The human ear consists of three main
parts: The outer ear, the middle ear, and the inner ear
(illustration courtesy of Virginia Merrill Bloedel Hearing Research,
UW, Seattle).
The outer ear, contains a largely
cartilaginous external projection called the pinna
and the auditory canal.
The middle ear, contains the tympanic
cavity, which is separated from the external ear by
the eardrum (tympanic membrane) and contains a chain
of three tiny bones (the malleus, the
incus, and the stapes). The auditory
bones, also called the auditory ossicles, have more
common names: the hammer, the anvil, and the stirrup,
respectively.
The inner ear
contains the cochlea. It takes its name from
the Greek word describing a snail shell. The cochlea
is a spiral tube that is coiled two and one-half
turns around the cochlear nerve. It forms a
cone approximately 9 millimeters in diameter at its
base and 5 millimeters in height. When stretched out,
the tube is approximately 30 millimeters long.
It is 2 millimeters in diameter at its widest and
tapers up to its apex.
Sound waves are funneled by the pinna
into the auditory canal. This causes vibrations
of the eardrum which are conducted and intensified by
the auditory ossicles through the tympanic cavity to
the oval window. Sound wave energy is then
transmitted to the fluid of the cochlea
and converted by the hair cells of the organ of
Corti into nerve impulses that are transmitted via
the auditory nerve to the brain.
Additional Resources:
Encyclopedia Britannica entry for "
ear, human"
extensively describes the anatomy and physiology of
the human auditory system with many figures:
MEdIC (Medical Education Information
Center) online lecture about the ear gives a good summary of auditory
anatomy and physiology with some figures by Beth A.
Hartwell, M.D.
Virtual Tour of the Ear from Augustana
College offers a large
collection of links by Perry C. Hanavan sorted by
hearing mechanism. Most links are to figures
illustrating the human auditory system.
An Inner Ear Primer from Tulane University gives a good
text-based tutorial of the inner ear.
The Cochlear Fluids Research Laboratory run by Alec N. Salt Ph.D. at the
Washington University School of Medicine contains
good brief descriptions of inner ear anatomy and
cochlear anatomy.
Promenade 'round the Cochlea is a brief tour of auditory anatomy
with attractive illustrations from the Centre Régional
d'Imagerie Cellulaire (CRIC) - Université
Montpellier 1 INSERM (Institut National de la Santé
et de la Recherche Médicale), Montpellier France.
