T4 spinal cord segment

At a glance

Level system

T4 segment (spinal cord level)

Lies opposite

T2-T3 disc to T3-T4 disc (vertebral levels)Model mapping; varies between people. Frostell et al. 2016; De Leener et al. 2018; Cadotte et al. 2014

Length along the cord

21.2 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 T4 nerve exits between the T4 vertebra and the T5 vertebra, below the T4 vertebra.Betts et al. 2022, §13.4

ISNCSCI key sensory point

Midclavicular line, fourth intercostal space (nipple line)Rupp et al. 2021; Kirshblum et al. 2011

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

  Intercostal nerves run between the ribs

  Thoracic nerves T2 to T11 do not join a plexus: each runs around the chest wall between two ribs.

  Betts et al. 2022, §13.4 · 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

• Sympathetic outflow

  Sympathetic outflow: thoracic and upper lumbar cord

  Every sympathetic signal to the body leaves the cord between T1 and L2, from neurons in the lateral horn, and passes through the chain of ganglia beside the vertebral column.

  Wulf and Tom 2023; Betts et al. 2022, §15.1 · Show on the body

• Sympathetic outflow

  Heart: sympathetic from T1–T4

  Sympathetic neurons for the heart sit in the lateral horn of segments T1 to T4. A spinal cord injury above these segments cuts them off from the brain's control, though they still work as part of spinal reflexes.

  Wulf and Tom 2023 · Show on the body

• Sympathetic outflow

  Airways and lungs: sympathetic from T1–T5

  Sympathetic neurons for the airways and lungs sit in the lateral horn of segments T1 to T5. A spinal cord injury above these segments cuts them off from the brain's control, though they still work as part of spinal reflexes.

  Wulf and Tom 2023 · Show on the body

• Sympathetic outflow

  Spleen: sympathetic from T4–T12

  Sympathetic neurons for the spleen sit in the lateral horn of segments T4 to T12. A spinal cord injury above these segments cuts them off from the brain's control, though they still work as part of spinal reflexes.

  Wulf and Tom 2023 · Show on the body