Jamal's Seminar

Orofacial Thermoreceptors

Thermoreceptors 

Definition: They are sensory nerve endings ( free nerve endings in the epithelium) that respond to a thermal stimulus.

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Thermal gradation are discriminated by: 

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A) cold receptors B) warmth receptors c) pain receptors which associated with extreme degree of cold and heat Cold receptors are Aδ myelinated nerve endings while warmth receptors are type C nerve fibers

CONTD 

Position of thermoreceptors:  The cold and warmth receptors are located immediately under the skin at discrete separated spots ( in the epithelium and mucus membrane ) 

Skin is generally sensitive to both cold and heat but most sensitive areas are:

contd 

For Heat receptors: finger tips, nose, elbows (hence hold hot drinks cupped in hands and close to face in a cold day)

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For Cold receptors: upper lip, nose ,chin, chest (hence sip cold drinks on hot day or put fan at face level)

Sensory Nerve Endings in Skin

contd 

Number of cold receptors 3-10 times more than warmth receptors

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Number of cold receptors in orofacial region:   

a) In lips 15-25/cm² b) about 4/cm²in oral cavity c) 3/cm² in other facial regions

Stimulation of Thermoreceptors 

In very cold regions, near the freezing point, or when even skin actually freezes, pain- cold fibers can not be stimulated, and that is why anesthesia is not needed in cryosurgery

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At 10-15°C pain-cold fibers cease

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Cold fibers reach peak level at 24°C and cease at 40°C interestingly cold receptors fire again at temperature higher than 45°C due to damage to cold sensory endings.

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Warmth fibers are stimulated at 30°C but faded out at 50°C

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Heat- pain fibers are stimulated at 45°C

Thermal stimulation

Adaptation of thermoreceptors 

When a cold receptor is suddenly subjected to an abrupt (rapid) fall in temperature ,it becomes strongly stimulated at first but this fades rapidly during few seconds, and progressively more slowly during next 30 minutes but never 100%

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This is why when temperature of skin is actively falling person fell much colder than when the temperature remains cold at the same level

Adaptation of thermoreceptors Diagram:

Contd 

Thermoreceptors respond transiently to the direction of a temperature change so the sensation produced by a small change in temperature depends on the current skin temperature. For example, a stimulus of 35°C feels warm if the skin is at 30°C, and cools if the skin is at 40°C.