b) Pressure : is a sustained sensation that is felt over a larger area than touch occurring with deformation of deeper tissues. Receptors for sensations of pressure include Meissner Corpuscles, Merkel Discs, and Pacinian Corpuscles aka Lamellated Corpuscles. Pacinian corpuscles are large, oval shaped, and are composed of multiple layers of connective tissue enclosing a dendrite. Pacinian corpuscles adapt rapidly and are widely distributed in the body: dermis and subcutaneous layer, submucosal tissues that underlie mucous and serous membranes; around joints, tendons, and muscles; in the periosteum; in the mammary glands, external genitalia, and certain viscera such as the pancreas and urinary bladder. c) Vibration : result from rapid, repetitive sensory signals from tactile receptors. These receptors are Messiner (lower frequency vibration) and Pacinian Corpuscles (higher frequency vibration). d) Itch : result from stimulation of free nerve endings by certain chemicals often because of a local inflammatory response. e) Tickle : stimulation of free nerve endings and typically only occurs when someone else touches you.
2) Thermal Sensations
Thermoreceptors are free nerve endings having receptive fields about 1mm in diameter on the skin surface. There are 2 sensations: cold and warmth . Cold Receptors : located in the stratum basale of the epidermis. Temperatures between 10 and 35 degrees Celsius activate cold receptors. Warm Receptors : not as abundant as cold receptors are located in the dermis and are activated by temperatures between 35 and 48 degrees celcius.
3) Pain Sensations
Pain is indispensable for survival. It serves as a protective signal for the presence of noxious, tissue-damaging conditions and may help pinpoint the location of an underlying pathology. Nociceptors : receptors for pain and are free nerve endings found in every tissue of the body except the brain. These receptors can be activated by intense thermal, mechanical, or chemical stimuli. Tissue injury releases chemicals that stimulate nociceptors. Pain may persist even after the stimulus is removed due to the fact that nociceptors have very little adapting ability. Conditions that elicit pain include excessive distention (stretching) of a structure, prolonged muscular contractions, muscle spasms, ischemia (inadequate blood flow to an organ or structure).
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