The sensory receptors are cells specialized to detect the signals of various senses such as vision, hearing, pain, touch, etc.
Sensory receptors can be classified by the type of stimulus that generates a response in the receptor. Broadly, sensory receptors respond to one of four primary stimuli:
- Chemicals (chemoreceptors)
- Temperature (thermoreceptors)
- Pressure (mechanoreceptors)
- Light (photoreceptors)
All sensory receptors rely on one of these four capacities to detect changes in the environment, but may be tuned to detect specific characteristics of each to perform a specific sensory function. In some cases, the mechanism of action for a receptor is not clear. For example, hygroreceptors that respond to changes in humidity and osmoreceptors that respond to the osmolarity of fluids may do so via a mechanosensory mechanism or may detect a chemical characteristic of the environment.
Sensory receptors perform countless functions in our bodies. During the vision, rod and cone photoreceptors respond to light intensity and color. During the hearing, mechanoreceptors in hair cells of the inner ear detect vibrations conducted from the eardrum. During taste, sensory neurons in our taste buds detect chemical qualities of our foods including sweetness, bitterness, sourness, saltiness, and umami (savory taste). During smell, olfactory receptors recognize molecular features of wafting odors. During touch, mechanoreceptors in the skin and other tissues respond to variations in pressure. Sensory receptors are found throughout our bodies, and sensory receptors that share a common location often share a common function. For example, sensory receptors in the retina are almost entirely photoreceptors. Our skin includes touch and temperature receptors, and our inner ears contain sensory mechanoreceptors designed for detecting vibrations caused by a sound or used to maintain balance. In some cases, the mechanism of action for a receptor is not clear. For example, hygroreceptors that respond to changes in humidity and osmoreceptors that respond to the osmolarity of fluids may do so via a mechanosensory mechanism or may detect a chemical characteristic of the environment.
Force-sensitive mechanoreceptors provide an example of how the placement of a sensory receptor plays a role in how our brains process sensory inputs. While the cutaneous touch receptors found in the dermis and epidermis of our skin and the muscle spindles that detect stretch in skeletal muscle are both mechanoreceptors, they serve discrete functions. In both cases, the mechanoreceptors detect physical forces that result from the movement of the local tissue, cutaneous touch receptors provide information to our brain about the external environment, while muscle spindle receptors provide information about our internal environment.
Adequate stimulus can be used to classify sensory receptors. A sensory receptor’s adequate stimulus is the stimulus modality for which it possesses the adequate sensory transduction apparatus.
Practice Questions
MCAT Official Prep (AAMC)
Sample Test B/B Section Passage 7 Question 39
Practice Exam 3 P/S Section Question 46
Practice Exam 4 B/B Section Passage 8 Question 42
Practice Exam 4 P/S Section Question 59
Key Points
• Chemoreceptors detect the presence of chemicals.
• Thermoreceptors detect changes in temperature.
• Mechanoreceptors detect mechanical forces.
• Photoreceptors detect light during vision.
• More specific examples of sensory receptors are baroreceptors, propioceptors, hygroreceptors, and osmoreceptors.
• Sensory receptors perform countless functions in our bodies mediating vision, hearing, taste, touch, and more.
• Sensory receptors perform countless functions in our bodies mediating vision, hearing, taste, touch, and more.
• Cutaneous touch receptors and muscle spindle receptors are both mechanoreceptors, but they differ in location.
Key Terms
Photoreceptor: A specialized neuron able to detect and react to light.
Mechanoreceptor: Any receptor that provides an organism with information about mechanical changes in its environment such as movement, tension, and pressure.
Baroreceptor: A nerve ending that is sensitive to changes in blood pressure.
Cutaneous touch receptor: A type of sensory receptor found in the dermis or epidermis of the skin.
Muscle spindle: Sensory receptors within the belly of a muscle that primarily detect changes in the length of this muscle.