THE BRAIN is Commander-in-Chief of the speech and voice equipment. It works something like a very sophisticated computer by creating and organizing ideas, turning them into language, then sending electrical-type signals through nerves to muscles that will contract and relax to make speech movements.
During speech, millions of brain cells send millions of impulses to many groups of muscles in just the right sequence so all the speech equipment will work properly.
The brain also integrates information from the ears and other body monitors as we talk and listen and adjusts our speech program based on this input.