What are the different elements along the auditory pathway?
- Hair cells
- Travels from hair cell to superior olive along vestibulocochlear nerve (CN VIII)
- Superior olive to inferior colliculus
- Inferior colliculus to medial geniculate of the thalamus
- Medial geniculate to the auditory cortex
What is the role of the ossicles?
They act as a lever to convert the vibration of the tympanic membrane into movement of fluid which amplifies sound and pushes the fluid in the cochlea
What are the scala tympani and scala vestibuli and what are their importance?
Perilymph filled cavities of the cochlear that transmit the sound waves from the oval window (SV) and round window (ST)
What is the scala media and what is its importance?
An endolymph filled cavity of the cochlear that establishes a potential gradient to allow sensory transduction
What is the role of the stria vascularis?
It maintains the ionic composition of the endolymph
How do inner hair cells transduce the sensory signals?
- Force on the tiplink opens channels
- This opens Ica and Ik channels allowing calcium influx and potassium efflux
- Ca2+ leads to exocytosis of the vesicles which releases neurotransmitters
- Depolarisation leads to firing of afferent fibres
- Tiplinks are moved in the opposite direction which leads to inhibition
- Inhibition causes Ica channels to close and Ik stays open, leading to hyperpolarisation
- Tip links move back and forth which leads to pulses of activity down the afferent fibres
What is the role of IHCs?
They transmit excitatory signals an store synaptic vesicles - they have a high rate of exocytosis due to the synaptic ribbon
How do IHCs and OHCs differ?
The OHCs are innervated heavily by efferent fibres with few afferent fibres
