What Is the Somatic Nervous System?

Somatic nervous system
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The somatic system is the part of the peripheral nervous system that is responsible for carrying motor and sensory information both to and from the central nervous system. This system is made up of nerves that connect to the skin, sensory organs and all skeletal muscles. The system is responsible for nearly all voluntary muscle movements as well as for processing sensory information that arrives via external stimuli including hearing, touch and sight.

Whether you want to learn ballet, throw a ball or go for a jog, the somatic nervous system plays a vital role in initiating and controlling the movements of your body. How exactly does this complex system work?

Let’s start by taking a closer look at the key parts of the somatic nervous system.

Parts of the Somatic Nervous System

The somatic nervous system derives its name from the Greek word soma, which means "body." The somatic nervous system contains two major types of neurons:

  1. Sensory neurons (or afferent neurons) that carry information from the nerves to the central nervous system
  2. Motor neurons (or efferent neurons) that carry information from the brain and spinal cord to muscle fibers throughout the body

The neurons of the somatic nervous system project from the central nervous system directly to the muscles and sensory organs. The system is a direct path with synapses to connect nearby neurons.

The body of the neuron is located in the CNS, and the axon then projects and terminates in the skin, sense organs or muscles. Electrochemical impulses then travel along the axon to the brain or spinal cord.

Reflex Arcs and the Somatic Nervous System

In addition to controlling voluntary muscles movements, the somatic nervous system is also associated with involuntary movements known as reflex arcs.

During a reflex arc, muscles move involuntarily without input from the brain.

This occurs when a nerve pathway connects directly to the spinal cord. Some examples of reflex arcs include jerking your hand back after accidentally touching a hot pan or an involuntary knee jerk when your doctor taps on your knee.

You don’t have to think about doing these things. Sensory nerves carry signals to the spinal cord that then sends signals via to the affected areas via the motor nerves of the somatic system. Reflex arcs that impact the organs are called autonomic reflex arcs while those that affect the muscles are referred to as somatic reflex arcs.

An Example of the Somatic System in Action

The primary function of the somatic system is to connect the central nervous system to the body's muscles and organs. Information taken in by sensory systems is transmitted to the central nervous system. The CNS then sends signals via the nerve networks of the somatic system to the muscles and organs.

For example, imagine that you are out for a jog in the park one brisk winter morning.

As you run, you spot a patch of slick looking ice on the path ahead. Your visual system perceives the icy patch and relays this information to your brain. Your brain then sends signals to engage your muscles to take action. Thanks to your somatic system, you are able to turn your body and move to a different part of the path, successfully avoid the icy patch and prevent a possibly dangerous fall on the hard pavement.

More Psychology Definitions: The Psychology Dictionary

References:

Ganong, W. F. (2001). Review of Medical Physiology. New York: McGraw-Hill Publishing.

Nervous system. (2001). Body Guide. A.D.A.M. Found online at http://www.besthealth.com/besthealth/bodyguide/reftext/html/nerv_sys_fin.html#pns

Somatic nervous system. (2007). Dorlands Medical Dictionary. Merck & Co., Inc.

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