The outer and
middle ear mostly collect and transmit sound. The inner ear analyzes sound waves
and contains an apparatus that maintains the body's balance.
The outer ear is
the part which is visible and is made of folds of skin and cartilage. It leads
into the ear canal, which is about one inch long in adults and is closed at the
inner end by the eardrum. The eardrum is a thin, fibrous, circular membrane
covered with a thin layer of skin. It vibrates in response to changes in the air
pressure that constitute sound.
The eardrum separates the outer ear from the
middle ear. The middle ear is a small cavity which conducts sound to the inner
ear by means of three tiny, linked, movable bones called "ossicles."
These are the smallest bones in the human body and are named for their shape.
The hammer (malleus) joins the inside of the eardrum. The anvil (incus) has a
broad joint with the hammer and a very delicate joint to the stirrup (stapes).
The base of the stirrup fills the oval window which leads to the inner ear.
The
inner ear is a very delicate series of structures deep within the bones of the
skull. It consists of a maze of winding passages, called the
"labyrinth". The front (see cochlea) is a tube resembling a snail's
shell and is concerned with hearing. The rear part is concerned with balance.
"Keeping one's ear to the ground" means to keep up on current trends.
The phrase dates back to early 20th century politicians and comes from frontier
lore of both pioneers and Indians, who listened for the sound of approaching
hoofbeats.
