The image below illustrates the structure of a typical neuron. Each neuron has three basic parts: cell body soma , one or more dendrites, and a single axon. In many ways, the cell body is similar to other types of cells. It has a nucleus with at least one nucleolus and contains many of the typical cytoplasmic organelles. It lacks centrioles, however. Because centrioles function in cell division, the fact that neurons lack these organelles is consistent with the amitotic nature of the cell.
Dendrites and axons are cytoplasmic extensions, or processes, that project from the cell body. They are sometimes referred to as fibers. Dendrites are usually, but not always, short and branching, which increases their surface area to receive signals from other neurons.
The number of dendrites on a neuron varies. They are called afferent processes because they transmit impulses to the neuron cell body.
Fast anterograde flow involves microtubules, and the microtubule motor protein called kinesin. This section shows a thick section from the cerebral cortex, stained using Golgi-Cox method, which stains neurons black. Note the variety both of neuronal shapes and of the branching patterns of their processes.
As most of the nerve cell bodies are either in the brain or spinal cord, or in ganglia, just outside the spinal cord, and the synapses at the end of the axon can be long distances away i. Therefore, because of their large size, and the length and branching of their processes it is difficult to examine the complete structure of an individual neuron in a single conventional sections, as it is unlikely that one section will contain all parts of the neuron.
The Schwann cells are underlain by the medullary sheath. The medullary sheath is interrupted at intervals by the nodes of Ranvier. Illustration of the Schwann Cells and the Myelin Sheath : Transmission electron micrograph of a myelinated axon. The myelin layer concentric surrounds the axon of a neuron, showing Schwann cells. The nervous system consists of nervous tissue, which is composed of two principal types of cells called neuron and neuroglia.
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.
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. Nervous tissue also includes cells that do not transmit impulses, but instead support the activities of the neurons.
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