2. Controls natural
mechanisms for inhibition
of pain in the body
1.periventricular nuclei of hypothalamus and
periaqueductal area -
Neurons of these areas give rise to fibers
which release enkephalines on raphae nuclei
Includes descending
inhibitory pathways
3. 1. Situated in midline in
lower pons and upper
medulla.
2. It's serotonergic fibers
extend to dorsal horns of
spinal cord
2.raphae Magnus
nucleus
4. Raphae nucleus ends on dorsal horn of
spinal cord which secret enkephaline,
which in turn causes presynaptic inhibition
of A delta and also dorsal root C fibers on
substantia gelatinosa.
Thus transmission of pain signals into
spinal cord is inhibited which persist for
few minutes to hours.
3. Pain inhibitory complex
in dorsal horn of spinal
cord
5. This natural analgesic
system is stimulated by
various factors
1. Endogenous analgesic substances-
Like beta endorphin, met and leu enkephaline
etc which are secreted by anterior pituitary,
adrenal medulla, and cells of GIT.
When they combine with receptors in
periaqueductal area, this area is s�mulated and
impulses pass through descending pathway
inhibi�ng entry of pain signals in spinal cord.
6. 2. Collaterals arising from ascending
spinothalamic tract-
Can also s�mulate raphae nucleus or
PAG area 2.
Simultaneous of large diameter touch
fibers decreases transmission of pain
impulses into spinal cord by causing
lateral inhibi�on of pain fibers- GATE
CONTROL THEORY OF PAIN.
