III. The Great Nerve Centers
(EN: Atkinson speaks based on the knowledge of his time, which is different than that of the present day. But it must be conceded that even in the present time, neurologists are not in agreement of how the brain is to be divided into parts and what functions are performed by each. So I'll annotate this chapter largely as written based on the author's perspective and the science of his time.)
The Spinal Cord
The thick rope of nerves that run the length of the spine is likened to the central cable of a telegraphic system, to which all other branches connect. Any injury to the spinal column disconnects entire branches of nerves from the brain, paralyzing and rendering senseless those parts of the body beneath the point of disconnection.
The Ganglia
Ganglia are bunches of nerve cells found in various parts of the nervous system. In the author's time they were believed to be "little brains" that perform various tasks related to reflexes and maintaining autonomous systems.
The example he uses is when a foreign object enters the eye, the ganglion nearest the eye causes the eyelid to close, and suggests that the same result ensues if an object approaches the eye without actually contacting it. The blink is a motor impulse, a reflex action over which a person has no control and is generally unaware.
He also suggests that the ganglia play a role in certain motor impulses, such as walking - once the skill has been learned the processing is delegated from the brain to the ganglia to manage. (EN: I don't believe this is supported by modern medical science.)
Further, he gives the example of the movements of dead bodies - if you decapitate an animal, its body continues to twitch and move. Because the brain is disconnected from the body, this is believed to be an action that is controlled by the ganglia.
The Three Brains
What is considered by laymen to be "the brain" is really three separate but proximate organs. Atkinson suggests when he uses the term "brain" he is referring to the cerebrum, as that is the organ most responsible to reason and conscious thought.
(EN: modern science still recognizes three brain systems, but they are not exactly the same physiologically or functionally as the systems described hereafter - but it's remarkably close given the time at which hthe book was written.)
The Medulla Oblongata
The medulla oblongata is an enlargement of the spinal cord at the base of the brain, and is similar to a ganglion in that it controls many of the involuntary activities of the body, such as respiration, circulation, digestion, and the like. It's chief concern is managing these autonomous systems and relieves the other parts of the brain from the burden of these tedious and incessant tasks.
The Cerebellum
The cerebellum is a distinct portion of the brain located just above the medulla oblongata and below the rear portion of the cerebrum. It is believed to be an area in which autonomous functions and reflex actions are further controlled, and is also the location within the brain that stores habitual motions.
It was believed that when a person developed habitual activities, such as typing or riding a bicycle, the procedures for performing motions "without thinking" was controlled by the cerebellum and did not bother the higher mind. (EN: electroencephalographic studies have disproven this theory.)
The Cerebrum
The cerebrum is the largest and most familiar part of the brain, and is regarded as being "the brain" by the average person. It is situated in the upper portion of the skull and constitutes the greatest mass of the brain system.
In the author's time it was believed that the cerebrum had various areas or zones that were specialized - such that one part of the brain was involved in vision, another in hearing, another in motion, another in memory, etc. (EN: This notion was inherited from phrenology, which is complete rubbish. Again, EEG studies show activity throughout the brain, but it is still noted that certain kinds of activity do seem to show activity in regular parts of the brain - though not as strictly as the phrenologists would have us believe.)
The Cortex
The cortex refers to the part of the cerebrum that are most active during intellectual activity: thinking, imagination, reasoning, etc. These activities are believed to be performed in the brain's fontal lobe.
He then repeats some outdated theories about the relationships between the wrinkles in the brain or the amount of gray matter to a person's intelligence. (EN: Both of which have been disproven.)
He does concede that mental activity has not "so far" been linked to the physiology of the brain in any satisfactory manner, such that the structure of the brain as an organ cannot tell us anything about the thoughts the mind contains. (EN: Which remains true even today.)