HEARING AND EQUILIBRIUM

PHYSIOLOGY OF HEARING

1. 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

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

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.

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

• 3 canals lie at right angles• Rotation of the head/body bends hairs,

which send an electrical signal to the brain.

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.

Balance involves many systems working together