Hearing and equilibrium in water in vertebrates.

Our ears not only let us detect sounds, but they also help us maintain balance. Receptors for two sensory modalities (hearing and equilibrium) are housed in the ear. The external ear, the middle ear, and the cochlea of the inner ear are involved with hearing. The semicircular canals, the utricle, and the saccule of the inner ear are involved with equilibrium. Both hearing and equilibrium rely on a very specialized type of receptor called a hair cell. There are six groups of hair cells in each inner ear: one in each of the three semicircular canals, one in the utricle, one in the saccule, and one in the cochlea. Receptors in the semicircular canals detect rotational acceleration, those in the utricle detect linear acceleration in the horizontal direction, and the ones in the saccule detect linear acceleration in the vertical direction.

STRUCTURE & FUNCTION OF THE EAR

EXTERNAL & MIDDLE EAR

The external ear funnels sound waves to the external auditory meatus. In some animals, the ears can be moved like radar antennas to seek out a sound. From the external auditory meatus, sound waves pass inward to the tympanic membrane (eardrum).

The structures of the external, middle, and inner portions of the human ear. Sound waves travel from the external ear to the tympanic membrane via the external auditory meatus. The middle ear is an air-filled cavity in the temporal bone; it contains the auditory ossicles. The inner ear is composed of the bony and membranous labyrinths. To make the relationships clear, the cochlea has been turned slightly and the middle ear muscles have been omitted.

Reference: Hearing & Equilibrium _ Ganong’s Review of Medical Physiology, 25e _ AccessMedicine _ McGraw-Hill Medical