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The sacral plexus is a network of nerve fibres that supply the skin and muscles of the pelvis and lower limb. The sacral plexus is formed by the anterior rami (divisions) of the sacral spinal nerves S1, S2, S3, and S4. The sacral spinal nerve 2 (S2) is a spinal nerve of the sacral segment that originates from the spinal column from below the 2nd body of the sacrum. S2 supplies many muscles, either directly or through nerves originating from S2.
| Characteristics | Values |
|---|---|
| Name | Sacral spinal nerve 2 (S2) |
| Type | Spinal nerve of the sacral segment |
| Origin | Spinal column, below the 2nd body of the sacrum |
| Functions | Motor and sensory |
| Muscles | Governs the toes |
| Innervation | Supplies many muscles, either directly or through nerves originating from S2 |
| Nerve Roots | L4, L5, S1, S2, S3, and S4 |
| Divisions | Anterior and posterior |
| Major Peripheral Nerves | Five |
| Destinations | Leave the pelvis via the greater sciatic foramen or remain in the pelvis |
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What You'll Learn
- The sacral plexus is a network of nerves that supply the pelvis and lower limb
- The inferior gluteal nerve is formed from L5, S1 and S2 spinal nerves
- The pudendal nerve is formed from S2, S3 and S4 spinal nerves
- The nerve to the piriformis muscle is formed from S1 and S2 spinal nerves
- The nerve to obturator internus is formed from L5, S1 and S2 spinal nerves
The sacral plexus is a network of nerves that supply the pelvis and lower limb
The anterior rami of the S1-S4 spinal roots (and the lumbosacral trunk) divide into several cords. These cords then combine to form the five major peripheral nerves of the sacral plexus. These nerves then descend down the posterior pelvic wall. They have two main destinations:
> 1. Leave the pelvis via the greater sciatic foramen – these nerves enter the gluteal region of the lower limb, innervating the structures there.
> 2. Remain in the pelvis – these nerves innervate the pelvic muscles, organs and perineum.
The sacral plexus provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, and part of the pelvis. The anterior branches supply flexor muscles of the lower limb, and posterior branches supply the extensor and abductor muscles. The lumbosacral trunk descends into the pelvis to join with the sacral nerves. The sacral plexus lies posterior to the internal iliac vessels and ureter and anterior to the piriformis muscle; on the left, it lies posterior to the sigmoid colon.
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The inferior gluteal nerve is formed from L5, S1 and S2 spinal nerves
The inferior gluteal nerve is formed from the L5, S1, and S2 spinal nerves. It is the main motor neuron that innervates the gluteus maximus muscle, which is the largest muscle of the posterior hip. This nerve is responsible for the movement of the gluteus maximus in activities requiring the hip to extend the thigh, such as climbing stairs. The inferior gluteal nerve branches out and then enters the deep surface of the gluteus maximus, supplying it.
The inferior gluteal nerve is one of the two gluteal nerves, the other being the superior gluteal nerve. The superior gluteal nerve passes through the sciatic notch above the piriformis muscle, supplying the gluteus medius and minimus, and tensor fasciae latae muscles. On the other hand, the inferior gluteal nerve passes under the piriformis muscle and supplies the gluteus maximus muscle.
The gluteal nerves are part of the sacral plexus, which is a network of nerve fibres that supplies the skin and muscles of the pelvis and lower limb. The sacral plexus is formed by the anterior rami (divisions) of the sacral spinal nerves S1, S2, S3, and S4, with contributions from the lumbar spinal nerves L4 and L5. The anterior rami of these spinal roots divide into several cords, which then combine to form the five major peripheral nerves of the sacral plexus.
These nerves have two main destinations. Some nerves leave the pelvis via the greater sciatic foramen, entering the gluteal region and innervating the structures there. Other nerves remain in the pelvis, innervating the pelvic muscles, organs, and perineum. The sacral plexus is located on the surface of the posterior pelvic wall, anterior to the piriformis muscle.
Myotome testing is an essential part of neurological examination when suspecting radiculopathy. It involves looking for muscle weakness in a particular group of muscles, which can indicate a lesion to the spinal cord nerve root or intervertebral disc herniation pressing on the spinal nerve roots.
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The pudendal nerve is formed from S2, S3 and S4 spinal nerves
The pudendal nerve is formed from the sacral plexus, a network of nerve fibres located on the posterior pelvic wall. It is derived from the ventral rami (anterior divisions) of the spinal nerves S2, S3, and S4. The pudendal nerve is responsible for supplying sensation to the penis and clitoris, as well as the skin around the anus, anal canal, and perineum. It also plays a role in controlling somatic muscles involved in penile and clitoral erection and ejaculation in males.
The pudendal nerve is paired, with one nerve on the left and one on the right side of the body. These nerves give off branches that innervate regions of the rectal canal, anus, perineum, and external genitalia. The pudendal nerve is also involved in carrying sensations from the labia minora, vaginal vestibule, the lower one-fifth of the vaginal canal, and the posterior aspects of the labia majora and scrotum.
After its formation, the pudendal nerve descends and passes between the piriformis and ischiococcygeus muscles. It then leaves the pelvis through the lower part of the greater sciatic foramen and crosses the sacrospinous ligament. Following this, the pudendal nerve re-enters the pelvis through the lesser sciatic foramen and accompanies the internal pudendal artery and vein.
The pudendal nerve is important for maintaining faecal and urinary continence. It innervates the external urethral sphincter and provides motor supply to the external anal sphincter. The pudendal nerve also innervates the levator ani muscles, which include the puborectalis, pubococcygeus, and iliococcygeus.
The pudendal nerve is challenging to visualise using routine CT or MR imaging. However, under CT guidance, a needle can be placed adjacent to the pudendal neurovascular bundle to facilitate treatment for chronic pain in the external genitalia, pelvic region, and anorectal area.
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The nerve to the piriformis muscle is formed from S1 and S2 spinal nerves
The piriformis muscle is a flat, pyramid-shaped muscle that arises from the anterior surface of the sacrum, between the sacral foramina. It passes through the pelvis and exits through the greater sciatic foramen, attaching to the gluteal surface of the ilium. The nerve to the piriformis muscle, also known as the piriformis nerve, arises from the anterior rami of the S1 and S2 spinal nerves. This nerve is a branch of the sacral plexus, a network of nerve fibres that supplies the skin and muscles of the pelvis and lower limb. The sacral plexus is formed by the anterior rami of the sacral spinal nerves S1, S2, S3, and S4, as well as contributions from lumbar spinal nerves L4 and L5.
The piriformis nerve supplies motor innervation to the piriformis muscle and is responsible for its neurovascular supply and function. In addition to the piriformis nerve, the arterial supply to the piriformis muscle comes from the superior gluteal and internal pudendal arteries, which are branches of the internal iliac artery. The superior gluteal nerve may also provide an additional branch to the piriformis nerve.
The piriformis muscle plays a crucial role in stabilising the hip joint by holding the head of the femur inside the acetabulum of the hip bone. It also contributes to the external rotation of the hip joint and the abduction of the thigh while in a flexed position. The piriformis muscle is closely associated with the sciatic nerve, which is the largest branch of the sacral plexus. In most individuals, the sciatic nerve exits the pelvis through the greater sciatic foramen, below the piriformis muscle.
The nerve to the piriformis muscle arises from the posterior divisions of the ventral rami of the first and second sacral nerves (S1 and S2). It enters the anterior surface of the piriformis muscle, piercing it. Unlike most nerves originating from the sacral plexus, the piriformis nerve remains within the pelvic cavity. Occasionally, the piriformis nerve may also receive a branch from the fifth lumbar nerve (L5).
The sacral plexus, from which the piriformis nerve originates, has two main destinations for its nerves. Some nerves leave the pelvis via the greater sciatic foramen and enter the gluteal region, innervating the structures there. Other nerves remain in the pelvis and innervate the pelvic muscles, organs, and perineum. The sacral plexus provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, and part of the pelvis.
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The nerve to obturator internus is formed from L5, S1 and S2 spinal nerves
The obturator nerve is a key component of the body's peripheral nervous system, providing motor and sensory functions to the lower limb. The obturator nerve arises from the lumbar plexus and provides sensory innervation to the thigh. Specifically, the obturator nerve provides motor innervation to the adductor muscles of the lower limb, including the external obturator, adductor longus, adductor brevis, adductor magnus, and gracilis. It also provides sensory innervation to the skin of the medial region of the upper thigh.
The obturator internus, on the other hand, is a muscle in the hip that helps with hip rotation and stability. It is innervated by the nerve to obturator internus, which is formed from the anterior (ventral) divisions of the L5, S1, and S2 nerve roots of the sacral plexus. The sacral plexus is a network of nerve fibres supplying the skin and muscles of the pelvis and lower limb. It is formed by the anterior rami of the sacral spinal nerves S1, S2, S3, and S4, as well as contributions from lumbar spinal nerves L4 and L5.
The nerve to obturator internus supplies innervation to the obturator internus muscle, as well as the superior gemellus muscle and the fascia of the lateral sidewall of the ischioanal fossa. This nerve exits the pelvis via the greater sciatic foramen, passing inferiorly to the piriformis muscle. The obturator internus muscle plays a crucial role in hip joint stability and movement, particularly in actions such as running, walking, and climbing stairs.
The obturator nerve and the nerve to obturator internus have distinct functions and innervate different structures in the lower limb and pelvis. While the obturator nerve primarily innervates the adductor muscles of the lower limb, the nerve to obturator internus is specifically responsible for innervating the obturator internus muscle and related structures. It's important to note that the obturator nerve is not responsible for the innervation of the obturator internus muscle, despite the similarity in their names.
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Frequently asked questions
The sacral plexus is a network of nerve fibres that supplies the skin and muscles of the pelvis and lower limb.
The sacral spinal nerve 2 (S2) is a spinal nerve of the sacral segment. It originates from the spinal column from below the 2nd body of the sacrum.
S2 supplies many muscles, either directly or through nerves originating from S2. These muscles govern the toes.
S2 is involved in knee flexion. Testing flexion at the knee can help evaluate the muscle strength of the hamstrings.
