S3 spinal nerve

At a glance

Level system

S3 nerve (named for its spinal cord segment)

Where it leaves the canal

The S3 nerve leaves through the S3 sacral foramina.Betts et al. 2022, §13.4

Distance down the canal before it exits

219 mmMeasured on one model: the Visible Human male, imaged as a supine cadaver. Not a normal range; drawn root, schematic

ISNCSCI key sensory point

Ischial tuberosity or infragluteal foldRupp et al. 2021; Kirshblum et al. 2011

Roots, ganglia and nerves are drawn schematically from each segment to its exit; their paths are not traced from imaging.

What the sources say

“The sacral nerves emerge from the sacral foramina along the length of that unique vertebra.” Betts et al. 2022, §13.4

“All of the spinal nerves are combined sensory and motor axons that separate into two nerve roots.” Betts et al. 2022, §13.4

“The sensory axons enter the spinal cord as the dorsal nerve root.” Betts et al. 2022, §13.4

“The motor fibers, both somatic and autonomic, emerge as the ventral nerve root.” Betts et al. 2022, §13.4

“The sacral plexus comes from the lower lumbar nerves L4 and L5 and the sacral nerves S1 to S4.” Betts et al. 2022, §13.4

Connections to the rest of the body

• Spinal nerves and plexuses

  Sacral plexus: the back of the thigh and the calf

  L4 to S4 form the sacral plexus, the source of the nerves to the back of the leg.

  Betts et al. 2022, §13.4 · Show on the body

• Spinal nerves and plexuses

  Pudendal nerve: voluntary control of the urethral sphincter

  Holding urine in is voluntary: the pudendal nerve, from S2 to S4, controls the external urethral sphincter.

  Betts et al. 2022, §25.2 · Show on the body

• Key sensory points (ISNCSCI)

  Key sensory points: one patch of skin per segment

  The examination tests light touch and pinprick at one key point per segment on each side, from C2 behind the ear to S4–5 beside the anus. The points here were placed on this body by following the standard’s written descriptions from bony landmarks, so they are approximate.

  Rupp et al. 2021; Kirshblum et al. 2011 · Show on the body

• Parasympathetic outflow

  Sacral parasympathetic: S2–S4 to the pelvic organs

  Parasympathetic neurons in sacral segments S2 to S4 leave in the pelvic splanchnic nerves to the lower large intestine, the bladder and the reproductive organs. They empty the bladder.

  Wulf and Tom 2023; Betts et al. 2022, §25.2 · Show on the body