ANATOMICAL ORGANIZATION of the NERVOUS SYSTEM

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					NERVOUS SYSTEM
     Lecture 1

     OVERVIEW
        and
  NEUROHISTOLOGY
ANATOMICAL ORGANIZATION of the
      NERVOUS SYSTEM
               Nervous
               System


CNS             PNS                ANS

                         CRANIAL
      BRAIN                              SYMPATHETIC
                         NERVES


      SPINAL             SPINAL             PARA-
       CORD              NERVES          SYMPATHETIC
Central Nervous System (CNS)
   Definition:
       Unpaired, bilaterally symmetrical structures
              extending along the longitudinal axis of the
              midsagittal plane of the body.
       Structures arising directly from the neural tube.
   Includes:
       Brain
       Spinal cord
Peripheral Nervous System (PNS)
   Definition:
       Made up of transmission pathways
       carrying information between the CNS and
       external/internal environments.
   Afferent (sensory) pathways:
       Carry information to the CNS.
   Efferent (motor) pathways:
       Carry information from the CNS.
Peripheral Nervous System (PNS)
   Includes:
       Cranial nerves (12 pairs).
       Spinal nerves (31 pairs).
Autonomic Nervous System (ANS)
   May be considered a subdivision of the
    PNS.

   Entirely motor.

   Innervates smooth muscle and glands
    (viscera).
            ANS Subdivisions
   Sympathetic system (fight or flight):
       Also called thoracolumbar.


   Parasympathetic system (feed or breed):
       Also called craniosacral.
            Parts of a Neuron
   Cell body:
       Trophic unit
       Perikaryon
   Dendrites:
       Receptive unit
   Axon:
       Conductive unit
          Cell Body Definition
   That part of a neuron that encloses the
    nucleus and other organelles necessary to
    maintain and repair the neuron.
       Cell Body Organelles
 Nucleus
 Golgi apparatus
 RER
    Ribosomes (=Nissl substance)
      Dendrites (Characteristics)
   Branches off the cell body that carry information
    to the cell body.
   Usually several to many.
   Relatively short.
   Often branched.
   Have receptors for neurotransmitters.
   Conduct local potentials.
        Axon Characteristics
 Carries information to another neuron or
  muscle cell.
 Often relatively long.
 Single (one per neuron).
 Conducts action potential
       Axon Characteristics
 Ends in short branched processes called
  telodendria.
 May have collateral branches.
 Cell membrane (= axolemma).
 Cytoplasm = (axoplasm).
          Axon Characteristics
   Covered by neurolemma:
       Made up of Schwann cells.
   Often myelinated:
       Myelin is formed by Schwann cells.
   Note: axon is the only part of a neuron that
    is ever myelinated.
            Axon Organelles
   Mitochondria

   Neurofilaments

   Neurotubules
            Axonal Transport
   Anterograde:
      Transports vesicles from cell body to end of
      axon.
      Kinesin
   Retrograde:
      Transports vesicles from end of axon toward
      cell body.
      Cytoplasmic dynein
            Axonal Transport
   Slow transport:
       1-5 mm/day


   Fast transport:
       200-400 mm/day
             General Terminology
   Nerve:
       Bundle of fibers in the PNS.
   Tract:
       Bundle of fibers in the CNS.
   Commissure:
       Tract in the CNS that crosses from one side
       to the other.
         General Terminology
   Nucleus:
      Aggregation of dendrites and nerve cell
      bodies in the CNS.
   Ganglion:
      Aggregation of dendrites and nerve cell
      bodies in the PNS.
          General Terminology
   White matter:
       Areas of myelinated axons.
   Gray matter:
       Areas of unmyelinated axons, cell bodies,
       and dendrites.
                      Synapse
   Definition:
       Composite structure that allows two neurons
        or a neuron and a muscle cell to “talk” to each
        other.
        Synapse Components
   Presynaptic membrane:
      With synaptic vesicles filled with
      neurotransmitters.
 Synaptic cleft:
 Postsynaptic membrane:
      With receptors for neurotransmitters.
 Monosynaptic pathways.
 Polysynaptic pathways.
                  Reflex Arc
   Afferent (sensory) pathways:
       Somatic.
       Visceral (splanchnic).
   Efferent (motor) pathways:
       Somatic.
       Visceral (splanchnic).
   Association neurons (interneurons).
          Neuroglial Cells
 Schwann cells
 Astrocytes
 Microglial cells
 Oligodendrocytes
 Ependymal cells
              Schwann Cells
   Derived from neural crest cells.

   Myelinate axons in the PNS.
                 Astrocytes
   Derived from neural crest cells.
   Function to physically support neurons.
   Channel materials between capillaries and
    neurons (= Blood-brain barrier).
   Support and guide neurons during embryonic
    building of cerebral cortex.
   Act as sinks for ions (i.e., K+).
   Remove neuroactive and potentially toxic
    substances.
             Microglial Cells
   Derived from embryonic mesenchyme.

   May transform into phagocytes within
    CNS.
            Oligodendrocytes
   Derived from neural crest cells.

   Function to myelinate axons within CNS.
             Ependymal cells
   Derived from neural crest cells.

   Line ventricles of brain.

				
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