Activation of pain transmission nerves

Cases studies
Activation of pain transmission nerves Muscle contraction Inflammation Nerve root compression

Nerve fibers that transmit pain ("pain nerves") are called Adelta-C or "capsaicin sensitive". They are very thin and numerous. They leave the spinal ganglions, where their cellular body is located, and branch into two extremities:

the peripheral end runs along the nerve root to sensory sites. You may find these nerve fiber endings in the external part of the disc fibrous ring as well as in the bone underneath the facet joint.

the central part contacts with a spinal cord cell, which transmits this sensitivity to the brain.

Pain nerves contain different substances (called "neurotransmitters" or "neuromodulators"). When nerves are activated they release these substances. Depending on the extremity and the delivered substance, the effects may differ. For example: in case of a disc herniation:

The nucleus pulposus substances activate the peripheral extremity of the pain nerves located within the fibrous sheath. When activation occurs, these ends:
1. Send their activation to its central extremity, transmitting the painful sensation to the spinal cord.
2. Release neurotransmitters that essentially contain Substance P (SP), CGRP and NKA, unleashing neurogenic inflammation of the herniated disc. From thereon, the herniated material may increase in volume, compressing the nerve root.
When the central extremity is activated:
1. It initially releases glutamate. Glutamate activates the spinal cord cell, that:
  1. Transmits pain to the brain, and the patient begins to notice pain as of this moment,
  2. Starts muscle contracture through a reflex mechanism
2. If pain nerve activation lasts longer, substance P is released and, if released during sufficient time, this neurotransmitter activates a special receptor at the spinal cord cell. Activation of this receptor, called the NMDA receptor, conditions cell structural changes and is responsible for constant activation. Consequently, if pain persists during sufficient time, it may remain, although its initial cause may have disappeared.

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