Chapter 11

The Brain & Spinal Cord

Introduction• Brain & s.c. comprise the CNS• Brain is protected by cranium & meninges – membranes that

surround brain• Consists of 3

layers:1. dura mater2. arachnoid

mater3. pia mater

Meninges

1. Dura mater – outermost;

tough, fibrous; attached to

inside of cranium; contains

many b.v. & nerves

Arachnoid mater – thin &

weblike; no b.v. or nerves

SUBARACHNOID SPACE – contains

cerebrospinal fluid (CSF)

3. Pia mater – delicate; w/b.v. & nerves; attached

directly to brain & follows contours

Importance of Meninges

• dural sinus – spaceformed when d.m.splits into 2 layers

• subdural hematoma –fluid & blood collectsunder d.m. from trauma

• Meningitis – inflammationof arachnoid or pia materfrom bacteria or virus

Partitions of Dura mater

1. Falx cerebelli – b/t rt. &lt. cerebellar hemispheres

2. Falx cerebri – b/t rt. & lt.cerebral hemispheres

3. Tentorium cerebelli – b/tcerebrum & cerebellum

Protection of Spinal Cord• S.C. protected by bony vertebrae & same 3

meninges• Epidural space –

b/t vertebrae &

d.m.; contains b.v.

and connective

tissue for protection

The Spinal Cord

• Consists of 31 segments• Each gives rise to a spinal

nerve• Provides 2-way communi-

cation b/t brain & body• 2 main functions:

1. center for reflexes2. conducts impulses to & from brain

The Spinal Cord

• Beginning pt. – foramenmagnum

• Ending pt. – conus medullaris (narrow pt. b/t L1-L2)

• Cauda equina – cord of connective tissue (a.k.a.filium terminale)

Cross Section – Spinal Cord

• Gray matter –horns

• White matter –funiculi

• 2 grooves divide s.c.into rt. & lt. halves:posterior median sulcusanterior median fissure

Cross Section - S.C.

• Central canal – contains CSF;

continuous w/spaces

in brain• Gray commissure –

connects “wings”

of “butterfly”

Nerve Tracts

• White matter in s.c.consists of fibers callednerve tracts; provide 2-waycommunication b/t brain & s.c.;

• 2 types:1. ascending – sensory fibers carry impulses to brain

*In the medulla, fibers cross over

Nerve Tracts

2. descending – motor

fibers carry impulses to muscles

* In the medulla, fibers cross over

Reflexes • S.C.- center for reflexes

(automatic, subconscious responses)

• Reflexes control many involuntary actions (HR, resp.rate, swallowing, sneezing, etc.)

• Pathway that neurons follow ina reflex - reflex arc.

• One of the simplest – patellar reflex (helps maintain an upright position)

• Involves only 2 neurons, sensory& motor (no interneuron)

Parts of a Reflex Arc

• Most reflexes include 5 structures:1. receptor2. sensory n.3. interneuron4. motor neuron5. effector

• Other examples:withdrawal reflex (occurswhen a person touches something painful) plantar reflex, Babinski reflex (abnormal in adults), biceps, triceps & ankle jerk reflexes

Ventricles of Brain

• Ventricles - Interconnected cavities in brain -

continuous w/central canal & subarachnoid space of s.c. ; filled w/CSF

• 4 ventricles:1st (left hemisphere)2nd (rt. hemisphere)3rd (midline of brain)4th (in brainstem)

Ventricles of Brain

Pathway of CSF Circulation

1. Most CSF produced in lat. ventr. by choroid plexuses

2. Interventricular foramina –openings; allow CSF toflow from lat. to 3rd ventr.

3. 3rd ventricle4. Cerebral aqueduct – narrow

canal; connects 3rd to 4th ventr.

5. 4th ventricle

CSF Circulation6. Flows into central canal & SA space of s.c. & back to subarachnoid space of brain7. CSF reabsorbed by

arachnoid granulations8. Drain into blood-filled

dural sinus into circ. sys.Humans secrete approx. 500mlof CSF daily.Only about 150 ml in CNS at anygiven time (continuously reabsorbed)CSF - clear fluid; nourishes cellsof the CNS; completely surroundsbrain & s.c. for protection.

Lumbar Puncture

• Needle inserted intosubarachnoid spaceof s.c. & CSF is withdrawn

• Site is usually b/t L1-L2 or

L3-L4 (a.k.a. spinal tap)• A manometer used to

measure CSF pressure• CSF can be analyzed for

viruses, bacteria, bleeding,tumors of the n.s., MS, & early-onset Alzheimers

Normal vs. Hydrocephalic Brain

←Normal

Normal Brain Hydrocephaly Normal intracranial Excessive accumulation pressure 7-15 mm Hg of CSF causes ventricles in brain to dilate; infant’s skull expands & incr. in circumference (bulging

fontanels possible)

Treatment of Hydrocephaly

• Shunt placed in brain to regulate pressure & reabsorb CSF into subarachnoid space

The Human Brain

• 5 Major Areas:

1. Cerebrum

2. Basal ganglia

3. Diencephalon

4. Brain stem

5. Cerebellum

Cerebrum

• Largest part of brain• Consists of 2 halves (hemi-

spheres)• Connected by corpus

callosum (collection of nervefibers)

• Convolutions – raised ridges• Sulci – shallow grooves• Fissures – 2 deep grooves

1. Longitudinal – divides brain into rt. & left halves

Cerebrum

2. Transverse –separates cere-brum from cere-bellum

• Cerebral cortex –thin, outer gray matter;contains cell bodies

• White matter – under gray;makes up most of the cerebrum

Functions of Cerebrum

• 3 basic functions:1. Motor area – sends

impulses to muscles2. Sensory area – interpret

impulses from sensory receptors

3. Association area – not primarily motoror sensory; interprets, analyzes, reasons,memory, problem solving, etc.

Lobes of the Brain

• Sulci divide each cerebral hemisphere into 5 functional areas called lobes (named for skull bones).

• 5th lobe - insula

(not shown) located

deep w/in lateral sulcus

& covered by parts of

frontal, parietal &

temporal lobes

Lobes of the Brain

1. Frontal• Association areas – problemsolving, planning,analyzing, etc.• Motor areas –(ant. to central sulcus) –control of voluntary muscles• Broca’s area – ant. to motor cortex & in left hemi.; coordinates muscles of speech

Lobes of the Brain

2. Parietal – • Somato-

sensory area – cutaneous & other senses

• Associationarea – under-standing speech& using words

Lobes of the Brain

3. Occipital – visual area

4. Temporal –auditory area& auditory memories

• Wernicke’s area – inleft temporal lobe; controlsanalysis of spoken language

5. Insula – deep w/inlateral sulcus & includesparts of frontal, parietal& temporal lobes; associated w/emotions

Basal Ganglia

• Also called basal nuclei

• Consist of gray matter deep within the cere-bral hemispheres

• Relay info from cortex to brainstem & s.c.

• Produce the ntm dopamine that inhibits motor functions (decr. levels assoc. w/Parkinson’s disease)

Diencephalon

• Includes 2 regions:1. Thalamus – receives

all sensory info &channels it to correctregion on cerebralcortex for interpret-ation

2. Hypothalamus – maintains homeo-stasis (i.e. heart rate, b.p., temp., hunger, sleep & wake cycles, growth)

Limbic System

• Also located in the

diencephalon is

the limbic system

• This area controls

emotions & is also

assoc.w/memory

Pineal & Pituitary Glands

• Also located in diencephalon

• Pineal gland –secretes melatoninin absence of light

• Controls sleep &wake cycles

• Pituitary gland – regulates growth & reproductive cycles under direction of hypothalamus

Brainstem

• Connects brain to s.c.• Includes 3 regions:

1. midbrain

2. pons

3. medulla

Midbrain

• 1st, short sectionof brainstem

• Relays info. fromlower parts of b.s.& s.c. to higher brain

• Contains corporaquadrigemina – structure that allows movement of eyes &head at same time

Pons

• Rounded bulge on

underneath side of

b.s.

• Sends impulses to

& from medulla &

cerebellum

Medulla Oblongata

• Enlarged contin-uation of s.c.

• All nerve tracts pass thru here &many cross over

• Acts as relay center b/t s.c. &cerebral cortex

Medulla

• Contains 3 centers:1. Cardiac center – area

that controls heart rate2. Vasomotor center –

constricts or dilates b.v.3. Respiratory center –

regulates rate & depth of breathing• Nonvital centers – coughing, sneezing, swallowing,

vomiting also located in medulla

Reticular Formation

• Nerve fibers scattered throughout the b.s.

• When sensory impulsesreach the r.f., it respondsby activating the cerebralcortex into wakefulness

• The cerebral cortex can alsoactivate the r.f. (intense cere-bral activity keeps a person awake)

• If the r.f. is destroyed, a personremains in a comatose state

Reticular Formation

• The r.f. filters incoming sensory info& decides what is important

• Decreased activity in the r.f. results in sleep

• Types of Sleep:1. Slow-wave (non-REM)- restful, dreamless; reduced b.p. & resp. rate; lasts from 70-90 min. & alternates w/REM sleep

Sleep

2. REM sleep (rapid eye movement) – “paradoxical sleep”; dream sleep; lasts 5-15 min.; heart & resp. rate irregular;

so important that if a

person lacks it one night,

it is made up for the

next night

Cerebellum

• Composed mostlyof white matter

• A treelike pattern is visible called thearbor vitae

• Integrates infoabout body position

• Coordinates skeletalmuscle activity

• Maintains posture &equilibrium