Comprehensive Notes on Nerve Supply of the Lower Limb
Nerve Supply of the Lower Limb
Basic Terminology & Anatomy of the Nervous System
- The nervous system serves as the body's control center and communication network.
- It senses, interprets, and responds to changes in the internal and external environment.
Anatomy of the Nervous System
- The nervous system consists of highly specialized cells called neurons that transmit information throughout the body.
- Sensory neurons (afferent neurons) transmit information about conditions inside and outside the body. They send signals from the periphery to the central nervous system.
- Motor neurons (efferent neurons) transmit information that controls the activity of muscles and glands, carrying signals from the central nervous system to the periphery to initiate actions.
- Glial cells (support cells) provide protection and nutrition to neurons.
Divisions of the Nervous System
Central Nervous System (CNS)
- Composed of the brain and spinal cord.
- Protected by the bones of the axial skeleton.
Peripheral Nervous System (PNS)
- Nerves that connect the CNS to peripheral structures such as skin, muscle, and glands.
- Includes cranial nerves and spinal nerves.
Cranial Nerves
- Emerge directly from the brain or brainstem.
- There are 12 pairs, each named and numbered.
- Supply the musculoskeletal structures of the head and neck.
- Supply the viscera of the thorax and abdomen.
Spinal Nerves
- Emerge from the spinal cord.
- There are 31 pairs, each numbered according to the vertebral level at which it emerges.
- 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
- Supply the structures of the trunk wall and the limbs.
Spinal Nerve Formation
- Sensory neurons enter the spinal cord at the back (dorsal/posterior).
- Motor neurons leave the spinal cord from the front (ventral/anterior).
- Motor and sensory neurons are grouped together in the spinal nerve.
- The spinal nerve divides into a dorsal (posterior) ramus and a ventral (anterior) ramus.
Branches of the Spinal Nerve
- Dorsal ramus: Distributed to the muscles of the back and the skin covering those muscles.
- Ventral ramus: Distributed to the muscles of the anterior and lateral trunk, and the corresponding skin; also distributed into the limbs to supply the muscles and skin there.
Sensory and Motor Distribution
- Sensory distribution to the skin: Sensation of hot, cold, pain, touch, pressure.
- Sensory distribution to joints: Sensation of joint position (proprioception).
- Hilton's law: 'Where a nerve supplies a muscle that moves a particular joint, that nerve will also supply that joint.'
- Motor distribution to muscles: Turns the muscle on, causing it to contract (concentric, isometric, or eccentric contraction dependent on task requirements).
- Motor distribution to glands: Increases secretion from the gland (usually); supply to sweat glands produces sweating.
Sensory & Motor Pathways
- Sensory (afferent) neurons carry impulses from receptors (e.g., pain receptors in the skin) towards the spinal cord.
- Motor (efferent) neurons carry impulses from the spinal cord to effectors (e.g., muscles) to produce a response (e.g., muscle contraction).
- Interneurons within the spinal cord connect sensory and motor neurons.
Ventral Rami and Plexi
- Ventral rami form plexi, which are networks of nerves:
- Brachial plexus (C5-T1): supplies the upper limbs.
- Lumbosacral plexus (L4-S3): supplies the lower limb.
- Cervical plexus (C1-C4): supplies structures in the neck and the diaphragm.
- Lumbar plexus (L1-L4): supplies the lower limb.
Arrangement of the Lumbar and Lumbosacral Plexuses
- The lumbar plexus arises from the ventral rami of L1-L4, with contributions from T12.
- The lumbosacral plexus is formed by the lumbar plexus and the sacral plexus (L4-S3).
- Key nerves arising from these plexuses include:
- Genitofemoral nerve (L1-L2)
- Femoral nerve (L2-L4)
- Obturator nerve (L2-L4)
- Lateral femoral cutaneous nerve (L2-L3)
- Lumbosacral trunk (L4-L5)
- Posterior femoral cutaneous nerve (S1-S3)
- Sciatic nerve (L4-S3)
Distribution of the Branches of the Lumbar Plexus
| Nerve | Root Value | Motor distribution | Sensory distribution |
|---|---|---|---|
| Femoral | L2-L4 | Iliacus, pectineus, sartorius, quadriceps group | Skin of anterior and medial thigh, knee and hip joints |
| Saphenous | XXX | None | Skin of the medial leg to base of great toe |
| Obturator | L2-L4 | Pectineus, adductor brevis, longus and half of magnus, obturator externus, gracilis | Skin of medial thigh and hip joint |
| Lateral femoral cutaneous | XXX | None | Skin of the lateral thigh |
| Genitofemoral | XXX | None | Skin of the medial thigh, skin of the external genitalia |
| Muscular branches | XXX | Iliacus and psoas major | Hip joint |
Distribution of the Branches of the Lumbosacral Plexus
| Nerve | Root Value | Motor distribution | Sensory distribution |
|---|---|---|---|
| Posterior femoral cutaneous | XXX | None | Skin of posterior thigh and leg to mid calf |
| Superior gluteal | XXX | Gluteus medius and minimus, tensor fascia lata | Hip joint |
| Inferior gluteal | XXX | Gluteus maximus | Hip joint |
| Muscular branches | XXX | External rotators except obturator externus | Hip joint |
| Sciatic | L4-S3 | Hamstrings and half of adductor magnus | Hip and knee joints |
Distribution of the Branches of the Sciatic Nerve
| Nerve | Root Value | Motor distribution | Sensory distribution |
|---|---|---|---|
| Tibial | XXX | Gastrocnemius, soleus, plantaris, popliteus, tibialis posterior (TP), flexor hallucis longus (FHL), flexor digitorum longus (FDL) | Knee and ankle joints |
| Medial plantar | XXX | Abductor hallucis (AbdHall), flexor digitorum brevis (FDB), flexor hallucis brevis (FHB), 1st lumbrical | Skin of the medial 3 and ½ digits and corresponding sole and joints in the foot |
| Lateral plantar | XXX | Flexor digiti minimi brevis (FDMB), adductor hallucis (AddHall), 2nd to 4th lumbricals, interossei, abductor digiti minimi (AbDM) | Skin of the lateral 1 and ½ digits and corresponding sole and joints in the foot |
| Sural | XXX | None | Skin of the lateral and posterior leg, heel and skin of the lateral side of the sole |
| Common peroneal | XXX | None directly (but see branches) | Knee joint, skin of anterior, posterior, and lateral upper leg (adjacent to knee) |
| Superficial peroneal | XXX | Peroneus longus and brevis | Skin of lateral leg, dorsum of foot except skin between digits 1 and 2, and ankle joint |
| Deep peroneal | XXX | Tibialis anterior (TA), extensor hallucis longus (EHL), extensor digitorum longus (EDL), peroneus tertius (PT), extensor digitorum brevis (EDB) | Skin between digits 1 and 2, and ankle and foot joints |
| Sural* | XXX | None | Skin of the lateral and posterior leg, heel and skin of the lateral side of the sole.* (Note: Sural nerve is formed by branches of both the tibial and common peroneal nerves) |
Course of the Major Nerves of the Lower Limb
Femoral Nerve
- The femoral nerve is the largest branch of the lumbar plexus.
- It enters the thigh deep to the inguinal ligament and passes lateral to the femoral artery.
- It innervates the iliacus, pectineus, sartorius, and quadriceps femoris muscles. It is responsible for knee extension and hip flexion.
- Sensory distribution includes the anterior and medial thigh via the anterior cutaneous branches, and the medial leg and foot via the saphenous nerve.
Saphenous Nerve
- This is the terminal cutaneous branch of the femoral nerve.
- It travels with the great saphenous vein.
- It provides sensory innervation to the medial leg and foot.
Obturator Nerve
- The obturator nerve exits the pelvis through the obturator foramen.
- It innervates the adductor muscles of the thigh (adductor longus, adductor brevis, adductor magnus, gracilis) and the obturator externus.
- Sensory distribution is limited to a small area of the medial thigh and the hip joint.
Genitofemoral Nerve
- The genitofemoral nerve pierces the psoas major muscle.
- It has two branches: the genital branch and the femoral branch.
- It supplies the skin of the medial thigh and the external genitalia.
Superior Gluteal Nerve
- The superior gluteal nerve exits the pelvis superior to the piriformis muscle.
- It innervates the gluteus medius, gluteus minimus, and tensor fascia lata muscles.
Inferior Gluteal Nerve
- The inferior gluteal nerve exits the pelvis inferior to the piriformis muscle.
- It innervates the gluteus maximus muscle.
Lateral Femoral Cutaneous Nerve
- This is a sensory nerve that supplies the skin of the lateral thigh.
- It can be subject to compression, causing meralgia paresthetica.
Posterior Femoral Cutaneous Nerve
- This is a sensory nerve that supplies the skin of the posterior thigh and leg.
Sciatic Nerve
- The sciatic nerve is the largest nerve in the body.
- It exits the pelvis through the greater sciatic foramen, usually inferior to the piriformis muscle (although variations exist where it passes through or above the piriformis).
- It travels down the posterior thigh, deep to the gluteus maximus and long head of biceps femoris.
- It typically divides into the tibial and common peroneal nerves in the distal thigh, but the division can occur higher up.
- Innervates the hamstrings (biceps femoris long head, semitendinosus, semimembranosus) and adductor magnus (hamstring portion).
- It provides sensory innervation to the hip and knee joints.
Tibial Nerve
- The tibial nerve is one of the two terminal branches of the sciatic nerve.
- It passes through the popliteal fossa and down the posterior leg.
- It innervates the muscles of the posterior compartment of the leg (gastrocnemius, soleus, plantaris, popliteus, tibialis posterior, flexor hallucis longus, flexor digitorum longus). It controls plantar flexion and inversion of the foot, as well as toe flexion.
- It continues into the foot as the medial and lateral plantar nerves.
Common Peroneal (Fibular) Nerve
- The common peroneal nerve is the other terminal branch of the sciatic nerve.
- It wraps around the fibular neck, making it vulnerable to injury.
- It divides into the superficial and deep peroneal nerves.
Superficial Peroneal Nerve
- Innervates the peroneus longus and brevis muscles, which evert the foot.
- It provides sensory innervation to the lateral leg and dorsum of the foot (except between the 1st and 2nd toes).
Deep Peroneal Nerve
- Innervates the tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius, and extensor digitorum brevis muscles.
- It controls dorsiflexion of the foot and extension of the toes.
- It provides sensory innervation to the skin between the 1st and 2nd toes.
Medial and Lateral Plantar Nerves
- These are the terminal branches of the tibial nerve in the foot.
- They innervate the intrinsic muscles of the foot and provide sensory innervation to the plantar aspect of the foot.