Receptors in the skin, muscles and organs turn pressure, heat, cold and tissue damage into nerve signals. Those signals travel to the brain by two separate pathways in the spinal cord.
Receptors
Mechanoreceptors sense touch, vibration and stretch. Thermoreceptors sense warm and cold, and nociceptors respond to tissue damage and give pain.
Fast and slow pain
Thin myelinated fibers carry the sharp, well localized first pain. Unmyelinated C fibers carry the slower, dull, burning pain that follows.
Two pathways
Fine touch, vibration and joint position travel up the same side of the spinal cord in the dorsal columns and cross in the brainstem. Pain and temperature cross within one or two segments and travel up the opposite side in the spinothalamic tract.
Referred pain
Pain from an organ can be felt in the skin served by the same spinal segment. Heart pain felt in the left arm or jaw is the classic example.
| Pathway | Carries | Crosses |
|---|---|---|
| Dorsal columns | Fine touch, vibration, joint position | In the brainstem (medulla) |
| Spinothalamic tract | Pain, temperature, crude touch | In the spinal cord, near the entry level |
At the bedside
Test light touch, pinprick, temperature, vibration and joint position, and compare left with right. A dermatome map tells you which nerve root or spinal cord level is involved.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).