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Classifications

According to their locations
o Exteroceptors: They are located at the body surface and detect external
stimuli. (e.g., touch, light pressure, deep pressure, cutaneous pain,
temperature, smell, taste, sight and hearing).
o Proprioceptors: Are located within the skeletal system and provide
information about orientation, skeletal position, tension and movement.
Such receptors include the vestibular apparatus of the ear, tendon organs
and neuromuscular spindles.
o Interoceptors: Are located within the visceral organs and respond to
stimuli from viscera (e.g., visceral pain, hunger and thirst).

According to energy sensitivity:
Mechanoreceptors: Are sensitive to mechanical distention (e.g., receptor for the state
of distention of hollow viscera such as gastrointestinal tract and urinary bladder).
Chemoreceptors: Are sensitive to changes in the chemical composition of the blood.
Thermoreceptors: Are sensitive to changes in body temperature.

According to their morphology:
• Non-encapsulated receptors: have no surrounding capsules.
• Encapsulated receptors: surrounded by capsule of perineural
epithelium.

Non-encapsulated receptors

Free nerve endings

• They are non-myelinated, small terminal branches of afferent nerve fibers
found in the connective tissue throughout the body.

• They detect sensory stimuli such as temperature, touch and pain.
Hair follicle terminals

• They are free nerve endings derived from myelinated axon and extend
among the epithelial cells of the hair follicles.

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