Biology 322 Human Anatomy I Histology of Nervous Tissue

Recall: Nervous system begins in trilaminar embryo as a “neural plate” of the ectoderm. This develops into a “neural groove” that closes over to form a “neural tube”

One end (caudal) of this neural tube thickens but stays tube-shaped to form the spinal cord. The other (cephalic) end of this neural tube enlarges and folds to form the brain and its various divisions, which we will discuss later.

The cranial nerves and spinal nerves will form as outgrowths of this embryonic brain and spinal cord.

Recall: All organs are composed of, at most, four tissues Epithelial tissue Connective tissue Muscle tissue Nervous tissue Nervous tissue: Connective tissue: Epithelium Muscle (smooth)

Cells of Nervous Tissue:

1) Excitable cells = Neurons

1) Neurons Classified by: Location

2) Neurons Classified by: Shape

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

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).

Non-excitable cells of Peripheral Nervous System 2)

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