Another problem is what wave is amplified by
pulling on the basilar membrane. A silent sound wave that generates an
electrochemical potential is a wave received by the receptor and the signal is
transmitted to the auditory cell, where it is analyzed. If the wave energy is
too low to reach the receptor, the wave is amplified at the molecular level in
the hair cell. Mechanical amplification cannot apply to the
foreign wave on the basilar membrane (which, according to Bekesy's theory, runs
at this time as a traveling wave). The intensity of this wave is unknown and
the message contained in this wave may have nothing to do with the received. amplified wave. The wave on the basilar membrane is delayed relative to
the amplified wave by tenths of a millisecond. There is
no explanation of how to amplify quiet polytones with numerous aliquots, length
of sound, and phase shifts when the polytone contains quiet and loud sounds of
different frequencies. Are quiet ones
separated from loud ones? Amplified and separately transmitted to the IHC and
then to the brain?
The next problem is the varying energy
requirements for amplifying quiet tones at different frequencies.
Conformational changes in prestin do not provide external energy - different
for all frequencies. Mechanical amplification
of quiet tones in the inner ear is impossible. There is intracellular amplification. Contractions of the hair cell pulling up the
basilar membrane loaded with the organ of Corti produce vibrations of different
frequencies. This vibrating conglomerate has mass, speed of movement and acceleration,
and inertia [8]. An increase in frequency by a certain amount causes an increase in
inertia proportional to the square of that amount. The generation of an
increase in basilar membrane vibration (according to Bekesy's theory) requires
a large increase in energy. The energy associated with depolarization is only
used to initiate conformational changes in presting; it does not have the
energy to pull up the basilar membrane.
Signal amplification according to the sub molecular theory of hearing
In all senses there is intracellular,
regulated, molecular amplification. Most chemical reactions and energy transfer
between small molecules take place in 10-14 s. These are reactions at the
atomic and electronic level. "Difficult" reactions take place 1000
times slower, but it is still 10-11 s. Intracellular
enhancement is a whole complex of factors such as: phosphorylation and
dephosphorylation of ion channels responsible for the conductivity of cell
membranes, ATP concentration, cAMP and cGMP levels, cell pH, osmotic pressure,
presence of ligands, and the work of Ca++ATPase pumps. These membrane-bound
pumps play an important role in maintaining fluctuating calcium levels within
the cell. Intracellular enhancement is also related to
the activity of calcium-binding proteins, where calmodulin plays an important
role by influencing the production and breakdown of cAMP and cGMP. It activates
protein kinases and phosphatases, regulates the functioning of the calcium
pump. It affects the contraction of muscle and non-muscle cells by activating
the cAMP-independent myosin light chain kinase. Calmodulin also affects the
transmitter’s exocytosis. Binding 4 calcium atoms to calmodulin increases its
effect 1000 times. The process of enzyme production or the rate
of their breakdown is regulated. Calcium is a second messenger of information
in the cell, acting faster than the other second messengers: cAMP, cGMP, DAG,
IP3, which are produced in connection with an increase in calcium levels or
activated by G protein. The stage of production of second messengers is one of
several mechanisms of intracellular amplification. One enzyme molecule can
produce several hundred-second messengers. Received tones of which energy is
too low to reach the brain are amplified. Intracellular
signal amplification is one of the main pillars of the “Sub molecular Theory of
Hearing” [9].