Billeder på siden

like a skull-cap, and is composed of a vast number of nerve-cells connected together by nerve-fibers, and forming many ganglia.


Under surface of the brain, showing the great complexity of its structure. At the lower part of the cut is the cerebellum.*

The Cerebral Ganglia.-The locations of some of the ganglia are known, but the construction of a reliable cerebral map is the work of the future. A classification of cerebral ganglia with reference to office is all that

* Taken by permission from "Anatomy, Physiology, and Hygiene," Tracy, Fig. 58, p. 195.

is here attempted. Such a classification is considered sufficient both for psychological and educational purposes:

1. The sensor ganglia are the portions of the cerebrum agitated by sensor waves. In some unknown way the mind feels these excitations. These feelings are called sensations.

2. The intellective ganglia are the portions of the cerebrum connected with knowing; as, when we perceive, remember, think. In some unknown way the mind uses these ganglia in perceiving, remembering, and reasoning.

3. The emotive ganglia are the portions of the cerebrum called into activity in feeling; as when we love or rejoice.

4. The motor ganglia are the portions of the cerebrum excited by volition. A mind is a creative first cause, and originates motion. Self, as will, starts motor nerve-currents—in some unknown way excites motor ganglia and thus originates motion.

Remarks.-1. The cerebral hemispheres are duplicates. Each is complete in itself. In case one is paralyzed, the soul in all its powers works through the other. The right hemisphere is connected with the left half of the body, and the left hemisphere with the right half of the body.

2. The cerebral ganglia are interconnected by nerve-fibers so as to form an organic unit. Each ganglion supplements all other ganglia. Thus may be seen the unity and harmony of the brain and local brain-centers.

3. Specific mental activities occur in connection with specific ganglionic areas. Thus, just behind the forehead, on either side, we find the language ganglia. Injure these, and we are unable to express ideas in words. The location of the special sensor ganglia by Ferrier and others seems to be now accepted.

4. The cerebrum dominates. Orders issued from headquarters

take precedence. Reflex action becomes the servant of volition. Walking is ordinarily reflex action; but, when we meet obstructions, action becomes intelligent and voluntary. Mental life is connected with the action of the higher nerve-centers. Only when the cerebrum is called to take part is there any distinct mental accompaniment. The cerebrum thus stands in relation to the lower centers somewhat as the head of an office stands in relation to his subordinates. The mechanical routine of the office is carried on by them. He is called on to interfere only when some unusual action has to be carried out, and reflection and decision are needed. Moreover, just as the principal of an office is able to hand over work to his subordinates when it ceases to be unusual, and becomes methodized and reduced to rule, so we find that the brain, or certain portions of it, are able to withdraw from actions when they have grown thoroughly familiar.

5. Cerebration is merely brain-action in knowing, feeling, and willing. The mind perceives, thinks, acts; but it works in connection with the ganglia. The brain produces no thoughts. Unconscious cerebration means unconscious mental activity. The cerebral ganglia are merely the instruments of mind.

6. Ganglia performing different offices may be near together, as in the spinal cord; while ganglia performing similar offices may be far apart. The difficulty of constructing a cerebral map is apparent.

7. We do not understand the precise nature of the relation of the body and the soul. In some unknown way the mind uses the gray matter of the brain to affect the body, or to gain impressions through the body.



By this is meant the capability to feel sensor excitation, as in seeing, hearing, and smelling.

Luminous bodies cause vibrations of luminiferous ether. Light-waves strike against the retina of the eye, causing sensor waves; these sensor nerve-currents, in

molecular waves, flash through the optic nerves, passing through the optic thalamus, and the tubercula quadrigemina to the optic ganglia. The sensor light-waves excite, agitate, or affect the optic ganglia of the cerebrum. The mind feels the agitation and is aware of the feeling. This conscious feeling of sensor excitation is called sensation.

Reflex Sensor Action. The mind in sensation is conscious of feeling the excitation. Sensor currents sent back from reflex centers are not felt-do not occasion sensation. Even agitations of the cerebral sensor ganglia do not necessarily occasion sensations. The clock struck ten, but I did not hear it, because I was absorbed in my work.

"What sees is mind,

What hears is mind;

[blocks in formation]

Diagram of the sensori-motor processes of cerebral activity. 1, optic thalamus with its centers and ganglionic cells. 2, corpus striatum. 3, course of the propagation of acoustic impressions: these arrive in the corresponding center (4), are radiated toward the sensorium (5), and reflected at 6 and 6' to the large cells of the corpus striatum, and thence at 7 and 7' toward the motor regions of the spinal axis. 8, course of tactile impressions: these are concentrated (at 9) in the corresponding center, radiated thence into the plexuses of the sensorium (10), reflected to the large cortical cells (11), and thence propagated to the large cells of the corpus striatum, and finally to the different segments of the spinal axis. 13, course of optic impressions: these are concentrated (at 14) in their corresponding center, then radiated toward the sensorium (at 15); they are reflected toward the large cells of the corpus striatum, and afterward propagated to the different segments of the spinal axis.-(Luys, "The Brain and its Functions," p. 61. Inserted by permission.)

« ForrigeFortsæt »