Download Notes Part 5

Protection of the Central Nervous System
 Enclosing it in bone
 Skull & vertebral column
 Enclosing it in membranes
 Meninges = connective tissue membranes that
cover & protect CNS structures
 Watery cushion
 Cerebrospinal fluid (CSF)
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Protection of the Central Nervous System (P. 249)
Figure 7.17a
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Meninges
 From most superficial to deepest: dura mater,
arachnoid mater, pia mater
 Dura mater
 Double-layered external covering
 Periosteal layer—attached to inner surface
of the skull
 Meningeal layer—outer covering of the
brain
 Folds inward in several areas
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Meninges
 Arachnoid mater
 Middle layer
 Web-like
 Pia mater
 Internal layer
 Clings to the surface of the brain
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Meninges
Figure 7.17b
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 The subarachnoid space is filled with
CSF;
 And arachnoid villi= specialized
projections
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Meningitis
 Inflammation of meninges
 Threat to brain because bacteria/viruses may
spread into CNS tissue
 Encephalitis = brain inflammation
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Hydrocephalus
 “Water on the Brain”
 CSF accumulates & exerts pressure on brain
because something obstructs its drainage
 In babies, brain size increases
 In adults, brain damage may occur because
nervous tissue is crushed
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Hydrocephalus in a Newborn
Figure 7.19
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Cerebrospinal Fluid (CSF)
 Similar to blood plasma composition (make-up)
 Different because contains less protein, more
vitamin C, & ion composition differs
 Formed by the choroid plexus continually
 Forms a watery cushion to protect the brain
 Circulated in arachnoid space, ventricles, and
central canal of the spinal cord
 Drains at a constant rate to maintain pressure &
volume
 Lumbar spinal tap is used to get a sample of CSF
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Cerebral Spinal Fluid
 Circluates from the 2 lateral ventricles
into the third ventricle, then through the
cerebral aqueduct of the mid brain and
into the fourth ventricle.
 Some of this fluid continues down the
spinal cord.
 Ordinarily it forms and drains at a
constant rate to maintain pressure and
volume.
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Ventricles and Location of
the Cerebrospinal Fluid
Figure 7.18a–b
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Ventricles and Location of
the Cerebrospinal Fluid (P. 250)
Figure 7.18c
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Blood-Brain Barrier
 Keeps neurons separated from bloodborne substances
 Includes the least permeable capillaries of the body
 Can pass through:
 Water
 Glucose
 Essential Amino Acids
 Fats
 Respiratory Gases
 Fat-Soluble Molecules (alcohol, nicotine, anesthesia)
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Blood-Brain Barrier Continued . . .
 CanNOT pass through:
 Metabolic Wastes (urea, toxins, proteins, most
drugs)
 Nonessential Amino Acids
 Potassium Ions
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Traumatic Brain Injuries
 Concussion
 Slight brain injury but no permanent brain damage
 Contusion
 Nervous tissue destruction occurs & tissue does
not regenerate
 Intracranial Hemorrhage
 Bleeding from ruptured vessels in the brain
 Cerebral Edema
 Swelling of brain due to inflammatory response
 May compress and kill brain tissue
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Cerebrovascular Accident (CVA)
 Commonly called a stroke
 Blood circulation to brain area is blocked by
blood clot or 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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 Transient Ischemic Attack (TIA)
 Temporary (5 – 50 minutes) brain
ischemia (restriction of blood flow)
 “incomplete stroke”
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Alzheimer’s Disease
 Progressive degenerative brain disease that
results in dementia
 Memory loss, short attention span, language loss
 Caused by shortage of ACh & structural changes
in the brain
 Drugs ease symptoms by inhibiting ACh
breakdown
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Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Parkinson’s Disease
 Basal nuclei problem caused by degeneration of
dopamine-releasing neurons
 As a result, basal nuclei become overactive,
causing tremors
 Drug L-dopa helps alleviate symptoms
 Drug deprenyl slows deterioration
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Huntington’s Disease
 Genetic
 Massive degeneration of basal nuclei & later the
cerebral cortex
 Wild, jerky, flapping movements called chorea
 Treated with drugs that block dopamine’s effects
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