receptors

Non-Capsulated Exteroceptors

Definition:
Receptors composed of unmyelinated nerve endings without a surrounding capsule. Located mainly in the skin and detect external stimuli.

1. Free Nerve Endings

• Terminal branches of unmyelinated sensory fibers

• Form a network in the superficial dermis, with some extending into the epidermis

• Sensitive to:

  • Temperature (heat and cold)

  • Pain (noxious stimuli)

  • Crude mechanical touch

2. Hair Follicle Receptors

• Free nerve endings that surround hair roots

• Function as mechanoreceptors

• Detect movement of hair, contributing to light touch sensation

3. Merkel (Tactile) Discs

• Located in the basal layer of the epidermis (especially in glabrous skin)

• A nerve ending expands into a disc-shaped structure contacting a Merkel cell

• Function:

  • Detect fine touch and pressure

  • Important for texture and shape discrimination

• Characteristic: slow-adapting receptors

Key Summary

• Free nerve endings: pain, temperature, crude touch

• Hair receptors: movement of hair

• Merkel discs: fine touch and sustained pressure