When discussing how the brain works you want to make sure to cover the communication between the brain and the muscle structure. Think of the brain as a giant computer. All the signals have to come from the brain to control the muscles and other functions of the body.
Then again there is a communication going on here. For muscles have to work together, they have to communicate with each other to send signals to the brain on how the muscles are working. To carry out a muscle movement some muscles have to relax when you use other muscles.
This coordination takes place in the cerebellum, an adjunct to the brain stem, our reptilian brain. It works like this. When you decide to make a voluntary movement, you send a signal from the front part of the cerebral cortex to the cerebellum by way of the pons. The cerebellum then sends directions to the muscle control centers in the back part of the frontal lobe of the cerebral cortex. Then the efferent nerve system carries the signal from here to the appropriate muscle groups. The proprioceptors then send signals back to the brain with the afferent nervous system. The signals enter the cerebellum by way of the medulla and appropriately modify the signals the cerebellum is sending to the muscle control centers in the frontal lobe.
When the cerebellum is not sending the appropriate signals to the muscle control circuits, the muscles do not interact properly, and you experience pain and limited range of motion due to overly tight (hypertonic), weak (hypotonic), and reactive muscles. If these conditions persist long enough they can lead to secondary problems such as tendonitis, neuritis, herniated discs, and damaged joints.
The stress and pain can be released by reestablishing the body-mind and brain-muscle communication through balancing weak, reactive and frozen muscles so that the cerebellum now sends the optimal messages to the muscle control centers in the cerebral cortex.