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B.Pharm Lab. Instruction Manuals

APHE Anatomy, Physiology, and Health Education

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# 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.

[http://higheredbcs.wiley.com/legacy/college/tortora/0470565101/hearthis_ill/pap13e_ch16_illustr_ audio_mp3_am/simulations/figures/pain.jpg]

Fig. 1. Referred pain