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Neuron
This is a cell which receives or relays information in the form of electrochemical impulses within the nervous system.
Most neurons (about 80%) are found in the Brain and particularly cerebral cortex.
There are three main kinds of neurons – sensory neurons (or afferent neurons), motor neurons (or efferent neurons) and interneurons (or connector neurons)
Sensory neurons carry information from the sense organs and pass it on to the central nervous system.
Motor neurons carry information from the central Nervous System to the muscles and glands.
Interneurons are mainly found in the central Nervous System and relay information to and from several neurons.
A Neuron consists of a cell body which houses the nucleus (which contains the genetic code) and the cytoplasm (which feeds the nucleus).
Dendrites branch out from the cell body and through these dendrites the Neuron makes electrochemical contact with other neurons by receiving incoming signals from neighbouring neurons. Extending from the cell body is an axon which is covered along most of its length by a protective myelin sheath. The axon carries the signal received by the dendrites to other neurons. The myelin sheath speeds up the rate of conduction of signals down the axon and towards the terminal buttons (or synaptic knobs). There are regular breaks in the myelin sheath called the nodes of Ranvier.
The terminal buttons house a number of synaptic vesicles which contain molecules of a chemical transmitter called a neurotransmitter. As an electrochemical impulse passes down the axon, it arrives at a terminal button and stimulates the vesicles to discharge their contents into the minute gap between the end of the terminal button and the dendrite of the receiving neuron. This is known as the synaptic cleft.
Although most neurons are minute some can be as long as several feet.
