Biology 211
Anatomy & Physiology I
Nerve Histology
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Recall: All organs are composed of, at most, four tissues
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
Nervous tissue: Excitable cells (neurons)
Nonexcitable (supporting) cells
Connective tissue: Meninges - in central nervous system
Endoneurium
Perineurium in peripheral nervous system
Epineurium
Epithelium
found only in blood vessels
Muscle (smooth)
Cells of Nervous Tissue:
1) Excitable cells = Neurons
Carry electrical signals from one place to another
Pass these signals to other cells
2) Nonexcitable cells = Glia in CNS
Satellite cells
Schwann cells
in PNS
1) Excitable cells = Neurons
Carry electrical signals from one place to another
Pass these signals to other cells
Found in either central
nervous system, peripheral
nervous system, or may
have parts in both
Do not divide
Long-lived
High metabolic rates
1) Neurons Classified by:
2) Neurons Classified by:
Stimulatory synapses
Inhibitory synapses
Cells of Nervous Tissue:
1) Excitable cells = Neurons
Carry electrical signals from one place to another
Pass these signals to other cells
2) Nonexcitable cells =
Non-excitable cells
By definition: Do not carry electrical information
Support, nourish, protect neurons
May divide
In CNS: Glia
In PNS: Satellite cells surround neuron cell bodies
Schwann cells surround cell processes
Glia: 4 types in central nervous system
1)
2)
3)
4)
Glia: 1) Astrocytes: Regulate environment around neurons
by controlling the passage of molecules into and
out of capillaries, and by absorbing or secreting
ions from/into extracellular matrix
Glia: 2) Oligodendrocytes: Produce myelin sheaths around
axons (and some dendrites) of neurons in C.N.S.
Glia: 3) Microglia: Phagocytic. Remove degenerating cells
and foreign debris from C.N.S.
Glia: 4) Ependyma: Line fluid-filled ventricles within C.N.S.
Non-excitable cells of Peripheral Nervous System
1) Satellite cells surround and protect neuron cell bodies
in P.N.S.
Non-excitable cells of Peripheral Nervous System
2) Schwann cells produce myelin sheaths which surround
axons (and some dendrites) in P.N.S.
Pathology of the Nonexcitable Cells
Loss of oligodendrocytes causes multiple sclerosis and a
group of diseases called leukodystrophies
Injury to astrocytes, usually from toxic substances, leads to
cerebral edema and swelling of the brain
Injury to Schwann cells causes degeneration of the neuron
processes and prevents their healing and regrowth. It is
also responsible for Guillain-Barre syndrome
Pathology of the Nonexcitable Cells
Tumors can arise from all four types of glia, and these tend
to grow rapidly and destroy nearby regions of the brain or
spinal cord
Tumors can also arise from satellite cells or Schwann cells,
compressing and destroying the neurons they surround