1. The Physics of Human Hearing

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

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

4. 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

5. 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

6. 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

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

8. 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)

9. 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

10. 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

11. 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

12. 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

13. 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

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

15. 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