Biology 211Anatomy & 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 vesselsMuscle (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