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Touch and Temperature Sensation

Touch Sensation

  • Sensation Mechanism

    • Touch is sensed by mechanoreceptors located in the skin.

    • Mechanoreceptors can be found in different layers of the skin, including:

    • Epidermis

    • Dermis

    • Layers beneath the dermis.

  • Types of Mechanoreceptors

    • Different mechanoreceptors respond to various types of mechanical stimulation. Examples include:

    • Steady pressure

    • Fluttering or stroking

    • Vibrations

    • Skin stretch

    • Some are linked with hair cells to sense hair movement.

  • Receptor Classification

    • Mechanoreceptors can be classified into:

    • Simple receptors:

      • Characteristics:

      • Free dendrites

      • Lack of complex coverings.

    • Complex receptors:

      • Characteristics:

      • Surrounded by specialized structures (often termed as fancy hats) to assist in sensation.

Receptor Adaptation

  • All mechanoreceptors exhibit quick adaptation.

    • Phasic receptors:

    • Definition: Receptors that rapidly adapt to constant stimuli and cease to respond even when the stimulus remains unchanged.

    • Example: A person feels their shirt's touch initially after putting it on but gradually does not notice it throughout the day.

Key Points about Touch Sensation

  • Touch is mediated by mechanoreceptors responsive to mechanical stimulation.

  • There are diverse types of mechanoreceptors that are specialized for distinct mechanical stimuli.

  • Mechanoreceptors, whether simple or complex, adapt quickly (phasic).

Temperature Sensation

  • Temperature is detected by two types of thermoreceptors:

    • Cells or neurons specifically designed to sense temperature changes.

    • Notable point: Extreme temperatures are sensed via pain receptors (nociceptors) rather than thermoreceptors.

  • Types of Thermoreceptors

    • Historically recognized two main types:

    • Warm receptors: Most active at warm temperatures.

    • Cold receptors: Most active at cold temperatures.

  • Recent Discoveries

    • Research has revealed the existence of a third type of thermoreceptor active in responding to both cold and warm temperatures, but comprehensive details on this will not be covered in the class.

Temperature Sensation Graph

  • A graph is used to illustrate:

    • The activity rate of thermoreceptors concerning temperature exposure.

    • Body temperature is around 35 degrees Celsius (or 98.6 degrees Fahrenheit).

Activity Characteristics of Thermoreceptors

  • Cold receptors:

    • Most active: Temperatures lower than body temperature.

  • Warm receptors:

    • Most active: At temperatures higher than body temperature.

  • Extremes:

    • At very hot or cold temperatures, both thermoreceptors' activity drops to zero, leading to sensations of pain mediated by nociceptors instead of thermoreceptors.

Additional Implications on Temperature Sensation

  • Temperature receptor sensitivity can vary based on:

    • Subcutaneous fat levels

    • Estrogen levels: These can affect receptor activity and the range of temperature detection.

  • Habituation: Repeated exposure to specific temperatures may influence thermoreceptor sensitivity.

  • Thermal Neutral Zone:

    • Definition: The range of temperatures in which the body does not exert energy to heat or cool itself.

    • Recent findings suggest that this zone has narrowed over time due to environmental protection (e.g., wearing jackets, staying in heated homes).