Balance, skin senses, smell and taste

The balance organ is the vestibular apparatus in the inner ear: two sacs (oval and round) and three semicircular canals. The sacs have hair receptors and tiny otoliths resting on them; when head position or straight-line movement changes, otoliths shift and excite receptors, while semicircular canals sense rotation. Impulses go through the vestibular nerve to the cerebellum and cortex. Dizziness and nausea after long shaking in a boat or car or long swinging on a swing are due to over-stimulation of these receptors; fresh air, resting the eyes and looking at one point help. Receptors in muscles, tendons and joints tell us the position of body parts even with eyes closed (muscle sense). Skin receptors sense touch, pressure, heat, cold and pain; they are especially numerous at fingertips, lips and the tip of the tongue. Pain is a signal of risk of harm: do not ignore strong or long-lasting pain, tell adults. Heat and cold receptors adapt: warm water seems hot at first, then pleasant. Skin sense protects from hot or sharp objects, but a burnt or frostbitten area can become numb.