The
cauda equina (Latin for "horse's tail") is a bundle of
spinal nerves and spinal nerve roots, consisting of the second through fifth
lumbar nerve pairs, the first through fifth
sacral nerve pairs, and the
coccygeal nerve, all of which arise from the
lumbar enlargement and the
conus medullaris of the
spinal cord. The cauda equina occupies the lumbar cistern, a subarachnoid space inferior to the conus medullaris. The nerves that compose the cauda equina innervate the
pelvic organs and
lower limbs to include motor innervation of the
hips,
knees,
ankles,
feet,
internal anal sphincter and
external anal sphincter. In addition, the cauda equina extends to sensory innervation of the
perineum and, partially,
parasympathetic innervation of the
bladder.