Unit 2: The Ear

This video summarised the function of the ear, including information on:

The Role of the Pinna in Identifying the Height of Sounds

• The pinna is the outer part of your ear. It may seem useless, however, it plays a major role in directing sound into your ears. It is able to do so through its round and curved shape.

The Middle Ear as Transducer

• The part of the ear commonly referred to as the eardrum is a very small and thin tissue which vibrates as sound hits.

Frequency Analysis and the Inner Ear

• The inner ear contains a plethora of parts, all working in unison to produce an electrical signal that will be sent to the brain.

• Due to the vibration of the eardrum, a series of 3 bones (ossicles) move in the motion of a mechanical lever, causing the transfer of energy to the endolymph fluid in the cochlea. The cochlea is a tiny snail-shaped structure consisting of 3 semicircular rings.
• The ossicles consist of the malleus, which picks up on the vibration of the eardrum. The vibrations then moves the incus and finally the stapes, which moves in and out of the oval window.

• The sound energy transferred to the cochlea causes inner and outer hair cells along the basilar membrane to vibrate. Different hairs along the membrane will vibrate based on the frequency (pitch) of the sound wave.

• The movement of the basilar membrane causes the outer hair cell stereocilia to interact with the nearby tectorial membrane.

• This then causes the stereocilia to bend, opening the ion gates and allowing chemical reactions to take place. These chemical reactions induce an electrical signal, and, as a byproduct, a neural impulse which travels up the auditory nerve to the brain. 

• This procedure is what allows you to almost instantaneously recognise a sound.

Directional Hearing (IADs and ITDs)

• Since you are equipped with 2 ears, both on opposite sides of your body, you can tell where a sound is coming from.

• IAD, Inter-aural Amplitude Difference, is one such way that your brain recognises the direction a sound is coming from. It means that one ear will receive a sound louder than the other, and the ear in which the sound is loudest dictates the direction of the sound.

• ITD, Inter-aural Time Difference, explains where a sound is coming from by determining which ear heard it first. To state the obvious, the side of the ear that hears the sound first is where the sound is coming from.

• Both IAD and ITD work together to form accurate Directional Hearing.

This is another interesting video surrounding the topic which covers essentially the same topics as the last video, albeit with more engaging visuals and narration.