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Nervous system origins in the trilaminar embryo as a neural plate, which transforms into a neural groove closing to form a neural tube. This tube thickens to become the spinal cord, while the other end expands and folds to form the brain and its divisions. The cranial and spinal nerves grow from this embryonic brain and cord. All organs consist of up to four tissues: epithelial, connective, muscle, and nervous tissues. Neurons, the excitable cells of nervous tissue, transmit electrical signals. Glia cells in the central nervous system regulate the environment around neurons, produce myelin sheaths, remove degenerating cells, and line fluid-filled ventricles. In contrast, non-excitable cells of the peripheral nervous system serve various functions. The pathology of nonexcitable cells can lead to diseases like multiple sclerosis, leukodystrophies, cerebral edema, Guillain-Barre syndrome, and the formation of tumors impacting brain and spinal cord regions.
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Biology 322Human 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 Carry electrical signals from one place to another Pass these signals to other cells 2) Nonexcitable 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.
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
