corpus albicans
85. Foramen of Monro connects (BHU 2002)                (c) Corpus quadrigemina
    (a) third ventricle with the fourth                 (d) None of these
    (b) two lateral ventricles
    (c) two cerebral hemispheres                    94. Nervous secreting hormone like substances
    (d) cerebellum and cerebrum                         are (HPMT 2003)
                                                        (a) sensory        (b) neurosecretory
86. Which cranial nerve controls the movement           (c) motor          (d) a and b
    of eyeball? (BHU 2002)
    (a) Occulomotor    (b) Optic                    95. The nature of nerve impulse conduction is
    (c) Opthalimic     (d) Trochlear                    (HPMT 2002)
                                                        (a) mechanical      (b) thermal
87. The Broca’s area and Wernicke’s center are          (c) electrochemical (d) chemical
    the association area situated in cerebrum.
    These are associated with (BHU 2000)            96. The number of spinal nerve in man are …..
    (a) voluntary actions(b) blind spot                 pairs (HPMT 2002)
    (c) memory           (d) none of these              (a) 42            (b) 31
                                                        (c) 15            (d) 12
88. Nissl’s granuales are absent in (BHU 1997)
    (a) dendrite         (b) cyton
                                                                                                25


97. Which part of our brain controls balance and       (a) brain           (b) retina
    co-ordination? (HPMT 2000)                         (c) vertebrate’s embryo(d) cochlea
    (a) Cerebrum
    (b) Cerebellum                                 106.Which of the following animal has a false
    (c) Medulla oblongata                              nervous system but not brain? (HPMT
    (d) Hypothalamus                                   1997)
                                                       (a) Hydra         (b) Amoeba
98. Centre of thirst and hunger is (HPMT 2000)         (c) Cockroach     (d) Earthworm
    (a) medulla oblongata(b) cerebellum
    (c) cerebrum         (d) hypothalamus          107.Heart is innervated by (HPMT 1996)
                                                       (a) trigeminal      (b) vagus nerve
99. When the direction of nerve impulse is             (c) glossopharyngeal(d) facial
    reversed the condition is (HPMT 2000)
    (a) axo-axentic                                108.Acetylcholine is a hormone secreted by
    (b) axo-dedrite                                    nerve which aids in (HPMT 1994)
    (c) axo-axendendrite                               (a) diastole of the heart
    (d) none of the above                              (b) blood clotting
                                                       (c) systole of the heart
100.Commissure       uniting two      cerebral         (d) both a and c
    hemispheres of mammalian brain is (HPMT
    2000)                                          109.Glands of Swammerdam are (HPMT 1994)
    (a) Corpus spongiousm                              (a) ganglia of sympathetic nervous system
    (b) Corpus callosum                                (b) glands which are secreting hormone
    (c) Corpus quadrigemina                            (c) calcareous bodies protecting the ganglia
    (d) Corpus cavernosum                              in frog
                                                       (d) none of these
101.The medulla oblongata enclose the (HPMT
    2000)                                          110.Corpus callosum is a bridge of nerve fibers
    (a) optic capsule   (b) optic lobe                 which connects (HPMT 1995)
    (c) third ventricle (d) fourth ventricle           (a) two cerebral hemispheres
                                                       (b) two cerebellar hemisphere
102.What is common between acetylcholine,              (c) cerebrum to cerebellum
    nor-adrenalin and serotonin (HPMT 2000)            (d) none of the above.
    (a) All are anticoagulants
    (b) All lower the blood pressure               111.Corpus callosum is absent in the brain of
    (c) All are neurotransmitters                      (DYPATIL 2003)
    (d) None of these                                  (a) Echidna       (b) Monkey
                                                       (c) Rat           (d)Rabbit
103.Anterior to enlargement of spinal cord is
    known as (HPMT 1998)                           112.Parasympathetic and sympathetic are
    (a) filum terminale                                (DYPATIL 2003)
    (b) conus terminale                                (a) Antagonistic
    (c) cervical swelling                              (b) Similar
    (d) cauda equine                                   (c) Parallel inactive
                                                       (d) Always working together at the same
104.The flow of tears in women is stimulated by        time
    (HPMT 1998)
    (a) CNS                                        113.Towards the periphery of the spinal cord is
    (b) Peripheral nervous system                      (DYPATIL 2003)
    (c) Parasympathetic system                         (a) grey matter   (b) white matter
    (d) Sympathetic system                             (c) cytons        (d) both a and b

105.Apolar nerve cells are found in (HPMT          114.Diencephalon has      no   command     over
    1997)                                              (DYPATIL 2003)
                                                                                              26


   (a) heat            (b) heart beat                (b) supplies diaphragm
   (c) love            (d) anger                     (c) muscles
                                                     (d) oesophagus, lungs, stomach
115.Anterior choroids plexus is formed in
    (DYPATIL 2003)                               124.Which chemical is released by vagus nerve
    (a) cerebral hemispheres                         to slow down the heart beat? (RPMT 1998)
    (b) olfactory lobes                              (a) Adrenalin       (b) Acetylcholine
    (c) medulla oblongata                            (c) Nor epinephrine (d) Epinephrine
    (d) diencephalon
                                                 125.The sound reception can be interpreted by
116.Which is activated in stress condition?          (RPMT 1998)
    (DPMT 2003)                                      (a) olfactory lobe (b) cerebral hemisphere
    (a) parasympathetic (b) sympathetic              (c) cerebellum     (d) medulla oblongata
    (c) somatic         (d) whole ANS
                                                 126.Which two extra cranial nerves are present
117.Acetylcholine helps in (DPMT 2003)               in amniotes? (RPMT 1998)
    (a) synaptic transmission                        (a) Laryngeal and hypoglossal
    (b) membrane permeability                        (b) Spinal accessory and hypoglossal
    (c) synaptic delay                               (c) Hypoglossal and facial
    (d) none of these                                (d) Trigeminal and glossopharyngeal

118.Cranial nerves numbering IV, V and VII are   127.Arbor vitae controls (RPMT 1996)
    respectively (DPMT 2001)                         (a) voluntary actions
    (a) Trochlear, trigeminal, auditory              (b) involuntary actions as group movement
    (b) Trochlear, trigeminal, facial                of muscles
    (c) Auditory, facial, trochlear                  (c) involuntary actions like secretion of
    (d) Auditory, trochlear, facial                  gland
                                                     (d) none above
119.Brain and spinal cord are (PPMT 2003)
    (a) Intermediary neurons                     128.VIII cranial nerve connects which part of
    (b) Effectors                                    the body? (BVP 2003)
    (c) Receptors                                    (a) Eye            (b) Ear
    (d) Sensory organs                               (c) Nose           (d) Tongue

120.Extension of sympathetic nervous system is   129.Decrease in heart beat is caused by (BVP
    (PPMT 2003)                                      2003)
    (a) pineal         (b) neurohypophysis           (a) parasympathetic system
    (c) adrenal cortex (d) adrenal medulla           (b) sympathetic system
                                                     (c) central nervous system
121.At a resting state a nerve cell has (PPMT        (d) reflex action
    2000)
    (a) high K+ outside and low of Na+ inside    130.Which of the following is not reflex action?
    (b) low K+ outside and high Na+ inside           (BVP 2003)
    (c) high K+ inside and low Na+ outside           (a) weeping        (b) sneezing
    (d) high K+ inside and high Na+ outside          (c) coughing       (d) yawning

122.The bridge of nerve fibres connecting two    131.Which part of the brain affects the
    cerebellar lobes is (PPMT1998)                   endocrine system the most? (BVP 2003)
    (a) corpus callosum (b) conus medularis          (a) Cerebellum     (b) Medulla
    (c) medulla oblongata(d) pons                    (c) Hypothalamus (d) Cerebrum

123.Pneumogastric branch of vagus nerve          132.The difference between cranial and spinal
    supplies (PPMT 1997)                             nerves is (BVP 2003)
    (a) muscles of larynx
                                                                                                     27


    (a) spinal nerves comprise sensory and           140.Which one of the following is a purely
    motor fibers and cranial nerve has only one          motor nerve? (MPPMT 2002)
    kind                                                 (a) Vagus        (b) Facial
    (b) spinal sensory nerve from dorsal root            (c) Abducens     (d) Trigeminal
    ganglia at their origin from spinal cord and
    cranial nerves originate from brain              141.The ventricles of cerebral hemispheres
    (c) both above                                       communicate through (BPMT 1997)
    (d) none above                                       (a) foramen magnum
                                                         (b) foramen opali
133.Duct of Sylvius is another name of (BVP              (c) foramen of Monro
    2002)                                                (d) optic foramen
    (a) Iter           (b) sulci
    (c) foramen of Monro(d) gyrus                    142.Which one of the ventricles helps in
                                                         communication of medulla oblongata of
134.Fourth cranial nerve is (BVP 2002)                   brain with spinal cord? (JIPMER 2002)
    (a) trochlear       (b) abducens                     (a) II               (b) III
    (c) trigeminal      (d) vagus                        (c) IV               (d) V

135.Longest nerve which ends in cephalic             143.Chemical substance released in synapse
    region is (BVP 2001)                                 during transmission of an impulse is
    (a) sciatic        (b) vagus                         (JIPMER 1997)
    (c) trigeminal     (d) pathetic                      (a) aceto-acetic acid (b) adrenine
                                                         (c) acetic acid       (d) acetylcholine
136.Corpus callosum in mammals joins (CMC
    2003)                                            144.Which one of the following is an excitatory
    (a) two cerebellar lobe                              neurotransmitter? (EAMCET 2001)
    (b) two pelvic girdles                               (a) Acetylcholine (b) Dopamine
    (c) two pectoral girdles                             (c) Glycine         (d) Oxytocin
    (d) two cerebral hemisphere
                                                     145.The cranial nerves which control the
137.During the period before excitation the              movement of eyeball are (EAMCET 1998)
    condition of nerve is (CMC 2002)                     (a) 4, 6and 7     (b) 3, 4 and 6
    (a) resting period (b) action potential              (c) 2, 3 and 5    (d) 5, 8and 9
    (c) reflex action    (d) spike potential
                                                     146.Which one of the following is sensory
138.The aqueduct of Sylvius is a duct (CMC               nerve? (EAMCET 1998)
    2002)                                                (a) Trigeminal nerve (b) Vagus nerve
    (a) connecting of the two lateral ventricles         (c) Pathetic nerve (d) Auditory nerve
    of brain
    (b) connecting utricle and saccule of inner
    ear                                              147.Synaptic fatigue is due to (EAMCET 1998)
    (c) passing through spinal cord                      (a) exhaustion of neurotransmitter
    (d) connecting the third and fourth ventricles       (b) release of more acetylcholine
    of brain                                             (c) release of more adrenaline
                                                         (d) none of these
139.During conduction of nerve           impulse
    (MPPMT 2002)                                     148.Sympathetic nervous system is also called
    (a) Na+ moves into axoplasm                          (EAMCET 1998)
    (b) Na+ moves out of axoplasm                       (a) visceral       (b) thoracico-lumbar
    (c) K+ moves into axoplasm                          (c) cranio-sacral  (d) mesentric
    (d) Ca++ moves into axoplasm
                                                                                                         28


                                              ANSWERS # 09

        1. b     2. b      3. a      4. b      5. c     6. c      7. b      8. d      9. d        10.b
       11. a    12. d     13. b     14. a     15. a    16. b      17. d     18. c    19. c       20. b
       21. d    22. a     23. a     24. a     25. c    26. d      27. d     28. b    29. d       30. a
       31. c    32. c     33. a     34. a     35. d    36. a      37. a     38. a    39. a       40. a
       41. b    42. c     43. b     44. d     45. d    46. a      47. a     48. d    49. b       50. c
       51. c    52. a     53. c     54. b     55. a    56. b      57. a     58. b    59. b       60. d
       61. d    62. a     63. a     64. b     65. a    66. d      67. d     68. d    69. c       70. b
       71. b    72. c     73. c     74. d     75. b    76. c      77. b     78. b    79. a       80. c
       81. d    82. a     83. d     84. b     85. b    86. a      87. a     88. c    89. d       90. c
       91. c     92. b    93. c     94. b     95. c    96. b      97. b     98. d    99. a       100.b
       101.d    102.c     103.c     104.c     105.c    106.a     107.b     108.d     109.c       110.a
       111.a    112.a     113.b     114.b     115.d    116.b     117.a     118.b     119.d       120.d
       121.d    122.d     123.d     124.b     125.b    126.b     127.b     128.b     129.a       130.a
       131.c    132.b     133.a     134.a     135.b    136.d     137.a     138.d     139.a       140.c
       141.c    142.c     143.d     144.a     145.b    146.d     147. b    148. b


                                         EXPLANATION # 09

1. (b) Ninth pair of cranial nerve in frog is glossopharyngeal, originating from the lateral sides of
   medulla oblongata. It is a mixed cranial nerve. It functions in the sense of taste and touch and
   movement of pharynx during swallowing.

2. (b) Vagus is the longest cranial nerve having maximum branching and so it is called as wondering
   nerve.

3. (a) Olfactory lobes are paired short club shaped structures present at the anterior part of the brain.
   They are responsible for the sense of smell and are not well developed in humans.

7. (b) Vagus, the longest cranial nerve controls the heart muscles, inhibiting the heart beat.

8. (d) Corpus callosum, a bundle of nerve fibres connecting the two cerebral hemispheres is absent in
   amphibians and present in mammals.

9. (d) In resting condition, there is high concentration of sodium ions on the outside of nerve fibre and
   less concentration of potassium ions on the inner side. This creates a negative potential of about 70
   mV relative to the outside called as resting membrane potential.

12. (d) Transmission is accomplished by a neurotransmitter, acetylcholine present in the synaptic vesicles
    of the presynaptic knob. This neurotransmitter diffuses in the synaptic cleft and activates the post
    synaptic membrane, so that the conduction starts again.

18. (c) sympathetic nervous system is represented by a chain of 21 sympathetic ganglia on either side of
    spinal cord. It receives preganglionic fibres from the spinal cord which make their exit along with
    thoracic and lumbar nerves and constitute thoraco-lumbar outflow.

19. (c) The grey matter of cerebellum is called cerebellar cortex, while the white matter inside formed a
    branched tree like structure called arbor vitae or tree of life.
                                                                                                            29


22. (a) In the peripheral nervous system, myelin is produced by Schwann cells, which surround the axon.
    Gaps (nodes) in the myelin sheath along the length of the axon are known as the nodes of Ranvier.

26. (d) Preganglionic parasympathetic fibres make their exit along with the 3 rd, 7th, 9th, 10th cranial nerves
    and 2nd, 3rd, 4th sacral nerves. They together form the cranio-sacral outflow.

36. (a) Myelin is made of special cells called Schwann Cells that forms an insulated sheath, or wrapping
    around the axon. There are small nodes or gaps called the nodes of Ranvier between adjacent myelin
    sheath cells along the axon. As an impulse moves down a myelinated (covered with myelin) axon, the
    impulse jumps form node to node instead of moving along the membrane, known as saltatory
    conduction.

47. (a) Pons consists mainly of nerve fibres which form bridges between the two cerebellar hemispheres
    and of fibres which pass between the higher levels of the brain and the spinal cord.

48. (d) Piamater is the innermost covering lying in close contact with the brain, arachnoid is the middle
    layer and also vascular and duramater is the outermost, thick, double layered and non-vascular.

53. (c) Cavities of the brain are called as ventricles which consist of four hollow fluid filled spaces inside
    the brain. (See ventricles of brain).

69. (c) Cerebrospinal fluid, present in the ventricles of brain is secreted by the anterior choroids plexus
    (formed by epithalamus and piamater) and posterior choroids plexus (formed by the roof of medulla
    oblongata and piamater).

78. (b) Iter or aqueduct of Sylvius is a narrow canal, which connects the third ventricle to the fourth
    ventricle.

83. (d) After a nerve impulse is period when the neuron is unable to conduct a nerve impulse called the
    refractory period. The refractory period is a very short period during which the sodium-potassium
    pump continues to return sodium ions to the outside and potassium ions to the inside of the axon.
    Thus returning the neuron to the resting potential.

87. (a) Broca’s area is present in the parietal lobe of cerebral hemisphere and is concerned with the motor
    speech area. Wernicke’s area is present in the temporal lobe of cerebral hemisphere and is concerned
    with the sense of understanding speech.

97. (b) Cerebellum helps in control of body posture, co-ordinates voluntary muscle activities and
    equilibrium of body.

98. (d) Hypothalamus contains reflex centres linked to the autonomic system. It includes appetite and
    satiety centre to control the desire for food.

112. (a) Sympathetic and parasympathetic nervous system work against one another which enables the
    body to make rapid and precise adjustment of involuntary activities in order to maintain a steady
    state.

115. (d) Anterior choroids plexus is formed by the association of epithalamus (roof of diencephalon) and
    piamater.

126. (b) In amniotes the last two pairs of cranial nerves are extra, i.e. spinal accessory (eleventh) and
    hypoglossal (twelfth).
                                                                                                       30


128. (b) Eight cranial nerve is auditory, distributed along the organ of Corti and semicuircular canals,
    functioning in hearing and equilibrium.

145. (b) Oculomotor (III), trochlear (IV) and abducens (VI) function in the rotation of the eyeball, iris,
    lens, eyelids and constriction of pupil.

				
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