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Robotic Spine Universe

Structures · Spinal cord segments

S1 spinal cord segment

The piece of spinal cord that gives rise to the S1 pair of spinal nerves. Segment names use the spinal cord level system, which does not line up with the vertebrae.

Show in the 3D spineSee what it connects to in the body

At a glance

Level system
S1 segment (spinal cord level)
Lies opposite
L1 (vertebral level)Model mapping; varies between people. Frostell et al. 2016; De Leener et al. 2018; Cadotte et al. 2014
Length along the cord
8.7 mmMeasured on one model: the Visible Human male, imaged as a supine cadaver. Not a normal range. De Leener et al. 2018; Frostell et al. 2016
Its nerve
The S1 nerve leaves through the S1 sacral foramina.Betts et al. 2022, §13.4
ISNCSCI key sensory point
Lateral heel (calcaneus)Rupp et al. 2021; Kirshblum et al. 2011
ISNCSCI key muscle
Ankle plantar flexors: tested by asking the person to plantar-flex the ankleRupp et al. 2021; Kirshblum et al. 2011

Cross-section at S1

left ventral hornright ventral hornleft intermediate zoneright intermediate zoneleft dorsal hornright dorsal hornAnteriorPosteriorLR
Regions in this section (text list)
  • left ventral horn
  • right ventral horn
  • left intermediate zone
  • right intermediate zone
  • left dorsal horn
  • right dorsal horn

Grey matter and white-matter tracts at this level. Outline from the PAM50 template and atlas, cut at the segment midpoint. De Leener et al. 2018; Lévy et al. 2015

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What the sources say

“The lateral horn , which is only found in the thoracic, upper lumbar, and sacral regions, contains cell bodies of motor neurons of the autonomic nervous system.” Betts et al. 2022, §13.2
“The posterior horn is responsible for sensory processing.” Betts et al. 2022, §13.2
“The anterior horn sends out motor signals to the skeletal muscles.” Betts et al. 2022, §13.2

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

  • Key muscles (ISNCSCI)

    S1: ankle plantar flexors

    In the standard neurological examination after spinal cord injury (ISNCSCI), the strength of the ankle plantar flexors is the key test of segment S1. 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, §11.6 · 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

Read more

  • Brain–spine interfaces

    A digital bridge around a spinal cord injury. Implants read movement intentions from the cortex and turn them into stimulation of the lumbar cord, so that a person with paralysis can stand and walk under their own control.

For learning only. Levels and sizes vary between people; nothing here describes a particular person or gives medical advice. Sources: Betts et al. 2022, §13.2; Frostell et al. 2016; De Leener et al. 2018; Cadotte et al. 2014; Betts et al. 2022, §13.4; Rupp et al. 2021; Kirshblum et al. 2011; Betts et al. 2022, §11.6.