Neurophysiology
Chapter 2 Outline

Structure & Function of Nerve Cells

Types & Shapes of Neurons

I. Neurons: are individual cells in the nervous system that receive, integrate,
    and  transmit information.

II.  types of neurons
  1. interneurons: this category makes up the majority of neurons

  2. sensory neurons (afferent): these neurons are sensitive to information
      outside the nervous system.  (transduction)

  3. motor neurons (efferent): these carry information from the central nervous
      system to the muscles & glands

III. shapes of neurons (Kingsley p. 56-57)
  1. multipolar: one axon but many dendritic trees come from the soma
  2. bipolar: one axon & one dendritic trunk protrude from the soma
  3. unipolar: one stalk emerges from the soma
    A. pseudounipolar: mammals have these (Kingsley p.57)
 

Neuron Internal Structure:

I. cell membrane: is called the plasma membrane (or plasmolemma).
  1. protein channels pass thru the membrane this allows for ion exchange

II. soma:
  1. nucleus: is surrounded by a membrane.
    A. The nucleus contains chromosomes
    B. a nucleolus which produces ribosomes
  2. Cytoplasm: jelly-like substance inside the cell that contains
    A. mitochondria: They extract energy from the breakdown of nutrients
    B. endoplasmic reticulum (ER): is involved in the storage and  transport
      a. Rough ER contains ribosomes
      b. Smooth ER transports substances around the cytoplasm
      c. Golgi apparatus serves as packaging material for chemicals
      d. lysosomes: these are derived from smooth ER
 

  3. intracellular matrix (cell skeleton):
    A. microfilaments (actin filaments): protein molecules (actin)
      a. smallest of the cytoskeletal elements
      b. abundant in the tips of growing neurites
 
    B. neurofilaments (intermediate filaments) provide structure for the cell
      a. tangled neurofilaments: associated with dementia & CNS disease
 
    C. microtubules are tube-like structures involved in cell transport.
      a. They transport chemicals down axons: axoplasmic ransport (AT)
         (1) fast AT:
         (2) slow AT:
 

External structure (Kingsley p. 56)

I. Soma (cell body): this contains the cell nucleus

II. dendrites (Greek for "tree"): specialized to receive information
  2. dendritic spines: are small projection found on dendrites

III. Axon: long thin fiber that transmits electrical signals away from soma
  1. This signal is called an action potential
  2. collateral branches: are branches of the axon
  3. axoplasm:  axon cytoplasm
  4. axolemma: axon membrane
  5. terminal branches (telodendria): branching toward the end of the axon,
    A. Terminal Buttons: synaptic boutons: These are found at the end of axons
      a. secrete chemicals called neurotransmitters  (NT).
  6. myelin: This is a white fatty substance that forms an insulating sheath
    A. derived from oligodendrocytes in the CNS &  Schwann cells in the PNS
  7. nodes of Ranvier: interruptions in the myelin

IV. Synapse: a space where information is transmitted from one neuron to
      another.
  1. There are axosomatic synapses, axodendritic synapses & axoaxonic
       synapses

Neuroglial (glial) Cells of the CNS

I. general information
 1. Glia: (glue) for structure, support, insulation of the nervous system.  They
      help maintain the chemical environment, supply nutrients, & remove waste

II. astrocytes: Look like stars: two types (Kingsley p. 75)
(1) fibrous and (2) protoplasmic astrocytes
1. perivascular end feet applied to blood vessels
2. form the external glial limiting membrane
3. form internal glial limiting membrane
4. clean up debris (digest thru phagocytosis)
  A. they undergo hypertrophy after CNS injury
  B. they form a glial scar
5. they serve as reservoirs for K+
6. astrocytes form lamellae around terminal branches of axons
7. corpora amylacea: found in normal CNS of middle-aged & elderly people

III. Oligodendroglia: two types:
1. interfascicular oligodendrocytes: these are found among myelinated axons.
  A. they produce the myelin sheath in the CNS
  B. Nodes of Ranvier divide segments of myelin
  C. each cell has several processes & each process wraps around a segment of
       a different axon (Kingsley p. 85)
  D. Myelin is 70% lipid and 20% protein
2. satellite obigodendrocytes: found close to cell bodies of large neurons

IV. Microglia: resting microglia make up 5% of all neuroglial cells.  These
       cells acquire phagocytic properties when the cell is damaged
 

Supporting cells of the PNS

I. Schwann cells:
  1. these enclose unmyelinated axons & separate them from each other
      i.e., neurolemma: a nucleated cytoplasmic layer
    A. they secrete substances that form a matrix (basal lamina) over axons

  2. they fill the spaces between neurons somas in the PNS
  3. they can become phagocytes in the PNS injury
  4. they produce myelin in the PNS (Kingsley p. 84)
    A. myelinated fibers have a myelin sheath & a neurolemmal sheath
         outside of the myelin.
      a. voltage gated ion channels exist at the nodes (Kingsley p. 83)
    B. Kingsley p.83-85 shows the layers of Schwann cell membrane that
         compose myelin.
    C. Each Schwann cell surrounds several axons but provides only 1
         segment of myelin for each axon
    D. Characteristics of myelin
      a. 70% of it is lipid & cholesterol is major ingredient of the lipid content
    E. diseases of myelin
      a. genet diseases of myelin are called leukodystrophies
       ?multiple sclerosis: directed against central myelin
       ?Guillain-Barre syndrome: directed against peripheral myelin
5. Schwann cells differ from oligodendrocytes in that they
   A. appear to wrap their cell bodies around axons where oligodendrocytes
        send out processes that wrap around axons (Kingsley 84-85)
 

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