Chapter 7 – Part 5
The Nervous System
Protection of the Central Nervous
System
1.
2.
3.
4.
Scalp and skin
Skull and vertebral column
Meninges
Cerebrospinal fluid
5. Blood brain
barrier
Meninges
 The three connective tissue membranes
covering and protecting the CNS
structures are meninges.
 Three Layers:
1. Dura Mater
2. Arachnoid Mater
3. Pia Mater
Meninges
1. Dura Mater – Outer
most layer
 Feels tough & leathery
 Folds inward in several
areas
 Double-layered external covering
1. Periosteum – Attached to the inner
surface of the skull
2. Meningeal Layer – Outer covering of
the brain
Meninges
2. Arachnoid
Layer – Middle
meningeal layer
 Web-like
3. Pia Mater – Innermost membrane of
the meninges
 Clings tightly to the surface of the brain and
spinal cord, following every fold
 Delicate layer
Cerebrospinal Fluid
 Similar to blood
plasma composition
 Formed by the choroid
plexus
 Forms a watery cushion to protect the
brain
 Continually circulated in arachnoid
space, ventricles, and central canal of
the spinal cord
Ventricles and Location of the
Cerebrospinal Fluid
Meningitis
 Meningitis - Inflammation of
the meninges
 Serious threat to the brain
because bacterial or viral meningitis
may spread into the nervous system of
the CNS.
 Usually diagnosed by taking a sample of
cerebrospinal fluid
 Procedure is called a lumbar (spinal)
tap
Blood Brain Barrier
 No other body organ is so absolutely
dependent on a constant internal
environment as is the brain.
 Other body tissues can withstand the rather
small fluctuations in the concentrations of
hormones, ions, and nutrients that continually
occur, particularly after eating or exercise.
 If the brain were exposed to such chemical
changes, uncontrolled neural activity might
result!
 Remember that certain ions are involved in
initiating nerve impulses and some amino
acids serve as neurotransmitters.
Blood Brain Barrier
 Neurons are kept separated
from bloodborne substances
by a blood-brain barrier.
 Composed of the least
permeable capillaries of the
body.
 Only water, glucose and
essential amino acids can easily
pass through the walls of these
capillaries.
 Metabolic wastes (urea, toxins,
proteins, and most drugs) are
prevented from entering the
brain.
Blood Brain Barrier
 The following contribute to the barrier:
1. Astrocytes
2. Relative impermeability of the capillaries Most responsible for providing this
protection
 Useless against some substances
 Fats and fat soluble molecules
 Respiratory gases
 Alcohol
 Nicotine
 Anesthesia
Traumatic Brain Injuries
 Concussion
 Slight brain injury
 May be dizzy, “see stars”,
or lose consciousness
briefly
 No permanent brain
damage
 Contusion
 Nervous tissue destruction
occurs
 Nervous tissue does not
regenerate
Shows an area of subarachnoid hemorrhage with
bleeding and an area of brain contusion where
the white ischemic brain has died
Traumatic Brain Injuries
Cerebral Edema –
Swelling of the brain
due to inflammatory
response to injury
Hemorrhaging –
Bleeding from
ruptured vessels
Traumatic Brain Injuries
 After head blows,
death may result from
intracranial hemorrhage
or from cerebral edema.
 Both may compress and
kill brain tissue
 Individuals who are
initially alert and lucid
following head trauma
and then begin to deteriorate neurologically later
are most likely hemorrhaging or suffering the
consequences of edema.
Cerebrovascular Accident (CVA)
 Commonly called a stroke
 Third leading cause of
death in the US
 Occur when blood
circulation to a brain
area is blocked (blood
clot or a ruptured blood
vessel)
 Brain tissue supplied with oxygen from that
blood source dies
 Loss of some functions or death may result
Cerebrovascular Accident (CVA)
• Fewer than 1/3 of those surviving a CVA
are alive 3 years later.
• Some patients recover at least partly,
because undamaged neurons spread
into areas where neurons have died and
take over some lost functions.
• Most of the recovery seen after brain
injury is due to this phenomenon.
Alzheimer’s Disease
 Progressive
degenerative
brain disease that
ultimately results in
dementia (mental
deterioration)
 Structural changes in
the brain include
abnormal protein
deposits and twisted
fibers within neurons
Alzheimer’s Disease
 Mostly seen in the elderly,
but may begin in middle
age
 Victims experience
memory loss, irritability,
confusion and ultimately,
hallucinations and death
 5-15% of people over 65
develop this condition.
Parkinson’s Disease
 Cause: Results from a
degeneration of the
dopamine-releasing
neurons, and as those
neurons degenerate, the
dopamine-deprived basal
nuclei they target become overactive
 Typically strikes people in their 50s and 60s
(Michael J. Fox is an exception)
 Cause of Parkinson’s is still unknown
Parkinson’s Disease
 Symptoms include:
1. Persistent tremor at rest
exhibited by head
nodding and “pill-rolling”
movement of the fingers
2. Forward-bent walking
posture and shuffling
gait
3. Stiff facial expression
4. Trouble initiating
movement or getting
their muscles going
Huntington’s Disease
 Genetic disease that leads to
massive degeneration of the
basal nuclei and later of the
cerebral cortex
 Strikes during the middle age
 Symptoms:
 Initial - wild, jerky, and almost continuous
flapping movements
 Later - marked mental deterioration
 Progressive and usually fatal within 15 years of
onset of symptoms
Treatment of Parkinson’s and
Huntington’s Disease
 Parkinson’s Disease
 Signs and Symptoms – Inhibition of the
motor drive
 Treatment – Usually treated with drugs that
enhance dopamine’s effects
 Huntington’s Disease
 Signs and Symptoms - Overstimulation of
the motor drive (opposite of Parkinson’s
disease)
 Treatment – Usually treated with drugs that
block dopamine’s effects