Hearing Lecture

 The Ear

Outer Ear - The Pinna and the Ear Canal basically act as a guide to sound waves, directing them down the ear to the ear drum. The Pinna also acts in such a way that it can collect information on the direction and source of a sound wave as it hits your ear. This part of the ear also acts as an amplifier for the sound that you hear. 

The Middle Ear - The sound heard travels down your ear canal to the ear drum causing it to vibrate. The vibration by the ear drum is transferred through small bones called Ossicles, and this vibration causes the Cochlea to vibrate. The vibrations actually reduce power loss in the sound wave and once at the Cochlea is transferred to the fluid medium in the Cochlea. Loud noises/sounds create excessive amounts of vibration in the Ossicles which can damage hearing, therefore, there is a neuro-muscular feedback system in your ear that helps to protects your hearing from damage.

The Inner Ear - Vibrations in the oval window creates waves in the cochlear fluid which in turn causes the cochlear perform a spectral analysis. Sensor cells cause neurons in the auditory nerve to react. The timing, amplitude, and frequency information is taken to the auditory brain stem where neural processing takes place.

Malleus - a small hammer shaped bone also known as an ossicle which is part of the middle ear.

Stapes - Transmits the sound vibrations from the incus to the cochlea.

Incus - Connects the Malleus to the Stapes.

Scala Vestibuli - filled cavity inside the cochlea that conducts the vibrations to the scala media.

Scals Media - Also know as Cochlea Dust, it is also a filled cavity inside the cochlea.

Scala tympani - function is the same as scala vestibuli and is to transduce the movement of the air that casue the vibrations in the ossicles.

Organ of Corti - This section contains the auditory sensory cells. which in turn connect to the brain. This is only found in mammals.

Impendance Matching is a very important mechanism in the middle ear. It transfers vibrations ceated by the sounds your hear from the large tympanic membrane to the smaller oval window in the middle ear. The reason this is vital is that the oval window is low impedance and this is needed as high impedance vibrations of the cochlear fluid will reduce the energy transmitted dramatically to 0.1%.

Auditory Brainstem

The main features of auditory brainstem processing are that there is a two channel set of time domain signals in contiguous, non linearly spaced frequency bands; There is separation of the left from the right ear signals; low from high frequency information; timing from intensity information; re-integration and re-distribution at various specialised processing centres; binaural lateralisation; binaural unmasking; listening in the gaps and channel modelling.