Sciatic nerve (sciatica): anatomy, functions and pathologies

We have all heard (or suffered in our own flesh) about the discomfort caused by a disorder like sciatica.

The main cause of this characteristic pain is compression of the sciatic nerve, which causes severe pain and numbness in the limbs. It is precisely this very important nerve that we will talk about throughout the article.

We tell you what it is and where it is, and what are its main functions. We will also talk about the different disorders associated with sciatic nerve damage.

    Sciatic nerve: definition, structure and location

    The sciatic nerve, also called the sciatic nerve, is the largest and longest peripheral nerve in humans. and other vertebrate animals. It begins in the pelvis, at the bottom of the sacral plexus, formed by the anterior roots of several spinal nerves, and continues through the hip joint, down the leg.

    In humans, the sciatic nerve is formed from the L4 and S3 segments of the sacral plexus, the fibers join to form a single nerve in front of the piriformis muscle. The nerve then passes under this muscle and through the large sciatic foramen, exiting the pelvis.

    From there, it travels along the back thigh to the popliteal fossa (colloquially known as the “curve”). The nerve passes through the posterior thigh compartment behind the adductor majora muscle, in front of the long head of the biceps femoris muscle.

    The sciatic nerve, in the lower thigh and above the knee (at the back), is divided into two nerves: the tibial nerve, which continues its descent to the feet and is responsible for the innervation of the heel. and the plant; and the peroneal nerve, which runs laterally along the outside of the knee and up to the upper area of ​​the foot.

    As we will see later, this nerve provides the connection to the nervous system for almost all of the skin on the legs., The muscles of the back of the thigh and those of the lower leg and foot. Next, we will see what functions this important nerve is responsible for.


    The sciatic nerve is what enables movement, reflexes, motor and sensory functions and strength in the leg, thigh, knee, Calf, ankle, toes and feet. Specifically, it serves as a connection between the spinal cord and the outer part of the thigh, the hamstrings located at the back of the thigh, and the muscles of the lower leg and feet.

    Although the sciatic nerve passes through the gluteal region, it does not invade any muscle here. However, it directly innervates the muscles of the posterior compartment of the thigh and the hamstring part of the adductor magnus muscle. Through its two terminal branches, it innervates the muscles of the calf and certain muscles of the foot, as well as those of the front and side of the leg, and certain other intrinsic muscles of the foot.

    On the other hand, although the sciatic nerve does not have proper cutaneous functions, it provides indirect sensory innervation through its terminal branches by innervation of the anterolateral posterolateral sides of the leg and the sole of the foot, as well as the side of the leg. and dorsal area of ​​the foot.

    Associated disorders: sciatica

    Sciatica is the result of damage or injury to the sciatic nerve and is characterized by a sensation which may manifest as symptoms of moderate to severe pain in the back, buttocks and legs. Weakness or numbness can also occur in these areas of the body. Typically, the person experiences pain that flows from the lower back, buttocks, and lower limbs.

    Symptoms usually worsen with sudden movements (eg, getting out of bed), in certain positions (eg sitting for a long time), or when exercising with weights (eg, moving furniture) or take a bag). Among the most common causes of sciatica, we can highlight the following:

    1. Herniated discs

    The vertebrae are separated by pieces of cartilage, Which is filled with a thick and transparent material that provides flexibility and cushioning when we move. Herniated discs occur when this first layer of cartilage is torn.

    The substance inside can compress the sciatic nerve, causing pain and numbness in the lower extremities. It is estimated that between 1 and 5 percent of the population will suffer at some point in their life from back pain caused by a herniated disc.

    2. Spinal stenosis

    Spinal stenosis, also called lumbar spinal stenosis, is characterized by abnormal narrowing of the lower spinal canal.. This narrowing puts pressure on the spinal cord and its sciatic nerve roots. Symptoms that may occur are: weakness in the legs and arms, lower back pain when walking or standing, numbness in the legs or buttocks, and problems with balance.

    3. Spondylolisthesis

    Spondylolisthesis is one of the conditions associated with degenerative disc disorder. When one vertebrae extends forward over another, the extended spinal bone can pinch the nerves that make up your sciatic nerve.

    Although it is a painful condition, it can be treated in most cases. Symptoms include: stiffness in the back and legs, persistent pain in the lower back, pain in the thigh, and stiffness in the hamstrings and gluteal muscles.

    4. Piriformis syndrome

    Piriformis syndrome is a rare neuromuscular disease in which the piriformis muscle involuntarily contracts or presses down, causing sciatica. This muscle is what connects the lower part of the spine to the bones of the thighs. When stretched, it can put pressure on the sciatic nerve.

    Clinical features of the syndrome include: radicular pain, muscle numbness and weakness, and buttock tenderness. Sometimes the pain can be exacerbated by the internal rotation of the lower hip extremity.

    The usual treatment is generally of the surgical type, with the aim of freeing the piriformis muscle; or non-surgical, with the injection of corticosteroids, the application of analgesic drugs and physiotherapy.

    Bibliographical references:

    • Cardinali, DP (2000). Manual of neurophysiology. Madrid: Editions Diaz de Santos.

    • Olmarker, K. and Rydevik, B. (1991). Pathophysiology of sciatica. Orthopedic Clinics of North America, 22 (2), 223-234.

    • Sobotta, J. (2006). Atlas of Human Anatomy (Vol. 2). Pan American Medical Edition.

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