Receptors Cutaneous and Referred Pain
Exercise 3.4
Sensory Receptors
Sensory receptors, in the skin, transduce mechanical or chemical stimuli into nerve impulses (action potentials)
Any mechanical or chemical stimuli that comes in contact with the skin will produce some form of AP along a sensory nerve
These impulses are conducted by sensory neurons into the CNS and ultimately to the region of the brain that interprets these AP
There's a region of the brain that interprets every stimuli depending on what region of the body is affected
Mapping the Temperature and Touch Receptors of the Skin
Four modalities of cutaneous sensation:
Warmth Cold Touch Pain
**pressure is excluded because it is mediated by receptors deep in the dermis
Receptors have punctate distribution which mean that sensory receptors are not generalized throughout the skin, like a grid, but rather they are clustered at different points
Two-Point Threshold
Density
of touch receptors in some part of the body is greater than in other parts Large areas (more dense) of receptors are devoted to the touch perception and motor activity of the face and hands Small areas (less dense) of receptors are devoted to the trunk, hips, and legs
Two-Point Threshold Test
Density of touch receptors is measured by the two-point threshold test.
Two points of a of pair adjustable calipers are placed on skin with equal pressure Subject is asked if two separate points are felt; if answer is yes, points are brought closer together and test is repeated until only one point is felt Minimum distance at which two points can be felt is the two-point threshold
Figure 10.5
Adaptation of Receptors
Sensory adaptation: sense receptors respond strongly to acute changes in our environment and then stop responding when these stimuli become constant
Ex. Sense of smell quickly adapts to odors One hand is placed in warm water, the other placed in cold water; both adapt to the new environmental temperature; then hands are placed in intermediate temperature water; the hand that was in the warm water now feels cold and the hand that was in the cold water now feels warm; this is because the "baseline" of the receptors has changed because of the adaptation
Our body adapts to temperature also
Referred Pain
Source of nerve stimulation is different from the perceived location of the stimulus
You hurt your back but you feel it in your leg
Phantom Limb Phenomenon: when amputees report feeling pain in their missing limb as if it were still attached Ischemic Heart Disease: pain referred to left shoulder/arm region Stomach Ulcers: pain maybe referred to region between the scapulae of the back