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Sciatic nerve: want to learn more about it?

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Sciatic nerve

The sciatic nerve is the largest nerve in the human body and is derived from the sacral plexus. It originates from the ventral rami of the lumbar (L4-L5) and sacral spinal nerves (S1, S2, S3). It contains fibers from both the posterior and anterior divisions of these spinal nerves.

The sciatic nerve arises in the lumbosacral region. It descends through the posterior aspect of the thigh. Before entering the popliteal fossa, the nerve terminates by splitting into two large terminal branches: the tibial nerve and common fibular (peroneal) nerve.

The main function of the sciatic nerve is to provide sensory and motor supply to the skin and muscles of the thigh, leg and foot.

This article will discuss the anatomy and function of the sciatic nerve.

Key facts about the sciatic nerve
Origin L4, L5, S1, S2, S3
Branches Muscular branches of sciatic nerve, tibial nerve, common fibular (peroneal) nerve
Supply Motor: Muscles of the posterior thigh, ischial portion of adductor magnus, muscles of the posterior, anterior and lateral compartments of the leg, foot muscles.
Sensory
: Posterior thigh, lateral and posterior leg, dorsum and sole of the foot.

Origin and course

The sciatic nerve is a terminal branch of the sacral plexus. It is formed from both anterior and posterior divisions of the anterior (ventral) rami of spinal nerves L4 through S3. The anterior branches of these five spinal nerves meet and converge in the posterior pelvic region to form a single large nerve. The sciatic nerve then descends posteriorly and leaves the pelvis through the greater sciatic foramen. It passes inferior to the piriformis muscle, accompanied by the posterior femoral cutaneous nerve, pudendal nerve, internal pudendal artery and vein, inferior gluteal nerve, inferior gluteal artery and vein.

The sciatic nerve then continues its course through the posterior thigh. It runs between the long head of the biceps femoris muscle and the adductor magnus muscle, and laterally to the semitendinosus and semimembranosus muscles.

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Branches

On its course through the posterior thigh, the sciatic nerve gives off several small motor muscular branches that innervate the several muscles of the thigh.

At the apex of the popliteal fossa, the sciatic nerve terminates by dividing into two terminal branches:

  • The tibial nerve
  • The common fibular (peroneal) nerve

The tibial nerve continues the course of the sciatic nerve and descends down through the posterior aspect of the leg as far as the heel of the foot. More specifically, the tibial nerve passes through the center of the popliteal fossa and runs below the tendinous arch of the soleus muscle. It continues its course in a neurovascular bundle through the posterior leg compartment and passes through the tarsal tunnel. When it reaches the foot, the tibial nerve divides into two terminal branches: medial and lateral plantar nerves that innervate the majority of the foot muscles.

In contrast to the tibial nerve, the common fibular (peroneal) nerve courses laterally towards the head of the fibula. When it reaches the anterior compartment of the leg, the nerve divides underneath the fibularis longus muscle into the superficial fibular (peroneal) nerve and deep fibular (peroneal) nerve. The superficial branch supplies the lateral compartment of the leg, while the deep branch supplies the anterior compartment of the leg and medial aspect of the foot.

The deep fibular (peroneal) nerve descends between the fibula and the superior part of fibularis (peroneus) longus, runs deep to extensor digitorum longus and anterior to the interosseous membrane.

Innervation

The sciatic nerve is a mixed nerve that provides numerous branches for sensory and motor supply for the skin and muscles of the lower limb. Additionally, it provides articular branches for the innervation of the lower limb joints.

Sensory distribution of the sciatic nerve
Sensory distribution of the sciatic nerve

Motor innervation

Sensory innervation

The sciatic nerve gives off sensory branches that provide sensory supply for the largest portion of the lower limb. First, on its course, the sciatic nerve innervates the skin of the posterior thigh. Then the sensory supply continues through its terminal branches;

  • The tibial nerve innervates the sole of the foot.
  • The branches of the common peroneal nerve innervate the lateral aspect of the leg and dorsum of the foot, as well as the skin between the first two toes.
  • The tibial nerve and common peroneal nerve make up the medial and lateral sural nerves. These nerves provide sensation to the calf and a small lateral portion of the foot.

Sciatic nerve: want to learn more about it?

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“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

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