MAIN FEATURES OF THE NERVOUS TISSUE
The main feature of nervous tissue are the neurons, the cells that command the nervous system and the whole body. Neurons cytoplasmic extensions that have the ability to be stimulated by chemical substances or electrical stimuli originated from other cells and in turn generate an action potential (“nerve impulse”). The action potential is transmitted along the plasma membrane that covers its extensions up to the synapses where the action potential is transmitted to other cells.
Main components of nervous system
1- Neurons. Cells that have a cell body and extensions of the cell body. The nucleus and large part of the cytoplasm surrounding it are located in the cell body.
Neurons have two types of extensions, dentrites and /strong>axons. The dendrites are generally shorter and highly branched at its ends. The axons have a constant thickness and branche mainly at their end.
Synapses are structures of close proximity between the membrane of a neuron and the membrane of another cell: another neuron, a secretory cell, a muscle cell. The action potential that reaches the synapse can extend to the next cell and/or trigger the release of chemical mediators.
2- Neuroglial cells. In addition to neurons, the central nervous tissue has another population of cells, called the glial cells or neuroglial cells. There are several types of neuroglial cells that perform several important functions in the nervous tissue, such as supporting and nourishing neurons, isolating neurons, phagocytosis, and repairing nervous tissue.
Nerve Fibers
Axons are always surrounded by other cells of the nervous tissue. The combination of an axon and its surrounding cells is called a nerve fiber. As axons are generally quite long, many cells are needed to cover their entire length.
The axons present in the central nervous system are covered by a type of neuroglial cell called oligodendrocyte. In the peripheral nervous system, this function is performed by cells called Schwann cells.
The cells surrounding the axons can produce a material called myelin, composed of complex lipid molecules and other types of molecules. Myelin is derived from the cell membranes of the surrounding cells. Nerve fibers whose outer covering cells contain myelin are called myelinated nerve fibers, as opposed to unmyelinated or nonmyelinated nerve fibers, not covered by myelin.
Regarding the position it ocupies in the body, the nervous tissue can be classified as:
1 – Central nervous system, formed by two continuous portions, one placed inside the cranial cavity, the brain and cerebellum, and the other its extension the spinal cord.The central nervous system holds cell bodies and extensions of neurons in addition to several types of neuroglial cells. The neurons of the brain are concentrated in the cerebral cortex and in clusters of varying sizes called cerebral or brain nuclei.
2 – Peripheral nervous system, distributed throughout the body in the form of:
– nerves, composed of bundles of nerve fibers.
– nerve ganglia, clusters of neuronal cell bodies, usually surrounded by connective tissue.
The organs of the central nervous system are covered by connective tissue membranes called meninges. There is very few connective tissue inside the central nervous system as opposed to the peripheral nervous system which contains a greater amount of this tissue.
Organization of nervous tissue in the central nervous system: white and gray matter
In the central nervous system, nervous tissue is organized in such a way that the cell bodies of neurons are concentrated in certain regions. These regions constitute the gray matter of the central nervous system.
The extensions of neurons (mainly their axons) are also organized and constitute regions called white matter. In the white matter, the axons form bundles of different calibers.
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