CN VIII and central Auditory nervous system

• -afferent and efferent fibers gather in a twisted bundle within the modiolus, which is the conically shaped central core of the cochlea
• -fibers from outside of bundle are for high Hz
• -fibers from inside or apex of bundle are for low Hz

• 1.mechanical deformation of stereocilia produces an electric potential which causes a liberation of neurotransmitters which initiate an electric potential  in the auditory nerve.
• 2.neural spikes are produces that travel along the nerve to the cochlear nucleus.  spike rate is proportionate to the size of BM displacement
• 3. the action potential of the whole auditory nerve is a combination of the spikes of many individual neurons

• as amp goes up so does the rate of firing(#of spikes/sec)
• -low intensities= the signal activates neurons at or near the characteristic freq
• -as intensity goes up more fibres at or near the characteristic freq start to fire too.

the auditory nerve is organized so that each freq corresponds to a place within the nerve bundle.

mapping freq of a sound wave to a place of max activity within an anatomical structure

cochlea -> cochlear nucleus -> superior olives of the pons -> inferior colliculi -> medial geniculate body -> Auditory cortex

• primary auditory area of cortex
• -low freq more lateral
• -high freq more medial
• there is a spatial component to freq representation in the cortex