Lecture Cns

8/10/2019 Lecture Cns

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15

THE NERVOUS

SYSTEM

C H A P T E R F I F T E E N


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Divisions of the nervous system


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Anatomical Organization of theNervous System


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Neuronal Organization: CNS

Found in both

brain and spinalcord:

1. centers= cellbodies

2. gray matter=cell bodies/centers,neuroglia,unmyelinatedaxons, anddendrites of motorneurons

- Clusters of cellbodies = nuclei

Tracts = white matter, bundles of axons For the conduction of nerve impulses

Two types: sensory and motor tracts(ascending anddescending)

Sensory tracts relay sensory information obtained fromreceptors throughout the body to the brain via the spinalcord

Responses to this information is relayed back to effectorsvia motor tracts


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Sensory pathway

Ascending

Information from sensory receptors to CNS

Motor pathway

Descending

Information from CNS to skeletal muscle or glands

Direct pathwayscause precise, voluntary movements

I ndir ect pathwaysresult in involuntary movement (from brain

stem)

Pathways

A neural pathway is comprised of centers/cell bodies andtracts


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An Introduction to the Organizationof the Brain


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Figure 15.1 Major Divisions of

the Brain

Major Regions of the Brain


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Major Regions of the Brain


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Figure 15.13b Sectional Views of

the Brain


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Cerebrum= largest portion-left and right cerebralhemispheresdivided by the longitudinal fi ssure

-connected by the corpus callosum-folded into ridges and grooves: grooves = sulci

-sulci divide the cerebrum into lobes

-ridges = gyri(gyrus)

Major Regions and Landmarks

Central sulcus

Frontal and parietallobes


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-cerebrum is comprised of:

1. white matter- neurons with

long, myelinated axons

-organized into tracts

2. basal nuclei or gray matter

-sometimes called the basal

ganglia4 nuclei found

deep within the cerebrum

- links to the midbrain

- receives input from the cortex& provides output to the motor

areas of the cortex via the

thalamus

-integrate motor commands

-regulates the initiation &

termination of muscle mve.-also functions to anticipate

body movements & controls

subconscious contraction of

skeletal muscle

Major Regions and

Landmarks


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- basal ganglia:multiple nuclei found deep within the cerebrum-first described by Thomas Wells - 1664

- links to the midbrain

-1. receives input from the cortex & provides output to the motor areas of the cortex via the

thalamus

-2. integrates motor commands-3. regulates the initiation & termination of muscle mve.

-4. also functions to anticipate body movements & controls subconscious contraction of skeletal

muscle


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Basal Ganglia comprised of the:

1. striatum

caudate nucleus:activity occurs prior to eye movements putamen:precedes or anticipates body movements

nucleus accumbens

2. globus pallidus:regulates muscle tone for movements

3. claustrum

4. substantia nigra:high concentration of dopanergic neurons 5. subthalmic nucleus


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Medical application: Basal Ganglia

-damage to the basal ganglia:

-results in uncontrollable, abnormal body movements

-muscle rigidity may develop and tremors

-Parkinsonneurons that extend from the substantia nigra

to the caudate nucleus and putamen

degenerate

-loss of dopamine releasing neuronsincrease in

muscle tone and stiffness

-Huntington - hereditary disorder-caudate nucleus and putamen degenerate with loss

of neurons that release GABA or ACh

-spasmatic muscle contractions and loss of mental

status


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Major Regions and Landmarks-outer layer = cerebral cortex

-area for specific processing of

sensation, -area of voluntary

movement, speech, all thought

processes

-plus association areasfor integration and

analysis of incoming info & help in

making of decisions

e.g. somatosensory, visual, auditory,

language and common integrative areas

-motor and sensory areas

e.g. pr imary somatosensoryarea (postcentral gyrus):touch,

proprioception, pain, itching,

thermal - forms a map of the

entire body

e.g. primary visual, auditory &gustatory areas

e.g. primary motor area

(precentr al gyrus):controls

voluntary contractions

e.g.Brocas speech area


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Major Regions and Landmarks-speech:involves complexactivities that involve sensory,

association & the motor areas ofthe cortex

-97% of the populationthese

language areas are located in the

left hemisphere

-planning and production ofspeechBrocas

-the left frontal lobe

-sends impulses to the premotor

area that controls contractions

of the larynx, pharynx & mouth-plus impulses are sent to the

primary motor area where

they control breathing

-aphasia:injury to language areas of the cortex

-inability to comprehend or use words

-damage to Brocas = nonfluent aphasia

(inability to form words)

-damage to auditory association area =fluent

aphasia(inability to comprehend spoken or

written words)


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-Amyotrophic lateral sclerosis:Lou Gehrigs disease

-unknown cause-attacks motor areas of the cortex, axons of motor neurons

in the spinal cord and motor neuron cell bodies

-muscle weakness and atrophy

-begins in regions of the SC that affect hands and arms and

then spreads


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Diencephalon

includes the hypothalamus, thalamus,epithalamus and subthalamus

thalamus: 80% of the diencephalon

paired oval masses of gray matter

organized into nuclei, interspersed

with white matter

major relay station for most sensory

impulses from the SC, brain stem

crude perception of pain, heat and

pressure (refined in cerebrum)

transmits motor information from

cerebellum to the cerebrum

relays nerve impulses to and from

different areas of the cerebrum


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Major Regions and Landmarkshypothalamus

-Emotions, autonomic

functions, hormone production

-mamillary bodiesserve as

relay stations for reflexes

related to eating

-supraoptic and preoptic

nucleithat in hormone

secretion (ADH) and body

temp

1. control of the ANS

integrates signals from the

ANS (regulated smooth and

cardiac muscle contraction)

major regulator of visceralactivities (heart rate, food

movements, contraction of

bladder)

2. produces hormones&

connects with pituitary to

regulate its activity

3. regulates emotional and behavioral patternsrage,

aggression, pain and pleasure + sexual arousal4. regulates eating & drinkinghypothalamus contains

a thirst center which responds to a rise in osmotic

pressure in the ECF (dehydration)

5. controls body temperaturemonitors temp of blood

flowing through the hypothalamus


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epithalamusconsists of the pineal glandand habenular nuclei

-pineal glandpart of the endocrine system

-secretes the hormone melatonin

-increased secretion in dark

-promote sleepiness and helps set the circadian

rhythms of the body (awake/sleep period)

subthalamusworks with the cerebrum and cerebellum to control bodymovements


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Major Regions and LandmarksBRAIN STEM

Medulla oblongata continuation of the SC

forms the inferior part of the brain stem

relays sensory information and controls

automatic motor functions

white matter contains sensory/ascendingand motor/descending tracts

contains several nuclei also

these regulate autonomic functions - reflex

centersfor regulating heartbeat and BP

(cardiovascular center), respiration

(respiratory center), plus vomiting,

coughing, sneezing, hiccuping and

swallowing

nuclei in the posterior part are associated

with sensations of touch, proprioception,

pressure and vibration

-injury to the medulla: hard blow to the

back of the head or upper neck can be

fatal-damages the medull ary rhythmicity

areaof the respiratory center (disrupts

pattern of breathing)

-non-fatal injury: paralysis and loss of

sensation, irregular breathing and heart

rate


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Pons

= bridge

- e.g. connects brain stem to the cerebrumvia bundles of axons

- superior to the medulla and anterior to thecerebellum

consists of nuclei (cell bodies in graymatter) and tracts

somatic and visceral motor responses

Pontine nucleicontrol voluntarymovements that originate in the cerebralcortex and are relayed through the ponsinto the cerebellum

Pneumotaxic areacontrols breathing(with medulla)

Apneustic areacontrols breathing (withmedulla)

BRAIN STEM

M j R i d L d k


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Midbrain (Mesencephalon)

relay station between the cerebrum andthe spinal cord

extends from the pons to the

diencephalon

sends motor tracts to the SC, medulla

and pons & conducts sensory tracts tothe thalamus

processes visual and auditory

information - posterior part of the

midbrain

transfers information from the retina tothe eye muscles - tracking & scanning

pupillary reflex, shape of the lens

reflexes that mediate movements of the

eyes, head and neck

relays impulses from hearing receptors

to the thalamus

Major Regions and LandmarksBRAIN STEM

-generates involuntary somatic

motor responsesrelease of dopamine from

substantia nigra(nuclei) - loss of

these neurons = Parkinsons

red nucleiforms synapses with

cerebellum to coordinate muscle

movements

M j R i d L d k


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Cerebellum

divided into hemisphere with

lobes - like the cerebrum anterior and posterior lobes

has a superficial layer of gray

matter called the cerebellar cortex

- like the brain

deep to the gray matter are tractsof white matter

adjusts voluntary and involuntary

motor activities

evaluates and coordinates

motor activities initiated by thecerebrum and corrects problems

by sending info back to the

cerebrum

regulate posture & balance

uses sensory data and stored

memories


Th Li bi S


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called the emotional brain

group of structures that surround

the brain stem

involved in olfaction and

memory

emotionanger, fear,

happiness

associated with specific

responsesbehavioralpatterns

basic behavioral patterns

preparing for attack,

laughing, crying, blushing

also includes sexualbehaviors for the

continuation of the species

connects with the

hypothalamus to regulate

these behaviors

The Limbic System

olfactory tract

amygdala

hippocampus

anterior thalmic nuclei

fornix

mamillary body

parahippocampal gyrus

corpus

callosum

hypothalmic nuclei

cingulate gyrus


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called the emotional brain

involved in olfaction and memory

main components:

1. limbic lobe:rim of cerebral cortex on the medial surface of

each hemispherecomprised of the cingulate and parahippocampal

gyri 2. dentate gyruscontaining the hippocampus

3. amygdala:stimulation - rage

4. olfactory bulbs

5. septal nuclei

6. mammillary bodiesof the hypothalamusmotor nuclei for

reflexes associated with eating (chewing, swallowing, licking

etc...)

7. fornixwhite tracts that connect the hypothalamus to the

hippocampus

fibers end at the mamillary bodies

The Limbic System


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Protection and Support of the Brain

Th C i l M i


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The Cranial Meninges Cranium is covered with protective membranes

= meninges

Cranial meninges are continuous with spinal

meninges

3 layers: 1. outer, fibrous dura materforms

sheets (falx) that separate the cerebrum and the

cerebellum into the hemispheres and the

cerebellum from the cerebrum

-comprised of an outer endosteal layerand andinner meningeal layer

2. middle arachnoid mater

3. inner, thin pia mater

-there are spaces between these membranes

A. subarachnoid space:between the

arachnoid and pia maters

B. subdural space:between the

arachnoid and the dura mater

C. epidural spacebetween the dura

mater and the vertebral canal in thespinal column

l d i i ( )


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Blood-Brain Barrier (BBB) Blood into brain via the internal carotid and vertebral arteries

Blood supply to brain must be continuous Brain stores no glucose Uses about 20% of the oxygen and glucose in the body

The BBB prevents harmful substances in the blood from reachingthe brain tissue

The endothelial cells lining the brain capillaries have very tighttight junctions

BBB allows passage of lipid-soluble substances (gases, alcohol,anesthetic agents), slows the passage of most water-solublesubstances (ions, urea) and PREVENTS the passage of proteinsand most antibiotic drugs (i.e. large molecules)


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Ventricles of the Brain & CSF

Ventricles Chambers in centralpassageway of the brain

2 lateral ventricles, 1 third

ventricle, 1 fourth ventricle

connects to the central canalwhich runs into the spinal

canal

These chambers contain

cerebrospinal fluid


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CSF:

80 to 150 mLglucose,proteins, lactic acid, urea,ions

made by specialized cellsin the lateral ventricleschoroid plexus

continually circulates -ventricles and central canalto subarachnoid space

Chemical and physicalprotectionprovidesproper ionic environment

for neuronal actionpotentials + shockabsorber

transports nutrients,chemical messengers andwaste products.

Ventricles of the Brain & CSF


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CSF is gradually reabsorbed into the

blood through fingerlike projections

into the dural venous sinuses = arachnoid

granulations

large spaces for the circulation

of blood can be found between the

two dural layers = sinuses

e.g. superior sagittal sinus

also large veins run through thesubarachnoid space

e.g. cerebral veins

interfering with the drainage of CSF

into the subarachnoid space can result

in accumulation of CSF in the ventricles

& CSF pressure rises = hydrocephalus

(implantation of a shuntlateral ventricle

into the superior vena cava or abdomen)


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Flow of CSF

The blood supply to the brain


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The blood supply to the brain

Arterial blood reaches brain viainternal carotid internal carotid arteries give rise to

the Circle of Willis loops around the optic chiasma

the loop is formed from anteriorand posterior communicatingarteries

from this loop branches theanterior and posterior cerebralarteries

the posterior communicating andcerebral unite to form the basilarartery

from the basilar artery branchesnumerous smaller arteriese.g.cerebellar and pontine

the basilar then splits to form thevertebral arteries

Venous blood leaves via internaljugular veins

Th bl d l t th b i


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The blood supply to the brain Arterial blood reaches brain via internal carotid, vertebral arteries

Venous blood leaves via internal jugular veins

-transient ischemic attacks (TI A):no permanent neurologic damage-temporary cerebral dysfunction caused by impaired blood

flow to the brain

-dizziness, weakness, blurred vision, slurred speech,

paralysis

-persists from 5 to 50 minutes

-caused by emboli (blood clots), atherosclerosis

-cerebral vascular accident (CVA): stroke

-affects 500,000 people per year

-third leading cause of death

-permanent cerebral dysfunction caused by impaired blood

flow to the brain

-sudden onset of symptoms

-caused by cerebral hemorrhage (anuerysm), blood clot, atherosclerosis

-treatmentrapid administration of clot-dissolving drugs (e.g. tPA) if stroke

is caused by a clot

Al h i Di


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Alzheimers Disease

-loss or reasoning, memory

-11% of population over 65 (4 million people)

-unknown causethought to be genetic factors + environmental &lifestyle

-mutations in 3 genes coding for: prenisil in-1, -2and amyloid precursor

proteinlead to early onset forms (less the 1% of all cases)

-also mutations in gene coding for apolipoprotein E (ApoE)

a protein that helps transport cholesterol in the blood

-brain abnormalities:

1. loss of ACh releasing neurons from the nucleus basalis(below

the basal ganglia subtypeglobus pallidus

2.beta-amyloid plaques

deposited outside of neurons3. neurofibr il lary tanglesabnormal bundles of protein filaments

in affected brain regions

-treatments:drugs that inhibit acetylcholinesterase improve alertness e.g. Tacrine

& Donepezil


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THE NERVOUS SYSTEM: THE

SPINAL CORD AND SPINAL

NERVES

S i l C d


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Spinal Cord length in adults = 16 to 18 inches

Cervical and lumbar

enlargements

cervical = C4 to T1, nerves to and

from upper limbs

lumbar = T9 to T12, nerves to and

from lower limbs Tapers to conus medullaris

fi li um terminalearises from the

CM - extension of the pia mater that

anchors the SC to the coccyx 31 segments each with

Dorsal root ganglia

Sensory neuron cell bodies

Pair of dorsal roots

Pair of ventral roots


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Inferior End of

Spinal Cord

Conus medullaris

cone-shaped end of spinal cord

Filum terminale

thread-like extension of pia mater

stabilizes spinal cord in canal

Caudae equinae (horses tail)

dorsal & ventral roots of lowestspinal nerves

Spinal segment

area of cord from which each pair of

spinal nerves arises


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External Anatomy of Spinal Cord

Some nerves to know

-phrenic

-ulnar

-radial

-medial

-musculocutaneous

-femoral

-obturator

-sciatic

-ilioinguinal

-thoracic (intercostals)

i l h i l d


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Histology of the Spinal Cord Central gray matter

Contains cell bodies of neurons and

glial cells + unmyelinated axons Gray matter projections are horns

Peripheral whi te matter

Myelinated and unmyelinated axons

Organized as tracts or columns

Organization of Gray Matter 1. Poster ior gray horns

Somatic and visceral sensory nuclei

2. Anter ior gray horns

Somatic motor control

3. Lateral gray horns Visceral motor neurons

Gray commissures

Axons of interneurons crossingcordated and unmyelinated axons

Organization of White Matter


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Organization of White Matter Six columns (funiculi )

Anter ior , lateral and poster ior

whi te columns

Contain tracts of myelinatedneurons

Ascending tractsrelay

information from spinal cord

to brain

Descending tractscarry

information in the oppositedirection

Spinothalamic tract

pain, temperature, deep pressure &

crude touch

Posterior columns

proprioception, discriminative touch,

two-point discrimination, pressure andvibration

Direct pathways (corticospinal)

precise, voluntary movements

Indirect pathways (rubrospinal,

vestibulospinal)

programming automatic movements,

posture & muscle tone, equilibrium &

coordination of visual reflexes

rubrospinalmidbrain to spinal cord

corticospinalcortex to spinal cord

reticulospinalRAS (brain stem) to spinal cord

vestibulospinalinner ear to spinal cord

spinocerebellarspinal cord to cerebellum

spinothalmicspinal cord to thalamus


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Motor tracts:

lateral corticospinal: cortex to spinal cord

anterior corticospinal

recticulospinal tracts (lateral & medial): RAS (brainstem) to spinal cord

rubrospinal tract: midbrain to spinal cord

vestibulospinal tract: inner ear to spinal cord

tectospinal tract: tectum to spinal cord Sensory tracts:

spinocerebellar (posterior & anterior): spinal cord tocerebellum

posterior column

spinothalmic (Anterior & lateral): spinal cord tothalamus

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