What Is the Somatic Nervous System?

Somatic nervous system

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What Is the Somatic Nervous System?

The somatic nervous 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 (CNS).

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.

Components

The term somatic is drawn from the Greek word soma, which means "body," which is appropriate considering it is this system that transmits the information to and from the CNS to the rest of the body.

The somatic nervous system contains two major types of neurons:

  • Sensory neurons, also known as afferent neurons, are responsible for carrying information from the body to the CNS.
  • Motor neurons, also known as efferent neurons, are responsible for carrying information from the brain and spinal cord to muscle fibers throughout the body.

The neurons that make up the somatic nervous system project outwards from the CNS and connect directly to the muscles of the body, and carry signals from muscles and sensory organs back to the central nervous system.

The body of the neuron is located in the CNS, and the axon then projects and terminates in the skin, sense organs, or muscles.

Functions

The primary function of the somatic nervous system is to connect the central nervous system to the body's muscles to control voluntary movements and reflex arcs. 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 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 avoiding the icy patch and preventing a possibly dangerous fall on the hard pavement.

Reflex Arcs

In addition to controlling voluntary muscle 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. Examples of reflex arcs include:

  • Jerking your hand back after accidentally touching a hot pan
  • Involuntary jerking 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, often connect with interneurons in the spine, and then immediately transmit signals down the motor neurons to the muscles that triggered the reflex.  

Reflex arcs that impact the organs are called autonomic reflex arcs, while those that affect the muscles are referred to as somatic reflex arcs.

Impact of Damage to the SNS

Somatic nervous system diseases are those that impact the peripheral nerves that are outside of the brain and spinal cord. Diseases that impact the peripheral nerve fibers of the somatic nervous system can cause what is known as peripheral neuropathy. This leads to nerve damage that causes numbness, weakness, and pain, often in the hands and feet. 

The causes of damage to the peripheral nerves found in the somatic system can include conditions present from birth as well as acquired conditions. Diabetes is one of the most common causes of peripheral neuropathy, but it may also be caused by autoimmune conditions, infectious diseases, and trauma.

Types of somatic nervous system diseases also include brachial plexus neuropathies, Guillain-Barre syndrome, myasthenia gravis, trigeminal neuralgia, and nerve compression syndromes.

Tips / Tricks

While diseases that impact the somatic nervous system are not always preventable, there are lifestyle changes that you can make that may help prevent peripheral neuropathy. Some strategies that may help include:

  • Avoiding alcohol
  • Correcting vitamin deficiencies
  • Eating a healthy diet
  • Getting regular exercise
  • Maintaining a healthy weight
  • Quitting smoking

It is also essential to treat chronic health conditions such as diabetes, which may play a role in the onset of peripheral neuropathy.

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Article Sources
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  2. Dorland. Dorland's Illustrated Medical Dictionary E-Book. Elsevier Health Sciences; 2011.

  3. Barrett KE, Barman SM, Boitano S et al. Ganong's Review of Medical Physiology 25th Edition. McGraw Hill Professional; 2015.

  4. Cleveland Clinic. Neuropathy (peripheral neuropathy). Updated December 16, 2019.

  5. Akinrodoye MA, Lui F. Neuroanatomy, somatic nervous system. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Updated April 2, 2020.

  6. Cleveland Clinic. Neuropathy (peripheral neuropathy): prevention. Updated December 16, 2019.

Additional Reading
  • Somatic nervous system. Dorland's Illustrated Medical Dictionary. Merck & Co., Inc; 2011.

  • Ganong, W. F. Review of Medical Physiology. New York: McGraw-Hill Publishing; 2015.