Where is nervous tissue located in the body

Nervous tissue, one of the four main tissue types, is composed of neurons and supporting cells called neuroglia. There are six types of neuroglia—four in the central nervous system and two in the PNS. These glial cells are involved in many specialized functions apart from support of the neurons. Neuroglia in the CNS include astrocytes, microglial cells, ependymal cells and oligodendrocytes. In the PNS, satellite cells and Schwann cells are the two kinds of neuroglia.

Astrocytes are shaped like a star and are the most abundant glial cell in the CNS. They have many radiating processes which help in clinging to the neurons and capillaries. They support and brace the neurons and anchor them to the nutrient supply lines.

They also help in the guiding the migration of young neurons. Astrocytes control the chemical environment around the neurons. Microglial cells are small and ovoid un shape with thorny processes. They are found in the CNS. When invading microorganism or dead neurons are present, the microglial cells can transform into a phagocytic macrophage and help in cleaning the neuronal debris. Ependymal cells are ciliated and line the central cavities of the brain and spinal cord where they form a fairly permeable barrier between the cerebrospinal fluid that fills these cavities and the tissue cells of the CNS.

Oligodendrocytes line up along the nerves and produce an insulating cover called myelin sheath. Satellite cells surround neuron cell bodies in the peripheral nervous system PNS. They are analogous to the astrocytes in the CNS. Schwann cells surround all nerve fibers in the peripheral nervous system and form myelin sheaths around the nerve fibers. They are found in the PNS. The main part of the cell, the part that carries on the general functions, is the cell body.

Dendrites are extensions, or processes, of the cytoplasm that carry impulses to the cell body. An extension or process called an axon carries impulses away from the cell body. Some neurons have a single long extension axon that reaches great distances, others are very small, star shaped cells without obvious axons See Figure Though neuron shapes vary greatly, every neuron houses its nucleus in a region known as the cell body also called soma from which cellular activity like repair or cell membrane recycling is controlled.

Neurons produce many proteins either for their cell membranes or for use when communicating with other cells and therefore also have many rough endoplasmic reticula that are visible with the light microscope; these rough ER are called Nissl bodies.

In figure These short projections are dendrites which receive most of the input from other neurons or stimuli in the extracellular environment; the location of the dendrites on the neuron marks the receptive region of the neuron. Dendrites are usually highly branched processes, providing locations for other neurons to communicate with the neuron.

Neurons have polarity—meaning that information flows in one direction through the neuron. In the Figure The first section of the axon where an action potential is generated is called the initial segment. Often axons are wrapped by myelin sheaths, leaving exposed sections node of Ranvier between segments of myelin. Myelin is produced by oligodendrocytes glial cells in the CNS and acts as electrical insulation, speeding information conduction down the neuron.

Once information reaches the terminal end of this neuron, it is transferred to another cell. The site of communication between a neuron and its target cell is called a synapse. The terminal end has several branches, each with a synaptic end bulb to store chemicals needed for communication with the next cell. Figure Visit this site to learn about how nervous tissue is composed of neurons and glial cells.

Neurons are dynamic cells with the ability to make a vast number of connections, to respond incredibly quickly to stimuli, and to initiate movements on the basis of those stimuli. They are the focus of intense research because failures in physiology can lead to devastating illnesses.

Why are neurons only found in animals? There are trillions of neurons in the nervous system and cell shape can vary widely. Three common shapes of neurons are shown in Figure Multipolar neurons have multiple processes emerging from their cell bodies hence their name, multipolar. They have dendrites attached to their cell bodies and often, one long axon.

Motor neurons are multipolar neurons, as are most of the CNS. Bipolar cells have two processes, which extend from each end of the cell body, opposite to each other. One is the axon and one the dendrite. Bipolar cells are not very common. They are found mainly in the olfactory epithelium where smell stimuli are sensed , and as part of the retina in the eye. Unipolar cells have one long axon emerging from the cell body, but the cell body is located at neither end of that axon.

At one end of the axon are dendrites, and at the other end, the axon forms synaptic connections with a target cell. Unipolar cells are exclusively sensory neurons and have their dendrites in the periphery where they detect stimuli. There are six types of glial cells. Table Astrocytes have many processes extending from their main cell body not axons or dendrites like neurons, just cell extensions.

Those processes extend to interact with neurons, blood vessels, or the connective tissue covering the CNS Figure Outside the myelin sheath is a cellular layer called the neurilemma or sheath of Schwann cells. The myelin sheath together with the neurilemma is also known as the medullary sheath. This medullary sheath is interrupted at intervals by the nodes of Ranvier. Nerve cells are functionally connected to each other at a junction known as a synapse , where the terminal branches of an axon and the dendrites of another neuron lie in close proximity to each other but normally without direct contact.

Information is transmitted across the gap by chemical secretions called neurotransmitters. It causes activation in the post-synaptic cell. Template:WikiDoc Sources. Category : Tissues.