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Sensory receptors

Sensory receptors enable us to see, hear, taste and smell, as well as to perceive touch, pain, temperature and body position. They also enable the body to subconsciously detect changes in blood volume and the concentration of mineral salts, gases and nutrients in the blood.

The sensory receptor transmits information

A sensory receptor is the ending of a neuron or of a part of a cell that responds to an internal or external stimulus by generating a nervous impulse. In human beings, sensory receptors may be classified by the type of stimulus to which they respond, like mechanical stimulation (or pressure), light, temperature or chemical substances. The particular stimulus to which they respond mainly depends on the sensory organ in which they are located and its location in the body.

A unique transmission mode for each sense

The body’s sensory receptors all respond in the same way to a specific stimulus through proteins that are activated at that moment. For example, light hitting the retina causes a small proportion of its cells to rotate (photopigments). In the inner ear, the proteins in some cells are sensitive to the force of sounds or head movements. Likewise, proteins in the membrane of some skin cells detect pressure applied to the skin. Last but not least, odour molecules bind with the proteins in the olfactory cells of the nose.

Whilst the signal transmitted, known as action potential or nervous impulse, is identical regardless of the receptor activated, it is the type of cell transmitting it and the body part where the cell is located that will enable the brain to interpret the message.

When our sensory system economises

The sensitivity of a sensory receptor depends on how frequently it has been stimulated recently. If stimulation is constant, like when we are exposed to continual background noise or a strong smell, the sensory receptor adapts by reducing the number of nervous impulses produced in response to the stimulus. Receptors are therefore more sensitive to irregular stimulation. This adaptation thus enables the sensory system to use nervous impulses more sparingly.