The Cells of the Nervous System

The central nervous system is made up of glial cells and neurons.

 

Glial Cells

Glial cells hold the central nervous system together by providing structural support, promoting communication between neurons, and removing cellular waste products.

 

Neurons

The smallest unit in the nervous system is the neuron. Neurons are the building blocks of the nervous system underlying the activity of the entire nervous system. All major structures of the brain are composed of neurons. Three major parts of the neuron are the cell body, dendrites, and axon. The soma, or cell body, contains a nucleus and other components needed for cell maintenance. Genes that direct neural change and growth are located within the nucleus. An axon is a long projection from the soma which transmits electrical impulses toward the adjacent neuron. The neuron's spiny projections that receive messages from other neurons are called dendrites. Axons that become myelinated are insulated in a fatty myelin sheath so that the impulse travels more efficiently.

Neurons specialize in communication. Information comes in from the outside through our sense receptors such as our eyes and ears. Transmission of this information through the neuron is an electrical process. The cell membrane of the neuron is semi-permeable. The passage of a nerve impulse through a neuron starts at a dendrite, and then travels through the cell body down the axon to an axon terminal. Axon terminals lie close to the dendrites of neighboring neurons. When the nerve impulse reaches an axon terminal, terminal buttons release chemicals known as neurotransmitters into the gap between neurons, known as the synaptic cleft.

There are three kinds of neurons. Sensory neurons receive incoming sensory information from the senses (eyes, nose, ear, skin, tongue). Motor neurons carry commands from the brain to muscles of the body. Interneurons are neurons that communicate only with other neurons. Interneurons are the most common kind of neurons in the brain.

Over the last 20 years, researchers have tracked neural activity in relation to certain stimuli. Some experts, however, suggest that research is too focused on a single neuron rather than populations of neurons listening to other groups of neurons.

For further discussion by Dr. Thomas Albright, Salk Institute for Biological Studies, and Dr. Gilles Laurent, California Institute of Technology, click here.

 

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