Hearing Flashcards
What is the function of the ossicles?
To transmit and amplify sound as it passes to the inner ear
How do sound waves travel from the oval window to the round window?
Sound waves cause vibrations of the oval window which are transmitted through the perilymph of the scala vestibuli and run up to the apex of the scala vestibuli where it is continuous with the scala tympani and then run down towards the round window at the base of the scala tympani cause it to bulge out into the middle ear.
How are sound vibrations transmitted to the basilar membrane?
Vibrations in the perilymph of the scala vestobuli cause the vestibular membrane to vibrate and this vibration is transmitted through the endolymph to the basilar membrane
How does the vibration of the basilar membrane cause depolarisation of the inner hair cells?
Vibrations of the basilar membrane cause displacement of the stereocilia which increases the tension in the tip link proteins causing the opening of ion channels. The inward flux of ions causes voltage gated calcium channels to open leading to depolarisation of the inner hair cell
How does depolarisation of the inner hair cells cause a nerve impulse to be sent to the brain?
The increased intracellular calcium levels cause the release of a neurotransmitter which stimulates afferent neurons innervating the inner hair cells to fire an action potential. This is conveyed via the vestibulocochlear nerve to the brain.
How do different frequencies of sound affect the vibrations of the basilar membrane?
Different frequencies make the basilar membrane vibrate in different areas. High frequencies causes shirt hairs to vibrate and low frequencies causes long hairs to vibrate
What is the range of frequencies that humans can hear?
20-20kHz
We cannot hear lower frequencies as we get older. T/F?
False - as we age we lose the ability to hear higher frequencies
Why does the middle ear need to amplify sound?
Because it is going to transmit sound waves to the inner ear where sound waves are transmitted through fluids. Fluids impede sound more than air does so amplification is required
What frequencies are the pinna and external acoustic meatus specialised to amplify the most?
Frequencies that human speech resonates at
How does the middle ear achieve amplification of sound?
The tympanic membrane has a much larger ara that the ossicles and the ossicles decrease in size as you move more medially. Thus, the same force is being exerted by a small area so this results in amplification
How do inner hair cells differ from outer hair cells?
Inner hair cells are innervated by afferent nerve fibres. Outer hair cells by efferent nerve fibres.
What is the purpose of outer hair cells and how do they perform this function?
To amplify sound vibrations. When stimulated they change their shape and stiffness which generates a force that is fed back to the basilar membrane to cause amplification
The loss of inner hair cells means that hearing at the frequencies where the hair have been lost is decreased. T/F?
Loss of inner hair cells causes complete loss of hearing, loss of outer hair cells causes decreased hearing/complete loss of hearing in that area of frequency
The arrangement of frequencies in the cochlea is maintained into the central auditory system all the way up to the auditory cortex. What is this called?
Tonotopic map
