THE EAR

The ear is responsible for hearing and equilibrium/balance, and has 3 parts:

1. OUTER EAR:

2. MIDDLE EAR:

3. INNER EAR:

BALANCE AND POSITION IN SPACE

  1. STATIC EQUILIBRIUM
  2. At the entrance to the inner ear is the VESTIBULE which contains two sacs of fluid called the UTRICLE and the SACCULE which are floating in perilymph. They are sensory organs responsible for detecting and transmitting information regarding balance, position in space, acceleration, and deceleration. Suspended in the fluid are calcium carbonate particles called OTOLITHS. As the head moves from one position to the other, these ear stones will move too. The otoliths brush against sensory nerve hairs that line the utricle and saccule, which depolarize and send a message to the brain.

  3. DYNAMIC EQUILIBRIUM

The SEMICIRCULAR CANALS also contain fluid and are responsible for detecting changes in motion. There are three semicircular canals (all at different angles), each responsible for detecting motion on a different plane. Within the canals are nerve hairs which sense changes in the movement of the perilymph fluid and depolarize, thus sending a message to the brain. Ex: spinning in a circle

HEARING

The events that take place to hear a sound are:

  1. Sound waves are collected by the pinna, travel down the auditory canal and cause the tympanic membrane to vibrate.
  2. The tympanic membrane causes the malleus (hammer) to vibrate, which transfers this energy to the incus (anvil) and then to the stapes (stirrup), amplifying the sound each time as the bones get smaller each time. The stapes rests on the oval window.
  3. The oval window vibrates and sets the perilymph of the inner ear in motion. The pressure waves travel through the canals of the cochlea and cause the basilar membrane to move.
  4. The hair cells resting on the basilar membrane vibrate against the overlying tectorial membrane, causing them to fire (the organ of Corti).
  5. This message is relayed to the auditory nerve that carries it to the brain for processing.
  6. The energy of the pressure wave in the cochlea is released when the wave hits the round window, which stretches out and absorbs the energy.

Conductive hearing loss occurs in the outer or middle ear and can be repaired with hearing aids and surgery. Sensory hearing loss is in the inner ear and cannot be repaired, hair cells cannot regenerate.