Brain’s Opiate System— Endorphins and Enkephalins Dynorphin is found mainly in the same areas as the enkephalins, but in much lower quantities.
Thus, although the fine details of the brain‘s opiate systemare not understood, activation of the analgesia systemby nervous signals entering the periaqu eductal gray and periventricular areas, or
inactivation of pain pathways bymorphine-like drugs, can almost totally suppress many pain signals
entering through the peripheral nerves.
Inhibition of Pain Transmission by Simultaneous Tactile Sensory Signals Another important event in the saga of pain control was thediscovery that stimulation of large-type
A
sensory fibers from peripheral tactile receptors can depress transmission
Periventricular nuclei
Figure 48-4 Analgesia system of the brain and spinal cord, showing (1) inhibition of
incoming pain signals at the cord level and (2)presence of enkephalin-secreting neurons that
suppress pain signals in both the cord and the brain stem.Unit IX The Nervous System: A. General Principles and Sensory Physiology588
of pain signals from the same body area. This
presumablyresults from local lateral inhibition in the spinal cord.It explains why such simple
maneuvers as rubbing the skin near painful areas is often effective in relieving pain.
