Theory question 101
Sense Organs(a) Explain briefly how the human ear carries out its function of balancing. (b)(i) Make a drawing 8 cm – 10 cm long of the structure of the human ear and label fully. (ii) Describe briefly the structure of the middle ear in humans.
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(a) Balance is controlled by the inner ear: the three semicircular canals (at right angles to each other, one for each plane) and the utriculus and sacculus are filled with endolymph. When the head moves, the endolymph moves and bends the sensory hair cells in the ampullae (or the otoliths in the utriculus/sacculus shift with gravity). The hair cells send impulses along the auditory (vestibular) nerve to the cerebellum, which interprets them and sends impulses to muscles to keep the body balanced.
(b)(i) Drawing 8–10 cm with title and labels: pinna, external auditory meatus, tympanum (eardrum), malleus, incus, stapes, oval window, round window, Eustachian tube, semicircular canals with ampullae, utriculus, sacculus, cochlea, auditory nerve; outer, middle and inner ear marked.
(ii) The middle ear is an air-filled cavity in the skull bone between the eardrum and the inner ear; it contains three small bones (ossicles): malleus (hammer) attached to the eardrum, incus (anvil) and stapes (stirrup) fitting into the oval window; they are linked to one another and pass and amplify vibrations; the Eustachian tube connects the middle ear to the throat (pharynx) and keeps air pressure equal on both sides of the eardrum; the round window is also on its inner wall.
Name the semicircular canals, endolymph and hair cells and say how they detect movement.