Chapter 11

The Brain & Spinal Cord

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

• Consists of 3 layers:1. dura mater2.

3. pia mater

Meninges

1. Dura mater –

2. Arachnoid mater – thin &

weblike; no b.v. or nerves

SUBARACHNOID SPACE –

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 –

Partitions of Dura mater

1. Falx cerebelli –

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 –

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. 2.

The Spinal Cord

• Beginning pt. – foramenmagnum

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

• Cauda equina –

Cross Section – Spinal Cord

• Gray matter –

• White matter –

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

Cross Section - S.C.

• Central canal

• 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 –

*In the medulla, fibers cross over

Nerve Tracts

2. descending –

* 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.)

• - 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. 3. interneuron4. motor neuron5.

• 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 -

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 –

5. 5. 4th ventricle

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

8. Drain into blood-filleddural sinus into circ. sys.

Humans secrete approx. 500mlof CSF daily.Only about 150 ml in CNS at anygiven time (continuously reabsorbed)CSF -

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.

3. Diencephalon

4.

5. Cerebellum

Cerebrum

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

spheres)•

• Convolutions – • Sulci – • Fissures – 2 deep grooves

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

Cerebrum

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

• Cerebral cortex –

• 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 –

Lobes of the Brain

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

• 5th lobe - insula

(not shown)

Lobes of the Brain

1. Frontal• Association areas –

• 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 –

Lobes of the Brain

3. Occipital – visual area

4. Temporal –

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

5. Insula –

Basal Ganglia

• Also called basal nuclei

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

•

• 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 –

Limbic System

•

• This area controls

emotions & is also

assoc.w/memory

Pineal & Pituitary Glands

• Also located in diencephalon

• Pineal gland –

• Controls sleep &wake cycles

• Pituitary gland –

Brainstem

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

1

2.

3.

Midbrain

• 1st, short sectionof brainstem

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

• Contains corporaquadrigemina –

Pons

•

• Sends impulses to

& from medulla &

cerebellum

Medulla Oblongata

• Enlarged contin-uation of s.c.

• All nerve tracts pass thru here &many cross over

•

Medulla

• Contains 3 centers:1. Cardiac center – area

that controls heart rate2. Vasomotor center –

3. Respiratory center –

• 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

•

• 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)-

Sleep

2. REM sleep (rapid eye movement) – “

Cerebellum

• Composed mostlyof white matter

• A treelike pattern is visible called thearbor vitae

•

• Coordinates skeletalmuscle activity