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					CENTRAL NERVOUS SYSTEM: Chapter 14 – Brain
2% of body weight but uses 20% of body’s energy
Human brain is about 85% water

5 Major brain regions:
       1. Telencephalon

       2. Diencephalon

       3. Mesencephalon: “midbrain”

       4. Metencephalon

       5. Myelencephalon

       Brainstem: mesencephalon, pons and medulla oblongata


Ventricles:
        hollow chambers contain CSF

       lateral ventricles:
                separated by septum pellucidum

       third ventricle:

               connected to the fourth via the cerebral aqueduct (mesencephalic aqueduct)


       fourth ventricle:

               circulates CSF into the central canal of the spinal cord


Protection of the Brain & Spinal Cord
1. Bone

2. Meninges (pg. 455):
       A. Dura Mater: outermost meninx
               •double layered

               •dural folds contain dural sinuses (large collecting veins)

                          falx cerebri – dural fold between cerebral hemispheres
                                   contains superior and inferior sagittal sinuses

                                  note sinuses collect venous blood and drain into internal jugular veins


       B. Arachnoid: middle layer
              •loose fitting

               •subdural space

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                •subarachnoid space
                       -filled with
                       -contains

                -gives rise to arachnoid villi – drain CSF into superior sagittal sinus


        C. Pia Mater: inner meninx
                •adheres tightly to brain & spinal cord

                •meningitis: inflammation of meninges


                •encephalitis: inflammation of brain


3. Cerebrospinal Fluid (CSF):
       - watery fluid
       - serves as a cushion for brain and spinal cord

        -transports nutrients, chemicals & waste products
                exchanges with IF of CNS


        - choroid plexuses (located in the roof of the 3rd ventricle, floors of lateral ventricles, and in roof of fourth
        ventricle)

        -CSF contains fewer proteins than plasma


        - ependymal cells

        - hydrocephalus (applications manual)



        - used for diagnostic purposes
        - lumbar puncture


4. BLOOD-BRAIN BARRIER
       -capillary cells bound with tight junctions

        -astrocytes

        -O2, CO2, fats, & fatty acids, lipid soluble materials diffuse through easily
        (note H+ ions cannot diffuse through blood-brain barrier)

        -blood-brain barrier is more permeable in areas which release hormones

        - main arteries transporting blood to brain: internal carotid and vertebral

        - head injury that damages blood vessels can cause bleeding into dura mater

                                                                                                                            2
       -CVA:

               Hemorrhagic


               Ischemic



MYELENCEPHALON (Medulla Oblongata)
      •most inferior part of brainstem
      •blends into spinal cord at

       •central canal of spinal cord continues into medulla where

       • sensory and motor (pyramidal) tracts run through medulla


       •contains cardiac, vasomotor, respiratory centers


METENCEPHALON (Pons & Cerebellum)
      A. Pons “bridge’
             Conduction tracts:
                     a. longitudinal tracts (ascending & descending)
                     b. transverse tracts

            contains respiratory centers (apneustic & pneumotaxic)


       B. Cerebellum: contains ½ of all neurons in the brain but only comprises 10% of the brain

               functions: controls muscles for posture, balance, proprioception
                       -receives proprioceptive information from spinal cord and monitors all proprioceptive, visual,
                       tactile, balance & auditory sensations received by brain.

               ataxia – damage to cerebellum by trauma or stroke (also temporary from alcohol)


               arbor vitae:

               transverse fissure:


MESENCEPHALON (midbrain)
      1.) corpora quadrigemina: superior and inferior colliculus
              both control reflex movements of eye, head, neck, trunk to stimuli

               superior colliculus: visual reflexes (receives info from lateral geniculate nucleus of thalamus on that side)
                       response to bright light

               inferior colliculus: auditory reflexes in response to loud noise


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       2.) Reticular activating system (RAS) headquarters
                Fires impulses to keep cerebrum awake and alert



       3.) Substantia nigra
               contains neurons that make/secrete dopamine
               controls (inhibits) basal nuclei

               Parkinson’s disease: chronic progressive disorder
                       neurons fire out of control making it difficult to control movement



DIENCEPHALON
      1. Epithalamus             2. Thalamus             3. Hypothalamus

       1. Epithalamus
               •choroid plexus

               • pineal gland:
                       secretes hormone: melatonin


       2. Thalamus: (Right and Left thalamic nuclei)
               •gray matter held together by intermediate mass
               •"traffic cop" and “filter” for sensory information

               • major groups of each thalamic nuclei
               1.) anterior group (nuclei) & lateral group (nuclei) – part of limbic system

               2.) medial group (nuclei) – connect emotional centers in hypothalamus with frontal lobe (awareness of
               emotional state)

               3.) ventral group (nuclei) – relay info from basal nuclei and cerebellum to somatic motor areas of
               cerebral cortex

                       -relay touch & proprioception information to cerebral cortex

               4.) posterior group contains
                       • lateral geniculate nucleus receives information from the optic tract and relays it to the
                       occipital lobe for interpretation

                       • medial geniculate nucleus relays auditory information


       3. Hypothalamus
              •extends from optic chiasm(a) to mamillary bodies


               mamillary bodies:
                      sensory: smell
                      motor: chewing, swallowing

                                                                                                                       4
                •infundibulum

                •main visceral (autonomic) control center

                1.) Controls pituitary gland

                2.) Secretes ADH & oxytocin

                3.) Control HR, RR, pupil size, BP, thirst, hunger, sex drive, body temperature, sleep/wake cycles
                (circadian rhythms)


                4.) Subconscious control of skeletal muscle contractions – in response to emotions – anger, pleasure,
                pain

                5.) Part of the limbic system

Limbic System mainly in cerebrum and diencephalon
        Functions:
        1.) emotions & motivation
        2.) linking conscious intellectual functions of cerebral cortex with unconscious functions of brain stem
        3.) memory storage and retrieval


        Main Structures:
        1.) amygdaloid body (amygdala) : links emotions with memories,
                Helps store and classify emotionally charged memories
                Fear & processes fight-flight response emotions/physical responses: sweaty palms, ↑HR


        2.) limbic lobe of the cerebral hemisphere contains the
                 hippocampus: involved in memory especially long-term memories


        3.) fornix: curved tract connects hippocampus to hypothalamus

        4.) mamillary bodies:


        • link between emotional stress and ill health “mind-body” connection
                 Psychosomatic illnesses:


        •communication between cerebral cortex & limbic system explains:

TELENCEPHALON: NEOCORTEX: CEREBRUM: 85% of the brain
      •cerebral hemispheres:
             each receives sensory info. and sends info(motor) to the opposite side of the body.

                each has different functions




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•gyri (gyrus):

•sulcus (sulci):
•fissure:

•lobes:            Frontal (41%) : command center for brain: reasoning, problem solving, judgement, impulse
                                    control
                                    Motor control, memory, higher emotion: empathy
                                    last part of brain to develop

                   Parietal (19%): processes pain & touch, home of the somatosensory cortex

                              Cognition (location & speed of objects), movement, orientation, speech, recognition

                   Temporal (22%): processes sound, home of the primary auditory cortex &
                                 Wernicke’s area (language)

                                     Involved in emotion, memory & speech

                   Occipital (18%): processes vision, home of the visual cortex


Cerebral Landmarks:
       1. longitudinal fissure

          2. central sulcus
                  precentral gyrus
                  postcentral gyrus

          3. lateral sulcus

          4. parieto-occipital sulcus

3 basic regions of each cerebral hemisphere:
         I. internal: white matter
         II. outer cortex: cerebral cortex
         III. basal nuclei:

I. Cerebral White Matter:
        •contains:
        •Fibers and tracts classified according to

          1. Commissures:
                 •corpus callosum


          2. Association Fibers:

          3. Projection Fibers:


II. Cerebral Cortex: all activities associated with being conscious
        all sensation, somatic motor control, memory, cognitive thought

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        -composed of

•3 kinds of functional areas:
        1. motor:
        2. sensory:
        3. association:

1. Motor Areas: posterior part of frontal lobes
       A.) Primary Motor Cortex: in precentral gyrus of frontal lobe
               voluntary control of skeletal muscles

                pyramidal cells (neurons) have cell bodies (in gyrus)

                axons of these neurons form pyramidal tracts which run from precentral gyrus, cross over to
                opposite side in medulla and continue down spinal cord to synapse in ventral horn of spinal cord
                gray matter


        B.)Premotor Cortex – frontal lobe
               located anterior to primary motor cortex

                coordination of learned movements

                relay information to primary motor cortex


2. Sensory Areas: in parietal, temporal, & occipital lobes
       A.) Primary Sensory Areas (Primary Somatosensory Cortex)
               •located in the postcentral gyrus (parietal lobe)


        B.) Visual Area (Visual Cortex)
                •in occipital lobe
                •receives input from retina


        C.) Auditory Area (Auditory Cortex)
                •in temporal lobes
                •receives input from cochlea


        D.) Primary Olfactory Area (Olfactory Cortex)
                •in temporal lobes
                •receives input from olfactory mucosa


        E.) Primary Taste (Gustatory) Cortex
                •in parietal lobes
                •receives input from taste buds




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       3. Association Areas: process sensory & motor responses
              - somatic sensory association area: recognition of touch

               - visual & auditory association area: reading & word recognition


               integrative centers: receive information from many different areas
               a. prefrontal cortex: abstract intellectual functions
                       processes reasoning, problem solving, judgement, impulse control
                       planning & predicting consequences
                       understanding of time
                       empathy and altruism
                       connects to other areas of brain: tension/anxiety generated by prefrontal cortex first


               b. speech center (Broca’s area or motor speech):
                      in frontal lobe –usually left side
                      patterns of breathing & vocalization for normal speech

               c. Wernicke’s area: ability to interpret what is heard or read


               Aphasia: disorder that affects the ability to speak or read

               Dyslexia: disorder affects comprehension & use of written words

       Lateralization: (split brain concept)
                right hemisphere: identification
                        recognizing faces and 3D relationships


               left hemisphere: reading, writing and speaking
                       analytical tasks


       III. Basal (cerebral) Nuclei:
                consists of corpus striatum
                coordination of learned motor movements

               controls/adjusts muscle tone/subconscious control

               inhibited by dopamine



Monitoring Brain Activity – Electroencephalogram (EEG)
       monitors the electrical activity (brain waves) of the brain
       1.) Alpha waves – resting, awake
       2.) Beta waves – concentration or stress
       3.) Theta waves – during children (abnormal in adults – may show tumor)
       4.) Delta waves – large waves seen during sleep

       thalamus – synchronizes electrical activity between hemispheres

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       seizure – electrical disturbance in brain – “electrical storm”
               vary – staring, abnormal movements, unusual sensations, inappropriate behavior
                        tonic-clonic (grand mal):

                         petit mal or focal seizures:

              causes: febrile, head trauma, tumors or idiopathic

              epilepsies – seizure disorders:
                      Tx – anti-seizure meds


Cranial Nerves
Nerve        Nerve Name                    Function             Innervates
Number
I            Olfactory                     Sensory              Smell

II           Optic                         Sensory              Sight

III          Occulomotor                   Motor                Eye & upper eyelid muscles (4 out of 6
                                                                eye muscles), pupil reflex in response to
                                                                light
IV           Trochlear                     Motor                Eye muscle for looking down
             (smallest nerve)
V            Trigeminal                    Mixed                1.) ophthalmic (s): skin of forehead,
                                                                upper eyelid, eyebrow
             3 branches                    ophthalmic (s)       2.) maxillary (s): branch lower eyelid,
             ophthalmic                    maxillary (s)        upper jaw, cheek & nose
             maxillary                     mandibular (s) (m)   3.) mandibular (s) lower jaw, (m)muscles
             mandibular                                         of mastication
VI           Abducens                      Motor                Lateral Eye muscles (look sideways)

VII          Facial                        Mixed                (s) taste anterior 2/3 tongue (m) muscles
             *Bell’s palsy caused by                            of facial expression, submandibular &
             inflammation of facial                             sublingual salivary glands
             nerve
VIII         Vestibulocochlear             Sensory              cochlear branch-hearing
             (Auditory)                                         vestibular branch-balance
IX           Glossopharyngeal              Mixed                (s)taste posterior 1/3 tongue & pharynx,
                                                                chemoreceptor info., gag reflex
                                                                (m) pharynx muscles for swallowing/
                                                                parotid gland – saliva production
X            Vagus                         Mixed                pharynx, heart, diaphragm, visceral
             (see page 487)                                     organs of thoracic & abdominopelvic
                                                                cavitites (s & m)
XI           Accessory                     Motor                muscles of pharynx, larynx,
                                                                sternocleidomastoid & trapezius
XII          Hypoglossal                   Motor                muscles of tongue




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Brain Disorders:
1.) Alzheimer’s Disease:
        Irreversible progressive disease which destroys memory and thinking skills (dementia)

       β amyloid plaques and neurofibrillary tangles develop in the brain, neurons become damaged and shrink
       Often occurs in hippocampus first – affects memory

       Genetics, lifestyle are contributing factors




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