Sacral Plexus: Nerves, Function & Injury

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

The sacral plexus is a region where several spinal nerves come together and then branch out to innervate most of your lower body. In this lesson, learn about the structure and function of the sacral plexus.

What Is the Sacral Plexus?

In most houses, there is a circuit box where all of the electrical wires come together and are then sent out to all the different rooms of your house. Did you know that you have places like this in your body too?

Each of these is a nerve plexus, which is a group of interconnected nerves that come together and then branch out to serve a region of your body. There are several nerve plexuses in your body, including five that are located just off the spinal cord and are known as the spinal nerve plexuses.

One spinal nerve plexus, called the sacral plexus, contains nerves that innervate the lower half of your body, including parts of your pelvis, the backs of your thighs, and most of your calves, ankles, and feet.

Structure

The sacral plexus is located inside your pelvis, just in front of the piriformis muscle in the posterior part of the pelvis, and it is made up of a network of interconnected spinal nerves. Spinal nerves come directly out of your spinal cord and are mixed, meaning they contain both sensory and motor neurons.

The lower part of your spine is known as the sacrum, and it is primarily nerves from this region that form the sacral plexus. In fact, that is why it is called the sacral plexus! The nerves come from the sacrum!

The sacral plexus is formed by spinal nerves originating from the sacral (S1, S2, S3, and S4) and lumbar regions (L4, L5) of the spinal cord.
spinal column

Four nerves that come from the sacral region of the spinal cord (S1, S2, S3, and S4), form most of the sacral plexus. Parts of two lumbar nerves, L4 and L5, which originate a little higher in your back are also part of the sacral plexus.

sacral plexus image

Nerves of the Sacral Plexus

In the sacral plexus, the spinal nerves split and form sensory and motor nerves that go to parts of your pelvis, legs, feet, and genitals. Without these important nerves, you wouldn't be able to stand or walk, you would lose control of your bladder and bowels, and you wouldn't be able to feel if anyone touched you on the back of the leg at all!

You can remember the five main nerves that come out of the sacral plexus if you think of this saying Some Irish Sailor Pesters Polly. The first letter of each of these words stands for Superior Gluteal nerve, Inferior Gluteal nerve, Sciatic nerve, Posterior cutaneous nerve, and Pudendal nerve.

What do each of these nerves do in your body?

The superior gluteal nerve is a motor nerve that serves the gluteus medius, gluteus minimus muscles. It also serves the tensor fascia lata muscle which is near the other gluteal muscles.

The inferior gluteal nerve is also a motor nerve, but it serves only the gluteus maximus muscle.

The sciatic nerve is a really important one and is the largest nerve to come out of the sacral plexus. It is both a motor and sensory nerve. The motor nerve part of the sciatic nerve innervates the muscles in the back of your leg and the sole of your foot. Sensory neurons of the sciatic nerve are found in the skin of parts of your leg and your foot.

The posterior cutaneous nerve is a sensory nerve that serves the skin of the back of your thigh and lower leg, as well as the perineum.

Finally, the pudendal nerve has both sensory and motor functions. It innervates your genitals and anal and urethral sphincters. This is the nerve that controls when you go to the bathroom, and damage to it can cause serious problems!

Injury to the Sacral Plexus

The sacral plexus is well protected inside your pelvis, so injuries are pretty rare. However, they do happen, usually because of severe trauma like a car accident or another traumatic event that results in crushing the pelvic girdle. In other cases, things like large blood clots (called hematomas) or tumors can press on the sacral plexus and cause it to lose function.

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