The Nervous System_2_

The Nervous System

• 2 categories in nervous system.

• Central nervous system (CNS) –

brain, spinal cord

• Peripheral nervous system (PNS) –

nerves outside CNS.

• 2 divisions of PNS – somatic

(voluntary), autonomic (involuntary)

http://lumen.georgetown.edu/faculty/che3/bvl/images/nervous.jpg

• Autonomic divided into 2:

1sympathetic (during stress),

2parasympathetic (normal



functioning)

http://www.drstandley.com/images/nervous5.bmp

Nerve Tissue

• 2 types of cells:

1neurons (responsive cells that



conduct impulses at fast speeds)

2neuroglia (support, maintain



neurons)

http://www.greenspine.ca/media/neurons_and_glial_cells.jpg

5 types of neuroglia

• 1astrocytes (anchor neurons)

• 2ependymal (form cerebrospinal

fluid)

• 3microglia (eat invading

microorganisms)

• 4oligodendrocytes (provide

insulation around CNS – myelin)

• 5Schwann cells (insulation around

PNS)

http://www.nrc-cnrc.gc.ca/education/images/bio/gallery/pl_astrocytes.jpg

Neuron made up of…

• 1cell body (cytoplasm, nucleus,

organelles)

• 2dendrites (branching extensions

from cell body – receive impulses)

• 3axons (conducts impulse away from

body)

http://pami.uwaterloo.ca/~gsdharwa/b_c_i/neuron.gif

• Axons enclosed with Schwann cells

forming layers rich in fat.

• Provides insulation – myelin.

• Insulation not continuous (gaps –

nodes of Ranvier)

http://www.sirinet.net/~jgjohnso/neuronsandsynapsel.gif

• Gray matter is made of

unmyelinated fibers – shorter with

no myelin

• White matter is made of

myelinated fibers – can be longer

and have myelin

http://cache.eb.com/eb/image?id=54745&rendTypeId=4

Types of Neurons

• Structurally, 3 different types.

• 1Multipolar – many dendrites – carry

impulses to skeletal muscle.

• 2Bipolar – single dendrite, single

axon – special sensory areas (ears,

eyes)

• 3Unipolar – one nerve fiber (from

skin to spinal cord)

http://homepage.psy.utexas.edu/homepage/class/Psy332/Salinas/Cells/multipolar.gif

• Functionally, 3 different types of

neurons.

• 1Sensory (afferent) – carry from

body to CNS)

• 2Association (interneurons) – links

between neurons

• 3Motor (efferent) – from CNS to

body

http://www.nsbri.org/HumanPhysSpace/focus7/f7-290.jpg

Impulse Transmission

• Difference in voltage across cell

membranes.

• Openings in membrane are called

ion channels. They regulate

movement of ions.

• Greatest influence – Na+, K+

http://www2.montana.edu/cftr/images/IonChannel2.gif

• Sodium-potassium pump –

transports sodium out of cell,

potassium inside.

• Every 3 Na+ pumped out, 2 K+ back

in.

• Nerve impulse – wave of ion

reversals (changing charge of

membrane)

• Potential on inside -70 mV.

• Change in membrane permeability

to sodium – ions flow outward;

inside becomes more positive –

depolarization (+ 30 mV)

• Restored to normal – repolarization

– potassium inward through ion

channels, sodium channels close.

http://scienceblogs.com/clock/upload/2006/06/ActionPotential.jpg

• Node of Ranvier – gaps in axon of

myelinated fibers

• Impulse jumps across myelin sheath

from node to node – fastest

conduction in body.

http://www.getbodysmart.com/ap/nervoussystem/celltypes/menu/image.gif

Types of Stimuli

• All-or-none – either impulse

conducted or not.

• Threshold – minimum strength of

stimulus needed for action

potential.

• Subthreshold – no action potential.

• Series of subthreshold – summation

(lead to action potential)

http://www.octc.kctcs.edu/gcaplan/anat/images/Image370.gif

• Synapse is a gap between adjacent

neurons.

• Presynaptic neuron receives impulse

and sends it to a postsynaptic

neuron.

• Axon of presynaptic – contain

neurotransmitters in synaptic

vesicles.

http://www.colorado.edu/intphys/Class/IPHY3430-200/image/figure7m.jpg

2 effects of neurotransmitters

• 1Excitatory – increase membrane

permeability to sodium ions (cause

action potential) – accetylcholine,

norepinephrine

• 2Inhibitory – lowers chance of impulse

crossing synapse – endorphins, GABA

(inhibit pain)

http://www.ainenn.org/images/bio-sinapse.PNG

Central Nervous System

• 1Spinal cord – from base of brain to

1st, 2nd lumbar vertebrae.

• Enters through foramen magnum of

skull.

• Protected by vertebral column,

fluid, and meninges (layers of

membrane)

http://www.csuchico.edu/~pmccaffrey//syllabi/CMSD%20320/images/SpinalCord2.JPG

Layers of Meninges

• Dura mater - Outermost layer –

thick sheath around cord

• Epidural space – area filled with fat

tissue (insulation)

• Arachnoid - middle layer – made of

collagen fibers

• Pia mater - innermost layer –

attached to outer surface of spinal

cord

http://www.infovisual.info/03/img_en/024%20Spinal%20cord.jpg

• Subarachnoid space - between

arachnoid and pia mater – filled

with fluid CSF

• CSF is cerebrospinal fluid, a shock

absorbing liquid

• 31 segments of spinal cord – each

give rise to spinal nerves through

spinal roots.

http://www.frca.co.uk/images/epidural-anatomy7.gif

Direction of Impulses

• Ascending tract (up towards brain)–

sensory information

• Descending tract (away from

brain)– motor information

• Spinal cord also serves for reflexes

– rapid response to emergency.

Reflex arc

• Receptor (generates action

potential) sends message along

sensory neuron to CNS (spinal

cord).

• Examples: Withdrawal reflex,

patellar reflex, vomiting- smooth

muscle reflex, heart rate- cardiac

muscle reflex

http://webanatomy.net/anatomy/reflex_arc.jpg

The Brain

• 3 major regions: 1forebrain,

2midbrain, 3hindbrain.



• Forebrain – cerebrum, diencephalon

• Midbrain – below diencephalon

• Hindbrain – pons, medulla oblongata,

cerebellum.

• Brain stem – midbrain, pons, medulla

http://www.dhushara.com/book/brainp/brainil/brain.jpg

• Brain protected by cranium, CSF,

meninges.

• CSF – cushions organs, nourishes

brain, removes wastes.

• Contained in 4 ventricles (cavities

in brain)

• CSF formed in ventricles by

filtration of plasma through

capillaries.

• Choroid plexus forms blood-brain

barrier – selectively permits

certain substances to enter (water,

glucose, oxygen); blocks bacteria.

• Head injuries, tumors, blockage of

flow channels – causes ventricles to

expand with CSF (hydrocephalus) –

pushes brain into cranium.

• Infants - skull will expand (sutures

in skull); adults – pressure.

• Treatment – install shunt to drain

fluid (dumps into stomach)

http://healthcare.utah.edu/healthinfo/images/ei_0433.gif

Cerebrum

• Cerebrum – higher brain – conscious

thought, memory, learning.

• Divided into left and right cerebral

hemispheres.

• Wrinkled structure (convolutions) –

result from rapid growth during

development.

http://www.web-books.com/eLibrary/Medicine/Physiology/Nervous/cerebrum_lobes.jpg

• Foldings project upward – gyri;

downward – sulci.

• Deep grove – fissure; 2 major ones

– longitudinal (divides hemispheres),

transverse (cerebrum from

cerebellum)

http://cas.bellarmine.edu/tietjen/HumanBioogy/giri_and_sulci.gif

• Cerebrum divided into lobes

(frontal, parietal, occipital,

temporal)

• Frontal, parietal – separated by

central sulcus; frontal, temporal –

lateral sulcus.

http://universe-review.ca/I10-80-prefrontal.jpg

• External region (gray) – cerebral

cortex; internal (white).

• Inside white matter, sections of

gray (basal ganglia) – unconscious

movement (i.e. swinging arms while

walking)

• Hemispheres separated by corpus

callosum.

• Diencephalon – inferior to corpus

callosum – made of gray matter; 2

features – thalamus, hypothalamus.

• 2 endocrine glands – pineal,

pituitary.

http://www.web-books.com/eLibrary/Medicine/Physiology/Nervous/diencephalon.jpg

• Thalamus – surrounds 3rd ventricle –

pineal gland here.

• Relay station for sensory impulses

(no smell) traveling to cerebral

cortex + involuntary motor impulses

traveling outward.

• Responsible for primitive sensations

(temp, touch, pain, pressure)

http://z.about.com/d/psychology/1/0/F/thalamus.jpg

• Hypothalamus – below thalamus –

within sella turcica.

• Controls homeostatic activities –

digestion, respiration, heart rate)

• Intermediary between nervous,

endocrine system.

• Waking, sleeping patterns, sex

drives, stress symptoms.

http://www.becomehealthynow.com/images/organs/nervous/glakgar_pit_hypothalamus_cra.jpg

• Midbrain – between diencephalon

and pons.

• Pathway between cerebrum,

cerebellum.

• Reflex center for rapid eye, head,

trunk movements.

http://universe-review.ca/I10-80-midbrain.jpg

• Pons – below midbrain – helps

regulate breathing rhythm.

• Relays messages from peripheral

nerves.

http://academic.kellogg.cc.mi.us/herbrandsonc/bio201_McKinley/f15-20a_pons_longitudin_c.jpg

• Medulla oblongata – below pons,

unites with spinal cord.

• Contains cardiac center (regulates

heart), vasomotor center (regulates

blood pressure), respiratory center

(depth, rhythm of breathing)

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/BrainLS.gif

• Cerebellum – posterior part of

hindbrain.

• 2 hemispheres – connected by

vermis.

• Cortex on outside (gray), mass of

white on inside – forms tree

pattern (arbor vitae)

http://www.mult-sclerosis.org/cerebellum.gif

Peripheral Nervous System

• Nerves, ganglia, sensory receptors.

• Communication between CNS and

other areas of body.

• Nerve – composed of more than 1

type of tissue; responsible for

transporting nerve impulses.

http://www.nrc-cnrc.gc.ca/education/images/bio/gallery/pl_nerve.jpg

• Nerves with sensory fibers –

afferent nerves; motor fibers –

efferent nerves; both – mixed

nerves.

• Ganglia – clusters of neurons

outside CNS.

http://content.answers.com/main/content/wp/en/f/f0/ReflexArc1.jpg

• Sensory receptors – respond to

stimuli (changes in environment)

• Most endings of dendrites from

sensory neurons.

• Also found in special sensory organs

(eye, taste bud, etc)

http://health.yahoo.com/media/mayoclinic/images/image_popup/r7_eyefluid.jpg

• Cranial nerves – attach directly to

brain.

• Can be sensory, motor, or mixed.

http://www.chiro.org/chimages/diagrams/cranialn.jpg

12 Pairs of Cranial Nerves

• 1olfactory (smell) • 8vestibulocochlear

• 2optic (sight) (hearing)

• 3oculomotor • 9glossopharyngeal

(movement of eye) (taste)

• 4trochlear • 10vagus (speech,

(movement of eye) swallowing)

• 5trigeminal (chewing) • 11accessory (speech,

• 6abducens (eye swallowing)

movement) • 12hypoglossal (tongue

• 7facial (taste) movement)

• Spinal nerves – 31 pairs – attach to

spinal cord.

• 8 cervical, 12 thoracic, 5 lumbar, 5

sacral, 1 coccygeal.

http://www.apparelyzed.com/_images/content/spine/spinenerves.jpg

• Fibers between cord and spinal

nerve – root.

• Sensory – dorsal roots; motor –

ventral roots.

• Dorsal root contains large swelling

when unites with ventral root

(dorsal root ganglion)

http://www.stanford.edu/group/hopes/rltdsci/trinuc/f_f06drg&ah_s.jpg

• Plexus – complex network of nerves.

• Cervical plexus – innervates

diaphragm (breathing movements) –

paralyzing C3-C5 inhibits breathing.

• Brachial plexus – supply skin,

muscles of upper limbs.

• Lumbosacral plexus – skin, muscles

of lower limbs.

http://www.anaesthesiauk.com/images/cervical-plexuses1.gif

• Autonomic system of PNS –

stimulates or inhibits glands,

cardiac muscle, smooth muscle.

• Adrenergic fibers – release

norepinephrine; cholinergic fibers –

acetylcholine.

http://www.mhhe.com/biosci/esp/2001_saladin/folder_structure/in/m3/s6/assets/images/inm3s6_1.jpg

Diseases

• 1ALS – Degeneration of motor

neuron cell bodies; progressive; also

known as Lou Gehrig’s disease.

• 2Bacterial meningitis – infection of

the meninges – causes severe

headaches, can lead to brain

damage.

http://services.epnet.com/GetImage.aspx/getImage.aspx?ImageIID=5184

• 3Schizophrenia – social withdrawal,

hallucinations, inability to

distinguish reality.

• CAT scans reveal enlarged lateral

ventricles.

http://www.scienceclarified.com/images/uesc_09_img0510.jpg