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