The Neuron

Generalities.

    The neuron is the basic unit of the nervous system. This is the cell type that transmits information, using electrical impulses, to the rest of our body. In addition to neuron our brain contains two more cell types, astrocytes and microglia, performing housekeeping and immune functions. All neurons do not look alike; some are short, being only 1 mm long, and others can reach one meter. Most of them conduct electricity in only one direction, but some can send messages to several other neurons. The figure below shows some types of neurons that could be found in our brain.

Examples of different types of neurons.

    The figure on the left shows a typical neuron and describes its main components. Please, notice the soma, which is the cell body containing the nucleus. It is in the soma where the molecules/proteins are produced. This is also where the neurotransmitters are synthesized, and then they are transported to the terminals where they will be released to transmit their messages.

    It is the dendrites that receive chemical from other neurons. Hundreds of endings release their neurotransmitters which can be exciting or inhibiting the cell. It is the sum of these electric currents, positive and negative, transmitted at dendrites, that determines whether an action potential (a positive electrical) will be initiated at the hillock.

    Thereafter, the action potential will travel along the axon, acting as a long electrical wire, to the nerve endings. Most axons are surrounded by a discontinuous layer of myelin (Schwann cells wrapped around the axon). This myelin serves as the wire insulation and helps to accelerate the electrical conduction. When the action potential reaches the endings, it triggers the release of neurotransmitters that propagate the message to the next neurons.