Neuropsychology: The Neuron

Neuron is an individual nerve cell. Neurons are the smallest units of the nervous system. There are more than 100 nerve cells, or neurons, in the brain of an average human being. Each neuron has a cell body, which contains a nucleus where metabolism and respiration take place. The nucleus contains the genetic material that directs all its functions, including the manufacture and release of the chemical messengers that enable the neuron to communicate with other cells and, ultimately, the brain. The cell body is enclosed by a cell membrane. Neurons have tiny fibers extending from the cell body that enable the neuron to receive messages from surrounding cells and pass them on to other cells.

The short fibers branching out from the cell body are called dentrites. The dendrites pick up messages coming in from surrounding areas and carry them to the cell body. There is a single long fibre, which is called axon. The axon is very thin and is usually much longer than the dendrites. In adults, axons that run from the brain to the base of the spinal cord,or from the spinal cord to the tip of the thump, may be as long as 3 feet. But most axons are only 1 to 2 inches long. A group of axons bundled together like parallel wires in an electric cable is called a nerve. The axons carries outgoing messages from the cell. By the end an axon splits into many terminal branches. Since there may be hundreds of dendrites on a single neuron, and sice the axon itself may brance out in numerous directions, one neuron can be in touch with nundreds of others at both its input end (dendrites) and its output end (axon)

Axon is covered by a fatty substance called myelin sheath. The sheath is pinched at intervals, which makes the axon resemble a string of microscopic sausages. All the axons might not be covered by myelin sheath. But myelinated axons are found throughout the body. The sheaths help neurons act with greater efficiency as well as provide insulation to the neuron.

All neurons relay messages. The kind of information each neuron collect and the places to which the information is carried, however, vary. Neurons that collect messages from sense organs to the spinal cord or to the brain are called sensory (or afferent) neurons. Neurons that carry messages from the spinal cord or the brain to the muscles and glands are called motor (or efferent) neurons. Neurons that carry messages from one neuron to another are called interneurons (or association neurons).