The Physics of Human Hearing

Ear overview The ear consists of three sections : the outer ear, middle ear and inner ear

The Outer Ear The outer ear consists of the pinna, the auditory canal and the ear drum (tympanum)

The Outer Ear The pinna acts as a concave reflector focusing sound into the ear The pinna also acts to magnify the volume of sounds within human hearing range The auditory canal allows for the transfer of sound vibrations to the ear drum The auditory canal also protects the ear drum through the use of ear wax

The Outer Ear : Ear Drum The Ear drum or tympanum is a thin tissue which is free to vibrate The ear drum should completely close off the auditory canal

Problems with the Ear Drum The ear drum is incredibly thin so it is susceptible to damage through punctures A puncture will alter the vibrational characteristics of the tissue

Middle Ear The middle ear consists of a chain of small bones collectively called the ossicular chain

The ossicular chain consists of three small bones linked together. These bones are free to move The bones create a chain connecting the ear drum to the opening of the inner ear (the cochlea)

Function of the middle ear The ossicles serve two important functions To transmit vibrations from the outer ear to the inner ear To act together as a system of levers capable of increasing the amplitude of the vibration by a factor of three

Inner Ear The inner ear consists of the cochlea which is a snail-shell shaped organ The cochlea is filled with a fluid and tiny little hairs

Cochlea The end of the ossicular chain connects to a thin window of tissue on the cochlea referred to as the oval window Movement of the ossicular chain creates waves within the fluid of the cochlea The hairs embedded in nerve cells can pick up these vibrations

Different frequencies of sound will excite vibrations within the cochlea at different regions Low frequency sounds travel the length of the cochlea High frequency sounds vibrate at the oval window

When the hairs inside the cochlea are excited it causes a pulse of electricity to be generated at the nerve cell The cochlea acts as an analog to digital converter This pulse of electricity is sent along the auditory nerve to the brain to be interpreted as sound

Other structures within the ear Semi circular canals Fluid filled tubes responsible for our sense of direction Use gravity Also useful for sensing acceleration

Eustachian tube Connects the middle ear to the outside world Acts as a pressure release valve In many children the Eustachina tube is not fully developed upon birth and these children require tubes