This up-and-down arrangement shows three so-called "levels" of function.
Beginning with the spinal cord, we find the simplest processes, and they grow more complex as we go up toward the brain.
The lowest, or "third level," includes all the functions which the spinal cord, and its upper termination, called the "medulla," are able to perform alone--that is, without involving necessarily the activity of the nervous centres and brain areas which lie above them.

Such "third-level" functions are those of the life-sustaining processes generally: breathing, heart-beat, vasomotor action (securing the circulation of the blood), etc.

These are all called Automatic processes.

They go regularly on from day to day, being constantly stimulated by the normal changes in the physiological system itself, and having no need of interference from the mind of the individual.
In addition to the automatic functions, there is a second great class of processes which are also managed from the third level; that is, by the discharge of nervous energy from particular parts of the spinal cord.

These are the so-called Reflex functions.