In both instances the vocal cords close tightly. These behaviors are automatic responses of lower, more primitive centers of the brain. The evolutionary onset of speech coincided with the development of higher centers of the brain. As the Nobel Laureate, George Von Bekesy observed, the study of higher centers is the study of greater levels of inhibitory control, with higher centers serving to inhibit gross, less discriminating responses from lower ones. This is particularly true for the vocal cords.
Speech requires extremely precise, graded, time varying neural inputs to the vocal cords.
A gross tensing would be inappropriate and markedly interfere with the precise prespeech tensions on the vocal cords. In the condition known as Spasmodic Dysphonia we see clinical examples of this loss of inhibitory control. Each time the person intends to speak the vocal cords appear to close as in a swallow. Let us see how the six sources of prespeech vocal cord tension can be used in a consideration of stuttering. The vast majority of people who stutter report they are fluent when they speak to themselves out loud alone.