3. BRAIN ANALGESIA SYSTEM
Endogenous capability of the brain itself to suppress the input of
pain signals to the nervous system by activating a pain control
system, called an analgesia system.
4. THE ANALGESIA SYSTEM
1) The periaqueductal gray and periventricular areas
of the mesencephalon and upper pons surround
the aqueduct of Sylvius and portions of the third
and fourth ventricles.
from these areas signals (via enkaphalic neurons)
to
2) The raphe magnus nucleus -
located in the lower pons and upper medulla
The nucleus reticularis paragigantocellularis-
located laterally in the medulla and send to
dorsal horn of Via serotoninergic neurons
5. second-order signals are transmitted to
(3) a pain inhibitory complex located in the dorsal horns of the spinal
cord.
These serotoninergic neurons terminate at interneurons that
presynaptically inhibit the transmittion of impulse from primary
afferent fibers to second order neurons.
• Analgesia signals can block the pain before it is relayed to the
brain by release of Enkaphalin hat inhibits the release of
substance p from pre synaptic endings; inhibiting the pain
pathway of dorsal column.
6. GATE CONTROL THEORY OF PAIN
• Dorsal column act as a gate for transmission of pain.
Activation of large myelinated fibres reduce pain,
giving collaterals in substanstia gelatinosa and dorsal
horn of spinal cord inhibiting the pain fibres
presynaptically
• Thus, the dorsal horn is the GATE through which the
pain impulses reach the lateral spinothalamic system
7. MECHANISM OF ACTION
Opioid receptors. Acts on G-Protein coupled receptors. Inhibits Adenyl
cyclase.
Promotes opening of K* channels & inhibits opening of Ca² channels.
↓
Reduces neuronal excitability & increases K conductance.
↓
Causes hyper polarization & shows inhibitory pathway & relieves pain.
8.
9. FUNCTIONS OF ENKEPHALIN
• Enkephalin cause
• Presynaptic and
• Postsynaptic
• Inhibition of incoming
• Type C and
• Type A Delta pain fibers….
• Where they synapse in the dorsal horns.
• The analgesia system can block pain signals at
the initial entry point to the spinal cord.
10. BRAIN’S OPIATE SYSTEM
• Injection of minute quantities of morphine
• Either into the periventricular nucleus around the third
ventricle or
• Into the periaqueductal gray area of the brain stem
• Causes an extreme degree of analgesia.
• Morphine-like agents – opiates:
• Act at many other points in the analgesia system,
including the dorsal horns of the spinal cord
11. Activation of
THE ANALGESIA SYSTEM
by nervous signals entering
the periaqueductal gray and periventricular areas,
or
Inactivation of
Pain pathways by morphine-like drugs,
can almost totally
suppress many pain signals entering through
peripheral nerves.
12. INHIBITION OF PAIN TRANSMISSION BY TACTILE
SENSORY SIGNALS
• Stimulation of large type Aβ sensory fibers
• from peripheral tactile receptors
• depress transmission of pain signals
• from the same body area.
• Local lateral inhibition in the spinal cord
• The simultaneous
• physical and
• psychogenic excitation of the central analgesia
system
• the basis of pain relief by ACUPUNCTURE.
