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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
mater
2. arachnoid
mater
3. 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 – space
formed when d.m.
splits into 2 layers
• subdural hematoma –
fluid & blood collects
under d.m. from trauma
• Meningitis – inflammation
of arachnoid or pia mater
from 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/t
cerebrum & 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 communication b/t brain & body
• 2 main functions:
1. center for reflexes
2. conducts impulses to &
from brain
The Spinal Cord
• Beginning pt. – foramen
magnum
• 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 sulcus
anterior 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 called
nerve tracts; provide 2-way
communication 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 in
a 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. receptor
2. sensory n.
3. interneuron
4. motor neuron
5. effector
• 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 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.
2.
3.
4.
5.
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 – narrow
canal; connects 3rd to 4th
ventr.
4th ventricle
CSF Circulation
6.
Flows into central canal &
SA space of s.c. & back to
subarachnoid space of brain
7.
CSF reabsorbed by
arachnoid granulations
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 - clear fluid; nourishes cells
of the CNS; completely surrounds
brain & s.c. for protection.
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. Basal ganglia
3. Diencephalon
4. Brain stem
5. Cerebellum
Cerebrum
• Largest part of brain
• Consists of 2 halves (hemispheres)
• Connected by corpus
callosum (collection of nerve
fibers)
• Convolutions – raised ridges
• Sulci – shallow grooves
• Fissures – 2 deep grooves
1. Longitudinal – divides brain into rt. & left halves
Cerebrum
2. Transverse –
separates cerebrum from cerebellum
• 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 muscles
2. Sensory area – interpret
impulses from sensory
receptors
3. Association area – not primarily motor
or 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 – problem
solving, 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 –
• Somatosensory area –
cutaneous &
other senses
• Association
area – understanding speech
& using words
Lobes of the Brain
3. Occipital –
visual area
4. Temporal –
auditory area
& auditory
memories
• Wernicke’s area – in
left temporal lobe; controls
analysis of spoken
language
5. Insula – deep w/in
lateral sulcus & includes
parts of frontal, parietal
& temporal lobes; associated w/emotions
Basal Ganglia
• Also called basal
nuclei
• Consist of gray matter
deep within the cerebral 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
•
1.
2.
Includes 2 regions:
Thalamus – receives
all sensory info &
channels it to correct
region on cerebral
cortex for interpretation
Hypothalamus –
maintains homeostasis (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 melatonin
in 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 section
of brainstem
• Relays info. from
lower parts of b.s.
& s.c. to higher brain
• Contains corpora
quadrigemina –
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 continuation 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 rate
2. 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 impulses
reach the r.f., it responds
by activating the cerebral
cortex into wakefulness
• The cerebral cortex can also
activate the r.f. (intense cerebral activity keeps a person awake)
• 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)- 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 515 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 mostly
of white matter
• A treelike pattern
is visible called the
arbor vitae
• Integrates info
about body position
• Coordinates skeletal
muscle activity
• Maintains posture &
equilibrium