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