Greg raised a very good question during last night's class. He wanted to know about the "neuro" in speech. The diagram that I showed in class diagrammed the SPEECH ORGANS. It did not deal with the brain functions that influence speech.
There is a good book called, The Man who Mistook his wife for a hat" by Oliver Sacks. This book has a series of cases that explain how certain brain impairments affect speech, language and communication. The web site: http://www.bookrags.com/The_Man_Who_Mistook_His_Wife_for_a_Hat will give you summaries of Sack's clinical stories (he doesn't call them studies).
One example of a neuromuscular disorder is dysarthria which is seen in many stroke and trauma victims, but can also be caused by various other diseases and disorders such as Parkinson's disease, cerebral palsy, and muscular dystrophy. This disorder prevents the muscles in the vocal tract from working properly. It commonly takes place within the oral cavity of the vocal tract and can affect articulation.
Muscle Weakness or Paralysis is one symptom caused by dysarthria. It causes damage in the area of their brain where the lower motor neurons, muscle fibers, and myoneural (myo=muscle) junctions are located. This type of damage causes weakness or paralysis of muscle contractions. This is known as flaccidity and it limits the function of a person's articulators and muscles necessary for speech.
Hope this helps. Please post any more questions or comments about language, communication and speech here.