Anatomy Physiology

The human ear is a unique structure in the body because of its specialized function of processing sound waves into electrical signals which are eventually perceived by us as voice.  The human ear is like the human eye limited by its ability to perceive all wave lengthes of the sound waves.  Animals probably hear better than humans, especially dogs who can perceive sound waves that are beyond the hearing capability of humans.

The ear has two important functions in humans.  These are: the processing of sound waves into electrical signals which are ultimately perceived by the auditory cortex in the brain.  The other important function of the ear is to maintain a state of equilibrium for the body.  The processing of sound waves into electrical signals is done in a structure of the inner ear which is called the cochlea.  The processing and maintaining of the equilibrium state of the body is controlled by a structure also of the inner ear and which is called the semicircular canals and the vestibule.  These two structures are connected with each other in the inner ear. 

The human ear is divided anatomically into three structures.  These are: the external ear and the middle ear in addition to the inner ear.  The external ear is composed of the auricle which is the most external part of the external ear.  It functions by collecting the sound waves and enters them inside the ear.  The auricle is connected with the auditory canal which communicates the sound into the eardrum.  The eardrum is the last part of the external ear. 

The eardrum separates the external ear from the middle ear.  In the auditory canal in the external ear there are spread hairs and specialized sweat glands that are called ceruminous glands.  These glands secrete a waxy material which is called cerumen.  This material along with the hairs in the auditory canal have a protective function for the ear in which it prevents foreign particles and pathogens from invading the ear.  Thus preventing its pathology.

The middle ear is the second anatomic structure of the ear.  It starts at the eardrum and ends at the oval window.  The middle ear is separated from the inner ear by two windows.  These two windows are covered by membranous structures that are called the oval window and the round window. 

In the middle ear there are three bones which are connected with each other by synovial joints.  They are also connected with the eardrum and the oval window in the middle ear.   These three bones are the malleus bone which is connected with the eardrum.  It vibrates when the eardrum vibrates by the impact of the sound wave which enters through the auditory canal in the external ear. 

To the malleus bone is another bone attached which is called the incus bone.  The connnection between these two bones is of the synovial joint type.  This also vibrates by the effect of the vibration of the malleus bone.  To the incus bone is attached another bone which is called the stapes.  This bone relies on the oval window and transmits through its vibration the sound waves to the inner ear structures. 

In the middle ear there is a canal which communicates with the middle ear with the throat.  This canal is called the eustachian tube.  This canal is important clinically since pathology in the throat by bacterial infection can spread to the middle ear causing otitis media or inflammation of the middle ear. 

The inner ear is composed of two physiologically distinct structures.  These are: the semicircular canal and the cochlea.  The semicircular canal is specialized in maintaining equilibrium state for the body.  There are two types of equilibrium in the body.  These are: static equilibrium and dynamic equilibrium.  These two types of equilibria are processed by two different structures in the semicircular canals and the vestibule which is a structure adjacent to the semicircular canals. 

The processing of hearing signals occurs in the structure of the inner ear which is called the cochlea.  The cochlea processes vibration that occurs in the endolymph which is a liquid material that is spread in the cochlea as a result to the vibration in the perilymph which is another liquid in the cochlea that is separated from the endolymph be a membrane. 

This process leads to activation of receptor potential in the hair cells in the spiral organ of corti.  This leads in turn to the initation of action potential that leads to the transmission of electric signals from the cochlea to the auditory area of the brain cortex.  There these signals are processed and interpreted as voices that we hear.

The nerve that receives signals from the cochlea and the semicircular canals is called the vestibulocochlear nerve.  This nerve supplies the sensory innervation from the cochlea and the semicircular canals from which the signals then are transmitted through synapting neurons to the auditory cortex in the brain.