The Nervous System

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The Nervous System

• Pt.B

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D. Reflex Arc 1. Reflexes are rapid,
predictable, and involuntary responses to
stimuli.   2. The nerve pathways that produce
reflexes are called reflex pathways.   3. There
are two types of reflexes in the body - autonomic
and somatic a. Autonomic reflexes regulate he
activity of smooth muscles, glands, and the
heart. b. Somatic reflexes stimulate skeletal
muscles.  
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4. All reflex arcs have at least five parts
(thee can be more connections). The five parts
are a. a sensory receptor b. an afferent
path c. an integration center (in the CNS) d.
an efferent path e. an effector organ
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Steps in Nerve Impulse Transmission   1.
Stimulus makes cell membrane permeable to Na
ions.   2. Na ions diffuse into the neuron
changing the membrane potential   3. Cell
membrane is depolarized and an action potential
is generated.   4. Cell membrane becomes
impermeable to Na ions.   5. Cell membrane
becomes permeable to K ions.   6. K ions
diffuse out of the cell.   7. Cell membrane is
repolarized.   8. Normal concentration of Na
ions and K ions reestablished by Na-K pump.
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IV. The Central Nervous System   A. The CNS
consists of brain and spinal cord   B. The
functional anatomy of the brain is discussed in
terms of its major parts - the cerebral
hemispheres, the diencephalon, the brain stem,
and the cerebellum   C. Anatomy of the cerebral
hemispheres 1. gyri - ridges 2. sulci -
grooves 3. fissures - deep grooves that separate
large areas of the brain 4. lobes - large areas
of the cerebrum that are named for the cranial
bones they lie under
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D. Functional areas of the cerebral
hemispheres   1. somatic sensory area -
located posterior to the central fissure in the
parietal lobe This area allows you to recognize
sensory information. Sensory neurons from each
area of the body reach neurons in a specific
area. Sensory neurons from the body cross over
at the level of the brain stem - input fro the
right side of the body ends up in the left
cerebral cortex. 2. primary motor area -
located just anterior to the central fissure in
the frontal lobe All conscious movement
originates here. Motor fibers also cross in the
brain stem   3. Broca's area - located on the
lateral aspect of the frontal lobe Allows us to
form the words we speak.
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4. Areas involved in higher reasoning are
believed to be in the frontal lobes.   5.
Memories are thought to be stored in the frontal
and temporal lobes   6. The visual area is
located in the occipital lobe.   7. The auditory
and the olfactory areas are located in the
temporal lobe.   8. Cerebral cortex - the outer
layer of the cerebrum. Consists of nerve cell
bodies without myelin. Is called the gray
matter.   9. Cerebral white matter consists of
nerve tracts located in the central areas of the
cortex. a. corpus callosum - nerve tract that
connects the cerebral hemispheres
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  10. basal nuclei - clusters of nerve cells
located deep in the white matter of the cerebral
hemispheres. They help regulate voluntary motor
activity - Huntington's chorea and Parkinson's
disease are diseases of the basal
nuclei.     E. The diencephalon sits one the
brain stem and is surrounded by the
cerebrum.   1. It consists of the thalamus, the
hypothalamus, and the epithalamus.   2. The
thalamus is a relay station for sensory impulses
ascending to the cerebrum.  
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3. The hypothalamus regulates body temperature,
water balance, and metabolism. a. It contains
the limbic center that is the center for many
drives and emotions. Ex. thirst, appetite, sex,
pain and pleasure b. The mammillary bodies are
reflex centers involved in the sense of
smell. 4. The epithalamus contains the pneal
body (part of the endocrine system) and the
choroid plexus that secretes CSF.
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F. The brain stem   1. Consists of the
midbrain, the pons, and the medulla
oblongata.   2. The reticular activating system
is found throughout the brainstem. The RAS plays
a role in consciousness, and wake-sleep
cycles.   3. The midbrain functions as a relay
station for ascending and descending nerve
impulses. It also serves as a center for
reflexes involving hearing and vision.   4. The
pons is involved in the control of
breathing.   5. The medulla oblongata contains
nuclei that control heart rate, blood pressure,
breathing, swallowing and vomiting. It is also
an important area of fiber tracts.
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G. Cerebellum   1. The cerebellum provides
control and coordination for skeletal muscle
activity. a. It coordinates and fine tunes our
movements. b. It plays a role in maintaining
our balance. H. Protection of the CNS   1.
The CNS is protected by three layers of tissue
called meninges.   2. The outer layer is
called the dura mater "tough mother". a. it is
a double layer of connective tissue. b. The
inner layer (the meningeal layer) forms the outer
surface of the brain and spinal cord. c. The
outer layer is attached to the skull.
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3. The middle layer is called the
arachnoid. a. Has spider-like fibers that
attach to the pia mater. b. The space below
the archnoid is called the arachnoid space. It
is filled with CSF. c. CSF helps cushion the
brain and spinal cord.   4. The inner most
layer is called pia mater (gentle mother). I.
Cerebrospinal fluid is formed from blood
plasma.   1. It is produced by clusters of
capillaries called choroid plexuses located in
the brain's ventricles.   2. CSF circulates in
and around the brain and spinal cord to cushion
them against blows.
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• J. The Blood Brain Barrier helps maintain
  homeostasis in the CNS.
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• 1. Neurons are extreemly sensitive to slight
  changes in chemical composition.
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• 2. Neurons are kept separated from the blood by
  the blood brain barrier.
• a. The capillaries in the CNS are the least
  permeable in the body - they play a major role.
• Astrocytes that cover the capillaries in the CNS
  also play a role.
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K. Traumatic Brain Injuries   1. Concussion -
slight brain injury. A patient may lose
consciousness briefly or may be dizzy. There
is no permanent brain injury but there could be
swelling in the braincase (edema).   2.
Contussion - significant destruction of tissue.
Brain stem contussions always result in coma
lasting from hours to a lifetime due to injury
to the RAS.   3. Cerebral edema may result from
any brain injury. The brain swells as a
response to the injury. The swelling causes
compression of brain tissue and resulting loss
of function. a. A patient who is alert
initially after a brain injury but then
deteriorates likely is developing cerebral
edema. b. Intracranial bleeding will cause a
similar set of symptoms.
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  L. Cerebrovascular accident - a stroke   1.
CVA's occur when the blood flow to an area of the
brain is nterrupted by a blood clot or a
ruptured blood vessel. a. When blood flow is
interrupted, brain tissue dies. b. The
patient shows symptoms related to the areas of
brain affected.   2. Transient ischemic attack
(TSA) - also called a mini-stroke. short term
episodes of restricted blood flow that last
usually from 5 to 50 minutes. Symptoms include
numbness, temporary paralysis and impaired
speech. These attacks are short lived but warm
that more serious CVA's are possible.