Classics in the
History of Psychology
An internet resource developed by
Christopher D. Green
ISSN
1492-3173
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Introduction to Psychology
George Sidney Brett (1929)
Authorized by the Minister of Education
First published in
Posted November 2001
Chapter IV
The Mechanism of Action
BODY
AND MND
The history of
the human race has always been a record
of two kinds of achievement, the physical and the mental. It is not necessary to begin any subtle discussions
about soul and body or mind and matter: we require to
approach the subject with no more or less than the simple practical
distinctions of daily life.
Every one
knows: what is meant by manual work: and in the same way every one knows what
is meant by intellectual work. Ordinary people use words which economize labour. When an action is called "manual",
the word is not used in such a way as to include all thinking: and when work is
called "intellectual", the word does not mean that nothing is
happening at the same time in any
other organ of the body except the brain. This warning against exaggerations
would not be necessary if there were not so many people to-day anxious to
invent theories called "idealistic" or "materialistic",
which, in fact, no reputable thinker ever held.
What the reader should never forget is the necessity of making
distinctions and the fact that all distinctions are artificial. We very rightly say that we think with the
brain: but if the brain is not properly nourished, if the blood-stream is not
of the right quantity and quality, the brain will not function at all. In short, the real agent is the organism:
manual and intellectual [p. 37] work are different
ways in which the organism achieves the total end of action.
Since the organism acts as a whole, it is impossible to understand an
action of any kind without a plan of the whole organism. For this reason a psychologist
requires to know such anatomy and physiology as will help him to realize how
the different parts of a total reaction or response are united. The most
important part of the organism for this purpose is called the nervous system:
after the nerves the muscles and glands need to be considered. It may be argued
that the list should be extended; that all bodily changes should be considered;
that the chemistry of digestion, for example, is an important factor. This argument would be quite valid, and
biochemistry does in fact contribute many important facts, but the answer to
this argument is the old proverb, "Art is long, life short". Many things must be taken for granted in
order that a few may be selected for special concentration.
THE NERVOUS
SYSTEM
The existence of nerves in the body was discovered in the third century
before Christ. At a very early date experiment showed that motion and sensation
were dependent on different groups of nerves.
But more exact knowledge was not attained until the beginning of the nineteenth
century. The anatomists proceeded from "gross
anatomy" (the general position of bones and muscles), to the finer anatomy
of tissues (histology) and nerves (neurology). At a later date the study of
pre-natal growth (embryology) revealed the stages of development and greatly
increased our knowledge of the structure of the brain and nerves. To this were
added the results of many experiments which showed the localization of areas on
the brain surface differing in structure [p. 38] and function. The differences
in structure of the surface layer or cortex are due to the formation of
distinct layers of cells at different stages of development. These facts and the terms now introduced will
be explained as we come to them.
It is best to begin by forming a general picture of the organism. The outer surface (periphery) is the boundary
of the body and the area which is exposed to all stimulation from without. This surface is in various ways sensitive,
because in it are the ends of nerves which run from
that surface inward to some centre. In the case of animals that are not highly
organized, this centre
will be a relatively independent knot (ganglion): but as we ascend the scale of
animal life, there is a greater complexity of arrangement and the formation of
multiple nerve-centres (ganglia) each controlling a segment of the animal. By nervous connections between these ganglia
the segments of the animal gradually become less and less independent, until, eventually,
it become necessary to develop a controlling ganglion at the foremost end of
the animal -- the higher nerve-centre or brain.
This evolution
of a higher centre for control of lower centres is called the integration of
the nervous system. Integration is a very important fact and must be constantly
kept in mind. All the possibilities of
co-ordination, that is making many separate movements harmoniously at one time,
depend on integration. The opposite -- disintegration
-- is equally important in all cases where we have to explain inability to
co-ordinate either movements or ideas.
The body, as we know it, is the product of a very long development, and
the stages of its growth are marked by levels of integration.
The first and most
essential functions were nutrition and growth; this system was first built up.
Then the [p. 39] range of action was increased, and the receptors, such as nose
and ear and eye, became specialized organs. Finally, the inner mechanism was so
far integrated as to form the rudimentary brain.
Human development, speaking generally, follows this line of development,
and the fact is important because it explains at once the necessity of genetic
psychology; for, by studying "genesis"
or development in time, we learn the right order in which the forms of training should be
used so as to meet the requirements of different ages from infancy to maturity.
For convenience in stating the facts we began with the surface and the
senses. But these are not to be separated
from the mechanism of motion which
is organic response to stimulus. The
organism in all higher animals is sensori-motor. The instrument of motion is the muscle. The motor nerves start from the nerve centres
in animals and control the muscular response. Muscles, tendons, and joints all
contain sense-organs, known as "proprio-ceptors",
so that the higher centres are kept informed
of changes in those parts, a third class of nerves called "intero-ceptors" are tile means by which we become
aware of stimulations of our internal organs, such as the alimentary
canal. A summary of this brief account
can be made as follows:
1. The main classes of nerves are sensory and motor.
2. Sensory nerves are classed according to their functions as extero-ceptor, proprio-ceptor, intero-ceptor.
3. The unit of action consists of the sensory (afferent) and the motor
(efferent) nerve, with the connector.
'This unit is called a reflex are because it may function in some cases
independently (v. p.
31). [p. 40]
THE STRUCTURE OF NERVES
In ordinary language the word "nerve" is used in a general
sense. The minute investigations of
modern anatomists have shown that a nerve is in reality a structure which has a variety of distinct parts. As this fact has some relation to the
problems of conduct, it is necessary to understand what is known about the structure and function of nerves.
When people think of a nerve, they think of a slender, string-like
object, of a whitish colour, and soft to touch. This is really a nerve fibre inclosed in a sheath of fatty substance called the medullary sheath. If
this nerve fibre was traced back from its termination in the skin surface or other
locality, it would prove to be a process or outgrowth of a cell-body which
consists of a nucleus [p. 41] and a quantity of protoplasm immediately surrounding
it. A nerve is thus seen to be much more
complex and organized than it appeared to be. To avoid confusion with older
ideas the nerve cell with all its branches is called a "neurone".
A neurone is a physiological unit comprising (1)·the nucleus, (2) the protoplasm surrounding it, and (3) two branches growing out from the cell body. One of these branches is a kind of main branch, and is called the "axis-cylinder" or "axon". The other reaches out a shorter distance and is called a "dendrite" (Greek for "tree") because it looks very much like a tree branch with fine twig-like extensions. These outgrowths from the [p. 42] body of the nerve cell must ;be distinguished from the side branches which are put out by the axis-cylinder and connect one neurone with another.
The sensory neurones have processes by which they are attached to the
posterior part of the spinal cord, and their cells lie outside the cord. The
motor nerves, on the contrary, are the axonal processes of cells lying in the
anterior part of the cord. These are the essential facts about the structure
and position of the sensory and motor
nerves.
The nerves act as conductors. The process of conduction is most probably a chemical process. It consists of a series of changes passed on from cell to cell, somewhat like the passage of a spark along a fuse, and capable of going in one direction only. It is called the nervous impulse. The neurones are not actually continuous according to the usually accepted view, though [p. 43] there is still some dispute about these difficult points of microscopic analysis. Whether continuous or not, the neurones have some form of conjunction which is called "synapse" (Greek synapto, join together). It is a form of connection between the end of an axon of one neurone and the end of a dendrite of another neurone. The place of the synaptic union offers some special degree of resistance to the transmission of the impulse along the neurones.
This point in the theory of neural action is important, because it must be assumed that the state of
affairs at a synapse will determine the total course of the impulse and the
ease or difficulty with which the wave of impulse continues its course. We may
assume that the facility of a response is explained by the reduction of
the resistance at the synapses, which would be the equivalent of that
facilitation which results from habit, that is to say the repeated use of a
certain track through certain synapses.
In the higher centres it might [p. 44] explain the capacity for acts of
memory, which would be a positive association between brain
areas through which the stimulus passes.
Since habit is a, kind of memory and memory a kind of habit, the
usefulness of this explanation will be obvious.
The actual processes taking place in the brain when a person
thinks or learns or remembers cannot be observed. The psychologist is, therefore, compelled to construct
an explanation which appears to harmonize with what is known and will give a
picture of the possible mechanism. This he
does by representing the process as travelling along a path in the brain. The existence of the path makes it easy for
the next mental process to travel the same way.
Like a track across a common or a path in the snow, the brain-path is a
line of least resistance. The facility
of habits is due to the fact that the path is made easier each time it is used.
What is called "motor memory" or habit is an example of this process
of path-making: the child cart repeat the multiplication table until it is an automatic process requiring
little or no attention. On the other
hand, when a particular multiple (9 times 7 is 63) is wanted, the path is
easily found, and the knowledge revived.
LEVELS OF INTEGRATION
The nerves which have been described above are
integrated or brought into union at different levels according to the degree to
which the organism is developed. The less developed organisms are those in which
the reflex arcs are relatively independent, and stimulation of one segment
produces motor response limited to that segment. As the development progresses, these arcs become
more complex, because branches front the axons run out and meet at other
points. The effect of this more complex
arrangement is that the movement of an [p. 45] [figure] [p. 46] impulse through
the original are ·can be checked (inhibition) and either wholly restrained or redirected.
Thus there comes into existence,
over and above the primary arcs, a more complex system of arcs forming the
lowest or "spinal" system of arcs, so called because the whole of the are is contained within the spinal cord.
The next higher level is formed by further developments from the spinal
ganglia. These new outgrowths are
grouped together at the anterior extremity of the spinal cord and form the
rudimentary brain in animal development or the basal ganglia of the brain in
all vertebrates.
Finally, the highest centres are developed, and the brain is produced to
form the centre of complete integration.
The arrangement of the nervous system in different levels is important
for various reasons. It provides a clear
meaning for the phrase "mental development" when this is applied in
comparative psychology to the relation between animals and man. A comparison between different animals can be
made by observing the extent to which the total mass of matter is developed at the
foremost end of the spinal cord where the arcs of the second level are
united. A comparison between human and
other animal organisms shows a similar difference in the development of the
brain both in its total mass and its special parts. It is also true that arrested development or
retardation shows the same features, for the ·first or lowest level may be
completely constructed, but the failure to progress is shown by relatively poor
co-ordination if the mechanism of the second level is not adequate, or by
intellectual inferiority if the mechanism of the third level is not normal.
The experimental
method shows the same results. [p. 47] If the higher centres are destroyed, the
lower centres will continue to function and will revert to the simpler forms of
combination of reflex arcs. Various
stages of intoxication afford a good example of the facts, as the obvious signs
are the different degrees to which control over the ideas, perception, and movements
is progressively lost.
Another aspect of this doctrine of levels is seen in its relation to learning. The primary level is so firmly established in the structure of the organism that its [p. 48] functions do not require to be learned at all. The functions of this level are performed from the beginning of life as the hereditary endowment of the organism. The beating of the heart, the action of the stomach, and reflexes in general belong to this primitive class of organic functions.
The functions of the second level are less well established. The general or diffused character of the movements
in young animals and in children is due to the spread of stimulation through
different channels with no fixed or orderly connection to bring about a
definite selection of preferred paths.
The effect of training is to select and establish the most suitable
lines of discharge, giving a preference to some and inhibiting, others. This
may be observed in the way a child learns to write. The first efforts are
diffused over the neural centres, so that many muscles (hand, arm, face,
tongue) are brought into action. As the operation becomes more defined and the
correct habits are acquired, the surplus movements are inhibited. This
"economy of effort" is made more and more complete, until only the
absolutely necessary movements are employed.
Finally, the highest
degree of organization and
orderly conduct is reached when the functions of the third level are
established. When, for example, a
particular order is given, its meaning is properly understood, the sensory and
motor centres are properly co-ordinated, and the whole behaviour is the result
of a complete unification of the various factors, we may call the result a
complete form of organic response. In physical training, after the individual
movements have been acquired, a single word of command is enough to begin the
whole exercise. If we consider the complexity of the response when the pupil is
told to draw an object from memory, it will not be difficult to understand the
importance of the selection [p. 49] and co-ordination which is characteristic
of this highest level.
AUTONOMIC SYSTEM
The autonomic system is an important part of the bodily mechanism. This consists of ganglia (groups of nerve-endings)
which lie outside the spinal cord and form chains of neural centres running
parallel to the spinal cord. The word
"autonomic" is used to cover three large groups of nerves--the
cranial or upper part, the sympathetic or intermediate part, and the sacral or
lower part. This division is not important for the present purposes, but is
mentioned because the term "sympathetic system" is often loosely used
for the whole autonomic system. The word
autonomic (cf. autonomy) means "self-regulating". It is
sometimes called "involuntary", because it is not controlled by the
intellect or rational will.
The autonomic system
governs the action of the smooth muscles, and is, therefore, chiefly concerned
with visceral organs and
glands. For psychology its importance lies in the fact that it controls the
kind of reaction which accompanies emotional states
and constitutes their peculiar
quality. If an animal is excited by fear
or anger, several bodily changes take place.
The secretion of gastric juice may be reduced, the heart may beat more
violently, breathing becomes deeper, and the adrenal glands are excited to pour
into the blood an enlarged
quantity of adrenalin. Apparently all these changes are spontaneous forms of
adaptation to the situation, and they all serve to heighten activity. The most quoted case is that of the adrenal
glands, because the action of these glands increases the strength and endurance
of the creature. While all these
activities [p. 50] are in progress, it is unlikely that the intellectual powers will remain
undiminished.
It is, therefore, necessary to remember that, if emotions are aroused,
intelligence, control, and forethought will be reduced. The use of methods which frighten or irritate
a child will never be likely to
promote understanding or assist the progress of intellectual work.
MUSCULAR ACTION
A few facts about the muscles are important for the student of human
action. Muscles are bundles of fibres covered
by a sheath. They have a power of
contracting or relaxing, and this is a persistent quality called the "tone"
of the muscle. The motor-nerve which runs to a muscle
gives it the necessary stimulus and causes it to contract sharply; after this
it relaxes again, unless some peculiar condition causes a failure in this
process, and muscular rigidity ensues.
The muscular mechanism is arranged on the principle of antagonism or
balance. The extensors and flexors counteract each other, producing in normal
cases a proper rhythm of action: defective action of this mechanism produces jerky
and erratic movements. The muscles of
the skeleton are classed as "striated" or striped muscles, because
the fibres in the sheath are marked with alternate light and dark bands across
them. The visceral muscles, such as
those of the alimentary canal, arteries, bladder, and other organs, have no
such stripes, and are called "unstriped" The heart is a muscle constructed of muscular
tissue in which the fibres are lightly striped, but are not made exactly like
those of the ordinary striped muscles.
For general
purposes it is sufficient to remember that muscles are classed as striped or
unstriped: that these practically correspond to skeletal and visceral muscles:
[p. 51] that, accordingly, the striped muscles are employed for voluntary and
the unstriped for involuntary action. The skeletal muscles act
as levers: the visceral muscles produce action in the walls
of the organs in which they are found, causing contraction or expansion by
which the contained space is decreased or increased. Pallor, flushing, quickening of the pulse,
and the contraction of the large intestine are examples of the activity of visceral
muscle.
GLANDS
Emphasis has been laid throughout this account of the body on the organic
character of action, which means chiefly that all the parts co-operate and
depend on each other for support. This
feature is shown even more clearly when we consider the glands.
The glands commonly known are masses of cells which produce
characteristic secretions and periodically discharge the secretion through some
duct. To this class belong the liver
(bile), the pancreas (pancreatic juice), lachrymal or tear glands, sweat
glands, etc. about these glands nothing need be said beyond noting that they
are "organs of response", and that they take a significant place in
a, person's total reaction. They may be excited by external stimuli,
for example, tear gas; or ;by internal stimuli, for
example, bad news. The relation between
these kinds of stimuli and the response is an interesting problem to be
discussed in relation to emotions.
The glands mentioned
above have ducts: others are not so constructed and are called ductless. Modern physiology has made so much progress
in the study of the ductless (endocrine) glands, that they form the subject of
the special science called endocrinology. These glands operate on the whole
system, because their [p. 52] cells produce chemical compounds in minute
quantities which are taken up into the blood-stream as it flows around them.
The products of these glands are called "hormones" or excitants, and
they operate on the body by accelerating
(or sometimes depressing) the activity of other organs.
The chief ductless glands
are the thyroids, parathyroids, pituitary, pineal,
and adrenal glands. The thyroid secretion
affects the whole growth of the body: defective thyroid activity produces the
type called Cretin -- stunted, thick-skinned, and permanently infantile. The
adrenal glands which produce adrenalin are specially
interesting, because this secretion has the power of increasing muscular
activity and endurance. Biologically it serves to make animals more capable of
endurance in the excitement of rage or fear and in the acts of fighting or escaping. The other glands have important functions for
which we may refer inquirers to the works on general physiology. The details are not essential to the present
purpose. If the reader will form, from
what is here said, a mental picture of the complete machinery of the body,
analyzed into nerves, muscles, and glands, that picture will serve to make
intelligible the physiological references which inevitably occur in the
explanation of psychological functions.