Nerves: what they are, structure, types, functions

You nerves are structures formed by bundles of nerve fibers, which are part of the peripheral nervous system and act guaranteeing the communication between different parts of the body and the central nervous system. Depending on the types of fibers they present, nerves can be classified into sensory, motor and mixed.

The nerves that protrude from the spinal cord are called the spinal nerves, while the nerves that depart from the brain are called cranial nerves. Nerve damage can be responsible for loss of movement and changes in sensation.

Read more: Nervous system - system responsible for capturing, interpreting and responding to stimuli

What are nerves?

nervousness nerve fibers grouped in bundles that are located outside the brain or spinal cord. Nerve fibers are nothing more than axons (prolongation of the neurons, which act by ensuring the passage of the nervous impulse) and its wraparound hems.

The nerves are covered by an outer fibrous layer, formed by connective tissue dense, the call epineurium.

In addition to involving the nerve, the epineurium also fills the spaces between the nerve fibers. Each bundle is lined with several flat cells, which make up the perineuro. These cells they are very close to each other and are joined by tight junctions, forming an important barrier against harmful agents.

Within the perineural sheath are located axons, each surrounded by Schwann cells and a connective envelope made up of fibers produced by the Schwann cells themselves. This wrap is called endoneurium.

Look closely at the structure of a nerve.
Look closely at the structure of a nerve.

Depending on the type of fiber they present, nerves can be classified into sensory, motor and mixed.

  • Sensory nerves: formed only by afferent fibers, that is, fibers responsible for carrying the information obtained in the environment and inside the body to the nervous centers.
  • Motor nerves: have only efferent fibers, which are responsible for carrying information from the nerve centers to the organs effectors.
  • Mixed nerves: as the name suggests, they have both efferent and afferent fibers. Most nerves have both types of fibers.

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Cranial and spinal nerves

The nerves are called cranial or spinal depending on the region from which they project.

  • Cranial nerves: are those that come from the brain. They exist 12 pairs of cranial nerves, they are: (I) olfactory, (II) optic, (III) oculomotor, (IV) trochlear, (V) trigeminal, (VI) abducens, (VII) facial, (VIII) vestibulocochlear, (IX) glossopharyngeal, (X) vagus, (XI) accessory and (XII) halibut.
  • Spinal nerves: are those that depart from the region of spinal cord. There are 31 pairs of spinal nerves and they are named according to the region of the spine from which they emerge. Of these 31 pairs: 8 pairs are cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal nerves.

Read too: What are joints?

What is the function of the nerves?

Nerves ensure integration between different parts of the body and the central nervous system.
Nerves ensure integration between different parts of the body and the central nervous system.

The nerves are responsible for promoting communication between the nerve centers (brain and spinal cord) and the effector organs, such as glands and muscles, and sensitivity. The nerves, therefore, in making this connection, ensure that our body be able, for example, to move and respond to different sensations.

Like the role of nerves is to carry information, when they are injured, this information is no longer passed on to the nerve centers and other parts of the body, so injuries to these structures can be responsible, for example, for:

  • loss of sensitivity,
  • tingling sensations,
  • muscle atrophy,
  • loss of strength,
  • weakness in the affected region.

Nerve injuries can have different causes, most of them being triggered by trauma. However, some diseases may be responsible for causing injuries in these structures, such as autoimmune diseases and diabetes, and the use of certain medications and alcoholic beverages.

By Vanessa Sardinha dos Santos
Biology teacher

Would you like to reference this text in a school or academic work? Look:

SANTOS, Vanessa Sardinha dos. "Nerves"; Brazil School. Available in: https://brasilescola.uol.com.br/biologia/nervos.htm. Accessed on June 27, 2021.

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