Читать книгу Neurology - Charles H. Clarke - Страница 46

Gating (also Chapter 23) means control of synaptic transmission between one set of neurones and the next. The RF has a role in gating sensory stimuli.

 Tactile sensation is gated at the posterior column nuclei. Nociceptive transmission from the trunk and limbs is gated in the posterior grey horn of the cord, and from the head in the spinal V nucleus. One crucial cord structure is the substantia gelatinosa, rich in excitatory glutaminergic neurones and inhibitory GABAergic and enkephalinergic neurones.

 Unmyelinated C fibres mediate dull, intense, prolonged, poorly localised pain. Short, sharp, well‐localized pain is mediated by finely myelinated Aδ fibres. These synapse directly on relay neurones of the lateral spinothalamic tract.

 Large A (mechano‐receptor) afferents from hair follicles and skin synapse on anterior spinothalamic cells and send collaterals to inhibitory (GABAergic) gelatinosa cells. These then synapse on lateral spinothalamic tract relay cells.

 Enhancement of RF inhibition from the magnus raphe nucleus, by rubbing, TENS, implanted stimulators, sleep and pain‐modulating drugs reduces – that is, gates – C fibre activity.

Figure 2.11 Reticular formation: (a) Nuclei (b) Principal neurotransmitter cell groups.

Source: Fitzgerald (2010).