How does music get from an instrument,
radio, or voice into our consciousness? The brain can detect harmony
because the inner ear can tell the difference between different frequencies.
What this implies is that the brain's ability to differentiate between
notes and chords relates to the differences in frequency and harmonics,
while our "sense" of music is more of an enculturation from observation
of accepted harmonies through time. The ear is the objective listener;
the brain decides whether the music sounds beautiful or not, which tends
to be more subjective.
Sound is made
The sound waves enter
the ear
The brain eventually processes the
sounds
The human's ability to hear sounds
comes from the anatomy of the inner ear and the brain, and of course, whatever
is out there causing a ruckus. Sound is a combination of the mechanical
energy of waves and the electric response produced by receptors in the brain.
Each sound wave has an amplitude and a frequency (ƒ = 1/T, ƒ is the frequency; T is the period).
The amplitude of a vibration is defined by volume using decibels. Frequency
relates to differences in pitch. The higher the frequency, the higher
the pitch. Mathematically, pitch (another name for "note") is defined
as the number of vibrations per second.
http://en.wikipedia.org/wiki/Amplitude
Amplitude is a component of sound, along with frequency.
In vertebrates, once sound waves
penetrate the outer ear, they hit the ear drum which sends the message to
the cochlea (fancy name for inner ear) where the sound is changed into chemical
energy. The cochlea has fluid in it along with stereocilia (fancy
name for tiny little hairs). Sound waves travel through
this fluid, and stimulate the stereocilia which prompts the release of K+
(potassium). Some ion channels open up so the potassium can move freely
into cells. Next, neurotransmitter release is dependent on the frequency
and amplitude (pitch and volume) of the sound waves. Sounds must be
loud enough and within a specific range of frequencies in order to cause
action potentials, depending on the vertebrate. For example, dolphins
create such high frequency sounds and whales such low frequency sounds that
human ears rae not able to process them. Different sounds create different
action potentials, which allows harmony to be discerned at the neural level.
Each of the stereocilia can best hear one frequency, and each stereocilia
is different - that is how many notes can be processed at the same time in
order to hear harmony. Cool!
http://en.wikipedia.org/wiki/Ear
A map of the ear (the stereocilia are inside the cochlea)
Once the pitch and volume have been
changed into action potentials, the sound travels along inner ear through
the auditory nerve, all over the brain, and at last to "the auditory cortex
of the temporal lobe" (the hearing department of the brain). From
there, memory can come into play along with emotion which leads to self-expression
and so many other wonderful things!