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The Spinal Cord

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					The Spinal Cord
             Spinal Cord Structure
• Interior
  – Composed of both white and gray matter.
  – Irregularly shaped.
     • Gray matter surrounded by white matter.
     • Gray matter extends up and down dorsally and
       ventrally, one on each side of center.
Spinal Cord Structure
     Functions of the Spinal Cord
• Divided into three categories:
  1. Reflex activities
     •   Simple, rapid, and automatic response.
  2. Conduction of sensory impulses
     •   Upward through ascending tracts to the brain.
  3. Conduction of motor impulses
     •   From the brain down through descending tracts to
         the efferent neurons that supply muscles.
                   Spinal Nerves
• There are 31 pairs of spinal nerves.
• Numbered according to where in the spinal cord
  they arise.
• Attached to the spinal cord in two places:
  – Dorsal root
  – Ventral root
Spinal Nerves
                 Spinal Nerves
• Dorsal Roots
  – Composed of sensory nerve fibers.
  – These are the nerve fibers that send sensory
    information, in the form of nerve impulses, to the
    spinal cord.
  – These impulses then move up the spinal cord to the
    brain.
                  Spinal Nerves
• Ventral Roots
  – Composed of motor (efferent) nerve fibers.
  – These are nerve fibers that have the ability to effect
    muscles, involuntary muscles, etc.
  – These impulses originate in the brain, move down the
    spinal cord and into the ventral roots.
         Spinal Nerve Branches
• Spinal nerves emerge from the spinal cord,
  but don’t go very far before branching out.
• The branches are called “plexuses.”
• The plexuses distribute nerves to the body
  parts.
                    The Plexuses
• Cervical plexus
  – Supplies nerve impulses to the muscles of the neck.
     • What kind of nerves would these be?
        – Motor (efferent) nerves.
  – Receives nerve impulses from the neck and back of
    the head.
     • What kind of nerves would these be?
        – Sensory (afferent) nerves.
  – The phrenic nerve which controls the diaphragm,
    originates from this plexus.
                The Plexuses
• Brachial plexus
  – Supplies motor and sensory nerves to the
    shoulder, arm, forearm, wrist, and hand.
• Lumbosacral plexus
  – Supplies motor and sensory nerves to the lower
    extremities.
  – The largest nerve branch in the sciatic nerve.
The Plexuses
  The Autonomic Nervous System
• The neurons associated with the functioning
  of the organs are arrange very differently from
  those associated with the functioning of
  muscles.
  – Called “visceral efferent” neurons.
• Because of these differences, they are
  associated with a subsystem called the
  “autonomic nervous system.”
  The Autonomic Nervous System
• This is the system that controls the actions of the
  glands and smooth muscles associated with the
  organs including the heart.
• All actions associated with these structures
  happen automatically (without conscious
  control).
   – The signals relayed by the neurons in this system
     never reach the conscious part of the brain.
• Broken into two parts:
   – Sympathetic Nervous System
   – Parasympathetic Nervous System
     Sympathetic Nervous System
• Acts as an accelerator for the organs that respond to
  stress.
• Associated with the instinctive “fight or flight”
  response.
   – Stimulation of adrenal glands (adrenaline rush).
   – Dilation (widening) of the pupil, reducing ability to focus
     on near objects…why?
   – Auditory exclusion…why?
   – Increase in heart rate…why?
   – Increase in blood pressure.
   – Dilation of bronchial tubes…why?
   – Increase in metabolism…why?
   – Decrease in ability to feel pain…why?
Sympathetic Nervous System
 Parasympathetic Nervous System
• Acts as a balance to the sympathetic nervous
  system.
• After stress has passed, this system brings the
  body back to a normal state.
  – Constriction of the pupils.
  – Slowing of the heart rate.
  – Constriction of bronchial tubes.
     Disorders of the Spinal Cord
• Polio (poliomyelitis)
  – Caused by a virus.
  – Effects mostly children.
  – Enters through the nose and/or mouth.
  – Multiplies in the gastrointestinal tract and travels
    to the CNS.
  – Here it can destroy the motor nerves associated
    with the spinal cord.
     • What would happen if this occurred?
     Disorders of the Spinal Cord
• Multiple Sclerosis
  – Myelin around gray nerve fibers is destroyed by
    the immune system (autoimmune disease).
  – Axons also begin to deteriorate.
  – Progresses very slowly.
     Disorders of the Spinal Cord
• ALS (Amyotrophic Lateral Sclerosis)
  – Motor neurons are destroyed.
  – Causes muscles to stop working (atrophy).
  – Loss of motor control until person is unable to
    swallow or talk.
  – What famous person had and eventually died
    from this disease? Hint: Major League Baseball
     • Lou Gehrig’s Disease

				
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posted:11/30/2011
language:English
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