Neurons And The Nervous System

Robert Fettgather, Ph.D. is a counselor, educator, writer and activist residing in Grass Valley, California.  He holds a doctorate in psychology and master degrees in both psychology and education. Robert Fettgather has served as Special Consultant in psychometrics to the Departments of Education and Developmental Disabilities for the State of California. Robert Fettgather also holds a specialist credential in learning handicapped and community college credentials in both learning and developmental disabilities.

The role of the nervous system is to carry information to and from all parts of the body. The cells in the nervous system that relay and carry information are referred to as neurons. Neurons use an electrical signal to send information from one end of its cell to the other end. At rest, a neuron has a negative charge on the inside and a positive charge outside. When a signal arrives, "gates" in the cell wall next to the signal open and the positive charge moves inside. The positive charge inside the cell causes the next set of gates to open to allow those positive charges to move inside. So in this manner, the electrical signal makes its way down the length of the cell.

Neurons relay messages on to targeted cells using a chemical signal. Dendrites receive information from other neurons, and axons send information to other neurons. When the electrical signal makes its way down the axon and arrives at other end of the neuron (the axon terminal), it enters the outermost tip of the terminal (the synaptic knob). That engenders  the neurotransmitters in the synaptic vesicles to be released into a space between the two cells that is filled with liquid. This fluid-filled space is called the synapse or the synaptic gap. The neurotransmitters are the chemical signals the neuron uses to communicate with its target cell. The neurotransmitters fit into the receptor sites of the target cell and create a new electrical signal that then can be transmitted down the length of the target cell.

The central nervous system (CNS) is made up of the brain and the spinal cord. The spinal cord is an elongated bundle of neurons that relays information between the brain and the rest of the human body.  Afferent (sensory) neurons relay messages from our senses to the spinal cord. For example, sensory neurons would relay information about a sharp pain in your finger or when you touch your hand on a hot stove. Efferent (motor) neurons direct commands from the spinal cord to our muscles- for example, a command to pull your finger back.

Interneurons connect sensory and motor neurons and help to coordinate the signals. All three of these neurons act together in the spinal cord to form a reflex arc.