Somatic Nervous System Definition Psychology: Its Function In A Human Body

The nervous system in the human body is divided and spread, performing its individual function to make your body move and exist according to the environment. Read this article to learn about one part of the peripheral nervous system, called the somatic nervous system, and its functionality in our body.

The nervous system controls all the activities of the body and makes the human body perform voluntary or involuntary functions. This nervous system is branched all over the body and has been classified on the basis of its functionality and location. The nervous system is divided into the central and peripheral nervous systems. The peripheral nervous system is further divided into somatic and autonomic nervous systems.

The somatic nervous system plays an important role in the sensory processing and movements taking place in our body. Continue reading this article to learn about the somatic nervous system definition, its location in our body, and its function through which it transmits information to different organs and makes sense of the environment.

What is the somatic nervous system?

Our nervous system is divided into several categories. One of the nervous systems is called the peripheral nervous system, which is further divided into AND (autonomic nervous system) and SNS (somatic nervous system). The branch of the peripheral nervous system, which includes all the nerves stretching from the brain to the spinal cord, is called the somatic nervous system. It covers nearly most parts of the human body. These nerves transmit the messages from your brain to different parts of the body so that the body functions in a healthy way.

All the voluntary movements of our body rely on the somatic nervous system as it carries the commands generated by our brain and then delivers them to the muscles so that we can move in the expected position. The sensory information related to our senses, such as taste, smell, hearing, and touch, is also transmitted with the help of the somatic nervous system.

In this process, sensory information is received from our external stimuli and then conveyed to the brain. For instance, when you touch a hot utensil, the somatic nervous system commands your body to pull away the hand quickly, or when you are in a cold place, you rub your hand to make yourself warm. This action is called somatic reflex, through which sensations are transduced by receptors in the skin. Somatic nerves are divided into two types:

  • Cranial nerves
  • Spinal nerves

Cranial nerves:

Cranial nerves refer to the nerves extending from the brain in the back and neck area of the body. These nerves send and bring electrical signals from the brain to other parts of the body, including the neck, torso, and head. Through these signals, the human body can smell, hear, taste, move muscles, and feel the external force on the skin. There are 12 pairs of cranial nerves in our body, and each pair spreads evenly on both sides of the brain and body. These 12 pairs are as follows:

  1. Olfactory nerve
  2. Optic nerve
  3. Vagus nerve
  4. Accessory nerve
  5. Hypoglossal nerve
  6. Glossopharyngeal nerve
  7. Facial nerve
  8. Auditory nerve
  9. Oculomotor nerve
  10. Trigeminal nerve
  11. Abducens nerve
  12. Trochlear nerve

All these nerves have their own functions in the body and are located in their respective places to carry out the function. A defect in any of these nerves can lead to neuromuscular disorder.

Spinal Nerves

Spinal nerves refer to the nerves extending from the spinal column of your body. Each spinal nerve is branched into two roots: sensory fibers and motor fibers. Sensory fibers enter the spinal cord from the dorsal root of the brain while its cell lies in the outside area of the spinal cord called the ganglion. Motor fibers leave the spinal cord from the ventral root while its cell lies inside the spinal cord.

There are 31 pairs of spinal nerves in our body, evenly distributed on both the left and right sides of the body, where each pair is connected to the spinal cord through a specific area of the body. These pairs are further divided in the following manner:

  • Twelve pairs in the thoracic area.
  • Eight pairs in the cervical area of the spine.
  • Five pairs in the lumbar area.
  • Five pairs in the sacral area.
  • One pair in the coccygeal area.

Damage in any of the spinal nerves can lead to loss of sensation, where a person will not be able to feel any atmospheric sensation on the skin. It can also increase the risk of paralysis.

Difference between the autonomic nervous system and the somatic nervous system

The peripheral nervous system plays an important role in the transmission of sensory messages between the central nervous system to other organs of the body. The peripheral nervous system is divided into two major parts called SNS (somatic nervous system) and ANS (autonomic nervous system).

The autonomic nervous system deals with the involuntary muscular movements of the body, which does need your consciousness as it deals with the functions that help the human body stay alive. All the muscular movements take place in different organs inside your body, such as heartbeat, digestion, blood pressure, and urination. Moreover, it also controls the movement of the glands, such as saliva, sweat, and digestive glands, so that the body functions in a normal and healthy way.

The somatic nervous system deals with the voluntary muscular movements which need your consciousness. All the movements that your body consciously senses are controlled by SNS. There are sensory receptors in your body that provide stimuli to skeletal muscles and control their operations. It consists of both efferent and afferent nerves which are connected by the central nervous system and interneurons. The efferent nerves transfer the information from the central nervous system of our body to the effector organs, whereas afferent nerves transfer the information from sensory receptors to the central nervous system.

Somatic nervous system Autonomic nervous system


It controls the voluntary movements of the body It controls the involuntary movements of the body
Controls the functions of sensory stimuli such as sense, touch, vision, etc control s the function of salinity, blood pressure, etc
There are only thick nerve fibers in SNS There are both thick and thin nerve fibers in ANS
Consist of only a single neuron between the effector organ and the CNS Consist of two neurons with a single synapse between the effector organ and CNS
Body postures are controlled through SNS Body secretions are controlled through ANS

Location of the somatic nervous system:

The somatic nervous system extends from the outside part of the brain and spinal cord. It is surrounded by the neck and head area through 12 pairs of cranial nerves. Below the neck somatic nervous system is connected to 31 pairs of spinal nerves that are spread out throughout the body. Part of the nerves are sensory and perform sensory transmission by conducting information towards the brain area. Other parts of the nerves conduct information to the respective muscles from the brain area.

These two nerves, called spinal and cranial nerves, are branched as the smaller nerves are divided into all the parts of the body beneath the skin area. This branch ends in the hand or leg area at the tip of the finger or toes. The somatic nervous system is composed of a system of neurons that perform their own functions.

They transmit the required signals into all parts of the body through an axon which enables the signals to be transferred to the destined part and also the longest part of the cell. At the end of each neuron, there are dendrites present, which allow more than one signal to be spread out so that it passes on to the next neuron. Based on their functions, they have been divided into two major types:

  • Motor neurons
  • Sensory neurons

Sensory neurons

Sensory neurons are also called afferent neurons, which carry information in the body from different organs, including muscles, glands, and skin, to the central nervous system. For instance, when we touch a hot utensil, it is through sensory neurons that we feel the hotness and make efforts to stay back from it.

Motor neurons

Motor neurons are also called efferent neurons, which carry motor information from the central nervous system to the destined organs in the body. All the muscle movements taking place in our body are controlled by these neurons when signals are transmitted from the spinal cord to the skeletal and smooth muscles. All the contraction and relaxation of the muscles are caused by motor neurons.

It has a chemical messenger called acetylcholine which works as a neurotransmitter and is present in the neurons through which messages are conveyed. Acetylcholine is present in both the autonomic and somatic nervous systems. In the autonomic nervous system, acetylcholine has an inhibitory effect, while in the somatic nervous system, it has an excitatory effect. When electrical signals are sent from the motor neurons in the form of chemical messages, acetylcholine is released by the motor neuron.

Cranial nerves in the somatic nervous system play an important role in transmitting information from the brain to all body organs, such as the mouth, eyes, nose, etc., and then transmit the electrical signals from these organs to the brain. For example, the optic nerve of the cranial nerve will convey motor messages from the eyes to the brain and then generate the messages to be sent back to the eye so that it responds according to the environment.

Ten different types of cranial nerves are created from the brainstem, which controls the voluntary movements of the head. The spinal nerves in the somatic nervous system transmit sensory information to the spinal cord and then the information of the spinal cord back to the brain through receptors. The rest of the body movements and functions in the head and neck area are controlled by these nerves.

Other parts of the somatic nervous system

Some of the key components that play an important role in the functionality of the brain are as follows:

  • Ganglia
  • Nuclei
  • Glial cells

Ganglia is a large group present in the form of clusters in the autonomic and voluntary branches of the peripheral system or nerve cells that carry nerve signals throughout the body. Nuclei are also present in the form of clusters in the midbrain, medulla, and pon area. Glial cells do not directly participate in the transmission of the signals but provide physical and chemical support to the proper functioning of the nervous system.

Functions of the somatic nervous system

The somatic nervous system controls some important functions in the body. The activity of the somatic nervous system in the body’s functionality is listed as follows:

Sensory input

All the sensory information is traveled all over the body through the somatic nervous system. This sensory information is captured through external stimuli of the body, such as skin, mouth, nose, etc. Whatever a human smells, tastes, and touches is through the proper functioning of the somatic nervous system. All the signals transmitted to the brain through the somatic nervous system are integrated, and then an appropriate response is generated, which is then traced back to the destined organ in the form of chemical messages.

Movement of the muscles

All the movements of the body are also controlled by the somatic nervous system. The muscles do not move on their own and depend on the command and messages to make the movements and move around. For instance, the neurons transmit the signal to the leg muscles to move when we walk or run. Hence, this process takes place within seconds.

Reflex arcs

Reflex actions in the body are also linked to the somatic nervous system. These movements, known as reflexes, are managed by a pathway called a reflex arc. This pathway transmits information from an organ to muscle cells by traveling through afferent neurons to the CNS and then back via efferent neurons. This process involves sensory nerves, which connect to interneurons in certain areas, allowing the signal to reach the muscles that activate the reflex.

Reflex actions cause involuntary muscle movements without input from the brain. For example, grinding teeth when cold to generate heat or quickly withdrawing a hand after touching a hot object.

This occurs in dangerous situations when sensory neurons detect external threats, and the signal is sent directly to the spinal cord instead of the brain. The spinal cord then generates a response, sending it through motor neurons to the muscles. This happens within nanoseconds, making it seem like an automatic function.

Impairment in the somatic nervous system

The whole body’s functionality is based on sensory information. This information is received and sent by the somatic nervous system. This damage can lead to several harmful effects in the form of diseases, weakness, infections, and extreme pain. Some diseases also attack the somatic nervous system in our body, such as diabetes or other autoimmune diseases. If the diseases do not get controlled, they start spreading in the whole body through SNS.

Additionally, the axon is an important component of SNS, but an issue in this part can also damage the functionality of the somatic nervous system. Some of the diseases associated with SNS are as follows:

Motor neuron disease

When the neurons in the peripheral nervous system die, their functionality stops and results in neurodegenerative disease. People having this disease are unable to move their muscles properly. Hence, these muscles waste away eventually. It starts with a weakness that gets worse over time. This disease can not be cured completely, but one can make efforts to lower the harmful impacts it leads the body. The symptoms of this disease include:

  • Weakness in the knees and joints
  • Inability to speak properly
  • Can not sustain balance or grip on the surface
  • Muscles constantly have twitches
  • Can not control emotional responses such as laughing or crying.

Multiple sclerosis

When our body’s immune system attacks the nerve cells (nerve fibers and myelin sheath present in the brain and spinal cord) and damages the central nervous system, it can affect every individual with a different intensity. In some cases, it is mild, while in others, it can create sensory and motor problems, such as the inability to walk, run or speak.

If it gets diagnosed and treated in the initial stages, then the symptoms are neurological that get visible within a few hours and last maximum for a couple of days. However, the untreated multiple sclerosis symptoms worsen with time. These symptoms include:

  • Weakness
  • Numbness
  • Unclear vision
  • Unstable body movement

Nerve-compression syndromes

The nerves connected to different parts of the body, such as the hand and feet, are called the peripheral nervous system. Pressure on any of the nerves in the peripheral nervous system leads to nerve-compression syndrome. This can further cause pinched nerves and nerve damage if left untreated. It can be caused by repetitive injuries; usually, the areas of the torso and limbs are affected by nerve compression, which causes the following symptoms:

  • Pain
  • Numbness
  • Muscle weakness
  • Inflammation
  • Difficulty moving certain body parts

Trigeminal neuralgia

It affects the trigeminal nerve that is present on both sides of the face; it extends from the ear and leads to the face area towards the eye, cheek, and jaw. It can occur due to nerve lesions or nerve injury in facial trauma or any surgery when the blood vessels are pressed against the trigeminal nerve and making the arteries rub against the nerve and leave it sensitive.

It creates sudden and extreme burning or pain resembling electric shock in the face area that lasts for a few minutes, and the person is unable to eat or even drink for this duration. Depending on the intensity, it has two types: type 1 and type 2.

These diseases can be cured if they get diagnosed in the initial stages. Some people leave them untreated, and it becomes unpreventable. However, some medical aids and lifestyle changes can lower the symptoms of these diseases and the damage caused to the somatic nervous system.

A person suffering from any of the symptoms, be they mild or severe, should get it checked by a medical professional and move forward with his lifestyle according to his suggestions. Furtherly, a healthy diet and cutting out on harmful habits can help him maintain a good immune system which will decrease the risk of these diseases.


The somatic nervous system, a crucial part of the peripheral nervous system, extends throughout the human body in the form of nerves. These nerves transmit chemical messages to various body parts, facilitating sensory processing and muscle movement controlled by the brain.

The somatic nervous system enables muscular movements like walking, running, and touching objects. It is also responsible for sensations such as heat, taste, and smell, carried out by motor and sensory neurons. Damage to any part of the somatic nervous system can impair bodily functions and lead to diseases such as motor neuron disease, multiple sclerosis, and nerve-compression syndrome.