THE EAR is a sensory organ responsible for both hearing and maintenance of balance composed of three sections: the outer, middle and inner ear.

The Outer Ear: The Pinna: the outer flap that funnels sound towards the auditory canal Auditory Canal: a tube that carries sound towards the eardrum, it contains wax secreting cells; the wax traps dust etc.

The Middle Ear: Tympanic Membrane (Ear drum):a membrane that closes off entry into the middle ear; vibrates when sound waves reach it.

Ossicles: three small bones (Hammer, anvil and stirrup) that amplify the sound vibrations from the ear drum and carry them to the oval window.

Oval Window: a small membrane that seperates the middle from the inner ear. Transmits vibrations from the ossicles to the inner ear.

Eustachian Tube: a tube that connects the middle ear with the throat; used to equalize pressure between the atmosphere and the middle ear.

The Inner Ear: Vestibule: contains two small sacs called the Utricle and Saccule, aid in establishing head position. (Static Equilibrium)

Semicircular Canals: 3 tubes arranged at different angles, filled with a fluid that helps in establishing body position (Dynamic Equilibrium)

Cochlea: a snail shaped organ containing a fluid and specialized hair cells that move when vibrations from the oval window occur. The hair cells respond differently to sound waves of different frequencies and intensities.

Auditory Nerve: transmits information to the brain from the inner ear on balance and sound.

STEPS INVOLVED IN HEARING sound is a form of energy that travels in waves it is the movement of these waves that initiates the hearing process :

1.When sound waves reach your ear; they push against the tympanic membrane causing it to vibrate. 2.The vibrations are transferred to the ossicles; which concentrate and amplify the sound.

3.The vibrations from the last bone, the stirrup, cause the movement of the Oval Window inwards 4. The movement of the window initiates movement of a fluid found within the Cochlea.

5.This fluid movement stimulates the Basilar Membrane of the Organ of Corti; the technical name given to the hearing apparatus in the Cochlea.

6.Attached to the basilar membrane are Hair Cells that will bend in response to the stimulation.

7. The bending hair cells stimulate sensory neurons that transmit the information through the Auditory Nerve to the Temporal Lobe of the Cerebrum.

Different Hair cells have different threshold levels that will depolarize depending on the frequency or intensity of the sound.

Maintenance of Balance two components to balance:

1. Static Equilibrium: balance involving the position or movement of the head. head position is determined by the two fluid filled sacs (Utricle and Saccule) found in the vestibule.

in the fluid are suspended particles called OTOLITHS. when the head moves, the otoliths moves; this causes movement of the hair cells that line the interior of the sacs

the hair cells stimulate sensory neurons that carry information to the brain, through the auditory nerve, regarding head position

2. Dynamic Equilibrium balance involving the movement of the body involves the movement of the fluid found in the SEMICIRCULAR CANALS

when we move, the fluid moves causing the movement of hair cells that line the canals.

when the hair cells move, they stimulate sensory neurons which will carry information regarding body position to the brain through the auditory nerve.