Somatic Nervous System

What is the somatic nervous system?

Your somatic nervous system is a subdivision of your peripheral nervous system that stretches throughout nearly every part of your body. The nerves in this system deliver information from your senses to your brain. They also carry commands from your brain to your muscles so you can move around.

What’s the difference between the somatic and autonomic nervous systems?

Your somatic nervous system involves things you can consciously sense and do. Your autonomic nervous system works without you thinking about it, running the behind-the-scenes processes that keep you alive. Both are subdivisions of the peripheral nervous system, a subsystem of your overall nervous system.

What does the somatic nervous system do?

Your somatic nervous system has two main jobs:

• Sensory input. All but one of your senses travel through your somatic nervous system to reach your brain (sight is the exception because your retina and optic nerve connect directly to your brain). The other senses on your head — sound, smell, taste and touch — all use your somatic nervous system to reach your brain. Your sense of touch below your neck uses your somatic nervous system to reach your spinal cord, which then relays signals to your brain.
• Movement control. Your body’s muscles rely on signals that give them instructions to help you move around. The signals from your brain must pass through your somatic nervous system to reach those muscles and make them move.

How does the somatic nervous system help with other organs?

For most of your internal organs, your somatic nervous system only helps indicate organ pain using “referred pain.” This is when you feel pain in a specific area, but the pain is actually coming from a problem nearby. One of the best-known examples of this is pain from a heart attack that you feel in your left arm, back, jaw or abdomen.

One of the expert theories about why that happens has to do with your nervous system’s layout.

Another example of how your somatic nervous system can affect internal organs is controlling your breathing. Under most circumstances, you breathe automatically and without thinking about it. But you can also breathe manually, deliberately controlling when you inhale and exhale.

Where is it located?

Your somatic nervous system spreads outward from your brain and spinal cord. In your head and neck, it does that through your cranial nerves. These are 12 pairs of nerves (which use Roman numerals to set them apart), 11 of which have connections that are part of your somatic nervous system. Cranial nerve (CN) II, which connects to your eyes, is technically part of your brain, not your somatic nervous system.

Farther down, your somatic nervous system has connections in all 31 spinal nerves. The spinal nerves branch out further and become the nerves that spread out through your body. Some of the nerves in this system are sensory. They conduct information one way: Up to your brain. Others are motor, and they also conduct information one way: From your brain to your muscles.

Both your spinal and cranial nerves continue to branch outward as smaller nerves throughout your body. They usually end at nerve endings in places like the tips of your fingers and toes, or just underneath the surface of your skin.

What does it look like?

Your nervous system looks much like an upside-down tree, with your brain as the root of the tree and your spinal cord as the tree’s trunk. Your peripheral nervous system — especially your somatic nervous system — spreads out through the rest of your body. Because your somatic nerves end up underneath your skin’s surface or in your hands and feet, they’re like the farthest reaches of the tree’s limbs, branches and twigs.

What is it made of?

Your peripheral nervous system consists of various types of nerve cells and structures. The cell types are as follows, with more about them listed below:

• Neurons: These are nerve cells. They manage and convert signals into either chemical or electrical forms.
• Glial cells: These are support cells in your nervous system. While they don’t transmit or relay nervous system signals, they help the neurons that do.
• Nuclei: These are clusters of nerve cells with the same job or connections.
• Ganglia: Pronounced “gang-lee-uh,” these are larger groups of closely related nerve cells (one of these is a ganglion, pronounced “gang-lee-on”). Examples of this are your cochlear and vestibular ganglia, which are part of your senses of hearing and balance.

Neurons

Neurons are very specialized cells that only happen in your nervous system. There, they send and relay signals throughout your body. These signals, which come in electrical and chemical forms, are how systems in your body communicate with each other. Each neuron consists of the following:

• Cell body: This is the main part of the cell. It conducts and transmits signals throughout the various structures that extend outward from it.
• Axon: Each neuron has one axon, a long, arm-like extension that reaches outward from the cell body. The end of the axon has several finger-like extensions where electrical signals convert over to chemical signals. The finger-like extensions, synapses, convey those chemical signals to nearby nerve cells.
• Dendrites: These are small branch-like extensions (their name comes from a Latin word that means “tree-like”) that stick out of the cell body. Dendrites receive chemical signals sent out from synapses on other nearby neurons.
• Myelin: This thin, fatty layer surrounds the axon of many neurons. It’s protective and helps speed up certain signals as they travel through the neuron.

Neurons form web-like networks that are incredibly complex, with one neuron sometimes connecting to thousands of others. Neurons also come in different lengths, and some are longer or shorter, depending on location and what they do.

Glial cells

Glial (pronounced “glee-uhl”) cells have many different purposes, helping develop and maintain neurons when you’re young and managing how the neurons work throughout your entire life. They also protect your nervous system from infections, control the chemical balance in your nervous system and create the myelin coating on the neurons’ axons. Your nervous system has 10 times more glial cells than neurons.

What are the common conditions and disorders that affect this body system or organ?

Your somatic nervous system is a division of your peripheral nervous system. Your peripheral nervous system is all of the nervous tissue in your body that’s not part of your brain or spinal cord.

Because your somatic nervous system is part of your peripheral nervous system, it’s prone to conditions that cause peripheral neuropathy. This term means disease or damage to your peripheral nervous system, and some of the most common conditions and disorders that cause it include:

• Type 2 diabetes. Uncontrolled Type 2 diabetes slowly damages your somatic nervous system, especially in your legs and feet. This is why people with diabetes are at risk of losing feeling in their lower limbs. This type of diabetes is the most common cause of peripheral neuropathy.
• Autoimmune and inflammatory conditions. An example of one such condition is Guillain-Barré syndrome.
• Hansen’s disease (better known as leprosy). This disease — which is rare in developed countries — is most visible on your skin. However, its effects can run deeper and damage your somatic nerves.
• Congenital and genetic conditions. These are issues you have when you’re born. Genetic conditions are ones you inherit from one or both parents.
• Infections. Nerve damage from these can happen because of viruses such as HIV or bacteria such as Borrelia burgdorferi, which causes Lyme disease. Another common example is having shingles, which can lead to lingering nerve pain.
• Medications and medical procedures. Certain types of antibiotics and chemotherapy medications for cancer can damage areas of your somatic nervous system. This kind of nerve damage can also happen as a side effect of surgery.
• Poisons and toxins. Toxic heavy metals like mercury or lead can damage somatic nervous tissue, causing sensation and muscle control problems. Many industrial chemicals can also cause this kind of damage.
• Trauma. Injuries that cause nerve damage can result in long-term or even permanent damage to somatic nervous system tissue. Swelling from injuries can also put too much pressure on peripheral nerves. Carpal tunnel syndrome and sciatica are examples of nerve compression disorders.
• Tumors. Malignant tumors, better known as cancer, and benign (harmless) tumors can disrupt your somatic nervous system, interfering with your senses or how you control your muscles.

Common signs or symptoms of body organ conditions?

The symptoms of somatic nervous system problems depend on the types of nerves affected.

Damage to motor nerves affects your muscles by causing:

• Cramps, spasms, tremors or twitches.
• Wasting (shrinking of muscles).
• Loss of control.

Damage to sensory nerves causes the following symptoms:

• Loss of touch sensations. This effect can reduce your ability to feel, making it feel like you’re wearing gloves. It can also disrupt nerve transmission of temperature or vibration, so you can’t tell if you’re holding something hot. When this condition affects your hands or feet, you might struggle to walk, keep your balance or pick up small objects like coins or your keys.
• Tingling or numbness (paresthesia). Another way to describe this is the “pins and needles” feeling, like when part of your body, such as an arm or leg, falls asleep.
• Neuropathic pain. This often feels like a burning or sharp pain around the affected area. This pain happens because of signals firing from damaged or malfunctioning nerves, not because of something painful happening at the time. This pain is often severe enough to interfere with restful sleep or going about your usual routine.

Common tests to check the health of the body organ?

Many tests can help diagnose problems affecting your somatic nervous system. The most common starting point is a neurological exam, where your healthcare provider has you use different parts of your body, especially arms, hands, legs and feet, in certain ways. This can help them narrow down the source of a problem to certain nerves, areas of your spine or parts of your brain.

Other common tests include:

• Blood tests (these can detect many issues, ranging from immune system problems to toxins and poisons, especially metals like mercury or lead).
• Electroencephalogram (EEG).
• Electromyogram (nerve conduction test).
• Genetic testing (especially when it’s possible you inherited a congenital condition from a parent).
• Magnetic resonance imaging (MRI).

Common treatments for somatic nervous system problems?

The treatments for issues in your somatic nervous system strongly depend on the underlying cause, related conditions or the symptoms you have. In many cases, treating the underlying cause of peripheral nervous system problems can relieve the effects on that system.

Potential treatments can include:

• Medications. Many medications can treat somatic nervous system issues. These can treat symptoms like pain, muscle tremors or twitching and more.
• Surgery. This can decompress a nerve trapped by surrounding tissue or swelling, such as with carpal tunnel syndrome.
• Transcutaneous electrical nerve stimulation. This involves using a mild electrical current to interfere with how malfunctioning nerves send or relay pain signals.
• Nerve ablation. This technique involves intentionally damaging a malfunctioning nerve so it can’t send or relay signals. This treatment is useful for certain types of chronic pain.
• Physical therapy. This can help you recover from injuries or medical procedures, or improve pain symptoms. It can also help you learn how to live with or adapt to a new or worsening condition that affects your ability to move or sense objects in the world around you.
• Acupuncture. This technique, which involves inserting tiny needles at various points on your body, is usually best known for its role in traditional Chinese medicine. However, its use in modern medicine is growing. Many medical doctors (especially anesthesiologists or pain management specialists) use acupuncture to treat people who can’t or don’t want to take painkillers or other medications.
• Devices and wearable equipment. These include medical devices like braces, canes and walkers, prescribed footwear and more. These help you adapt to changes in your body so you can still navigate the world around you.

How can I prevent somatic nervous system conditions and problems?

Many of the conditions that affect your somatic nervous system are avoidable or preventable. While it’s impossible to prevent some conditions, it’s often possible to delay their effects or limit how severe they are. The ways you can avoid, prevent or delay issues include:

• Eat a balanced diet. Vitamin deficiencies, especially vitamin B12, can damage your nervous system. Other vitamins, especially B6, have toxic effects when you take too much.
• Stay physically active and maintain a healthy weight. This helps you have a body that’s strong and agile enough to avoid many injuries that could cause nerve damage. This can also prevent or delay the onset of Type 2 diabetes, especially when you also manage your diet. This avoids or delays when you feel the effects of nerve damage from Type 2 diabetes.
• Wear safety equipment. Injuries are a common cause of nerve damage, so safety equipment is essential. Whether you use this equipment when you work or during recreational activities, protective gear can help you avoid nerve injuries or limit their severity.
• Manage health conditions. Chronic health problems like Type 2 diabetes, or others that affect your nervous system, are often treatable. Managing these conditions usually involves seeing your healthcare provider regularly, taking medication and more. Managing conditions can prevent or delay when and how chronic conditions get worse.

A note from Cleveland Clinic

Your somatic nervous system is a system in your body that you use but don’t think about often. This part of your nervous system is how you receive information about the world around you, from the temperature outside to the smell of a favorite meal. Taking care of your somatic nervous system can make a big difference in your overall quality of life, so it’s important to prevent conditions that affect it or manage them as best you can.