Video: Sciatic nerve and its branches

Every now and then, we need a chance to escape from our studies. Whether you do that by busting a move on the dance floor or taking a hike in the countryside to convene with nature, you need those leg muscles. Today, we're going to talk about one of the nerves that innervate the muscles of the lower limb which is the sciatic nerve and its branches.

Before we begin, I'd like to give you a quick overview of what we're going to talk about in this tutorial. First of all, we're going to discuss the origin and location of the sciatic nerve. Then we'll take a look at the branches of the sciatic nerve and some other nerves of the sacral plexus. Lastly, we'll conclude our tutorial with some clinical notes about sciatica.

Okay, let's get started with the origin and location of the sciatic nerve.

The sciatic nerve originates from the sacral plexus, which we can see here highlighted in green. The sacral plexus is formed by the lumbosacral trunk which consists of contributions from spinal nerves L4 and L5 as well as the spinal nerves S1, 2, 3, and 4. Here we can see S1 highlighted in green, and below it, we can see S2 followed by S3, and finally, S4. Now we can see the sciatic nerve in all its glory. It is approximately two centimeters wide and is the longest and thickest nerve in the human body.

As I mentioned, the sciatic nerve originates from the sacral plexus. Specifically, it is formed by the anterior rami of spinal nerves L4 to S3. The sciatic nerve is a key nerve of the lower limb as it supplies most muscles and skin of the posterior compartment of the thigh, the leg, and the foot.

Okay, let's take a look at the anatomical course of the sciatic nerve.

The sciatic nerve exits the pelvis to enter the posterior compartment of the thigh via the greater sciatic foramen. If we add some musculature, we can see that the sciatic nerve emerges below the piriformis muscle. This is an easy way to identify this nerve, for example, for if you're in the dissection lab and you see a chunky nerve emerging below the piriformis, you're pretty sure to say that it's the sciatic nerve. The sciatic nerve then courses inferiorly through the posterior aspect of the thigh and when it reaches the apex of the popliteal fossa, it terminates by bifurcating into the tibial and common fibular nerves.

Okay, now that we're familiar with the origin and location of the sciatic nerve, let's move on to talk about its branches. It's worth noting that the sciatic nerve can also be described as two individual nerves bundled together in the same connective tissue sheath. As I mentioned previously, the tibial and common fibular nerves usually separate at the apex of the popliteal fossa; however, in some individuals, these nerves can separate as soon as they leave the pelvis.

Based on this principle, we can see the tibial division of the sciatic nerve highlighted in green. In this illustration, we can see that the tibial division is formed by the anterior divisions of spinal nerves L4 to S3. The tibial division of the sciatic nerve innervates most muscles of the posterior compartment of the thigh including the semitendinosus, the semimembranosus, and the long head of the biceps femoris. It also innervates the ischial part of the adductor magnus, which is a muscle of the medial compartment of the thigh.

In the next image, we can see the common fibular division of the sciatic nerve, which is formed by the posterior divisions of spinal nerves L4 to S2. In the posterior compartment of the thigh, the common fibular division of the sciatic nerve innervates the short head of the biceps femoris.

Okay, so assuming that the sciatic nerve does bifurcate at the apex of the popliteal fossa, let's take a look at its terminal branches. Here we can see the tibial nerve, which runs down the medial side of the posterior compartment of the leg. The tibial nerve innervates all muscles in the posterior compartment of the leg which are the gastrocnemius muscle as well as the plantaris, the soleus, the popliteus, the flexor digitorum longus, the tibialis posterior, and the flexor hallucis longus muscle.

In our next illustration, we can see the common fibular nerve, which is located on the lateral side of the leg. It's actually closely associated with the fibula, which is where it gets its name from. The common fibular nerve, however, is also known as the common peroneal nerve. The common fibular nerve provides sensory innervation to the posterolateral leg.

Alright, so let's have a look at some terminal branches of the tibial nerve, starting with the sural nerve which is formed by fibers derived from spinal nerves S1 and S2. The sural nerve descends down the leg and is joined at a variable level by the sural communicating branch of the common fibular nerve, which we can see here. This nerve provides sensory innervation to the lower posterolateral aspect of the leg and foot.

In our illustration, we can see two branches of the sural nerve. The first one that we can see is the lateral calcaneal branch. This branch provides sensory innervation to the lateral aspect of the heel. Next, we have the lateral dorsal cutaneous nerve, which is also a branch of the sural nerve. This nerve provides sensory innervation to the lateral aspect of the foot. We can also see how this nerve contributes to the innervation of the sole of the foot.

Now back to the tibial nerve and its branches. Here we can see the medial plantar nerve highlighted in green, which is a terminal branch of the tibial nerve. This nerve provides motor innervation to the abductor hallucis muscle, flexor digitorum brevis, flexor hallucis brevis, and the first lumbrical muscle of the foot. The medial plantar nerve also provides sensory innervation to the plantar surface of the medial three-and-a-half digits and the associated sole area as we can see in our illustration here.

If we have a medial plantar nerve, we must also have a lateral plantar nerve. This nerve is also a terminal branch of the tibial nerve and provides motor innervation to the abductor digiti minimi muscle, the flexor digiti minimi brevis, the interossei, the adductor hallucis, and the second to fourth lumbricals. It also provides sensory innervation to the plantar surface of the lateral one-and-a-half digits and the associated sole area.

The last branch of the tibial nerve we're going to talk about is the medial calcaneal branch. This branch provides sensory innervation to the medial aspect of the heel and associated sole area.

Now it's time to find out what happens to the common fibular nerve. The common fibular nerve divides into two terminal branches. We can see the first one in our illustration, which is the superficial fibular nerve. This nerve provides motor innervation to muscles of the lateral compartment of the leg which includes the fibularis longus and the fibularis brevis muscles. It also provides sensory innervation to the skin of the lower leg and the dorsum of the foot.

We can't see the next branch in our featured illustration for this tutorial, but it wouldn't feel right not to talk about it, so here we have the deep fibular nerve. The deep fibular nerve is a terminal branch of the common fibular nerve and as we can see, it runs along the anterior aspect of the leg. This nerve provides motor innervation to muscles of the anterior compartment of the leg including the tibialis anterior muscle, the extensor hallucis longus, the extensor digitorum longus, and the extensor digitorum brevis and fibularis tertius. It also provides a spot of sensory innervation to the dorsum of the foot between the first and second toes.

Alright, it's time to leave the sciatic nerve now and discuss some other branches of the sacral plexus.

It's worth noting that the sacral plexus gives off quite a few nerves, but for today, we're just going to focus on the ones that we can see in this illustration. The first branch we're going to talk about is the superior gluteal nerve. This nerve is formed by the posterior divisions of spinal nerves L4 to S1 and leaves the pelvis via the greater sciatic foramen to enter the gluteal region. If we add some musculature, we can see that the superior gluteal nerve emerges above the piriformis unlike the sciatic nerve which emerges below this muscle. The superior gluteal nerve provides motor innervation to the gluteus medius, the gluteus minimus, and the tensor fasciae latae muscle.

If we have a superior gluteal nerve then we must have an inferior gluteal nerve. This nerve is formed by the posterior divisions of spinal nerves L5 to S2 and like its superior sibling leaves the pelvis via the greater sciatic foramen. However, like the sciatic nerve, the inferior gluteal nerve emerges below the piriformis muscle. This nerve provides motor innervation to the gluteus maximus muscle.

The next branch of the sacral plexus we're going to talk about is the pudendal nerve, which is formed by the anterior divisions of spinal nerves S2 to S4. The root of the pudendal nerve is a little bit unusual. It leaves the pelvis via the greater sciatic foramen and then enters the perineum via the lesser sciatic foramen. This nerve gives rise to branches that innervates the external genitalia, the skin of the perineum, and the muscles of the perineum, which is this diamond-shaped region you can see here highlighted in green.

The last nerve of the sacral plexus we're going to talk about is the posterior femoral cutaneous nerve, which is formed by the anterior divisions of spinal nerves S1 and S2 and the posterior divisions of spinal nerves S2 and S3. The posterior femoral cutaneous nerve leaves the pelvis via the greater sciatic foramen and courses down the posterior aspect of the thigh. It provides sensory innervation to the skin of the inferior half of the buttock, the skin of the perineum, and the skin of the posterior thigh and the proximal posterior leg. Interestingly, it supplies the greatest surface area out of all the cutaneous nerves.

Alright, now that we're familiar with the sciatic nerve and its branches, let's get clinical.

In today's clinical notes, we're going to be talking about sciatica, which is irritation of the sciatic nerve due to rubbing or increased pressure. The most common causes of sciatica is lumbar disc herniation which can place increased pressure on its spinal nerves which form the sciatic nerve. Another cause is spinal stenosis where the vertebral foramen and spaces between the vertebrae gets smaller pinching the spinal cord and the nerves around it. Sciatica can also be caused by tumors within the spine or a back injury.

Patients may present with pain, tingling, numbness, weakness in their buttock, the back of their legs, their feet and even their toes. It's worth noting that sciatica only affects one side of the body. Sciatica will usually resolve itself in four to six weeks, but it can last longer. Symptoms can be managed with exercises and stretches as well as painkillers.

Before we bring our tutorial to a close, let's quickly summarize what we've learnt today.

We saw that the sciatic nerve originates from the sacral plexus which is formed by the lumbosacral trunk and the spinal nerves S1, S2, S3, and S4. We then looked at the sciatic nerve and its anatomical course. We moved on to look at the branches of the sciatic nerve starting with the divisions which are the tibial division of the sciatic nerve and the common fibular division of the sciatic nerve. At the apex of the popliteal fossa, the sciatic nerve bifurcates into the tibial nerve and the common fibular nerve.

The tibial nerve has several branches including the sural nerve which gives rise to the lateral calcaneal branch and the lateral dorsal cutaneous nerve. The tibial nerve also gives rise to the medial plantar nerve, the lateral plantar nerve, and the medial calcaneal branch whereas the common fibular nerve divides into two branches - the superficial fibular nerve and the deep fibular nerve.

Next, we looked at some other nerves of the sacral plexus starting with the superior gluteal nerve and the inferior gluteal nerve. Then we looked at the pudendal nerve followed by the posterior femoral cutaneous nerve. We then concluded our tutorial with some clinical notes about sciatica. And that brings us to the end of our tutorial on the sciatic nerve and its branches.