Behavior depends on the integration of numerous processes within the body. This integration is provided by the nervous system with the help of the endocrine glands.
What are the basic units of the nervous system? How do they work?
The brain is composed of some 10 to 12 billion specialized nerve cells called neurons. These form the basic units of the nervous system whose functions influence learning and mental functioning, emotion, and thought. Neurons are also responsible for the transmission of impulses.
Neurons receive stimulation by way of their dendrites and cell bodies and transmit impulses via their axons. The junction between the axon of one neuron and the cell body or dendrites of the next neuron is called a synapse. Neurons that carry messages from the sense receptors to the brain and spinal cord are called afferent neurons. Those that transmit signals from the brain and spinal cord to the effector organs, the muscles and glands are the efferentneurons. Axon fibers group together to form nerves; neuron cell bodies are grouped together into ganglia.
How may the organization of the nervous system be described? How is it divided?
The nervous system is divided into the central nervous system and the peripheral nervous system. The central nervous system includes all the nerves in the brain and the spinal cord. The nerves leading from the brain and the spinal cord to the other parts of the body compose the peripheral nervous system.
Subdivisions of the peripheral nervous system are the somatic system and the autonomic system. The nerves of the somatic system carry messages to the central nervous system from the sense receptors, muscles and body surface. They make us aware of pain, pressure, and temperature variations. They also carry impulses from the central nervous system back to the body parts where they initiate action. The muscles we use in posture and balance are controlled by these nerves.
The nerves of the autonomic system run to and from the internal organs, regulating such processes as respiration, heart rate, and digestion. The autonomic system plays a major role in emotion. The nerve fibers running from various parts of the body to and from the brain are gathered together in the spinal cord. Simple reflexes, such as the knee jerk, are carried out within the spinal cord by a three-neuron arc consisting of afferent and efferent neurons and interneurons.
How is the hierarchical structure of the brain described? What are the functions of each part?
The human brain is composed of three concentric layers: a central core, the limbic system, and the cerebrum.
1. Central core - includes the medulla responsible for respiration and postural reflexes; the cerebellum concerned with motor coordination; the thalamus, a relay station for incoming sensory information; and the hypothalamus, important in emotion and in maintaining homeostasis. The reticular system, which crosses through several of the above structures, controls the organism's state of arousal.
2. Limbic system - controls some of the "instinctive" activities like feeding, attacking, fleeing from danger and mating. These are regulated by the hypothalamus. The limbic system also plays an important role in emotion and memory.
3.Cerebrum - is divided into two cerebral hemispheres. The cerebrum is more highly developed in human beings than in any other organism. It is covered by a thick layer or nerve cell bodies, the cerebral cortex. In Latin, cortex means "bark", hence the term, "gray matter". The cortext is convoluted and controls discrimination, choice, learning and thinking referred to as the "higher mental processes". Certain areas of the cortex represent centers for specific sensory inputs or for control of specific movements. The remainder of the cortex consists of association areas.
How is the brain said to be divided?
The two cerebral hemispheres are connected by nerve fibers, the corpus callosum. The major, left hemisphere, which is almost always larger than the minor, right hemisphere, is skilled in the use of language while the right is specialized for mental imagery and the understanding of spatial relationships. The left cerebral hemisphere controls the right side of the body and the right hemisphere, the left side.
As early as 1861, the anthropologists, Paul Broca examined the brain of a patient with speech loss and found damage in an area of the left hemisphere. This region, known as Broca's area, is involved in the production of speech sounds.
What are the divisions of the autonomic nervous system?
The autonomic nervous system is made up of two parts, the sympathetic division and the parasympathetic division. The sympathetic division is usually involved in excited action and the parasympathetic division during quiescent states.While the two divisions are often antagonistic, they interact in complex ways, and their interaction is not fully understood.
Why are the endocrine glands important?
The endocrine glands are also called ductless glands. These ductless glands are important regulators of our behavior. The pituitary at the base of the brain is thought to exert a regulatory control over the adrenals, thyroid, and gonads. From the pituitary comes the "growth hormone", (ACTH). Over secretion of the hormone causes giantism; undersecretion causes dwarfism.
The adrenal glands lying above or near the kidneys have two physical parts: 1) medulla which secrets adrenaline; and 2) adrenal cortex, which relates to salt and carbohydrates metabolism. The glandular system pours out a chemical called norepinephrine, which slows down the very activity stimulated by the adrenaline.
The thyroid at the trachea just below the larynx secrets thyroxin. It helps to regulate the basal metabolic rage. When there is undersecretion the person tends to be lazy and easily tired, often gains excessive weight. Other factors can also cause these symptoms. On the other hand, excessive secretion causes an elevation of metabolism, resulting in overactivity, excitability, and sometimes loss of weight. Goiter is an enlargement of the thyroid gland.
The gonads, which are the testes in the male and ovaries in the female are also important. The androgen or male hormone and estrogen for female hormone are related to the development of secondary sex characteristics, such as hair around the organs. In the male, they may relate to voice change and skin problems. A female hormone, progesterone secreted by the ovary and placenta during pregnancy helps to keep the uterus in a relatively quite state during the development of the fetus.
From the pancreas comes the hormone insulin. When the blood sugar rises above a certain level, insulin causes the liver to absorb and store the excess amount. When the blood sugar level drops, the liver releases more blood sugar in the form of glucose. If sufficient insulin is produced by the pancreas, blood sugar escapes through the kidneys instead of being stored in the liver. This condition, called diabetes, may be corrected by the artificial injection of insulin.
How is behavior influenced genetically?
To understand the biological foundations of behavior we need to know something about hereditary influences. The hereditary units we receive from our parents and transmit to our offspring are carried by microscopic particles, known as chromosomes, found in the nucleus of each cell in the body. Most body cells contain 46 chromosomes. At conception, the human being receives 23 chromosomes from the father's sperm and 23 chromosomes from the mother's ovum. These 46 chromosomes form 23 pairs. Each chromosome is composed of many individual hereditary units called genes. The total number of genes in each human chromosome is aroung 1,000 or more. Chromosomes and genes will influence psychological as well as physical characteristics. Most genes are dominant, others are recessive, and some are sex-linked.
How is the influence of heredity studied?
One method is by selective breeding. Another method is twin studies. Selective breeding is mating animals that are high in a certain trait or low in a certain trait. Twin studies is sorting out the effects of environment and heredity in which the characteristics of identical, or monozygotic are compared with those of fraternal, or dizygotic twins.
The hereditary potential with which an individual enters the world is very much influenced by the environment that he or she encounters. All behavior depends on the interaction on the individual's potential, but what happens to this potential depends on the environment.
What specific studies on hereditary influence can be cited?
Psychological literature cites the following.
1. The Jukes Family. Max Jukes who was born about 1720 was believed to be an ignorant backwoodsman. Max and his wife a mentally retarded woman, started a long line of offspring that, for the most part, consister of paupers, feeble-minded persons, and criminals.
2. The Homny Family. The study of this family line begin woth a mother who was feeble-minded and sexually promiscuous; and with a father who had no visible means of support and lacked personal pride. Their home was dirty. Their offspring became sex offenders; at least five of the seven children were feeble-minded.
3. The Edwards Family. Jonathan Edwards, an able, upright man who was born in 1703, and his brilliant wife Sarah Pierrpent were the forebears of an outstanding line of Americans. Among their famous descendants are included well-known lawyers, scientists, physicians, clergymen, army and navy officers, statesmen and college professors and presidents.
4. The Darwin Family. Charles Darwin and his wife started a line of descendants that included at least five British scientists whose eminence can be measured by the fact that they achieve the distinction of being elected as Fellows of the Royal Society.
5. The Kallikak Family. As can be observed in this case, Martin Kallikak (fictitious name), sired two family lines that displayed very different inherited potentialities. During the Revolutionary War, Martin Kallikak, a soldier, mated with a feeble-minded girl. The son, born of this woman, started a family line of which 480 descendants were traced. Of this number only about 46 were considered normal, the others were feeble-minded or below normal in intelligence. The story of these "bad" Kallikas is one of prostitution, shiftlessness, depravity, and crime.
After the Revolutionary War, Martin Kallikak married a woman of good family stock. Among the 496 descendants resulting from this marriage, all but five were normal. Many of them became worth-while citizens, including lawyers, successful businessmen, doctors, judges, college presidents, teachers, and other professional leaders.
Evaluation. These studies should not be accepted as representative of the fact that biological inheritance has a greater effect upon an individuals life pattern than his environment to which he is exposed, upon individual's behavior cannot be ignored.
How is human behavior controlled by the physiological processes? How does it make adjustment?
According to Herbert Spencer "life is a continuous adjustment of internal relations to external relations". Our adjustment to environmental changes is possible only within narrow physiological limits. Example: The human body can adjust itself to changes in external temperature only when these changes are very moderate. It can be viewed that life is a stimulus-response phenomenon wherein the organism adjusts itself to the environment or adjusts the environment to itself. Generally, the adaptation made in order to survive as an individual or as a role can be seen in three ways:
1. Protection - This is in the form of defense, avoidance, and escape reactions.
2. Maintenance - This is seen in procuring materials for the growth and maintenance of the protoplasm and to supply energy.
3. Reproduction - This is seen in the perpetuation of species.
The human body is a complex structure of living body - physiology. The study of one part demands a knowledge of all the other parts. The human body is composed of various parts; each of these performs a definite function. Such parts are called organs. Two or more organs may differ somewhat in their individual functions but collectively they may serve a definite purpose in the body. The ensemble of organs is a system.
