The Animal Spirits and Motion

32. How do the spirits enter into the nerves and create motion?

The animal spirits will not receive the impression of a certain idea if, in the innermost part of the brain, some of the tubes:

• are not more open, or
• are in a different manner than others

The spirits will then be dispersed haphazardly and indifferently in all directions.

• They pass through the pores around B into those around C.

Hence, the finer particles of them will flow out completely through the pores of the membrane that envelops it.

• The remaining parts of the spirits flowing towards D will pass into the nerves and muscles without producing any particular effect in them, as they are evenly distributed to all.

The action of an object on the sensing agent will open some of those tubes:

• more or less
• in a different way than their neighbors

This will cause the filaments composing the substance of the brain (therefore some being slightly more intense or relaxed than others) will lead the spirits to a certain part of their base.

From there those spirit flow into certain nerves with greater or lesser force than others. This is sufficient to stimulate different movements in the muscles, as explained more extensively above.