Structures · Spinal nerves
T1 spinal nerve
The pair of spinal nerves from the T1 segment, one on each side. Each forms from a dorsal (sensory) and a ventral (motor) root.
At a glance
- Level system
- T1 nerve (named for its spinal cord segment)
- Where it leaves the canal
- The T1 nerve exits between the T1 vertebra and the T2 vertebra, below the T1 vertebra.Betts et al. 2022, §13.4
- Distance down the canal before it exits
- 21 mmMeasured on one model: the Visible Human male, imaged as a supine cadaver. Not a normal range; drawn root, schematic
- ISNCSCI key sensory point
- Medial (ulnar) side of the antecubital fossa, just proximal to the medial epicondyle of the humerusRupp et al. 2021; Kirshblum et al. 2011
- ISNCSCI key muscle
- Finger abductors: tested by asking the person to abduct the little 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
“For the thoracic and lumbar nerves, each one emerges between the vertebra that has the same designation and the next vertebra in the column.” 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.
Key muscles (ISNCSCI)
T1: finger abductors
In the standard neurological examination after spinal cord injury (ISNCSCI), the strength of the finger abductors is the key test of segment T1. 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.
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.
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.
For learning only. Levels and sizes vary between people; nothing here describes a particular person or gives medical advice. Sources: Betts et al. 2022, §13.4; Rupp et al. 2021; Kirshblum et al. 2011; Betts et al. 2022, §11.5; Wulf and Tom 2023; Betts et al. 2022, §15.1.