Lower limb nerves (wk5)

Question 1

Lumbar plexus:
-Explain what a plexus is

Answer 1

-A plexus is a bundle of intersecting nerves. A nerve plexus is composed of afferent and efferent fibres that arise from the merging of the anterior rami of spinal nerves and blood vessels
-The lumbar plexus is made up of the nerve fibres which are coming out of the spinal cord at the lumbar level of L1,L2,L3,L4 and L5. As they come from the levels, there is mixing of nerve fibres from more than one nerve root, into the peripheral nerve which is then applied to the skin or the muscles

Question 2

Lumbar plexus:
-Describe the course and location of the obturator nerve

Answer 2

-Made up of some of the nerve fibres that leave the vertical column at L2, L3 and L4
-Made up of distinct fibres with the femoral nerve
-Vertical columns (L2,L3,L4) -> Pelvis -> Gap between pubis and ischium (obturator foreman)/ obturator canal -> medial side of the thigh
-Innervated muscle -> Muscles in the medial compartment of the thigh and medial parts of the thigh (skin)

Question 3

Lumbar plexus:
-Describe the course and location of the femoral nerve

Answer 3

Describe the course and location of the femoral nerve:
-Made up of some of the nerve fibres that leave the vertical column at L2, L3 and L4.
-Made up of distinct fibres with the obturator nerve
-Femoral nerve (L2,L3,L4) -> Anterior of the pelvis + femoral triangle (inguinal ligament, ASIS, anterior of the pubis) -> Sartorius muscle + adductor longus (femoral triangle) -> anterior compartment of thigh -> anterior cutaneous nerve of medial and lateral branch (skin) -> branches extend to the medal side of the ankle (Safina nerve) (supplies skin as it’s made up of sensory nerves)

Question 4

Lumbar plexus:
-Describe the course and location of the lateral cutaneous of the thigh

Answer 4

-Lateral cutaneous of thigh (L2,L3) -> More lateral to the femoral nerve course and comes out underneath the inguinal ligament before it crosses over the hip joint -> Lateral side of the thigh
-Only consists of sensory nerves
-Supplies skin over the lateral aspect of the thigh

Question 5

Lumbosacral plexus
-Describe the course of the gluteal nerves

Answer 5

-Superior gluteal nerve -> L4, L5
-Inferior gluteal nerve -> L5, S1, S2
-Gluteal nerve -> lumbar sacral trunk -> into the inside of the pelvis
-Superior gluteal nerve -> come from the posterior of the pelvis -> supply the muscles on the medial side of the hip e.g. gluteus Medius
-Inferior gluteal nerve -> Smaller branches inferior to the superior gluteal nerve -> Supplying the muscles such as the gluteus maximus

Question 6

Lumbosacral plexus
-Describe the course and location of the sciatic nerve

Answer 6

-Sciatic nerve, made up of the common peroneal -> made up of the posterior branches of the lumbosacral plexus (blue)
-Sciatic nerve, made up of the tibial branches -> made up of the anterior nerves of the lumbosacral plexus
-Sciatic nerve (L4,L5, S1,S2,S3) -> Tibial nerve (serve the anterior section) -> sheath on thigh shared as the sciatic nerve (split is in the middle section)-> splits off as the common peroneal (posterior) -> passes down the thigh in the posterior compartment (supplies muscles in the posterior compartment)

Question 7

Lumbosacral plexus
-Describe the course and location of it’s tibial and common peroneal branches

Answer 7

1. Tibial nerve-> enters the foot medially as it wraps around the back of the ankle -> medial and lateral plant on the foot
2. Common peroneal nerve -> Runs on the lateral side of the knee -> splits into 2 different branches (deep and superficial peroneal nerve) -> superficial stays lateral when running down the leg and supplies the muscles and some of the skin on the lateral side of the lower leg -> deep peroneal nerve is going to come down the anterior compartment at leg, where it can supply the movements to perform toe extension and ankle dorsi flexion -> both branches extend all the way to the ankle and into the foot

Question 8

Describe the sensory nerve distribution:
-Femoral and obturator nerve damage

Answer 8

Damage to nerves along some paths, such as the femoral or obturator nerve, then there would be a clinical loss of sensation in a defined area. Example -> damage to the common peroneal nerve -> lose sensation in the areas supplied by the common peroneal nerve and the deep and superficial peroneal nerves -> down the outside of the leg, onto the foot and in between the toes
-Damage to the femoral nerve -> lose some sensory sensation on the front of the thigh and the medial aspect of the leg

Question 9

Describe the sensory nerve distribution:
-Loss of sensation and example of sensory nerve distribution

Answer 9

-Loss of sensation can result from damage to the nerve where the nerves are coming out from the vertebral column (point of the nerve roots)
-Example: Damage to the nerve root at the 2nd or 3rd lumbar would result in a mixed pattern of sensory loss across the obturator nerve and femoral nerve areas. This is because nerve axons that were travelling down both the peripheral nerves could have been damaged at the point that they were leaving the spinal cord

Question 10

Describe what dermatomes are:

Answer 10

-Dermatomes -> Dermatome distribution is where nerves are split up into sections at which the nerve roots leave the spinal cord. For example, the nerves that the vertebrae at L2, no matter their course, will ‘service’ the area of L2.

Question 11

Explain the muscular nerve supply:
-Includes: skeletal muscle, motor supply, sensory supply and muscle spindles

Answer 11

-Skeletal muscle is supplied by somatic nerve. The nerve to a skeletal muscle is a mixed nerve containing 60% motor and 40% sensory fibres
-Motor supply -> Extrafusal fibres of the muscle which produce movements are innervated by motor neurons of the anterior horn of spinal cord or motor nuclei of cranial nerves. Intrafusal fibres of the muscle spindle are innervated by the gamma motor neurons
-Sensory supply -> Sensory nerve fibres innervate muscle spindles and tendons, ligaments and joint capsules to carry proprioceptive impulses to the central nervous system
-Muscle spindles are sensory end organs present within the skeletal muscles which provide proprioceptive information to sensory nerves that carry this information to the CNS to regulate the contraction of extrafusal fibres.

Question 12

Complete the table for the hip muscles and their innervations:
-Adductors, iliopsoas, gluteus max, min, medius and tensor fasica latae

Question 13

Complete the table for the knee muscles and their innervations:
-Rectus femoris, vastus medialis, vastus lateralis, vastus intermedius, biceps femoris, semitendinosus and semimembranosus

Question 14

Complete the table for the ankle muscle and their innervations:
-Gastrocnemius, soleus, tibialis posterior, flexor digitorum longus, flexor hallucis longus, tibialis anterior, extensor digitorum longus and extensor hallucis longus