Peripheral Nervous System (PNS)

What is the peripheral nervous system?

Your peripheral nervous system (PNS) is that part of your nervous system that lies outside your brain and spinal cord. It plays key role in both sending information from different areas of your body back to your brain, as well as carrying out commands from your brain to various parts of your body.

Some of those signals, like the ones to your heart and gut, are automatic. Others, like the ones that control movement, are under your control.

What’s the difference between the peripheral and central nervous systems?

Your nervous system consists of two main parts: your central nervous system and your peripheral nervous system. Your central nervous system includes two organs, your brain and spinal cord.

Your peripheral nervous system is everything else and includes nerves that travel from your spinal cord and brain to supply your face and the rest of your body. The term “peripheral” is from the Greek word that means around or outside the center.

What does the peripheral nervous system do?

Your peripheral nervous system has two main subsystems: autonomic and somatic.

• Autonomic: These are nervous system processes your brain runs automatically and without you thinking about them.
• Somatic: These are functions you manage by thinking about them.

Those two subsystems are how your peripheral nervous system does its three main jobs:

• Senses: Your PNS is a key part of how your brain gets information about the world around you. This job falls under the somatic nervous system.
• Movement: Your peripheral nerves deliver command signals to all the muscles in your body that you can consciously control. This job also falls under the somatic nervous system.
• Unconscious processes: This is how your brain runs critical processes that don’t depend on your thinking about them. Examples of this include heartbeat and blood pressure. This job depends on your autonomic nervous system.

Senses

Your brain is like a powerful supercomputer. However, it knows nothing about the world outside your body without outside input. That’s why your peripheral nervous system is so important. A computer needs peripheral devices like a camera, microphone or keyboard to give it information from outside itself, and your brain is the same.

Your peripheral nervous system is how your brain gets information about the outside world. Most of your peripheral nervous system travel to the rest of your body by exiting or entering your spinal cord. Your cranial nerves are unlike other peripheral nerves in that these very special nerves connect directly to your brain. These nerves carry signals from your nose, ears and mouth, as well as many other organs. Your cranial nerves also give you a sense of touch in the skin of your face, head and neck.

Other peripheral nerves intertwine throughout every part of your body. They stretch out everywhere, including to the tips of your fingers and toes. The sensory nerves in your hands and feet are also part of your brain’s ability to get information from the outside world. The motor nerves allow you to move various parts of your body.

Movement

Your peripheral nerves that branch outward throughout your body deliver command signals from your brain to your muscles. That allows you to move around and do all kinds of tasks, ranging from simple ones, like scratching your nose, to complicated ones, like juggling.

Unconscious processes

Your autonomic nervous system functions without you thinking about it. Part of your brain is always working, managing processes that keep you alive. Your brain needs your peripheral nervous system to control those functions. Examples of these processes include your heart rate, breathing, blood pressure and your gut’s digestion of food.

Types of nerve signals

Your nerves consist of bundles of nerve cells, which have long, arm-like extensions called axons. The nerve cells and their axons twist and intertwine together to form nerve fibers. This is similar to how multiple strands of spun cloth fibers twist together to form sewing thread. Some of the nerves in that bundle carry information into your brain, while others carry information out of your brain.

• Sensory: These nerves carry information to your brain and spinal cord. They either connect directly to your brain through your cranial nerves or carry information to your spinal nerves, which then feed into your spinal cord. The sensory nerve connections to your spinal cord are on the back of your spinal cord.
• Motor: These nerves carry command signals from your brain to various parts of your body. They only carry information away from your brain. The motor nerve connections are on the front of your spinal cord; meaning, these nerves are for sending muscle movement commands only.
• Autonomic: These nerves control the automatic functions of the organs and systems in your body. Your autonomic nerves often involve mixed nerve fibers, some of which carry commands from your brain to their destination, and others that carry information about an organ’s function back to your brain.

How does the peripheral nerve system help with other organs?

Your autonomic nervous system, which is a part of your peripheral nervous system, helps your brain control all of the vital organs in your body. That also helps your brain care for itself. An example of this is your brain controlling your heartbeat, which ensures your heart pumps blood to your body and brain. Without that blood flow, your brain would die in minutes.

Your peripheral nervous system also relays nerve signals from those organs to your brain. Examples include feeling warmth inside of your stomach when you drink a hot beverage or feeling full after a meal.

Where is the peripheral nervous system located?

Your peripheral nervous system extends everywhere in your body that isn’t your spinal cord or brain. It includes:

• Cranial nerves: There are 12 pairs of nerves that connect directly to your brain, and 11 of them are part of your peripheral nervous system (the second cranial nerve, which controls your vision, is part of your central nervous system). These 11 nerves are part of your senses of smell, sound, taste, and the sense of touch you have in the skin on your head, face and neck. One of the 11, the vagus nerve, extends down and attaches to all vital organs from your neck to your colon.
• Spinal nerves: These are 31 pairs of nerves that attach to your spine at about the same level as each segment bone (vertebra) in your spine.

The above nerves all branch out and become smaller nerves that spread throughout your body. They eventually end at places like the tips of your fingers and toes or just underneath the surface of your skin.

What does it look like?

One way to imagine the nervous system is 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 spreads out through the rest of your body like limbs, branches and twigs of the tree.

What is it made of?

Your peripheral nervous system consists of various types of nerve cells and structures. Peripheral nerves and cranial nerves have command centers that are neurons as well as highways that send information called axons and dendrites. The cell types are as follows, with more about them listed below:

Neurons

Neurons are the cells that send and relay signals through your nervous system, using both electrical and chemical signals. Each neuron consists of:

• Cell body: This is the main part of the cell.
• Axon: This is a long, arm-like part that extends outward from the cell body. At the end of the axon are several finger-like extensions where the electrical signal in the neuron becomes a chemical signal. These extensions, known as synapses, lead to nearby nerve cells.
• Dendrites: These are small branch-like extensions (their name comes from a Latin word that means “tree-like”) on the cell body. Dendrites are the receiving point for chemical signals from the synapses of other nearby neurons.
• Myelin: This is a thin layer composed of fatty chemical compounds. Myelin surrounds the axon of many neurons and acts as a protective covering.

Neuron connections are incredibly complex, and the dendrites on a single neuron may connect to thousands of other synapses. Some neurons are longer or shorter, depending on their location in your body 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?

There are many conditions and causes of peripheral neuropathy, which means disease or damage of your peripheral nervous system. Some of the most common examples include:

• Type 2 diabetes. Unmanaged or untreated type 2 diabetes slowly damages your peripheral nervous system. This is why people with diabetes are at risk of losing feeling in their feet and lower legs. This type of diabetes is the most common cause of peripheral neuropathy.
• Autoimmune and inflammatory conditions. These include lupus, Guillain-Barré syndrome, rheumatoid arthritis and more.
• Hansen’s disease (better known as leprosy). While effects of this disease — which is rare in developed countries — are most visible on your skin, it also damages your peripheral 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 peripheral nerves. 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 peripheral nerves. Many industrial chemicals can also cause this kind of damage.
• Trauma. Injuries can cause nerve damage, which may be long-term or even permanent. 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 both disrupt your peripheral nervous system.

Your peripheral nerves may also show effects of conditions that affect any part of your central nervous system. While these don’t directly affect your peripheral nervous system, they can still disrupt how it works.

Common signs or symptoms of peripheral nervous system conditions?

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

Damage to motor nerves affects your muscles by causing:

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

Damage to sensory nerves causes the following symptoms:

• Little or no sense of touch in the affected area. Decreased sense of touch can make it feel like you’re wearing a glove or something else that interferes with your sense of touch. You can also lose the ability to feel temperature or vibrations. If this condition affects your hands or feet, it can make simple actions like walking or buttoning a shirt much more difficult.
• Tingling or numbness (paresthesia). This feeling is like when an arm or leg falls asleep. Another way to describe this is the “pins and needles” feeling in the affected area.
• Neuropathic pain. Also known as nerve pain, this often feels like a burning or sharp pain around the affected area. In some cases, the pain can be severe enough to keep you from sleeping or going about your normal routine. Some conditions, such as allodynia, can cause you to feel pain from even light contact with a soft object like clothing or bedding.

Damage to your autonomic nerves can affect the following organs and systems:

• Circulatory system: Autonomic nerve damage can interfere with your body’s ability to manage blood pressure.
• Digestive system: This can cause trouble digesting food, depending on the location of the affected part of your digestive tract.
• Skin and temperature control: People with autonomic nerve damage may have trouble feeling comfortable when it’s hot. They may also sweat too much (hyperhidrosis) or not enough (anhidrosis).

Common tests to check the health of the body organ?

Many tests can help diagnose conditions that affect your peripheral 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.

Some of the most common tests include:

• Blood tests (these can detect many problems, ranging from immune system problems to toxins and poisons, especially metals like mercury or lead).
• Nerve conduction tests.
• Electromyogram.
• Nerve ultrasound.
• Nerve biopsy.
• Genetic testing.
• Magnetic resonance imaging (MRI).

Common treatments for the body organ?

The treatments for peripheral nervous system problems are as varied as the problems themselves. In many cases, treating the underlying cause of peripheral nervous system issues can relieve the effects on that system. It’s also common that treatments for a condition (or similar conditions) won’t work for other kinds of problems.

Potential treatments include, but aren’t limited to, the following:

• Medications. Many medications can treat peripheral nervous system problems. These can come in many forms, including injections, oral medications or slow-release patches.
• Surgery. Surgery can help reconnect cut nerves and relieve pain due to trapped nerves.
• Transcutaneous electrical nerve stimulation. This involves using a mild electrical current to interfere with how nerves transmit pain signals.
• Nerve ablation. This technique involves intentionally damaging a malfunctioning nerve. That damage can help treat chronic pain by stopping the malfunctioning nerve from sending signals to your brain.
• Physical therapy. This can help you recover from injuries or medical procedures or improve pain symptoms. It can also help you adapt to nervous system changes.
• Acupuncture. This technique involves inserting tiny needles at various points on your body. Though this technique is often known for being an ancient Chinese practice, its use in modern medicine is growing. Many medical doctors, especially anesthesiologists or pain management specialists, use acupuncture to treat neurological problems.
• Devices and wearable equipment. These include medical devices like braces, canes and walkers, prescribed footwear and more.

How can I prevent peripheral nervous system conditions and problems?

Prevention is key for many of the conditions that can cause peripheral nervous system damage. Some of the most important things you can do include:

• Eat a balanced diet. Certain vitamin deficiencies, especially vitamin B12, can affect your nervous system and cause major problems. Other vitamins, especially B6, are toxic and cause peripheral neuropathy at high levels.
• Stay physically active and maintain a healthy weight. This is important to prevent injuries that can cause nerve damage. This, along with managing your diet, can help prevent or delay the onset of Type 2 diabetes, which damages your peripheral nerves over time.
• Wear safety equipment as needed. Injuries are a major source of nerve damage. Using safety equipment during work and play activities can protect you from these injuries or limit how severe the injuries are.
• Manage chronic conditions as recommended. If you have a chronic condition that can affect your peripheral nerves, especially Type 2 diabetes, it’s important to manage it as recommended by your healthcare provider. That can limit the effects of the condition or delay how long it takes to get worse.

A note from Cleveland Clinic

Your peripheral nervous system is a key part of your life. It helps you move around and delivers vital information from your senses to your brain. Prevention is key when caring for this part of your nervous system. If you have conditions that affect your peripheral nerves, there’s a wide range of ways healthcare providers can diagnose and treat these conditions. Even with incurable conditions, it’s usually possible to limit how the symptoms of these conditions affect your life.