Chapter 7

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Chapter 7 Part 4The Nervous System
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• Protection of the Central Nervous System

1. Scalp and skin
2. Skull and vertebral column
3. Meninges
4. Cerebro-
   spinal fluid
5. Blood brain
   barrier

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• Meninges

• The three connective tissue membranes covering
  and protecting the CNS structures are meninges.
• Three layers
• Dura mater
• Arachnoid mater
• Pia mater

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• Meninges

• Dura mater outer
  most layer
• Feels tough leathery
  
• Folds inward in several
  areas
• Double-layered external covering
• Periosteum attached to the inner surface of the
  skull
• Meningeal layer outer covering of the brain

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• Meninges

• Arachnoid
  layer middle
  meningeal
  layer
• Web-like
• Pia mater innermost membrane of the meninges
• Clings tightly to the surface of the brain and
  spinal cord, following every fold
• Delicate layer

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• 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

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• Ventricles and Location of the Cerebrospinal Fluid

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• 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

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• 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.

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• Blood Brain Barrier

• Neurons are kept separated from bloodborne
  substances by a blood-brain barrier.
• Composed of the least permeable capillaries of
  the body
• Of water-soluble substances, 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.

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• Blood Brain Barrier

• The astrocytes contribute to the barrier, but the
  relative impermeability of the capillaries is
  most responsible for providing this protection.
• Useless against some substances
• Fats and fat soluble molecules
• Respiratory gases
• Alcohol
• Nicotine
• Anesthesia

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• 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
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• Traumatic Brain Injuries

• Hemorrhaging and Edema
• Cerebral edema - swelling of
  the brain
  due to inflammatory
  response to injury
• After head blows, death may
  result from
  intracranial
  hemorrhage (bleeding from
  ruptured
  vessels) 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.

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• 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

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• 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.

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• Alzheimers Disease

• Progressive degenerative brain disease that
  ultimately results in dementia (mental
  deterioration)
• Mostly seen in the elderly, but may begin in
  middle age
• Structural changes in the brain include abnormal
  protein deposits and twisted fibers within
  neurons
• Victims experience memory loss, irritability,
  confusion and ultimately, hallucinations and
  death
• 5-15 of people over 65 develop this condition.

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• Parkinsons Disease

• 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 Parkinsons is still unknown
• Symptoms include
• Persistent tremor at rest exhibited by head
  nodding and pill-rolling movement of the
  fingers
• Forward-bent walking posture and shuffling gait
• Stiff facial expression
• Trouble initiating movement or getting their
  muscles going

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• Huntingtons 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

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• Treatment of Parkinsons and Huntingtons Disease

• Parkinsons disease
• Signs and symptoms Inhibition of the motor
  drive
• Treatment usually treated with drugs that
  enhance dopamines effects
• Huntingtons disease
• Signs and symptoms - Overstimulation of the motor
  drive (opposite of Parkinsons disease)
• Treatment usually treated with drugs that block
  dopamines effects