PART II. AN INTRODUCTION TO THE HUMAN NERVOUS SYSTEM FOR SOCIAL SCIENTISTS

 

Why We Need a New Biology

It has become politically incorrect to talk about biology in liberal circles. Speaking to sociologists about biology one is likely to notice the eyes glazing over of the listener, or be subject to a polemical attack against the association between biology and conservative ideas.

The problem is that liberal sociologists assume their thought is non-racist and not conservative. However, in a previous volume, it has been shown that liberal sociology is really just the liberal version of the equality of opportunity racism doctrine of American laissez-faire capitalism. Thus, liberal sociology is itself tainted with racism. It is not biology that is the backbone of American racism, but rather equality of opportunity doctrines. And backing up American racism is American moralism. Sociology has a version of moralism because its sociological determinism stresses that people can change their ways of life if they just try hard enough or they get a little assistance from others. This idea plays into the hands of the racists who say that those people in poverty are there because they just do not try hard enough or do not seek the proper help.

Sociological moralism needs to be destroyed for several reasons. The first, is that sociological moralism is really just a liberal version of racism. Second, Americans can stop being so unnecessarily cruel to people they have traditionally labeled "deviants." Sociologists like this idea of deviancy because they have a sociological determinism that says it one need not suffer from deviancy if one just applies a little willpower and just stop doing the deviant act or seek the proper help. The third reason deals with shoddy thinking. A sociology without any biology is a completely biased discipline that cannot tell the difference between what is more strictly biological and what is sociological.

If we acknowledge that sociology is racist and moralist, then the debate over biology takes an entirely new look. We need to take another look at the doctrine of evolution. This new look is more likely today because there has been a biological revolution since the 1960s. This has provided the basis for a radical biology that backs up the radical biology of Darwin. Darwin was right all along, but was too radical for American sociologists to accept. Now we need to promote a new radical biology that can serve as an antidote to the moralism of American sociology.

There are three areas which have contributed to the furtherance of the importance of biology to the social sciences. The first is an improved understanding of the role of physical evolution in the development of the human brain. In 1970 Paul Maclean published an article on the triune nature of the brain. He argued that the human brain is really an composite of three brains and that these brains had definite animal origins. A second area has been that of sociobiology and the understanding of social evolution in affecting human behaviors. And, finally, the third area is that of the role of neurotransmitters in mental illness. The biological and chemical bases of many mental illnesses has renewed interest in the biological bases of human behavior.

Each of these three areas will be investigated in a separate chapter. However, two introductory chapters are necessary. The chapter on the nervous system presents the basic concepts one needs to understand in order to understand the progress being made in the chemical and biological understanding of the brain. Crucial issues in brain (and the closely linked sexual) research are presented in a following chapter. These issues are the ones that are discussed in the third part of the book that deal with the subjects traditionally treated as deviancy in sociology.

CHAPTER 6. THE HUMAN NERVOUS SYSTEM

To really understand what happens in the human brain the reader has to become familiar with at least the basic parts of this structure. Therefore, a brief review will be presented. Since this is a very voluminous subject the details will be presented in accompanying tables, while the text will present just the highlights.

Neurons

The human nervous system is composed of nerve cells called neurons. There are more than two hundred varieties of neurons, but a typical neuron consists of just several parts. The first part is the cell body, which contains the nucleus. The second part consists of branching nerve fibers known as dendrites (from the Latin word "dendron" for tree). Most of them receive nerve signals, while others send signals. At the opposite side of the cell body from the dendrite is the axon. Longer than a dendrite, the axon is insulated by a thick coating of myelin. The dendrites have thousands of sprouts or "spines" which make contact with other dendrites and also with axons and nerve cells.

Nerve Messages

The actual nerve messages that travel through the nervous system are both electrical and chemical in nature. Nerve messages start out as electrical impulses that are transmitted through the neuron from axon to cell body to dendrite. The message is not solely electrical however as most dendrites and axons do not make direct contact. Rather they end at a slitlike gap that separates them from a target cell or another nerve fiber. The gap is called a synapse, from the Greek word "synapsis," meaning junction. A cubic millimeter of the adult brain cortex (about the size of the head of a pin) contains approximately 10 trillion synapses. To send the message over this synapse the message has to be "ferried" across by special chemicals called neurotransmitters.

Neurotransmitters are recycled. Broken down by MAO and recycled back.

Spinal Cord

When looking at the human brain several key parts stand out. The first part one really notices is the cerebrum. This is the huge, much convoluted gray matter that is the main rational center of the brain. The cerebrum, however, hides a multitude of other brain parts. Indeed, the cerebrum lies over the evolutionarily older parts of the brain.

The other part of the brain that most people immediately notice is the spinal cord. The spinal cord relays messages from the parts of the body to the brain and then from the brain to the parts of the body. The afferent nerves transmit nerve impulses into the central nervous system, in contrast to efferent nerves that transmit nerve impulses away from the central nervous system.

The spinal cord and brain constitute the central nervous system. Those parts of the nervous system outside the spinal cord and brain constitute the peripheral nervous system. This system includes the cranial and spinal nerves, and is further divided into the somatic nervous system and the autonomic nervous system (ANS). The somatic system is concerned with the activity of the musculature, which is the means whereby overt behavior is produced. The ANS, on the other hand, controls the visceral structures -- the glands and internal organs -- and regulates the primarily involuntary bodily activities. It is subdivided into the parasympathetic nervous system, which is mainly dominant when a person is at rest, and the sympathetic nervous system, which is dominant when activity is called for and energy needed for action. Despite the term autonomic, however, the ANS is not independent from the brain. For example, the hypothalamus and medulla of the brain are important structures controling of ANS functions.

Hind Brain

At a quick glance the spinal cord appears to lead directly to the cerebrum. In between the cerebrum and the spinal cord, however, there is a great many parts of the brain with which most people are just not familiar. We will quickly review some of these main parts.

The spinal cord actually ends when it enters the hole at the bottom of the skull, known as the foramen magnum. From this point upwards the brain stem takes over. The brain stem consists of two parts: the hind brain and the midbrain. The hind brain in turn consists of two parts, the medulla oblongata and the pons. Thus, the brain stems consists of the medulla oblongata, the pons, and the midbrain.

Cerebellum

Three pairs of peduncles attack the cerebellum (considered a part of the hindbrain) to the brain stem. This structure is situated under the rear of the cerebrum. The cerebellum is responsible for controlling such bodily movements as muscle control. When one says practice makes perfect, they are referring to the process of fine adjustments in the accuracy of muscle control applied by the cerebellum.

Midbrain

Reticular Formation

Part of the brain stem is the central part of the medulla oblongata, pons, and midbrain known as the reticular formation. The reticular activating system in this formation acts like a central clearing house sifting through the flood of information that comes into the brain. This structure sends the important material on to higher brain structures while blocking out other, less important matters, such as otherwise irritating background noise when one is trying to concentrate.

Diencephalon

Sitting on top of the upper most part of the brain stem (the midbrain) is the diencephalon. This is one part of the forebrain (along with the telencephalon.) The diencephalon consists of the thalamus, epithalamus, hypothalamus, and subthalamus. These structures are very important in controlling the emotional aspects of human feelings.

The largest physical part of the diencephalon is the thalamus. As the name indicates, the hypothalamus sit under the thalamus. It is the main controlling center of the autonomic nervous system. The epithalamus lies, in part, over the top of the thalamus. The subthalamus also lies below the thalamus.

Telencephalon

After having discussed the hindbrain and midbrain, and part of the forebrain, the diencephalon, we now turn our attention to the remaining parts of the brain that are all parts of the forebrain known as the telencephalon. This includes the basal ganglia, the limbic system, and the cerebrum.

Basal Ganglia

So far we have been adding each newly introduced part of the brain (with the exception of the cerebellum) to the top of the spinal cord. This has been true of the parts of the brain stem and the diencephalon. However, we are now going to add items to the sides of the diencephalon. On each side of the thalamus we add a structure for each side of the brain, the right side and the left side. The parts we add are parts of the basal ganglia, which surrounds and overhang the thalamus. The parts of the basal ganglia are the archistriatum (containing the amygdala), the paleostriatum (containing the globus pallidus), and the neostriatum (containing the corpus striatum which in turn consists of the caduate nucleus and putamen).

Limbic System

Another important part of the telencephalon that surrounds the basal ganglia are parts of the extensive limbic system, which colors our thoughts with emotions. The limbic system gets its name from "limbus" meaning border or edge. There is an arc of cortical material that surrounds the structures that bind together the two halves of the cerebrum (among these the corpus callosum). There are two main components to this part of the limbic system. The ring of cortex around the corpus callosum includes the subcallosal, cingulate, and parahippocampal gyri, as well as the small paraterminal gyrus. The partial ring contains the hippocampal-dentate complex and the supracallosal gyrus.

Cerebrum

Covering all the above parts is the cerebrum, which looks something like a boxing glove. This, the largest structure of the brain, consists of many different lobes. The front part of the glove corresponds to the frontal lobe. The part of the glove that covers the back of the hand corresponds to the parietal lobe. Corresponding to the skirt around the boxing glove that surrounds the wrist is the occipital lobe . The thumb of the glove corresponds to the temporal lobe.

The cerebrum is divided into two halves called hemispheres, with a right and left hemisphere. The outer few millimeters of gray matter covering the cerebral hemispheres are called the cerebral cortex or pallium. The cortex is bumpy-looking, these bumps being "humps" known as convolutions or gyri.

The lateral ventricles, one in each cerebral hemisphere, are roughly C-shaped cavities filled with cerebrospinal fluid. Each lateral ventricle consists of a central part in the region of the parietal lobe from which horns extend into the frontal, occipital, and temporal lobes. The horns are known as the frontal, occipital, and temporal horns.

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I. Prosencephalon

(forebrain)

I.1 Telencephalon

Cerebrum

Frontal planning of the future

lobes

Parietal abstract functions; mathematics

lobes

Occipital visual capacities such as those used in

lobes architecture

Temporal musical talent

lobes

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LIMBIC

SYSTEM

Ring of cortex:

subcallosal this and next one constitute septal

gyrus area

paraterminal part of septal area

gyrus

cingulate sexual behavior; obsessive

gyrus compulsion

parahippocampal

gyrus

Partial ring

of cortex:

hippocampal- learning, long-term memory, emotional

dentate reactions, sexual behavior

complex

supracallosal

gyrus

fornix

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BASAL integration of motor activity

GANGLIA

Archistriatum:

amygdala rage, aggression, sexuality

Paleostriatum:

globus

pallidus

Neostriatum: high in DA

corpus

striatum

caudate

nucleus

putamen

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I.2 Diencephalon

Thalamus where sensations are first consciously

experienced

reticular nucleus

intralaminar

ventral group

posterior group

lateral group

medial group

anterior group

Hippocampal

formation

hippocampus important for forming long-term memories

parahippocampal

gyrus

dentate

gyrus

Cingulate

gyrus

Amygdala electrical stimulation of the amygdala DA

in humans induces feelings of fear

or anger; part of medial forebrain

bundle

Septal area along with hypothalamus and raphe nuclei

of the reticular formation, is inter-

connected via the medial forebrain bundle o1o-

Hypothalamus works with the autonomic nervous system:

blood pressure; heartbeat rate adjustment;

and defensive reactions (heart beats fast,

increases blood clotting materials, and

stops digestive process)

the hypothalamus controls the pituitary gland

(the master gland that controls the work of

the other glands, including the sex glands)

center: hunger center; satiety center -- sense

of fullness; hormone vasopressin, or ADH, tells

kidneys to conserve water; sex center; fear center

anger center; pain center; and pleasure center.

part of medial forebrain bundle

lateral

preoptic

supraoptic

tuberal

mammillary when posterior nuclei stimulated results in

increased heart rate; inhibition of secreto-

motor activity in gastrointestinal tract

Epithalamus lies above thalamus

medial habenular

nucleus

lateral habenular

nucleus

pineal gland light sensitive; biological clock SE

and stalk

stria

medullaris

Subthalamus motor control

subthalmic

nuclei

zona

incerta

field of

Forel II

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BRAIN STEM

RETICULAR FORMATION a stream of exciting impulses keeps body muscles

in tone

raphe cell part of medial forebrain bundle

group

lateral reticular

group

central cell

groups

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II. Mesencephalon

(Midbrain)

Upper:

red nuclei receives afferents from cerebellum and cerebrum

substantia receives afferents from basal ganglia DA, GABA, substance P

nigra and reticular formation; involved in

Parkinson's disease

Lower:

periaqueductal electrical stimulation reduces perception ENK B-END

gray of pain

raphe nuclei overlapping nuclei that are specialized SE ENK

components of the reticular formation

(lie along the midline of the tegmentum)

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III. Rhomencephalon

(hind brain)

Metencephalon

Pons part of a relay between the cerebral hemi-

spheres and the cerebellum

tegmentum ventral portion of pons; ventral tegmental

area is the reward center for heroin

Locus sleep, wakefulness, control of mood most important source of NE

ceruleus

Cerebellum motor control; balance

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Myelencephalon

medulla

oblongata

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Spinal cord

 

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