In case a small stimulus causes more pain, it is called:

- Increase in sensitivity of pain receptors is called hyperalgesia (mostly due to inflammatory mediators) - Small Noxious stimulus giving exaggerated pain sensation - Causes Excessive sensitivity of pain receptors => primary hyperalgesia Facilitation of sensory transmission => secondary hyperalgesia (mainly due to lesions of spinal cord and thalamus) Hypersensitivity - Undesirable reactions produced by normal immune system - E.g. allergies & autoimmunity Allodynia - Non - noxious stimulus gives pain - E.g. trigeminal neuralgia Causalgia - Burning type of pain caused by crushing, injuries to nerves. (neuropathic pain) Nociceptive pain: - Noxious stimulus leads to corresponding degree of pain