Spinal nerves: what they are, types and functions in the body

The spinal cord is a long, fragile tubular structure that begins at the end of the brainstem and continues almost to the end of the spinal column. Its main function is to transmit signals and orders that are created in the brain to the trunk, neck and 4 extremities (function efferent) and in turn collect all the sensations and perceptions recorded throughout the body and send them to the brain (function afferent).

Understanding life without a spinal cord is really complex, and proof of this are patients with injuries to some part of this fragile but essential structure. Depending on where the trauma occurs, from the legs to the entire body may experience loss total (complete) or partial (incomplete) of sensation and motor capacity below the neurological level of the injury.

Without a doubt, we could define the spinal cord as the transmission center for all the information in the body. It is a neurological highway, whose task is to emit and receive signals to each and every part of our body with a specific physiological objective. To accomplish this task, the spinal cord is not alone:

It has 31 pairs of spinal nerves whose function is to innervate the entire body plane (except the head). Here we tell you the most relevant information about them.

• Related article: "Parts of the Nervous System: anatomical structures and functions"

What are spinal nerves?

As we have hinted in previous lines, the spinal nerves or spinal nerves are those that extend from the spinal cord and cross the vertebral muscles to be distributed to all areas of the body.

The skeletal muscles of our body are innervated by both motor and sensory nerves, whose function is to collect and transmit information to the central nervous system (CNS), from where a response is generated effector. This muscle group comprises more than 600 muscles that can be moved at will, and together they comprise the muscular system. The smooth and cardiac muscles are left out of this motor conglomerate, since the movements they carry out are not conscious and occur "automatically".

So that, the spinal nerves are directly related to this muscle portion, so that human movements and development are possible in a three-dimensional environment. It should be noted that each of these nerves emerges through the spaces of the vertebrae in the form of 2 short branches, called spinal nerve roots. We tell you its peculiarities quickly.

1. Motor nerve root

This root, located in the anterior part of the spinal cord, is responsible for transmitting impulses from the spinal cord to the skeletal muscles to promote their contraction and, therefore, the production of movement.

Radiculopathies (injury or damage to one or more nerves and their roots) usually cause a characteristic weakening of the muscles innervated by the affected motor root. These become weak, atrophic, flabby, and twitching.

2. Sensitive nerve root

On the other hand, the sensory root enters the posterior part of the spinal cord. The nerve fibers that compose it carry sensory information, which will ultimately be interpreted by the brain. Examples of this information are the position of the body, the degree of luminosity, the touch, the environmental temperature and pain when suffering an injury, among many other exogenous and endogenous.

For this reason, the affectations of the sensitive nerve roots translate into a lack of sensitivity in the areas innervated by the injured nerves. Due to this “double” composition of the spinal nerves, it is affirmed that they fulfill a function of a mixed nature: they send and collect information equally.

• You may be interested in: "Afferent pathway and efferent pathway: the types of nerve fibers"

The 31 pairs of spinal nerves

Yes, you read it right. 31 pairs of spinal nerves emerge from the spinal cord and innervate practically the whole of our body, except for the head and certain sections of the neck.. Head work is relegated to the cranial nerves, which are 12 nerve pairs whose function is to connect the brain with the eyes, ears, nose, throat and various parts of the head and neck.

Next, we present the functionality of all the spinal nerves by blocks, since these are divided based on the structures they innervate. Go for it.

1. Cervical nerves (C1-C8)

They are the nerves of the first 7 cervical vertebrae. They are born from the spinal cord, emerge through the foramina of the vertebral column and are distributed by specific sensitive and motor areas.

The cervical nerves innervate the sternohyoid, sternothyroid, and omohyoid muscles. In general, these muscle groups can be defined as fleshy ribbons that extend from the breastbone / shoulder blade to certain parts of the neck. As a curious fact, it should be noted that the first cervical nerves lack posterior roots in 50% of people.

2. Thoracic nerves (T1-T12)

They are a total of 12 spinal nerves that emerge from the thoracic vertebrae. Almost all of them are located between the ribs (intercostals), with the twelfth located below the last rib (subcostal nerve). For their part, the intercostal nerve endings are distributed along the walls of the thorax and abdomen.

These thoracic nerves participate in the functions of the organs and glands of the head, neck, chest, and abdomen. They are responsible for the innervation of the mammary glands, the thoracic wall, the abdominal wall and the pelvis. Due to their importance at the nervous level, these spinal nerves are the therapeutic targets of choice for many treatments aimed at managing chronic pain in patients.

3. Lumbar nerves (L1-L5)

There are 5 spinal nerves that arise from the lumbar vertebrae. They are divided into 2 compartmentalized sections, anterior and posterior. These nerve elements emerge from the spine through the foramina of conjunction. In any case, these nerves should not be conceived as a series of isolated entities: the first 3 and the most of the fourth are connected to each other in this situation by anastomotic ties, forming the plexus lumbar.

Thus, the lumbar plexus is established between the anterior branches of the L1 and L4 spinal nerves. On the other hand, the smallest part of the fourth nerve joins with the fifth to form the lumbosacral trunk, which participates in the formation of the sacral plexus.

4. Sacral nerves (S1-S5)

They are the 5 spinal nerves that emerge from the sacrum (bone that is below the L5 lumbar vertebra and above the coccyx) and constitute the lowest segment of the spinal cord.. Although the vertebral components of the sacrum are fused to form a single bony entity, each of these nerves are named after the vertebra to which they would be associated.

These nerves are divided into branches, but many of them end up joining each other, and also to the lumbar and coccygeal plexuses. As we have said before, this series of interconnections form plexuses, specifically the sacrum and lumbosacral. The branches of these plexuses supply the hip, thigh, leg, and foot.

5. Coccygeal nerve

The coccygeal nerve is the last of the spinal nerves, that is, number 31. It arises in the medullary cone, helps to form the coccygeal plexus and innervates the sacrococcygeal joint and a part of the levator ani.

8 cervical nerves + 12 thoracic nerves + 5 lumbar nerves + 5 sacral nerves + 1 coccygeal nerve: 31 spinal nerves.

Resume

In this space, we have covered the general characteristics of the 31 spinal nerves that run throughout our body, except for the head and certain parts of the neck. Its function is to emit information from the brain and allow muscle contraction (motor work) and, in turn, Once, receive all the essential information provided by the limbs and innervated areas (sensitive work).

Thanks to these spinal and cephalic nerve pairs, human beings are able to develop in a three-dimensional environment, being aware of our own internal state and of what surrounds us in the environment. After reading these lines, a clear concept is clear to us: without our nerve endings, human beings are nothing.

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