Sensory Receptors: Classification

The body possesses a whole family of sensory receptors -- specialised structures able to detect a particular type of stimulus from the external or internal environment and turn it into a nerve impulse (an action potential) that is then carried to the appropriate part of the brain for processing and interpretation; a receptor's nature is entirely defined by the stimulus type it responds to, e.g. a photoreceptor responds specifically to light. Receptors are grouped into two broad classes by where their stimulus comes from. Exteroceptors receive stimuli from the external environment and include phonoreceptors (sound, in the organ of Corti), statoreceptors (balance, in the semicircular canals), photoreceptors (vision, in the retina), thermoreceptors (heat and cold, in the skin), mechanoreceptors (touch/pain/pressure, in the skin) and chemoreceptors (gustatoreceptors for taste on the tongue, and olfactory receptors for roughly 10,000 distinguishable smells in the nasal epithelium). Interoceptors instead receive stimuli arising from within the body: enteroceptors (hunger, thirst, pain, osmotic change, from internal organs), proprioceptors (joint/tendon/muscle movement, pain, tension, vibration) and baroreceptors (blood-pressure change, in the walls of the atria, venae cavae, aortic arch and carotid sinus, restoring homeostasis through vasodilation or vasoconstriction; these are also considered a kind of mechanoreceptor). The eye and the ear, covered next, are the two most elaborate exteroceptor organs in the human body. …