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Home > Neuron

In vertebrates, they are found in the brain, the spinal cord and in the nerves and ganglia of the peripheral nervous system.

1 Classes

There are three classes of neurons: afferent neurons, efferent neurons, and interneurons.

• Afferent neurons convey information from tissues and organs into the central nervous system.
• Efferent neurons transmit signals from the central nervous system to the effector cell s.
• Interneurons connect neurons within the central nervous system.

2 Anatomy and histology

Many highly specialized types of neurons exist, and these differ widely in appearance. Characteristically, neurons are highly asymmetric in shape. Neurons consist of:

• The soma, a relatively fat central cell.
• The axon, a much finer, cable-like projection which may extend tens, hundreds, or even tens of thousands of times the diameter of the soma in length.
• The dendrite, a short, branching arbor of cellular extensions.

Axon and dendrites alike are typically only about a micrometerA micrometer is a widely used device in mechanical engineering for precisely measuring thickness of blocks, outer and inner diameters of shafts and depths of slots. Micrometers have several advantages over other types of measuring instruments like the Ver thick, while the soma is usually about 25 micrometers in diameter and not much larger than than the cell nucleusIn cell biology, the nucleus is an organelle, found in most eukaryotic cells, which contains most of the cell's genetic material. Nuclei have two primary functions: to control chemical reactions within the cytoplasm and to store information needed for cel it contains. An axon of a human motoneuronIn vertebrates, motoneurons (also called motor neurons are efferent neurons that originate in the spinal cord and synapse with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity. Anatomy and physio, meanwhile, can be a meter long.

Nerve cell bodies stained with basophilic dyes will show numerous microscopic clumps of Nissl substance (named after German psychiatrist and neuropathologist Franz Nissl, 1860 - 1919), which consists of rough endoplasmic reticulumThe endoplasmic reticulum or ER (endoplasmic means "within the cytoplasm", reticulum means "little net") is an organelle found in all eukaryotic cells. The ER modifies proteins, makes macromolecules, and transfers substances throughout the cell. Prokaryot and associated ribosomes. The prominence of the Nissl substance can be explained by the fact that nerve cells are metabolically very active, and hence, involved in large numbers of protein synthesis.

The cell body of a neuron is supported by a complex meshwork of structural proteins called neurofilaments, which are assembled into larger neurofibrils. Some neurons also contain pigment granules, such as neuromelanin (a brownish-black pigment, byproduct of synthesis of catecholamines) and lipofuscin (yellowish-brown pigment that accumulates with age).

3 Connectivity

Neurons join to one another and to other cells through synapsenerve cells to communicate with one another through axons and dendrites, converting electrical signals into chemical ones. For the technology festival, see Synapse Festival. Synapses are specialized junctions through which cells of the nervous system signs, which connect the axon tip of one cell to a dendrite of another, or less commonly to its axon or soma. Neurons of the cortexThe outermost layer of the brain, the cortex is rich in neurons and is the site of most sophisticated neural processing (See also: cerebral cortex). Or, more generally, the outermost portion of certain biological structures (See below). The human cortex i in mammals, such as the Purkinje cell s, have over 1000 dendrites apiece, enabling connections to tens of thousands of other cells.

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Topics: Neuron Neurons Cells System Cell Nervous Axon Action Axons...

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