Structure and Function: Sensory Receptors

Sensory receptors respond to stimuli and transmit data about them to the brain. In the skin, receptors detect touch, pressure, vibration, temperature, and pain. Elsewhere in the body, more specialized receptors detect light (see How the eye works), sound (see The mechanism of hearing), smell, and taste. Internal receptors called proprioceptors sense body position and the location of body parts in relation to each other.

Touch

Touch receptors are found all over the body. The most common are free nerve endings, which sense pain, pressure, and temperature in addition to touch. Other touch receptors include Merkel’s discs and Meissner’s corpuscles, which detect light touch, and Pacinian corpuscles, which sense deep pressure and vibration.

Receptors in the skin

Merkel’s discs and Meissner’s and Pacinian corpuscles end in a capsule. Free nerve endings are uncovered.

Pacinian corpuscle

This receptor consists of a nerve ending surrounded by layered membranes. Pacinian corpuscles are found in the palms, soles, genitals, and nipples.

Smell

Olfactory receptors in the roof of the nasal cavity are stimulated by odours. Nerve impulses from these receptors travel to the olfactory bulb (the end of the olfactory nerve) and then to the olfactory centres in the brain. Our sense of smell is thousands of times more sensitive than our sense of taste, and we can detect more than 10,000 odours.

Olfactory receptors

When odour molecules enter the nose, they stimulate the cilia (tiny hairs) attached to receptor cells, causing nerve impulses to pass to the olfactory bulb and then to the brain.

Taste

There are about 10,000 taste buds on the upper surface of the tongue. Each bud contains about 25 sensory receptor cells, on which tiny taste hairs are exposed to drink and food dissolved in saliva. Buds sense the five basic tastes: bitter, sour, salty, sweet, and umami (a savoury, meaty taste). A combination of odours and these basic tastes produce more subtle tastes.

Taste bud structure

Substances in the mouth come into contact with taste hairs on the tongue. These tiny hairs generate nerve impulses that travel along nerve fibres to a specialized area of the brain.

Proprioceptors

Proprioceptors are types of internal sensory receptors that monitor the degree of stretch of muscles and tendons around the body. This information gives us our sense of balance and our awareness of the position of various parts of the body in relation to each other.

Muscle proprioceptors

Two types of muscle proprioceptor are annulospiral sensory endings, which wind around the muscle fibres, and spray endings, which lie on top of the fibres.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

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