sacral nerves or sacral spinal nerves

The sacral nerves or sacral spinal nerves are 5 of the 31 pairs of spinal nerves. They are vital to human physiology, and we will detail them below.

Last update: 28 January, 2022

The sacral nerves, also known as sacral spinal nerves, are a group of five spinal nerves that arise from the spinal cord and emerge from the sacrum. They are a set of structures that constitute the lowest segment of the spinal cord.

These are listed based on each vertebra they relate to, despite the fact that these are fused forming the sacral bone. They are distributed by both sensory and specific motor territories.

spinal nerves or spinal nerves

The sacral nerves encompass 5 spinal or spinal nerves. In turn, these are a set of structures belonging to the somatic nervous system. More specifically, there are a total of 31 pairs of nerves whose function is to innervate the entire body except the head and some areas of the neck.

They manage to reach their goal thanks to the fact that they contain a sensitive root, which is responsible for the sensitivity of the area they innervate, and a motor root, which will allow the muscles to contract. The spinal nerves are the following:

  • 8 pairs of cervical nerves (C1-C8).
  • 12 pairs of thoracic nerves (T1-T12).
  • 5 pairs of sacral nerves (S1-S5).
  • 5 pairs of lumbar nerves (L1-L5).
  • 1 pair of coccygeal nerves.

Characteristics of spinal nerves or spinal nerves

Without the presence of spinal nerves, human physiology as we know it would not be possible.

The sacral nerves present a series of characteristics that are typical of the spinal nerves. Let’s see what are the main characteristics of these. To begin with, they are mixed, that is, both sensory and motor.

On the other hand, all the branches of the ventral rami, except the thoracic ones (T1 to T12), They form several branches that are known as nerve plexuses.. These plexuses appear in the cervical, brachial and lumbosacral areas.

Within these interconnected branches, fibers originating from the ventral rami intersect and redistribute so that each resulting branch contains fibers from different spinal nerves. In addition, those that come from each ventral branch travel to the periphery of the body via different routes in the ramifications.

For this reason, each muscle in a limb will receive innervation from more than one spinal nerve. As a consequence, if there is damage to one of the segments of the spinal cord or one of the roots, the limb does not have to be totally useless.

Sacral Nerves Anatomy

The sacral nerves originate from the spinal cord and pass through the vertebral foramina of the sacrum. Both the motor and sensory roots converge outside the spinal ganglion and emerge together in two branches:

  • Later: They leave the posterior sacral foramen and form the posterior branches of the sacral nerves.
  • Previous: They leave the anterior sacral foramen and contribute branches to the sacral plexus and the sacrococcygeal plexus.

As for the sacral nerves S3 and S4, they have fibers that join the inferior hypogastric plexus, which innervates the smooth muscles of:

  • Descending and sigmoid colon.
  • Straight.
  • Both internal and external genitalia.
  • The bladder.
  • the urethra

posterior branch of sacral nerves

These are 4 small nerve divisions that decrease even more as they distance from their point of origin. They emerge, with the exception of the last innermost branch, from the posterior sacral foramina.

anterior branch of sacral nerves

As for the anterior branches of these nerves, they are formed in the sacral plexus. This provides innervation to the pelvis and lower limbs. The bundles and fibers coming from it, especially those from the anterior sacral nerves (S4 and S5), join with the coccygeal nerve and form, as we have seen, the sacrococcygeal plexus.

Finally, it ends forming the anococcygeal nerve, which innervates the skin of the anus region and the sacrococcygeal joint.

Functions of the sacral spinal nerves

The simple act of going to the bathroom requires the active participation of the sacral nerves for the contraction and relaxation of the sphincters.

The role of the parasympathetic contribution is to relaxation of the sphincters and contraction of the muscular walls. With this, they cause urination, defecation and erection of the genital organs.

In addition, the fibers carry sensory signals, such as pain and sensation of fullness, from both the bladder and the rectum. As a curiosity, sacral nerve stimulation is one of the medical procedures used for the treatment of fecal incontinence.

In short, these are structures of vital importance for the body, like the rest that are part of the nervous system. Know the anatomy of the human being contributes to understanding and caring for health from a different perspective.

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