Logan Steele
The sacral plexus is a network of nerve fibres that supplies the skin and muscles of the pelvis and lower limbs. The sacral plexus is formed by the anterior rami of the sacral spinal nerves S1, S2, S3, and S4. The S3 nerve supplies many muscles, either directly or through nerves originating from S3. These muscles include the obturator internus, superior gemellus, levator ani, and ischiococcygeus. The sciatic nerve, the largest branch of the sacral plexus, is responsible for vital motor and sensory functions in the leg, including movement, strength, and overall functionality.
| Characteristics | Values |
|---|---|
| Type | Spinal nerve of the sacral segment |
| Origin | Spinal column, below the 3rd body of the sacrum |
| Muscles Innervated | Skeletal muscles in the perineum, external urethral sphincter, external anal sphincter, levator ani, pelvic muscles, organs, and perineum |
| Additional Functions | Innervates the penis, clitoris, and skin of the perineum |
| Related Nerves | Sacral plexus, sciatic nerve, pudendal nerve, perforating cutaneous nerve, pelvic splanchnic nerves, inferior gluteal nerve |
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What You'll Learn
The sciatic nerve and leg muscles
The sciatic nerve is the largest branch of the sacral plexus, a network of nerve fibres that supplies the skin and muscles of the pelvis and lower limbs. The sacral plexus is formed from the anterior fibres of the spinal nerves S1, S2, S3, and S4, as well as contributions from the lumbar spinal nerves L4 and L5. These nerves descend down the posterior pelvic wall and leave the pelvis via the greater sciatic foramen to enter the gluteal region of the lower limb.
The sciatic nerve supplies major parts of the skin and muscles in the thigh, leg, and foot. It provides vital motor and sensory functions throughout each leg, including the facilitation of leg movements such as walking, running, climbing, ankle movement, and toe raises. The sciatic nerve powers the leg muscles and plays a crucial role in movement, strength, and overall functionality of the lower limbs.
The sciatic nerve innervates the four hamstring muscles and the short head of the biceps femoris muscle along the back of the thigh. It also partially supplies the adductor magnus muscle along the inner front side of the thigh. The tibial branch of the sciatic nerve, derived from the L5, S1, S2, and S3 spinal nerves, supplies the calf muscles along the back of the leg. The common peroneal branch of the sciatic nerve, on the other hand, is derived from the L4, L5, S1, and S2 spinal nerves.
The sciatic nerve provides a range of motor functions, including inversion, eversion, and dorsiflexion of the foot. If the sciatic nerve is impaired, the affected nerve root or portion of the nerve determines which motor functions are affected. For example, when the L5 nerve root in the lumbosacral joint is involved, a condition called foot drop can occur, characterised by difficulty in lifting the front part of the foot.
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Sacral plexus and lower limb
The sacral plexus is a network of nerve fibres that supplies the skin and muscles of the pelvis and lower limb. It is located on the surface of the posterior pelvic wall, anterior to the piriformis muscle. The sacral plexus is formed by the anterior rami (divisions) of the sacral spinal nerves S1, S2, S3 and S4, and receives contributions from the lumbar spinal nerves L4 and L5.
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 of the sacral plexus supply the flexor muscles of the lower limb, while the posterior branches supply the extensor and abductor muscles.
The sciatic nerve is the largest branch of the sacral plexus and is formed from both the anterior and posterior divisions of the anterior rami of spinal nerves L4 to S3. The sciatic nerve supplies major parts of the skin and muscles in the thigh, leg, and foot. It provides a wide range of motor functions, including powering movement to the muscles that move each thigh, leg, and foot. Important motor functions include inversion, eversion, and dorsiflexion of the foot. The sciatic nerve also innervates the hamstring muscles, the short head of the biceps femoris muscle, and partially supplies the adductor magnus muscle.
The pudendal nerve is formed by the anterior divisions of the anterior rami of spinal nerves S2, S3, and S4. It provides motor innervation to the skeletal muscles in the perineum, the external urethral sphincter, the external anal sphincter, and the levator ani. The pudendal nerve also provides sensory innervation to the penis, clitoris, and most of the skin of the perineum.
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Pudendal nerve and perineum
The pudendal nerve is one of the main nerves in the pelvis, carrying motor and sensory axons from the ventral rami of the sacral spinal nerves S2-S4. It is closely associated with the internal pudendal artery and vein branches, and together, they form the neurovascular pudendal bundle. This bundle enters the perineum through the lesser sciatic foramen, which is located on the medial wall of the obturator internus muscle. The pudendal nerve gives off three consecutive branches: the inferior rectal nerve, the perineal nerve, and the dorsal nerve of the penis or clitoris.
The pudendal nerve is important for carrying sensations from the penis or clitoris, the labia minora, vaginal vestibule, the lower one-fifth of the vaginal canal, and the posterior aspects of the labia majora and scrotum. It also plays a role in controlling somatic muscles involved in penile and clitoral erection and ejaculation in males. Additionally, the pudendal nerve innervates the external anal and external urethral sphincters.
Pudendal neuralgia is a condition caused by damage to the pudendal nerve, resulting in sharp, burning, or tingling pain or numbness in the genitals, perineum, bottom, and anus. The pain may worsen when sitting down and throughout the day. Other symptoms can include frequent urination, constipation, difficulty in erection and orgasm, and pain during urination, defecation, and sexual activity. Pudendal neuralgia can be challenging to diagnose due to its rarity and similar symptoms to other conditions. Treatment options include medications for nerve pain, strong painkillers, and lifestyle changes.
The sacral plexus, formed by the anterior rami of the sacral spinal nerves S1-S4, supplies the skin and muscles of the pelvis and lower limb. It is located on the posterior pelvic wall, anterior to the piriformis muscle. The sacral plexus has two main destinations: leaving the pelvis via the greater sciatic foramen to innervate the gluteal region and remaining in the pelvis to innervate the pelvic muscles, organs, and perineum.
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Pelvic splanchnic nerves
The pelvic splanchnic nerves (also known as nervi erigentes) are splanchnic nerves that arise from the sacral spinal nerves S2, S3, and S4. They provide parasympathetic innervation to the pelvic cavity's organs. The pelvic splanchnic nerves originate from the anterior rami of the sacral spinal nerves S2-S4 and enter the sacral plexus. The sacral plexus is a network of nerve fibres that supply the skin and muscles of the pelvis and lower limbs. It is located on the surface of the posterior pelvic wall, anterior to the piriformis muscle.
The pelvic splanchnic nerves have three main branches. The majority of the fibres join the inferior hypogastric plexus, while a smaller portion joins the hypogastric nerves and travels to the superior hypogastric plexus. The smallest portion of the fibres runs across the pelvic brim to the retroperitoneal space to innervate the mesentery of the sigmoid and descending colon. These nerves contribute to the innervation of the pelvic and genital organs. They regulate the emptying of the urinary bladder, control the opening and closing of the internal urethral sphincter, influence rectal motility, and play a role in sexual functions such as erection.
The pelvic splanchnic nerves provide parasympathetic innervation to the urinary bladder, descending colon, sigmoid colon, rectum, ureter, prostate, urethra, penis, and clitoris. Activation of the parasympathetic fibres in these nerves leads to vasodilation of the erectile tissues in the penis and clitoris, secretion in the hindgut, and motor activity in the hindgut and urinary bladder. These nerves also supply parasympathetic function in the distal 1/3 of the transverse colon, the sigmoid and rectum, and the cervix in females, including transmitting the sensation of pain.
Damage to the sacral spinal nerve roots can result in neurogenic bladder dysfunction and faecal incontinence. The sacral spinal nerve S3 (S3) supplies numerous muscles, either directly or through nerves originating from S3. These muscles include the skeletal muscles in the perineum, the external urethral sphincter, the external anal sphincter, and the levator ani.
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Gluteal branches
The gluteal region is supplied by the superior and inferior gluteal arteries, which are branches of the internal iliac artery. The gluteal region consists of superficial and deep muscles. The superficial muscles include the three glutei (gluteus maximus, gluteus medius, and gluteus minimus) and the tensor fascia lata. The gluteus maximus is the largest and most superficial muscle, producing the shape of the buttocks.
The superior gluteal nerve is a mixed motor and sensory nerve of the sacral plexus that originates in the pelvis. It provides motor innervation to the gluteus medius, gluteus minimus, and tensor fasciae latae. The superior gluteal nerve exits the pelvis through the greater sciatic foramen, superior to the piriformis muscle. It is accompanied by the superior gluteal artery and vein. The nerve passes between the gluteus medius and gluteus minimus muscles, supplying the gluteal region.
The inferior gluteal nerve is formed from the lumbosacral plexus, specifically from the fourth lumbar through to the third sacral segments (L4-S3). It exits the pelvis through the greater sciatic foramen, inferior to the piriformis muscle, and innervates the gluteus maximus muscle. The gluteus maximus is a major hip extensor and is important for maintaining stance.
The gluteal region also includes deep muscles such as the piriformis, which is a key landmark and the most superior of the deep muscles. The obturator internus forms the lateral walls of the pelvic cavity and, along with the gemelli muscles, is sometimes considered part of the triceps coxae.
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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.
S3 supplies many muscles, either directly or through nerves originating from S3. These include the obturator internus, superior gemellus, gluteus maximus, and the pelvic floor muscles.
The muscles innervated by S3 are responsible for various motor functions, including movement of the thigh, leg, and foot, such as inversion, eversion, and dorsiflexion of the foot.
