www.FootDoc.caNeurology
Neurology is the study of nerves, and this web page should give you an overview of the subject of the nerves that relate to the foot and lower extremity. We will divide this discussion on nerves into their anatomical locations--beginning with the brain and moving downwards.
Communication Between The Brain & The Feet
The brain and the feet communicate through nerve signals. The brain sends signals down to the foot and leg to tell them to carry out an action, and the foot sends sensory signals up to the brain to give the brain information about what they are experiencing. The signals are transmitted through the spine by what are known as Spinal Tracts.
Listed below are the major families of spinal tracts:
The major pathways extending from the foot to the brain (the afferent nerves):
Spinothalamic Tract This tract sends sensory signals to the portion of the brain that is conscious. Light touch (like when someone touches your big toe with a cotton ball) and tickling sensations are sent up in the Anterior Spinothalamic Tract, located on the front of the spine. Normal touch and positional sensation is sent via the Posterior Spinothalamic Tract, located on the back of the spine. Pain and temperature are sent to the brain via the Lateral Spinothalamic Tract, located on each side of the spine.
Spinocerebellar Tract This tract sends signals from the feet to the cerebellum in the lower back of the skull to give input with regards to balance (which the cerebellum controls unconsciously).
The major pathways extending from the brain to the foot (the efferent nerves):
Corticospinal Tract Also known as the Pyramidal Tract because it starts from a pyramid-shaped area of the medulla in the brain, this tract carries signals from the cortex of the brain to the muscles of the extremities. If you wiggle your toes, you are using this tract.
Extrapyramidal Tract This tract consists of those structures involving involuntary, unconscious or automatic movement of the skeletal system. If you unconsciously adjust your position while standing, for example, you are using this tract.
Reticulospinal Tract This tract predominately carries autonomic function (the signals carried without your thinking about them, such as perspiration and whether to open or close the arteries) down to the extremities.
The Nerves of the Lower Extremity
Nerves of the Thigh
The nerves of the foot are all branches of one of two nerves--the Femoral Nerve, which provides only a small amount of innervation (nerve supply) to the foot), and the Sciatic Nerve, which provides the vast majority of the innervation to the foot.
The Femoral Nerve (pictured on the right) arises from nerve fibers from the the L2-L3-L4 portion of the lumbar spine. (This means that the nerves leave the spinal cord beneath the 2nd, 3rd and 4th Lumbar vertebrae.) The Femoral Nerve then passes down the inside edge of the thigh, past the inside of the knee and towards the ankle and foot.
The Sciatic Nerve (pictured below) is the largest nerve in the body and it is comprised of nerves from the L4-L5-S1-S2-S3 level of the spine. (This means that the nerve fibers that make up the Sciatic Nerve leave the spinal cord beneath the fourth and fifth lumbar and the first, second and third sacral vertebrae.) It then descends down the back of the thigh.
You can learn about the most common injury to the sciatic nerve by visiting our webpage on sciatica.
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The sciatic nerve passes down the back of the thigh, and near the bottom third of the thigh, it branches into two nerves:
Common Peroneal Nerve, comprised of nerve fibers from L5, S1, S2, and S3.
Tibial Nerve comprised of nerve fibers from L4, L5, S1, S2 and S3)
Each of these nerves then continues down the leg towards the knee joint.
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Nerves Below the Knee and Above the Ankle
Shortly after crossing the knee joint, the Common Peroneal Nerve divides into three branches--the Lateral Sural Cutaneous Nerve, the Deep Peroneal Nerve and the Superficial Peroneal Nerve.
The Lateral Sural Cutaneous Nerve merges with the Medial Sural Cutaneous Nerve (a branch from the Tibial Nerve described below) to form the Sural Nerve. The Sural Nerve then runs down the outside edge of the leg.
The Deep Peroneal Nerve begins at the outside edge of the upper leg, then moves across the tibia bone in the leg to supply nerve function to the muscles on the front of the leg (the Tibialis Anterior, Extensor Hallucis Longus, Extensor Digitorum Longus and Peroneus Tertius muscles). The Deep Peroneal Nerve then continues down the leg towards the foot.
The Superficial Peroneal Nerve supplies nervous function to the Peroneus Longus and Peroneus Brevis muscles, then continues down the leg. It eventually branches into two nerves, the Medial Dorsal Cutaneous Nerve and the Intermediate Dorsal Cutaneous Nerves.
The first branch off the Tibial Nerve is the Medial Sural Cutaneous Nerve, which as mentioned above, connects with the Lateral Sural Cutaneous Nerve (a branch of the Common Peroneal Nerve) to form the Sural Nerve.
The Tibial Nerve then supplies the nervous function to the muscles in the back of the leg--the Popliteus, Gastrocnemius, Soleus, Plantaris, Tibialis Posterior, Flexor Digitorum Longus and Flexor Hallucis Longus muscles. The Tibial Nerve then continues down the back of the leg towards the ankle and foot.
Nerves of the Ankle Region and Foot
There are five major nerves heading from the leg that impact the foot--the Sural Nerve, the Saphenous Nerve, the Tibial Nerve, the Deep Peroneal Nerve, and the Superficial Peroneal Nerve.
The Sural Nerve crosses behind the lateral malleolus (the bump on the outside portion of the ankle). Once in the foot, the Sural Nerve's name changes to the Lateral Dorsal Cutaneous Nerve, and it supplies the sensory information back to the brain concerning the outside edge of the foot, including the small toe.
The Saphenous Nerve crosses behind the medial malleolus (the bump on the inside portion of the ankle). This nerve retains its name and supplies the sensory information back to the brain concerning the inside edge of the foot including the small toe.
The Posterior Tibial Nerve crosses the ankle behind the medial malleolus (the bump on the inside portion of the ankle). It has three branches.
1. Medial Calcaneal Nerve--The Medial Calcaneal Nerve is the smallest branch. It run along the medial (inside) portion of the heel, and it provides the sensory innervation for that portion of the heel.
2. Medial Plantar Nerve--The Medial Plantar Nerve is the larger of the two major nerves on the bottom of the foot. (See diagram below.) The fibres that make up this nerve originate at the S2-S3 level. The Medial Plantar Nerve gives sensory perception to the bottom of the big toe, the second and third toes and half of the fourth toe, as well as the medial (inside) 2/3's of the the bottom of the foot. This nerve provides innervation (nerve connection) with the Flexor Digitorum Brevis (FDB), Flexor Hallucis Brevis (FHB),Adductor Hallucis, and 1st Lumbrical muscles.
3. Lateral Plantar Nerve--The Lateral Plantar Nerve is the smaller of the two nerves on the bottom of the foot. (See diagram to the right.) As with the Medial Plantar Nerve, The fibers that make up the Lateral Plantar Nerve left the spine at the S2-S3 level. The Lateral Plantar Nerves provides sensory perception to the the outside 1/3 of the bottom of the foot, including the fifth toe and half of the fourth toe. It innervates the Quadratus Plantae, Abductor Digiti Quinti, Flexor Digiti Quinti Brevis, 1st, 2nd, 3rd and 4th Dorsal Interossei, the 1st, 2nd and 3rd Plantar Interossei and the 2nd, 3rd and 4th Lumbrical muscles.
We should probably mention here that a branch from the medial plantar nerve with a branch from the lateral plantar nerve join together in the fourth interspace of the foot, and this is the primary location for a neuroma to develop. For more information about neuromas, please visit our web page by clicking on the word neuroma.
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The Deep Peroneal Nerve (also known as the Anterior Tibial Nerve) passes on the front of the ankle. It divides into the medial and lateral branches. The medial branch advances down the foot and supplies nervous sensation to the space between the big toe and second toe. The lateral branch supplies the nervous input to the Extensor Digitorum Brevis muscle, then divides into three branches which supply the nervous input to the 2nd, 3rd and 4th Interosseous muscles.
