The text discusses how movements can be automatic, without conscious will, aligned with our body's natural functions, such as during sleep. Our will also guides our actions and decisions through the coordination of spirits, nerves, and muscles, driven by impulses from the soul. Our movements, whether conscious or instinctive, vary based on the method and intensity of these internal dynamics.
Nature and Service of Muscles.
The type of movement does not require the assistance of our will; (although it does in many cases) because the human body's structure is such that the change of spirits through the functioning of the nerves in the muscles is directed, allowing the body to move instinctively as it was originally exercised.
Therefore, it occurs that in our sleep, or otherwise outside our conscious thought, we can make various movements, with our hands, grasping, scratching, turning ourselves, speaking, even getting up and walking.
For, due to psychological spirits being warmed by the heart, flowing from the purest part of the blood, from the brain into the nerves, and from there into the muscles, they create such a movement in the limbs as the nature of such a muscle permits, to be able to be moved. These movements vary depending on the course of the spirits.
However, the actions that are agreed upon and thoughtfully performed by the will, based on our previous reasoning, are established in work; and when actions of the soul within the body are determined, they happen as follows: When we desire something, whether walking, running, lifting, raising, striking, etc.
Thus, such accommodations necessary for actions or motion are determined by the soul, and found from the brain to the muscles, as needed for the intended task or movement: and then the will is either strong or weak, ensuring the effectiveness of the instruments, more or less, and the resultant according to the strongly moved parts, powerful, intense.