Innervation of the Lower Limb Flashcards
Which ventral rami form the lumbar and sacral plexuses?
Lumbar L1-L4, Sacral L4-S3
What nerve fibres are carried to the lower limbs in the 2 plexuses?
Somatic motor, sensory, and sympathetic fibres.
What structures are innervated by the SNS
Arrector Pili, blood vessels, sweat glands.
What is a dermatome?
The area of skin supplied by a single spinal nerve
In which direction do the limbs rotate in development?
Lower = medially, Upper = laterally.
How do you count the dermatomes of the lower limb?
Counted from L1 -L3 in the thigh, then L4-S1 medially to laterally in the lower leg, then medially and superiorly on the back of the leg from s1-s4 (down the front and up the back)
What is a myotome?
The area of skeletal muscle supplied by a single spinal nerve.
How can you test myotomes clinically?
MRC grading scale, and deep tendon reflexes.
What are the components of the monosynaptic stretch reflex?
1) Receptor
2) afferent fibre
3) integration centre (spinal cord)
4) efferent fibre
5) effector.
What is the myotome and reflex for L4?
Quadriceps, patella tendon
What is the myotome and reflex fro S1?
Gastrocnemius/soleus OR peroneus longus + brevis. Reflex is Achilles.
Where is the most common location for herniation?
L5/S1
What does L5/S1 herniation affect?
S1 related structures. E.g. S1 dermatome (posterolateral aspect of leg), diminished S1 (achilles tendon) reflex, S1 myotome (weak plantarflexion / eversion of the foot.)
The lumbar plexus is deep to which muscle?
Psoas Major.
There are direct nerves from the lumbar plexus to certain muscles. What are these muscles?
Psoas major, quadratus lumborum, and sometimes iliacus.
What are the major nerves of the lumbar plexus?
Femoral, obturator and lateral femoral cutaneous nerves
The L4 and L5 spinal nerve join together to form which structure?
Lumbosacral trunk
The lumbosacral trunk joins which spinal nerves to form the sacral plexus?
S1-S3
Sacral plexus lies anterior to which muscle
piriformis
Through which foramen do most of the sacral plexus nerves pass?
Greater sciatic foramen
What are the main nerves of the sacral plexus?
Sciatic nerve, superior + inferior gluteal nerves.
What are the root values of the lateral femoral cutaneous nerve?
L2/L3
What are the root values of the femoral nerve?
L2 L3 L4
What are the root values of the obturator nerve?
L2 L3 L4
What are the root values of the lumbosacral trunk?
L4 L5
What are the root values of the Superior gluteal nerve
L4 - S1. Innervates gluteus medius, gluteus minimus and tensor fascia lata
What are the root values of the inferior gluteal nerve?
L4 - S2. Innervates gluteus maximus.
What are the root values of the sciatic nerve?
L4-S3. Remember this is also the same as the tibial nerve.
What sympathetic fibres do the nerves of the lumbar/sacral plexuses contain?
Post-ganglionic sympathetic fibres
What is the root value of the lateral cutaneous nerve of the thigh? Where does it pass?
L2L3. Under lateral border of psoas major and under inguinal ligament to skin over lateral thigh.
What is the root value of the obturator nerve, and where does it pass?
L2-L4. Medial border of the psoas major and around the pelvis and through the obturator foramen. Supplies medial thigh.
What is the root value of the femoral nerve, an where does it pass?
L2-L4. Lateral border of psoas major and under inguinal ligament. Lateral to blood vessels in femoral triangle. It divides below inguinal ligament to give saphenous nerve which supplies medial leg and foot.
What is the root value of the superior/inferior gluteal nerves, and where do they pass?
Superior - L4-S1. Inferior - L4-S2. They both exit the pelvis via the greater sciatic notch to supply the gluteal muscles.
What are the root values of the sciatic nerve and where does it pass?
L4-S3. Through greater sciatic foramen, between greater trochanter and ischial tuberosity. Splits into tibial nerve (posterior) and common peroneal (anterior, split into superficial laterally and deep anteriorly). Sciatic nerve splits at mid-thigh level.
What are the root values of the tibial nerve?
L4-S3 (all of sacral plexus)
Where does the tibial nerve begin and pass?
Begins around the mid-thigh levels where the sciatic nerve splits. It passes through the popliteal fossa and into the leg between gastrocnemius and soleus. Enters the foot behind the medial malleolus.
What does the tibial nerve split into, and what do they supply?
Medial and lateral plantar nerves. Supply muscles over the sole of the foot and skin over medial and lateral aspects of the sole of the foot.
What does the tibial nerve innervate?
Muscles of the posterior compartment of the leg and foot.
What are the root values of the common peroneal nerve?
L4-S3. Lies in the lateral part of the popliteal fossa, and curves around the fibula.
Which muscles are innervated by the superficial peronal nerve?
Peroneus longus + brevis. It also supplies the skin on the anterolateral distal 1/3 of the leg and the dorsal surface of the foot
Which muscles are supplied by the deep peroneal nerve?
Anterior compartment of leg muscles, and skin over adjacent sides of 1st + 2nd toes. This nerve accompanies the anterior tibial artery
Which nerves contribute to the sural nerve?
Common peroneal and tibial nerves. The sural nerve is cutaneous, which supplies skin on the posteriolateral surface of leg and lateral foot.
