S1 spinal nerve

Nervus spinalis S1

NervousNervesPelvisLeft and right

View left in 3D View right in 3D

What it is
The S1 spinal nerve leaves the spinal canal between the first sacral foramina. Its sensory (dorsal) and motor (ventral) roots meet just beyond the dorsal root ganglion; the short mixed nerve then splits into a small dorsal ramus for the back muscles and skin and a larger ventral ramus, which joins the sacral plexus.
Function
Carries motor fibres to the muscles of its segment (myotome) and sensation back from its strip of skin (dermatome): the lateral border and sole of the foot and the little toe.
Size
About 4-5 mm thick; the mixed nerve is only ~1 cm long before it divides
Clinical note
Test: the ankle-jerk reflex and standing on tiptoe; the L5/S1 disc is the other classic sciatica level.

Nearby nervous structures Co1 spinal nerve, Ganglion impar, Pudendal nerve, S2 spinal nerve, S3 spinal nerve, S4 spinal nerve, S5 spinal nerve, Superior and inferior hypogastric plexuses