Stuttering is neurological in origin. There is a moment of loss of control in speech, and then the stuttering is the tension that one creates as a reaction to the loss of control. It’s like when your car hydroplanes or slides on ice- that’s the loss of control that is neurological in origin- and you grip the steering wheel tight and try to swerve suddenly and instinctually- that’s the tension that comes up as the speaker tries to regain control. The tension can occur anywhere in the speech production system- which includes lungs, vocal folds, and articulators in the mouth (lips, tongue, jaw). If someone has a block, which is a type of stutter where no sound is coming out, that’s because the tension in that particular instance is indeed in the vocal folds. But that is not where the loss of control originated. It’s the location of the involuntary reaction.