The human senses

The senses are the systems through which the body gathers information about its surroundings and its own internal state. The traditional five senses are sight, hearing, smell, taste and touch, but human perception also includes balance, the sense of body position, temperature and pain. Each sense begins with specialised receptor cells that respond to a particular form of energy or chemical and convert it into nerve signals, which travel to the brain to be interpreted.

Smell and taste are the chemical senses, because they respond to molecules rather than to light or vibration. Receptors in the lining of the nose detect airborne odour molecules, while taste buds on the tongue distinguish basic qualities usually listed as sweet, sour, salty, bitter and savoury. The two senses work closely together, which is why food seems to lose its flavour when the nose is blocked. In many animals, and possibly to a limited degree in humans, chemical signals called pheromones influence behaviour between members of the same species.

Hearing and sight rely on physical energy. The ear converts pressure waves in the air into nerve impulses, allowing both hearing and the sense of balance. The eye focuses light through the cornea and lens onto the retina, where light-sensitive cells begin the process of vision. The skin provides the sense of touch, with separate receptors for pressure, vibration, warmth, cold and pain. Pain is a protective sense that warns of injury or harmful conditions. Together these systems give a continuous, integrated picture of the world that guides movement, feeding and survival.

Frequently asked questions

Why are smell and taste called the chemical senses?

Because their receptors respond directly to molecules — airborne odour molecules in the nose and dissolved substances on the tongue — rather than to light or sound.

Why does food taste bland when you have a cold?

Much of what is perceived as flavour comes from smell. When congestion blocks odour molecules from reaching the nasal receptors, food seems to lose its taste.

What are pheromones?

Pheromones are chemical signals released by an animal that can affect the behaviour or physiology of other members of the same species.