Algonquin College
8.6 - The Senses
The senses help guide our experiences and physiological functions by gathering information about our external environment. There are two categories of senses: general and special senses.

Types of receptors

Receptors for sensory organs come in three basic types: mechanoreceptors, photoreceptors and chemoreceptors.

Mechanoreceptors detect the physical forces of movement. The neurons of mechanoreceptors send action potentials when they are stretched and moved physically.

Photoreceptors are sensitive to light, which is electromagnetic radiation in the visible spectrum. Different photoreceptors respond to different colours of light, which represent higher energy and lower energy light.

Chemoreceptors respond to dissolved chemicals, which come into contact with the cell membranes of chemoreceptors. The contact of specific chemicals with a matching chemoreceptors triggers the chemoreceptors to send action potentials. Olfactory (smell) and gustatory (taste) receptors are chemoreceptors and respond to many of the same stimuli.

General senses

The mechanoreceptors of the general senses gather information about our body position and contact between our body and objects and surfaces. The general senses guide our somatic sensation or "body sense", which tells us where our limbs are positioned in space and about contact and pain on our skin.

Touch receptors are cutaneous sense organs which sense mechanical pressure and can detect light touches with light touch receptors or deep pressure with deep pressure receptors. Specialized touch receptors can also detect pain to prevent further injury if the skin is damaged.

Proprioceptors are found in muscles and tendons and sense tension in those tissues. The degree of tension in specific tendons and muscles is interpreted by our CNS to tell us where our limbs are positioned in space.

Special senses

The special senses include vision, hearing, taste and smell. Each special sense is designed to accurately detect specific types of stimuli. Taste and smell detect dissolved chemicals with chemoreceptors. Vision detects light and colour with photoreceptors. Hearing detects sound with mechanoreceptors.

Sensory adaptation

Both the general and special senses adapt quickly to repetitive stimuli. If any sense has been exposed to the same stimulus (ie. a certain smell) for an extended period of time (seconds to minutes), the sensory receptors become less sensitive to that stimulus. The receptors decrease the rate at which they send action potentials, which dampens our perception of the repetitive stimulus. This sensory adaptation is crucial in allowing us to sort new and relevant information from unimportant (consistent) information in our environment.