This chapter covered auditory and vestibular system. One new concept was eustachian tube that maintains the pressure equilibrium between inside the middle ear and outside the ear. When the outside pressure becomes higher than in the middle ear the eustachian tube opens and pressure difference stabilizes. This system helps to balance the pressure differences between middle ear and surroundings, for example on the landing airplane the air pressure increases momentarily and the pressure in the middle ear does not keep up.
It was interesting to notice that even most of the cochlear output comes from inner hair cells. The outer hair cells also have a big role in hearing. Their mission is to amplify the movement of the basilar membrane. If they could not amplify the basilar membrane the peak-movement could be 100-fold smaller.
Totally new concept was superior olive, which are significant when we handle hearing pathways. It is middle of pathway where afferents arrive from the cochlear nuclei and departure of efferents to the inferior colliculus. It can have something to do with localization of sound, because the binaural neurons are present their first and olive neuron compute the interaural time delay between left and right cochlear spikes. The neurons in the superior olive responses to this delay.
Neurons have one frequency which they are most responsive and that is called neuron’s characteristic frequency. If we are on other frequencies, they are less responsive. This characteristic frequency system is mostly cause by the mechanics of the basilar membrane: from the apex to the base, the basilar membrane resonates with decreasingly higher frequencies. It is interesting that even though we are surrounded by many different sounds all the time, we do not pay attention to most of them. Yet our brains work all the time with the frequencies, but we don’t pay attention to them.
The mechanism of hearing has been gone through previously, but the sound localization was something that has not come to mind. It was interesting to read about the localization of sound in the horizontal plane versus vertical plane and how we can localize vertical sounds better with one ear than horizontal sounds.