Detection of pain: central nervous system

Detection of pain: central nervous system

The superficial layers of the dorsal horn of the spinal cord laminae I to III are crucial for the reception and modulation of nociceptive input, altering the relationship between stimulus and response In this zone there are complex interactions between primary afferent sensory neurones, the second-order neurones with which they synapse, excitatory and inhibitory local interneurones, and descending polysynaptic pathways from the limbic system, hypothalamus and brainstem regions including the periaquaductal grey matter and nucleus raphe magnus . Descending fibres releasing serotonin (5-HT), noradrenaline and gamma-aminobutyric acid (GABA) contact dorsal horn neurones. Many of the modulatory interneurones release enkephalins, a family of endogenous opioid peptides that inhibit nociceptive input at presynaptic and postsynaptic sites.

In this topic:

Diagram of nerve pathways and some of the neurotransmitters involved in nociception (Figure 1.2)

Ascending pathways

Descending pathways

The spinal cord and the first central synapse

Central analgesic receptors

Summary of possible receptors on presynaptic and postsynaptic structures in the dorsal horn of the spinal cord, and sites of analgesic/adjuvant action (Figure 1.3)