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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
mater
2.
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 – space
formed when d.m.
splits into 2 layers
• subdural hematoma –
fluid & blood collects
under 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/t
cerebrum & 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 communication b/t brain & body
• 2 main functions:
1.
2.
The Spinal Cord
• Beginning pt. – foramen
magnum
• 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 sulcus
anterior median fissure
Cross Section - S.C.
• Central canal
• Gray commissure –
connects “wings”
of “butterfly”
Nerve Tracts
• White matter in s.c.
consists of fibers called
nerve tracts; provide 2-way
communication 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. receptor
2.
3. interneuron
4. motor neuron
5.
• Other examples:
withdrawal reflex (occurs
when 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.
3.
4.
Most CSF produced
in lat. ventr. by choroid
plexuses
Interventricular foramina –
openings; allow CSF to
flow from lat. to 3rd ventr.
3rd ventricle
Cerebral aqueduct –
5.
5. 4th ventricle
2.
CSF Circulation
6.
Flows into central canal &
SA space of s.c. & back to
subarachnoid space of brain
7.
8.
Drain into blood-filled
dural sinus into circ. sys.
Humans secrete approx. 500ml
of CSF daily.
Only about 150 ml in CNS at any
given time (continuously
reabsorbed)
CSF -
Lumbar Puncture
• Needle inserted into
subarachnoid space
of 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
Normal intracranial
pressure 7-15 mm Hg
Hydrocephaly
Excessive accumulation
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 (hemispheres)
•
• Convolutions –
• Sulci –
• Fissures – 2 deep grooves
1. Longitudinal – divides brain into rt. & left halves
Cerebrum
2. Transverse –
separates cerebrum from cerebellum
• Cerebral cortex –
• White matter – under gray;
makes up most of the cerebrum
Functions of Cerebrum
• 3 basic functions:
1. Motor area – sends
impulses to muscles
2. 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 –
• Somatosensory area –
cutaneous &
other senses
• Association
area –
Lobes of the Brain
3. Occipital –
visual area
4. Temporal –
• Wernicke’s area – in
left temporal lobe; controls
analysis of spoken
language
5. Insula –
Basal Ganglia
• Also called basal
nuclei
• Consist of gray matter
deep within the cerebral hemispheres
•
• Produce the ntm
dopamine that inhibits motor functions (decr.
levels assoc. w/Parkinson’s disease)
Diencephalon
•
1.
2.
Includes 2 regions:
Thalamus – receives
all sensory info &
channels it to correct
region on cerebral
cortex for interpretation
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 section
of brainstem
• Relays info. from
lower parts of b.s.
& s.c. to higher brain
• Contains corpora
quadrigemina –
Pons
•
• Sends impulses to
& from medulla &
cerebellum
Medulla Oblongata
• Enlarged continuation of s.c.
• All nerve tracts
pass thru here &
many cross over
•
Medulla
• Contains 3 centers:
1. Cardiac center – area
that controls heart rate
2. 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 impulses
reach the r.f., it responds
by activating the cerebral
cortex into wakefulness
•
• If the r.f. is destroyed, a person
remains 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 mostly
of white matter
• A treelike pattern
is visible called the
arbor vitae
•
• Coordinates skeletal
muscle activity