In speech and language therapy

Animals which feed and breathe through the same opening need a way of ensuring that the food does not get into the structures for getting oxygen out of the air – the lungs.

What we call the ‘voice box’, or the larynx, is a mechanism in the throat, halfway between the lungs and the mouth, which does just this. Two lumps of cartilege suspended by muscles can brought tightly together to form a valve sealing off the lungs. These lumps of cartilege are hinged at the front inside a larger lump of cartilege, forming the larynx.

Animals with skeletons, including amphibians like frogs, reptiles like lizards, birds of all sorts, and mammals, including humans, all have a larynx. In humans the larynx is visible as the ‘adam’s apple’.

A cough is the action of clearing any sort of solid, food or particles in the air, from the entrance to the larynx by first closing the the larynx tight shut and then breathing out violently, expelling whatever was in the way. Coughing is thus a life-preserving reflex action.

But if the lumps of cartilege are brought close together but not actually touching and in a given state of relaxation along their length and air is breathed out through them they vibrate, creating a buzzing sound. This sound is then modulated as it passes through the upper part of the throat and the mouth. The resulting sound is what we know as ‘voice’ in humans, song in birds, croaking in frogs. But voice is not the primary function of the larynx. The primary function is to protect the lungs, which have to work continuously throughout life from birth to death. Any interuption of this function is fatal within a few minutes. Food is less critical.

The vibration of the lumps of cartilege is like the fluttering of a flag. The point of contact ‘rolls’ along them. They are known as the vocal folds or the vocal cords, because voice appears to be their main function.

William Holder, arguably the first speech and language therapist in the 17th century, was the first to identity the whole structure between the lungs and the lips as the ‘vocal tract’.

The pitch of the voice is raised by increasing the front-to-back tension of the vocal cords and raising the larynx in the throat. Singers know combinations of these things as different ‘registers’. Everyday use in speech and in untrained singing involves variation within around an octave, equivalent to the notes at the top and bottom of the neck of a traditional acoustic guitar.

The vocal function of the larynx is highly vulnerable. Prolonged shouting or just talking at peak volume leads to hoarsess. Prolonged hoarseness can lead to polyps or nodules forming on the cords. Smoking can lead to cancers. All of these are using the larynx in a way for which it did not evolve. Most of these ill effects can be prevented by prompt and early intervention in the form of speech therapy and resting the voice.