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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. arachnoid
mater
3. pia mater
Meninges
1. Dura mater – outermost;
tough, fibrous; attached to
inside of cranium; contains
many b.v. & nerves
Arachnoid mater
SUBARACHNOID SPACE – contains
cerebrospinal fluid (CSF)
3. Pia mater –
Importance of Meninges
• dural sinus –
• 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 –
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. –
• Cauda equina – cord of
connective tissue (a.k.a.
filium terminale)
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.)
• Pathway that neurons follow in
a reflex –
• One of the simplest – patellar
reflex (helps maintain an upright
position)
•
Parts of a Reflex Arc
• Most reflexes include 5
structures:
1.
2. sensory n.
3.
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.
2.
Most CSF produced
in lat. ventr. by choroid
plexuses
Interventricular foramina –
3.
4.
3rd ventricle
Cerebral aqueduct –
5.
5. 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
• Lumbar puncture video
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.
2. Basal ganglia
3. Diencephalon
4.
5. Cerebellum
Cerebrum
• Largest part of brain
• Consists of 2 halves (hemispheres)
• Connected by corpus
callosum (collection of nerve
fibers)
• Convolutions (gyri)–
• 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 –
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
Lobes of the Brain
1. Frontal
•
Association
areas –
• Motor areas –
(ant. to central sulcus) –
control of voluntary
muscles
•
Broca’s area –
Lobes of the Brain
2. Parietal –
• Somatosensory area –
cutaneous &
other senses
• Association
area –
Lobes of the Brain
3. Occipital –
4. Temporal –
auditory area
& auditory
memories
• Wernicke’s area
• 5. Insula – deep w/in
lateral sulcus & includes
parts of frontal, parietal
& temporal lobes; associated w/emotions
Girl with Half a Brain
• https://www.youtube.com/watch?v=2MKN
sI5CWoU
Right vs Left Brain
Preferences of the Two Sides of the Brain
Description of the Left-Hemisphere Functions
• Constantly monitors our sequential, ongoing behavior
• Responsible for awareness of time, sequence, details, and order
• Responsible for auditory receptive and verbal expressive strengths
• Specializes in words, logic, analytical thinking, reading, and writing
• Responsible for boundaries and knowing right from wrong
• Knows and respects rules and deadlines
Description of the Right-Hemisphere Functions
• Alerts us to novelty; tells us when someone is lying or making a joke
• Specializes in understanding the whole picture
• Specializes in music, art, visual-spatial and/or visual-motor activities
• Helps us form mental images when we read and/or converse
• Responsible for intuitive and emotional responses.
• Helps us to form and maintain relationships
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
• Also located in the
diencephalon is
the limbic system
•
Pineal & Pituitary Glands
• Also located in
diencephalon
• Pineal gland –
• Controls sleep &
wake cycles
• Pituitary gland –
Memory
• Hippocampus- Part of Limbic system
–
• Short term memory- around 7 items for 20
to 30 seconds.
• Long Term- can store unlimited info
indefinitely with rehearsal.
• Memory Video
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
• 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 –
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
• 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
•
• 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
Sleep Video
• sleep video
Cerebellum
• Composed mostly
of white matter
•
• Integrates info
about body position
• Coordinates skeletal
muscle activity