Briefly, the nerves might be called the telegraph system of the body. There is a great central station called the brain where messages are received and sent out; there are many sub-stations that make up the spinal cord. Twelve great nerves pass directly from the brain to the body; all others pass from the spinal cord.
Extent of nervous system
Every nerve leaving these centres divides and sub-divides into little threads as the arteries divide and sub-divide into arterioles and capillaries, until every part of the body—every muscle and part of the skin—has its nerve.
Voluntary and reflex action
Every time you choose to move your hand, your brain sends to the necessary muscles an instantaneous order to act. This is called voluntary action. If you put your finger against a hot stove you jerk it away before you could have time to choose to do it. This happens as an order from a sub-station and is called reflex action.
Messages travel both ways and it is necessary that the nervous connection with every part of the body remain unbroken, and important that the nervous condition be kept healthy.
[NOTES TO THE TEACHER]
A false delicacy has often prevented the teaching of vital lessons to growing children. The day is how at hand when foolish sentiment must no longer prevent the spread of any knowledge which is necessary to exterminate the plagues that have afflicted the race.