Thursday, January 3, 2008

Phonation 2 (Laryngeal Anatomy- Intrinsic musculature)

This edition will come slowly because the research required to provide video and image links as well as definitions that are accurate and understandable is time-consuming. And since I want this to be accessible and not a collection of scientific jargon, I hope you will bear with me. I have decided to provide one paragraph at a time, as I go through. In this manner you will have something to read.

Phonation is simply the oscillation (vibration) of the vocal folds. On the surface view of the vocal folds, as seen through laryngoscopy (laryngoscopy for singing research is normally done via a flexible fiber optic laryngoscope), vibration includes a sequence of open and close phases. Because the vocal folds vibrate hundreds of times every second, the current video is seen using stroboscopy. By flashing a strobe light at the speed that the vocal folds are vibrating, the visual effect is one of slowing down the vibration. Where as it would be impossible to view a single oscillation of the vocal folds singing middle C (approximate 280 vibrations per second), by flashing the strobe light 280 times a second the visual effect it that of one vibration per second which is very beneficial for scientific study and diagnosis of vocal malfunction. The video of fold vibration offers a view of the surface of the vocal folds. So we are able to see only opening and closing of the surface. At the end of the video we get a view of the open folds, which allows us to see that the folds have vertical thickness, as seen on this drawing. Therefore, the vibration of the vocal folds occurs like a wave. In fact it is called the mucosal wave, referring to the vibrating cover of the vocal folds which is a mucous membrane. The wave action is usually represented by the following drawing. Following the steps from 1 to 10, the drawing begins with the folds in a close position. The gradually open from the bottom and are fully open at number 5. They begin to close at number 6 leading with the bottom edge, touching at number 8. They are fully closed again at number 10 completing the cycle. Imagining the folds vibrating on an average of 200 times per second in the male singer, at G3 (a fourth below middle C) and twice that for the average female singer (400 vibrations per second or 400 Hertz), as soon as the folds are fully open at the top edges, the bottom edges come together.

The vibration of the vocal folds, including their specific frequency (how many times per second, pitch) is controlled by a number of tiny intrinsic laryngeal muscles, so called because they are inside the larynx, and so distinguishable from those muscles outside the larynx, called extrinsic muscles. Before we begin with a detailed discussion of the intrinsic laryngeal musculature, it is important to understand the basic structure of the larynx and where precisely it is. In the following image of the respiratory system, we can see the lungs and the bronchial trees inside responsible for the exchange of air. Traveling upward, the bronchial trees from each lung end with a branch-like tube called the bronchial tube. The tubes join and become one tube called the trachea (another view of the respiratory system). The structure right on top of the trachea is the voice box or larynx (front view). The larynx is made up of two main cartilages. The ring-like Cricoid cartilage is attached to the trachea, and the Thyroid cartilage rests on top of the Cricoid, connected at its inferior horns (one on each side) by means of the Cricothryroid joints. The Thyroid is able to rock back and forth from these joints. © 01/03/2008

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