Answer: Muscular activity belongs to the activity of the nervous system; it is a response issued after the brain's central nervous system gives a command, and the brain's central nervous system is regulated by the manas. Once the manas makes a decision, the cerebral cortex becomes active, the central nervous system issues commands, which are transmitted to the corresponding nerves of the body, producing the phenomenon of muscle contraction. Although bodily, verbal, and mental actions are directed and commanded by the manas, their concrete operations must be jointly completed by the mind consciousness and the five sense consciousnesses. If the six consciousnesses cannot arise normally, the body cannot function.
Although the contraction and relaxation of the nervous system are both regulated by the manas and are subconscious behaviors, they are very hidden and very subtle. Breathing, for example, includes a part in which the mind consciousness participates, but a large part does not require the mind consciousness's participation. The movement of the body, without the mind consciousness, can never be accomplished no matter what; subtle nervous system activities can occur without the mind consciousness, such as the twitching of the body after falling asleep, the fluttering of the eyelids, slight bodily movements—these can occur without the mind consciousness, and slight breathing can also occur without the mind consciousness. However, the mind consciousness can actively regulate breathing, such as deep breathing and so on.
The muscular and neural activities closely connected with the physical body can be regulated by the manas alone, without the cooperation of the mind consciousness; the mind consciousness may also participate, but it can only guide the manas and cannot command the whole body, because the manas alone can control the central nervous system, issuing commands there that can be transmitted throughout the body. Neural activities in which the mind consciousness participates are called conscious behaviors; those in which the mind consciousness does not participate are called unconscious behaviors. For example, breathing, the stretching and contracting of muscles, incontinence of urine and feces, gastrointestinal peristalsis, the circulation of qi and blood, and some special emotional activities—such as being so startled that the heart pounds and the flesh jumps, flying into such a rage that the hair stands up under one's hat, or being scared out of one's wits—can all be accomplished without the participation of the mind consciousness; the manas alone can complete them. But the motor activities of the body root must have the body consciousness and the mind consciousness operating and regulating together with the manas.
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