We use the term childhood apraxia to denote a particular kind of speech sound disorder. Childhood apraxia is just a label then for a subset of children who have speech sound disorders. It's an important label, though, because it signifies those kids who have specific difficulty with planning and programming movement for speech. They don't have weakness. They aren't having difficulty talking because they can't move the muscles. The muscles move quite well for other activities, like eating, chewing, swallowing, but when they try to talk, the parts of the brain that plan and program those movements aren't working efficiently. So the children will end up having difficulty making the sounds correctly.
When children, or anyone for that matter, goes to speak or to talk, they're basically making movements with the jaw, tongue, lips, and palette to create the sounds. In order for those movements to occur correctly, some mechanism has to plan when the structure will begin to move, in what direction, with a certain speed, with a certain amount of muscle contraction. All of that happens because of sensory proprioceptive information that comes in, gets processed by the brain, and then, other areas of the brain will actually specify those parameters of movement. And that's what we mean by planning and programming movement for speech sounds.
Children with CAS don't necessarily have brain damage. Certainly some children have strokes and may end up with the speech characteristics that we call apraxia of speech. Other children may have surgery for brain tumors, or other kinds of real neurologic problems from which they might have in apraxia of speech. Most children with this label, however, for their speech disorder, don't have any signs of damage to their brain. We know, though, that the brain controls pretty much everything that we do and that the behaviors, the speech difficulty that they have, leads us to believe that there are some inefficiencies in the way the brain is processing that proprioceptive information and planning movement that's impeding their ability to easily learn to talk.
Well the brain has to know where structures are and whether or not they're still, or moving, or tight, or loose, in order to specify what happens next. So, for example, if I want to say hi. The brain has to know is my jaw closed? Open? Where it has to start from in order to form the movements for the word hi. So basically it's receptors that bring in information about where structures are, whether those structures are moving or still? In what direction are they moving? Are the muscles that are involved tight? Are they loose? So that the brain can then plan and specify parameters of movement for the continuous action.