1. Hearing and Equilibrium

2. Physiology of hearing
Outer ear (auricle): collects, directs sound into the external auditory canal.
Ear wax and hairs keep foreign objects out.
2. Eardrum (tympanic membrane) vibrates when sound reaches it

4. Middle ear Small, air-filled cavity
3. Malleus, incus, & stapes transmit vibrations to the oval window
Eustachian tube connects to the throat – helps equalize pressure

5. Inner ear: Cochlea 4. Cochlea Fluid-filled organ
Pressure waves in the fluid cause hair cells to vibrate
5. Round window bulges outward
6. Bending hairs release impulses to the VIII nerve to auditory center in brain.

6. Inner ear: semicircular canals
Canals and vestibule are the organs of equilibrium and balance.
Cristae: hair cells in s.c. canals detect position of the head and linear acceleration

7. 3 canals lie at right angles
Rotation of the head/body bends hairs, which send an electrical signal to the brain.

8. Equilibrium pathways Impulses reach the medulla or cerebellum.
Messages are sent to regions that control eye, head, and neck movements
Cerebellum adjusts signals from the motor cortex to maintain equilibrium.

9. Balance involves many systems working together