Vocal cords, Vocal folds

What we term “vocal cord” is often compared to the edge of a string when viewed from above during vibration and this is possibly where the term cord came from. I also frequently see the term “vocal chord” though I believe chord is a mis-spelling as the vibrating portion of the larynx does not generally represent the straight line portion of a curve nor three musical notes, both definitions refering to a "chord". 

Viewed in cross section though, the vocal cord doesn’t look like a cord at all. It is more of a wedge in shape. Still, musically it does function like a cord and many analogies to a cord or string, such as a comparison to the string on a guitar, can be made.

Some people call them “vocal folds,” which is a more apt description of their three dimensional visual appearance. They are each a fold of soft tissue rising from the edges of the airway. However, the terms vocal cord and vocal fold can be, and are, used interchangeably.

Here, the vocal cords are viewed from above in the ABducted, “breathing in” position. The vocal cords are the white bands on either side. The apex at the front (anterior commissure) is attached to the inside of the thyroid cartilage. The left vocal cord is on the left side of this picture. The thyroarytenoid muscle within the vocal cord is attached to a slightly visible white ligament at the front and to the tip of a white cartilage at the back (the vocal process of the arytenoid cartilage).

A fullness (arrows) can be seen below the edges of the vocal cords that actually gives the vocal cord the shape of a fold along the wall of the airway. The fullness is from the thyroarytenoid muscle. These vocal cords are in an abducted position.

The vocal cord is essentially a muscle under a ligament with mucosa covering both of them. A layer of lubricant, the lamina propria, lies between the mucosa and the ligament-muscle combination. The muscle tightens and loosens to change the pitch of the vibrations. The lubricating layer allows the mucosa on the surface to vibrate easily. The muscle may oscillate to a small degree, like a string on a guitar or piano, but the lining on the surface is the primary oscillator or generator of sound. The mucosa is like a layer of silk draped over the edge of the ligament and the mucosa vibrates when air passes rapidly by it.

When we examine sound production, we will be able to establish typical configurations of the glottis for each of these problems. The vocal cords have two general positions: ABducted and ADducted. When ABducted, they are apart and in the configuration of a V.

When ADducted the vocal cords should come essentially into near alignment, often almost parallel to each other. The lungs generate pressure below and air can then be passed through the vocal cords from the windpipe below. As air passes through this narrow slot between the vocal cords, the mucosa starts to vibrate, creating sound. 

The vocal cords are the two white structures lying nearly parallel to each other in the center of this photo taken at the onset of  sound production at pitch B4 in this female. The vocal cords are in an ADducted position. The vocal cord margins are slightly concave, so there is a small gap even when the vocal processes have touched.

Let’s define how the vocal cords produce sound when all is normal.