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CoursesPhysiologyNervous systemGeneral sensesSensory receptors
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CoursesPhysiologyNervous systemGeneral sensesSensory receptors

Sensory receptors

Learning objectives

After completing this study unit, you will be able to:

  1. Define and classify sensory receptors based on structure, location and function.
  2. Explain the steps of sensory transduction.
  3. Understand how sensory receptors respond to changes in stimulus strength.
  4. Describe sensory receptor adaptation and distinguish between slowly and rapidly adapting receptors.

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Sensory receptors are specialized excitable cells that convert sensory stimuli into electrical impulses, which can then be interpreted by the brain. Structurally, they could be non-encapsulated (e.g., free nerve endings), encapsulated (e.g., lamellar corpuscles) or specialized sensory receptor cells (e.g., cochlear hair cells). Based on their location, sensory receptors could be exteroceptors (detect external stimuli), interoceptors (detect internal stimuli) or proprioceptors (detect joint and muscle position). Functionally, they can be classified into mechanoreceptors, photoreceptors, chemoreceptors, thermoreceptors and nociceptors.

Sensory receptors convert sensory stimuli into electrical signals by a process called sensory transduction. The stimulus generates a local potential in the receptor called a receptor potential, which in turn can trigger action potentials in the afferent neuron. The action potentials reach the brain, which can then perceive the stimulus.

Changes in stimulus intensity alter the magnitude of receptor potentials. Stronger stimuli increase the receptor potentials, which in turn lead to a higher frequency of action potentials along the afferent neuron. The stimuli also tend to spread over larger areas, activating more receptors. This helps the brain perceive stronger stimuli, while ignoring weaker ones.

However, continuous activation of the receptors reduces their firing rate. This is known as adaptation; receptors could be slowly adapting (tonic) or rapidly adapting (phasic). The slowly adapting receptors are useful for continuous monitoring of a stimulus, while rapidly adapting ones are beneficial for quickly changing stimuli.

Watch the following video to learn more about the types of sensory receptors and how they transduce stimuli.

Explore concepts

Classification of sensory receptors

Explore some of the different kinds of sensory receptors with this gallery!

Free nerve ending
Terminatio neuralis libera
1/15
Synonyms: Free nerve terminal

Sensory transduction and sensory neurons

Sensory adaptation

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Get a sense of how well you know sensory receptors with this quiz!

Summary

Key facts about sensory receptors
Definition A specialized excitable cell capable of converting sensory stimuli into electrical impulses
Structural classification Nonencapsulated receptors: Free nerve endings, hair follicle endings and epithelial tactile complexes (Merkel cell-neurite complexes)
Encapsulated receptors: Tactile (Meissner) corpuscles, bulbous (Ruffini) corpuscles, lamellar (Pacinian) corpuscles, muscle spindles, tendon organs
Specialized sensory receptors: Gustatory sensory epithelial cells, rod cells, cone cells, cochlear and vestibular hair cells
Location-based classification Exteroceptors: Detect external stimuli (cutaneous mechanoreceptors)
Interoceptors: Detect internal stimuli
(baroreceptors)
Proprioceptors: Detect joint and position sense (muscle spindles, tendon organs)
Functional classification Mechanoreceptors: detect mechanical stimuli
Photoreceptors: detect light stimulus
Chemoreceptors: detect chemical stimuli
Thermoreceptors: detect thermal stimuli
Nociceptors: detect noxious stimuli
Mechanoreceptors Cutaneous mechanoreceptors: Epithelial tactile complexes (Merkel cell-neurite complexes), tactile corpuscles, bulbous corpuscles, lamellar corpuscles, hair follicle endings
Proprioceptors: Joint proprioceptors, muscle spindles, tendon organs
Baroreceptors: Carotid sinus and aortic arch
Inner ear mechanoreceptors: cochlear and vestibular hair cells
Photoreceptors Rod cells: dim light
Cone cells: bright light, color vision
Chemoreceptors Gustatory sensory epithelial cells
Olfactory sensory neurons
Central and peripheral chemoreceptors (respiratory regulation)
Osmoreceptors (hypothalamus, vascular organ of lamina terminalis, subfornical organ)
Thermoreceptors Free nerve endings;
Cold receptors
Warm receptors
Nociceptors Free nerve endings; 
Respond to strong mechanical, chemical or extreme thermal stimuli
Sensory transduction The process by which sensory receptors convert sensory stimuli into electrical signals
Response to stronger stimulus Increase in receptor potential magnitude;
Temporal summation: Increased frequency of action potentials
Spatial summation: Activation of sensory receptors over a larger area
Adaptation With continuous activation, receptor potentials and thus action potential firing rates in the afferent neurons decline;
Tonic receptors (slowly adapting): continuous monitoring of stimulus presence
Phasic receptors (rapidly adapting): monitor change in stimulus

Continue your learning

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