Cauda equina

Function

Below the conus medullaris, the lumbar, sacral and coccygeal nerve roots stream downward inside the thecal sac like a horse's tail — hence cauda equina. Each root exits at its own foramen, doubling as a moving cable that tolerates the lumbar spine's flexion.

Because these are peripheral (not central) nerves, injury below L1 produces lower motor neuron signs — flaccid weakness, areflexia — and saddle anaesthesia with bladder retention when compression involves S2–S4.

Blood supply

Segmental lumbar arteries.

Nerve supply

L2–S5 roots.

Clinical relevance

Cauda equina syndrome

A massive central disc prolapse compresses the roots: saddle numbness, urinary retention and bilateral leg weakness — a surgical emergency inside 48 hours.

Lumbar spinal stenosis

Hypertrophied facets narrow the canal; leg pain eases when sitting and flexing (the shopping-cart sign).