Year 1 · Senses, behaviour and coordination · Section 5.2

Touch, smell and taste

The epidermis

The skin has two main layers: the epidermis and the dermis. In a simplified model, the epidermis has two important regions:

Horny layer: Dead, flattened cell remains forming a protective barrier against damage, water loss and microorganisms.
Basal layer: Living cells that divide to replace cells lost at the surface. New cells move outwards, accumulate keratin, become flattened and eventually die.

The dermis

The dermis contains sensory structures and other tissues:

Touch, temperature and pressure receptors: Different receptors occur at different depths. Some detect light touch near the surface; others detect deeper pressure.
Pain receptors, nerves, small hair muscles and blood vessels: These contribute to sensation, hair movement, blood supply and temperature regulation.
Sweat glands: Produce sweat. Its evaporation cools the body.
Hair follicles: Tubes formed from the epidermis extending into the dermis, where hairs grow. Sebaceous glands open into many follicles.
Sebum: An oily substance that helps keep hair and the skin surface supple.

Subcutaneous tissue

Beneath the dermis lies subcutaneous tissue. It stores fat as an energy reserve and provides insulation against heat loss.

Burns

Burns are skin injuries caused by heat, chemicals or electricity. Damage can reduce the skin's protection:

Microorganisms can enter, increasing the risk of infection.
More fluid and heat may be lost.

Superficial burns limited to the epidermis usually heal without scarring. Deeper burns involving the dermis may leave permanent scars; the outcome depends on their depth and severity.

Smell and taste

The olfactory epithelium, high in the nasal cavity, contains smell receptor cells. Scent molecules stimulate these cells, leading to nerve impulses to the brain.

Different receptors respond to different combinations of molecules. The brain interprets the overall pattern as a particular smell.

Taste buds, mainly in structures on the tongue, contain taste receptor cells. Some lie along the sides of folds and grooves. They detect five basic tastes: sweet, salty, sour, bitter and umami (savoury).

Smell and taste work together to create the full flavour of food.

Glossary

Burn: Skin damage caused by heat, chemicals or electricity, which can reduce the skin's protective function.
Hair follicle: A tube extending from the epidermis into the skin, in which a hair grows.
Horny layer: The outer layer of dead, keratin-rich cells protecting against damage, water loss and pathogens.
Basal layer: The dividing cells that continually replace cells in the epidermis.
Dermis: The layer beneath the epidermis containing receptors, nerves, blood vessels, follicles and glands.
Subcutaneous tissue: Tissue beneath the skin containing fat for energy storage and insulation.
Epidermis: The outer protective skin layer, including living inner cells and the dead surface layer.
Sense of smell: Detection of scent molecules by receptor cells high in the nasal cavity.
Taste buds: Structures containing receptor cells for sweet, salty, sour, bitter and umami tastes.
Sense of taste: Detection of dissolved substances by taste receptors, mainly on the tongue.
Sebaceous glands: Glands producing sebum, an oily substance helping keep hair and skin supple.
Sweat glands: Glands producing sweat, whose evaporation cools the body.