Simplify the following text for a Grade 6 native English-speaking person.
Original: Nerves move muscles in response to voluntary and autonomic ( involuntary ) signals from the brain . Deep muscles , superficial muscles , muscles of the face and internal muscles all correspond with dedicated regions in the primary motor cortex of the brain , directly anterior to the central sulcus that divides the frontal and parietal lobes .
Simplified: The Smooth muscles are the other muscles in the body that are involuntary .