Somatic nervous system: parts, functions and characteristics.

An overview of the parts and functions of the somatic nervous system, as well as its disorders.

The somatic nervous system is a part of the peripheral nervous system and is responsible for transmitting sensory information and sending motor control information to skeletal muscles.

It is the main system for managing voluntary movements and is the nerve center of dozens of sensory and motor nerves that enter and leave the central nervous system, in connection with the skin, organs and muscles of the body.

In this article we explain what is the somatic nervous system, what are its functions, its composition and the main diseases that affect it.

The nervous system

The somatic nervous system is part of a larger whole, the nervous system, The brain is the guarantor of the control and management of the vast majority of our body's vital functions.The nervous system is responsible for the control and management of most of our body's vital functions, capturing stimuli from the environment and from the organism itself in order to transmit, process information and generate effective responses according to what each situation requires.

From an anatomical point of view, the nervous system can be divided into two parts: the central nervous system (CNS), which includes the brain and the spinal cord; and the peripheral nervous system, which comprises the set of nerves and ganglia that connect the CNS with the rest of our body.

The peripheral nervous system can be divided, from a functional point of view, into two parts: the autonomic nervous system, which is composed of sensory and motor fibers that connect the central nervous system (CNS) with the visceral organs, smooth musculature and secretory glands; and the autonomic nervous system, which is composed of sensory and motor fibers that connect the central nervous system (CNS) with the visceral organs, smooth musculature and secretory glands. the somatic nervous system, which regulates the voluntary functions of the organism and of which we will give more details below. and of which we will give more details below.

The somatic nervous system (SNS)

The somatic nervous system is responsible for capturing sensory information from the environment, using the sensory receptors that we have scattered throughout our body that we have distributed throughout our body (mainly in the head, skin and extremities) and this information is transmitted to the central nervous system (CNS), which is responsible for executing the orders through the motor neurons that conduct the nerve impulses to the skeletal muscles.

This system is associated with the voluntary control of body movements, as well as the processing of information.as well as the processing of sensory information coming from the senses (sight, hearing and touch). The somatic nervous system is composed of afferent or sensory nerves and motor or efferent nerves.

The sensory nerves are responsible for transmitting bodily sensations to the CNS and the motor nerves are responsible for sending orders from the CNS to the body's organs, stimulating muscle contraction.

The 43 nerve segments of which our organism is composed are found in the somatic nervous system. Each segment is made up of a sensory nerve and a motor nerve.. Of the total, 31 emerge from the spinal cord (spinal nerves), while the remaining 12 emerge from the skull (cranial nerves).

Composition of the SNS

The nerves of which the somatic nervous system is composed can be classified according to where they enter and exit into: cranial nerves, those that emerge directly from the brain or at the level of the brain stem; and spinal nerves, those that emerge from the spinal cord.

Cranial nerves

There are 12 pairs of cranial nerves in the somatic nervous system.They emerge from the encephalon and their purpose is to transport sensory information, control certain muscles and regulate some glands and internal organs.

These are the twelve pairs of cranial nerves:

1. olfactory nerve

It is responsible for receiving olfactory sensory information and transmitting it to the olfactory bulb, a structure in the brain responsible for regulating certain glands and internal organs.The olfactory nerve, a structure of the brain that is in charge of processing and encoding this information to send it to higher structures of the brain.

2. Optic nerve

Receives visual sensory information to transmit it to higher brain regions responsible for vision.

3. Internal ocular motor nerve

Controls eye movements and regulates processes such as pupillary dilation and contraction.

4. Trochlear nerve

It innervates the superior oblique muscle of the eye and its main function is to control eye movements. control eye movements (upward and downward, and also outward).

5. Trigeminal nerve

It has a sensory and a motor portion, and is responsible for receiving somatosensory and is in charge of receiving somatosensory information (tactile sensations, pain, etc.) from receptors in the face and head, as well as controlling the muscles of mastication.

6. External ocular motor nerve, or abducens.

Its function is to control the movement of the lateral rectus muscle, allowing abduction of the eye (turning in the opposite direction to the eye). (turning in the opposite direction to the nose).

7. Facial nerve

Contains both sensory and motor fibers, is responsible for receiving information from the tongue receptors (gustatory) and somatosensory information from the ears, and manages the movements of the muscles of the neck and face involved in facial expressions.

8. Vestibulocochlear nerve

It is a sensory afferent nerve and is responsible for balance and auditory function. is responsible for balance and auditory function..

9. Glossopharyngeal nerve

This nerve emerges from the medulla oblongata of the brain and receives gustatory information from the back of the tongue, somatosensory information from the tonsils, pharynx, middle ear and auditory tube. It is also involved in swallowing.

10. Vagus nerve

It emerges from the medulla oblongata and innervates the pharynx, esophagus, larynx, trachea, bronchi, heart, stomach, pancreas and liver. It receives sensory information from all these glands and participates in cardiac and digestive processes, sending information to organs and muscles.sending information to organs and muscles.

11. Spinal accessory nerve

It is a motor nerve formed by the union of a spinal root and a neurocranial root. It controls muscles of the neck and head that are used for its movement.

12. Hypoglossal nerve

It is mainly responsible for managing the movements of the tongue.

Spinal nerves

The somatic nervous system is composed of 31 pairs of cranial nerves. These nerves connect organs and muscles to the spinal cord.They are responsible for transmitting sensory and visceral information to the medulla and from there to the glands, and to the skeletal and smooth musculature. They innervate the whole body, with the exception of the head and some parts of the neck.

Of the 31 existing pairs, 8 of them are cervical, 12 thoracic, 5 lumbar, 5 sacral and one coccygeal (located at the level of the pelvic floor). All of them are mixed; that is, they have a sensitive part or root, where the spinal ganglion is located, and another motor part.. These two roots join and form the spinal nerve trunk, which emerges from the vertebral canal through the corresponding intervertebral foramen.

Along its course, each spinal nerve emits four branches: the meningeal, which innervate the meninges of the spinal cord; the communicating, which connect with the sympathetic ganglia and are responsible for carrying information to the body related to stress and the classic fight or flight responses; the posterior, which innervate the deep muscles of the dorsum of the trunk and skin; and the anterior, which innervate the muscles and skin of the rest of the trunk and limbs.

Functions

The main functions of the somatic nervous system can be reduced to the following.The somatic nervous system is responsible for: transmitting sensory information to the brain and connecting the central nervous system with the organs, muscles and skin; sending and transmitting commands to the muscles to produce voluntary movements; and activating involuntary or reflex body movements.

The process is as follows: the sensitive or afferent neurons transmit electrical impulses to the central nervous system and the brain; these stimuli are then processed by the central nervous system; and finally, the motor or efferent neurons are responsible for receiving the signal and sending it to muscles and organs.

The somatic nervous system, in addition to managing the voluntary movements of the muscles, also controls reflex acts in which reflexes in which the muscles and organs are involved, also controls reflexes in which there is no direct intervention by the brain.. This occurs when a nerve pathway connects directly through the spinal cord. For example, the withdrawal reflex when we put our hand in a fire and get burned or the knee reflex, when we are hit with a hammer at the level of the patellar tendon.

Diseases of the SNS

Disorders affecting the somatic nervous system can severely incapacitate the person who suffers from them. The following are some of the most common:

1. Herniated disc

A herniated disc occurs when one of the discs in the spinal column is damaged.. The disc may move out of place (herniate) or rupture due to injury or strain. This puts excess pressure on the spinal nerves, causing pain, numbness or weakness in the patient.

Hernias can occur at any height of the spinal cord and symptoms will vary depending on where the injury or disc displacement occurs. When the symptoms occur in the legs, the disorder is called sciatica.

2. Neuralgia

Neuralgia is a pain that affects the nerves of the face, the skull or the neck, due to irritation, irritation, or pain.because of irritation, compression or infection of the nerves. It is one of the most frequent neuropathies (diseases of the nervous system).

The most common symptoms are more or less intense pain in different parts of the body, similar to an electric shock. This pain comes and goes suddenly, usually due to innocuous stimuli such as washing the face or chewing, and usually lasts a few minutes.

3. Spinal stenosis

Spinal stenosis involves a narrowing and constriction of the spinal canal (which houses the spinal cord). (which houses the spinal cord) due to Arthritis that causes overgrowth of the bones of the vertebrae and widening of the ligaments. When overgrowth occurs, the spinal nerves may be pinched and compressed, causing pain and loss of sensation in the patient.

The most common causes of spinal stenosis are: aging, arthritis (bone and rheumatoid), hereditary conditions (such as scoliosis or a narrow spinal canal) and vertebral tumors, injuries or fractures.

Bibliographical references:

• Brodal, P. (2004). The central nervous system: structure and function. Oxford University Press.
• Martin, J. H. (2014). Neuroanatomia-: Texto e Atlas. AMGH Editora.
• Moore, K.L and Agur, A.M.R. (2007). Fundamentals of Anatomy with clinical orientation. 2nd edition. Editorial Médica Panamericana