Sunday, May 3, 2009

A neuron is an excitable cell which is the functional unit of the nervous system. Also known as nerve cell, it processes and transmits information by electrochemical signalling from neuron to the next via synapse. Neurons are the core components of the brain, the vertebrate spinal cord, and the peripheral nerves.

The neuron consists of a cell body, which is called soma, and one or more long processes: a single axon and dendrites. The soma contains the nucleus and usual cytoplasmic organelles with an exceptionally large amount of rough endoplasmic reticulum, called Nissl substance in the neuron. The longest cell process is the axon, which is capable of transmitting propagated nerve impulses.

Neurons are highly specialized for the processing and transmission of electrochemical impulses generated by neurotransmitters which are secreted by the soma and released at the terminal ends of the axons during synaptic jumps.

The neuron's role as the primary functional unit of the nervous system was first discovered by the Spanish anatomist Santiago Ramón y Cajal in the early 20th century. Cajal wrote that neurons were discrete cells that communicated with each other via specialized junctions (synaptic gaps) between cells.

When a neuron has no dendrite, it is called unipolar neuron; when it has one dendrite, it is a bipolar neuron; if it has more than one dendrite, it is a multipolar neuron. In every neurons only the axon propagates nerve impulses.