3.5.3 Pharmacology I
Lab 11 Evaluation of analgesic action of Tramadol on rats using hot plate analgesiometer
Theory: Algesia or pain is a protective response against noxious, tissue damaging stimuli.
It is a somatic sensation arises from the stimulation of sensory receptors, called nociceptors. Nociceptors are free nerve
endings found in every tissue of the body except in brain and any kind of intense thermal, mechanical or chemical stimuli
can stimulate them. The threshold stimulus to initiate pain response is same for everyone, but the degree of tolerance of
the pain varies.
The impulse, generated due to activation of such type of receptors can be conducted towards central nervous
system (CNS) either by A $\delta$ fibre (long, myelinated) or C fibre (short, unmyelinated). The perception of fast pain (acute)
occurs, if propagation occurs through A $\delta$ fibre and the perception of slow pain (chronic) occurs, if it is propagated
through C fibre. Pain arises from the stimulation of the nociceptors in the skin is called superficial somatic pain
and stimulation of receptors, present in the skeletal muscles, joints, tendon and fascia causes the deep somatic pain.
Visceral pain arises from the stimulation of nociceptors of visceral organs. There is another type of pain that is felt
elsewhere of the body apart from the affected area due to diffuse stimulation of the receptors, called referred pain.
Fig. 1. Referred pain
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