Somatic Nervous System: Definition, Function & Example

One of the most complex systems in the body is the nervous system. In this lesson, you will learn about the somatic nervous system and how important it is to body functions. Examples and illustrations will be provided to assist your understanding of the lesson.
Definition
You are going to the bowling alley tonight with your friends. Do you know what muscles you need to use to bowl? How do your muscles know when and how to move to get the ball down the alley? The somatic nervous system is very important in getting that ball down the alley – especially if you want a strike.

The somatic nervous system is part of the peripheral nervous system, which is the entire nervous system outside of the brain and spinal cord. Specifically, the somatic nervous system is responsible for movement of voluntary muscles and the process known as a reflex arc. This system carries nerve impulses back and forth between the central nervous system, which is the brain and the spinal cord, and the skeletal muscles, skin, and sensory organs.

Nervous System Diagram (Red = Central Nervous System; Blue = Peripheral Nervous System)
nervous system
Parts of the Somatic Nervous System
The somatic system is made up of two different types of neurons, which are also called nerve cells. The two types of neurons are sensory neurons, or afferent neurons, which transmit messages to the central nervous system, and motor neurons, also called efferent neurons, which relay information from the central nervous system to other areas of the body. A neuron has a body and an axon; the body of the neuron is located in the central nervous system, and the axon is imbedded in the skeletal muscles, sensory organs, or the skin.

Now, we will speak about how the somatic nervous system fits into the peripheral nervous system. Within the peripheral nervous system, there are 12 pairs of cranial nerves and 31 pairs of spinal nerves, which are made of sensory neurons and motor neurons. Some nerve pairs have only sensory cells, some have only motor cells, and still others have both sensory and motor cells. The motor nerve cells are either somatic or autonomic. Since this lesson is about the somatic nervous system, we will not go into detail about the autonomic nerve cells.

Function
The primary role of the somatic nervous system is to connect the central nervous system to the organs, muscles, and skin. This allows you to perform complex movements and behaviors. The somatic neurons carry messages from the outer areas of the body having to do with the senses. It is like a passageway from the environment to the central nervous system. Sensory/afferent neurons carry the impulses to the central nervous system and the brain. After being processed by the central nervous system, the somatic motor, or efferent, neurons take the signal back to the muscles and sensory organs.

Afferent and Efferent Neurons
Afferent and Efferent Neurons
Remember the nerve pairs described above under the parts of the somatic nervous system? Some of the nerve pairs have only sensory neurons, such as those that are involved in smell and vision. Others have only motor neurons, such as those involved with eyeball movement (not vision). Finally, some nerve pairs have both sensory and motor neurons, such as those involved in taste and some aspects of swallowing.

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