C8 spinal nerve

At a glance

Level system

C8 nerve (named for its spinal cord segment)

Where it leaves the canal

The C8 nerve exits between the C7 vertebra and the T1 vertebra, below the C7 vertebra.Betts et al. 2022, §13.4

Distance down the canal before it exits

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

ISNCSCI key sensory point

Little finger, dorsal surface, proximal phalanxRupp et al. 2021; Kirshblum et al. 2011

ISNCSCI key muscle

Finger flexors: tested by asking the person to flex the distal phalanx of the middle fingerRupp 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 same occurs for C3 to C7, but C8 emerges between the seventh cervical vertebra and the first thoracic 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

Connections to the rest of the body

• Spinal nerves and plexuses

  Brachial plexus: the nerves of the arm

  Spinal nerves from the lower neck and first thoracic segment regroup in the brachial plexus and become the nerves of the arm.

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

• Key muscles (ISNCSCI)

  C8: finger flexors

  In the standard neurological examination after spinal cord injury (ISNCSCI), the strength of the finger flexors is the key test of segment C8. The muscle also receives other segments; the key muscle is a convention for testing, not the whole supply.

  Rupp et al. 2021; Betts et al. 2022, §11.5 · 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