SOMATIC NERVOUS SYSTEM: FUNCTIONS AND DISEASES - GEOGRAFÍA - 2025

The somatic nervous system is a set of neurons that fulfills a double function. On the one hand, it is responsible for transmitting the information collected by the sense organs to the brain. On the other, it transmits its orders to the skeletal muscles.

Thus, the somatic nervous system is the one that allows us both to interpret our environment and to respond to it. It is made up mainly of afferent and efferent neurons, and includes all the structures of the autonomic nervous system.

Somatic nervous system

Thanks to this set of neurons, we can interpret the information coming from the sensory organs (such as eyes, nose or tongue), and decipher the state of the muscles and tendons (such as in the form of pain). Thus, we are able to relate to our environment and develop appropriate responses to it.

In addition, this system is the one in charge of sending these responses to the muscles that are going to carry them out. Most of them are conscious; However, sometimes the somatic nervous system is also responsible for sending unconscious orders from our brain to the effector organs.

Composition

In the human body, there are 43 nerve segments, all of them belonging to the somatic nervous system. In each of these segments, there is a pair made up of a sensory nerve and a motor nerve. 31 of them come out of the spinal cord, while the other 12 are inside the skull.

Therefore, we could say that the somatic nervous system is divided into two parts. Next we will briefly see how each one of them is composed.

Spinal nerves

The first of them would be the one that includes the nerves that start from the spinal column. These are peripheral nerves that carry sensory information to the spinal cord, and carry orders from it to the effector muscles.

In total, there are 31 pairs of spinal nerves, which would be divided as follows:

- 8 cervical spinal nerves.

- 12 thoracic spines.

- 5 lumbar spines.

- 5 sacral spines.

- 1 coccygeal spinal.

Each of these nerves is actually a pair, being made up of a sensory and a motor one.

Cranial nerves

Also known as "cranial nerves," they are twelve nerves located within the skull that receive sensory information from the head and neck area and send it to the brain. In addition, they also send motor commands to the muscles in these two regions.

In total, there are twelve cranial nerves, which are as follows:

I. Olfactory nerve.

II. Optic nerve.

III. Common ocular motor nerve.

IV. Pathetic nerve.

V. Trigeminal nerve.

SAW. External abducens nerve.

VII. Facial nerve.

VII. Auditory nerve.

IX. Glossopharyngeal nerve.

X. Pneumogastric nerve.

XI. Spinal accessory nerve.

XII. Hypoglossal nerve.

Other components

In addition to this classification, it is also usually differentiated between four types of neurons that make up the somatic nervous system: motor, sensory, proprioceptive, and nociceptive. Next we will see the characteristics of each one of them.

Motor neurons

The neuronal connections whose function is the contraction of skeletal muscles can be divided into two groups. Both are responsible for controlling the muscles and producing both voluntary and involuntary movements.

One of these groups is made up of the upper motor neurons in the central nervous system. The other is made up of lower motor neurons. The latter can be part of both the spinal and cranial nerves.

Higher motor neurons have the cell body located in the precentral gyrus of the brain. This region is located near the end of the frontal lobe, in the cerebral cortex; and it is generally associated with the prime mover cortex.

Its axons, on the other hand, travel through the somatic nervous system through the corticospinal and corticobulbar tracts. Those that use this second path usually form synapses with lower motor neurons within the brain.

On the other hand, the axons of these lower motor neurons are those that form some of the cranial nerves, such as the trigeminal or oculomotor. These are involved in the contraction of some muscles located in the head, face and neck.

Types of lower motor neurons

In addition to the basic division between upper and lower motor neurons, the latter can be differentiated into three different types. The names of each of them are based on the first three letters of the Greek alphabet: alpha, beta and gamma.

Alpha neurons are especially thick, and their axons are lined with a layer of myelin. Furthermore, they are multipolar neurons. Its function is to activate most skeletal muscles and cause them to contract.

Beta neurons, for their part, are responsible for activating neuromuscular spindles, in addition to supporting alpha neurons in some parts of the body. Finally, the gamma perform a supporting function for the other two types of lower motor neuron.

The number of alpha neurons connected to a specific muscle gives us an idea of ​​the fineness of the movement that it can perform. So, for example, there will be many more alpha connections in a finger than in the biceps.

Sensory neurons

This type of neurons of the somatic nervous system is connected with sensory receptors that allow us to receive information from our environment. Thus, thanks to them, our brain is able to capture smells, flavors, images, sounds, textures…

In this way, for example, the sensory neurons that start from the eyes send the information captured by the retina through the optic nerve to the brain. Thanks to its function, we are able to interpret the light that enters the pupils and organize it in the form of a coherent image.

Proprioceptive neurons

In addition to the neurons responsible for receiving information from the senses, there are others that record information about the state of the muscles. They are the so-called proprioceptive neurons. They help us to interpret if the muscles are contracted or not, to maintain balance…

These cells send all this information to the brain through the spinal cord and cranial nerves. Thanks to them, our mind can know how our body is, and prepare responses based on this information.

Nociceptive neurons

The last type of neurons is made up of those that are responsible for sending the information received from pain receptors to the brain. These are activated when our body comes into contact with extreme forces, such as intense cold or heat, or a very sudden mechanical force.

In general, nociceptive neurons tend to activate involuntary responses in our body. These are responsible for making us carry out movements that will keep us away from harmful stimuli, with the intention of preserving our physical integrity.

Features

In general, somatic nervous system functions are usually classified into three types: transmitting sensory information to the brain, sending commands to the muscles to perform voluntary movements, and activating involuntary body movements (known as reflexes).

The neurons responsible for sending sensory information (sensory, proprioceptive and nociceptive) are known as afferents. The motor, on the other hand, are usually classified as efferent.

The role of the somatic nervous system is essential for our day-to-day functions. Without it, we could neither receive information from the environment, nor act in any way.

Therefore, scientists do not stop investigating all the possible diseases that this system can suffer and the cures that exist for them.

Below we will study several of the most common conditions of the somatic nervous system.

Diseases

Diseases that affect the somatic nervous system can cause great difficulties for people who suffer from them. Some of them are extremely severe, while others will only cause some discomfort. However, it is important to treat all of them to maximize the quality of life of patients.

Some of the more common somatic nervous system disorders include the following: herniated discs, spinal stenosis, neuralgia, multiple sclerosis, and amyotrophic lateral sclerosis (ALS). Below we will briefly see what each of them consists of.

Disc herniation

Herniated disc is a condition that occurs when one of the discs in the spine seriously deteriorates. In this way, the content of the spinal cord can begin to leak out of the spinal cord, often causing a pinching of the nerves in the area.

Herniated discs can occur at any level of the spinal cord; And depending on where they occur, the symptoms will vary slightly.

However, the most common are loss of sensation in some parts of the body, pain, and a tingling sensation in the affected areas.

If these symptoms occur in the legs, the resulting disease is known as sciatica.

Spinal stenosis

Spinal stenosis consists of the narrowing of the canal through which the motor and sensory nerves of the spinal cord travel. Due to this, pinching and compression of the same can occur, which will cause pain and loss of sensation in most cases.

Stenosis can be caused by various causes, the most common of which are aging, arthritis, tumors in the back or neck, scoliosis, or certain genetic conditions that cause these symptoms.

3- Neuralgia

Neuralgia is a group of diseases produced by a malfunction of the nervous system, a pinched nerve, or an alteration of the nerve pathways associated with the perception of pain (that is, of the nociceptive neurons).

Due to any of these causes, the person will notice a more or less intense pain in different areas of his body, usually not associated with a real physical cause. Because of this, neuralgia treatment should be focused on correcting the neurological problem.

Multiple sclerosis

Multiple sclerosis is a neurodegenerative disease that affects the population around the world. It is one of the most common nervous pathologies among people under 30 years of age, and it affects men much more frequently than women.

Its main symptom is the disappearance of the myelin that covers the axons of neurons, especially those located in the brain and spinal cord. Due to this, those affected suffer symptoms such as fatigue, lack of balance, pain, loss of muscle strength, sensory problems…

In general, multiple sclerosis does not result in the death of the patient in most cases. However, its impact on the quality of life of the people it affects is enormous. Those who suffer from this disease are seeing their bodily capacities diminish little by little over time.

For this reason, it is one of the neurological diseases that is currently being investigated the most.

Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis is similar to MS in its symptoms, but its prognosis is much worse than MS. It is a disease in which, for an unknown reason, the neurons of the central nervous system and the somatic one begin to die little by little.

Due to this, the person loses more and more bodily functions. Thus, you may experience difficulties to perform movements, loss of balance, sensory difficulties, muscle weakness…

Symptoms slowly get worse over the years. Generally, there comes a point where some vital function is affected, and the person ends up dying in most cases. There is no known cure for this disease, although certain medications can increase the life expectancy of those affected.

Without a doubt, ALS is one of the most serious disorders of the nervous system of all that exist. Furthermore, it is practically impossible to predict when the disease will occur, and the causes for which it occurs are still unknown.

Formerly it was thought that this problem could be genetic; but although it has been discovered that our inheritance predicts 10% of the cases of the disease, in the rest of them it is not known why it occurs. More studies are needed on the subject.

Amyotrophic lateral sclerosis mainly affects men between the ages of 40 and 50. However, it can occur in people of both sexes and at any age. Research on this disorder is essential in order to improve the living conditions of patients.

References

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