The Human Instrument

When listening to the voice of a great singer, such as Josh Groban, Sarah Brightman, or Steven Curtis Chapman, one may awed or inspired by music which they can produce; however, if the voice is lined up with other instruments in rank of size, it would be at the end of the group with the fifes. This is because marvelous it may be, the voice is only thirty-five centimeters long at the most, compared with other instruments, for example trombones, that stretch out to about three meters. The voice, or more specifically the vocal folds (the explanation of this will be presented later), contains everything an instrument does, except in a smaller and more efficient version.
The first scientists to study the voice thought the sound was fabricated via a linear theory of speech acoustics, but more recent studies have proven it is truly non-linear interactions, ones in which the source and resonator feed off of each other.
Every instrument contains the same basic parts: an origination for the sound that vibrates when air rushes past it to make fundamental pitches with higher ones that define timbre, or sound color, the human equivalent of which is air rushing past vocal cords (two specialized groups of pouchlike-tissue, hence vocal folds) and a glottis (the space between two folds); at least one resonator that reinforces the vibration and fabricate higher frequencies called overtones, or in other words a vocal tract and the laryngeal vestibule (an airway just above the larynx); and a radiating surface or opening to guide the sound into open space, also known as the mouth and lips.
There is one catch in how the voice works in comparison to an instrument, such as a viola: on an instrument like that, in order to increase frequency, one must increase tensile stress, or in simpler terms, tension while decreasing length, something that under normal circumstances is not possible. Nature, however, has solved this problem with a three-part material that exhibits qualities not normally found in instruments: the cords of the voice are made of a semi-stringlike ligament which has remarkable stretching characteristics--when stretched a little, the stress rises nonlinearly and it can be amazingly tense, but when not stretched, the ligament is quite limp.
The voice is also mostly made up of muscle tissue, which can shorten and become tenser concurrently. The voice also has groups of ligaments placed side-by-side with some having the ability to contract and others not, and a soft, flexible surface which ripples like waves when air blows across it. A mucous membrane is also in the muscle-ligament combination to provide greater energy transfer ability. The mucosa, a very thin epithelium with fluid-like substance on the bottom side of it, exists in the mucous membrane and is easily deformed, thus supporting the ripples of the membrane.
Now to put all of these ligaments, muscles, and mucous membranes to work. In order to sing low and moderate to loudly, the singer makes use of all the layers of the muscle folds, though the muscle itself does not vibrate--that's the mucosa's elasticity and ligaments' job. For higher tones, the singer's cords must become longer (in this case, ligament stress alone dictates frequency). The way these notes become energized enough to be heard by people is that the vocal tract can use energy from one oscillation cycle, keep it until the next one, and send that energy into the current cycle to give it a push to go farther. A simpler example of this is someone pushing a child in a swing. They push at just the right time to give the swing more energy to carry the child upwards. This is the same concept as what the vocal tract does with each oscillation cycle.
All of this to produce one sound.

My response:
Though the voice is amazingly small for the amount of "oom-pah-pah" it can produce, it is nonetheless a very intriguing part of the body in the way it weaves its way around what would normally be major hindrances or show-stoppers. In general, no one thinks about what all is happening when they speak or talk, but when it comes right down to it, there is a myriad of things which must occur for one note or sound to be made, all of which must work in perfect harmony. The beauty of this process and its orchestration can only logically be explained one way: by the work of a divine Creator.