The Bases of Human Behaviour

Activity . Structure of the Brain For the convenience of study, the brain can be divided into three parts: Hindbrain, Midbrain and Forebrain (Figure . ). Hindbrain This part of the brain consists of the following structures: Medulla Oblongata : It is the lowest part of the brain that exists in continuation of the spinal cord.

It contains neural centres, which Fig. . : Structure of the Brain Hypothalamus Pituitary gland Thalamus Cerebrum (cerebral cortex) Pineal gland Brainstem Midbrain Pons Medulla oblongata Spinal cord Cerebellum a vital role in our behaviour. It regulates physiological processes involved in emotional and motivational behaviour, such as eating, drinking, sleeping, temperature regulation, and sexual arousal.

It also regulates and controls the internal environment of the body (e.g., heart rate, blood pressure, temperature) and regulates the secretion of hormones from various endocrine glands. Thalamus : It consists of an egg-shaped cluster of neurons situated on the ventral (upper) side of the hypothalamus. It is like a relay station that receives all incoming sensory signals from sense organs and sends them to appropriate parts of the cortex for processing. It also receives all outgoing motor signals coming from the cortex and sends them to appropriate parts of the body.

The Limbic System : This system is composed of a group of structures that form part of the old mammalian brain. It helps in maintaining internal homeostasis by regulating body temperature, blood pressure, and blood sugar level. It has close links with the hypothalamus. Besides hypothalamus, the limbic system comprises the Hippocampus and Amygdala.

The hippocampus plays an important role in long-term memory. The amygdala plays an important role in emotional behaviour. The Cerebrum : Also known as Cerebral Cortex , this part regulates all higher levels of cognitive functions, such as attention, perception, learning, memory, language behaviour, reasoning, and problem solving. The cerebrum makes two-third of the total mass of the human brain.

Its thickness varies from . mm to mm, which covers the entire surface of the brain and contains neurons, neural nets, and bundles of axons. All these make it possible for us to perform organised actions and create images, symbols, associations, and memories. The cerebrum is divided into two symmetrical halves, called the Cerebral Hemispheres.

Although the two hemispheres appear identical, functionally one hemisphere usually dominates the other. For example, the left hemisphere usually controls language regulate basic life supporting activities like breathing, heart rate, and blood pressure. This is why medulla is known as the vital centre of the brain. It has some centres of autonomic activities also.

Pons : It is connected with medulla on one side and with the midbrain on the other. A nucleus (neural centre) of pons receives auditory signals relayed by our ears. It is believed that pons is involved in sleep mechanism, particularly the sleep characterised by dreaming. It contains nuclei affecting respiratory movement and facial expressions also.

Cerebellum : This highly developed part of the hindbrain can be easily recognised by its wrinkled surface. It maintains and controls posture and equilibrium of the body. Its main function is coordination of muscular movements. Though the motor commands originate in the forebrain, the cerebellum receives and coordinates them to relay to the muscles.

It also stores the memory of movement patterns so that we do not have to concentrate on how to walk, dance, or ride a bicycle. Midbrain The midbrain is relatively small in size and it connects the hindbrain with the forebrain. A few neural centres related to some special reflexes and visual and auditory sensations are found here. An important part of midbrain, known as Reticular Activating System (RAS), is responsible for our arousal.

It makes us alert and active by regulating sensory inputs. It also helps us in selecting information from the environment. Forebrain It is considered to be the most important part of the brain because it performs all cognitive, emotional, and motor activities. We will discuss four major parts of the forebrain: hypothalamus, thalamus, limbic system, and cerebrum.

Hypothalamus : The hypothalamus is one of the smallest structures in the brain, but plays behaviour. The right hemisphere is usually specialised to deal with images, spatial relationships, and pattern recognition. These two hemispheres are connected by a white bundle of myelinated fibers, called Corpus Callosum that carries messages back and forth between the hemispheres. Cerebral cortex has also been divided into four lobes - Frontal lobe, Parietal lobe, Temporal lobe, and Occipital lobe.

The Frontal lobe is mainly concerned with cognitive functions, such as attention, thinking, memory, learning, and reasoning, but it also exerts inhibitory effects on autonomic and emotional responses. The Parietal lobe is mainly concerned with cutaneous sensations and their coordination with visual and auditory sensations. The Temporal lobe is primarily concerned with the processing of auditory information. Memory for symbolic sounds and words resides here.

Understanding of speech and written language depends on this lobe. The Occipital lobe is mainly concerned with visual information. It is believed that interpretation of visual impulses, memory for visual stimuli and colour visual orientation is performed by this lobe. Physiologists and psychologists have tried to identify specific functions associated with specific brain structures.

They have found that no activity of the brain is performed only by a single part of the cortex. Normally, other parts are involved, but it is also correct that there is some localisation of functions, i.e. for a particular function, a particular part of the cortex plays a more important role than the other parts. For example, if you are driving a car, you see the road and other vehicles by the function of your occipital lobe, hear the horns by the function of your temporal lobe, do many motor activities controlled by parietal lobe, and make decisions by the help of frontal lobe.

The whole brain acts as a well coordinated unit in which different parts contribute their functions separately. Spinal Cord The spinal cord is a long rope-like collection of nerve fibers, which run along the full length inside the spine. Its one end is connected with the medulla of the brain and another is free at the tail end. Its structure all along its length is similar.

The butterfly shaped mass of grey matter present in the centre of the spinal cord contains association neurons and other cells. Surrounding the grey matter is the white matter of the spinal cord, which is composed of the ascending and descending neural tracts. These tracts (collections of nerve fibers) connect the brain with the rest of the body. The spinal cord plays the role of a huge cable, which exchanges innumerable messages with the CNS.

There are two main functions of the spinal cord. Firstly, it carries sensory impulses coming from the lower parts of the body to the brain; and motor impulses originating from the brain to all over the body. Secondly, it performs some simple reflexes that do not involve the brain. Simple reflexes involve a sensory nerve, a motor nerve, and the association neurons of the grey matter of the spinal cord.

Reflex Action A reflex is an involuntary action that occurs very quickly after its specific kind of stimulation. The reflex action takes place automatically without conscious decision of the brain. Reflex actions are inherited in our nervous system through evolutionary processes, for example, the eye-blinking reflex. Whenever any object suddenly comes near our eyes, our eyelids blink.

Reflexes serve to protect the organism from potential threats and preserve life. Though several reflex actions are performed by our nervous system, the familiar reflexes are the knee jerk, pupil constriction, pulling away from very hot or cold objects, breathing and stretching. Most reflex actions are carried out by the spinal cord and do not involve the brain. The Endocrine System The endocrine glands play a crucial role in our development and behaviour.

They secrete specific chemical substances, called hormones, which control some of our behaviours. These glands are called ductless glands or endocrine glands, because they do not have any duct (unlike other glands) to send their secretions to specific places. Hormones are circulated by the bloodstream. The endocrine glands form the endocrine system of the body.

This system works in conjunction with different parts of the nervous system. The whole system is thus known as neuroendocrine system. Figure . shows the major endocrine glands of the body.

Some hormones are secreted at a steady rate throughout life, while others are secreted at an appropriate time in life. For example, the growth hormone is released steadily through childhood, with some spurt during adolescence, but gonadotropic hormones are secreted at the age of puberty, which stimulates the secretion of appropriate sex hormones among boys and girls. As a result, primary and secondary sexual changes take place. Thyroid Gland This gland is located in the neck.

It produces thyroxin that influences the body’s metabolic rate. Optimum amount of thyroxin is secreted and regulated by an anterior pituitary hormone, the Thyroid Stimulating Hormone. (TSH). The steady secretion of this hormone maintains the production of energy, consumption of oxygen and elimination of wastes in body cells.

On the other hand, underproduction of thyroxin leads to physical and psychological lethargy. If thyroid gland is removed in young animals, their growth is stunted and they fail to develop sexually. Adrenal Gland This gland is located above each kidney. It has two parts, adrenal cortex and adrenal medulla , each secreting different hormones.

The secretion of adrenal cortex is controlled and regulated by Adrenocorticotrophic Hormone (ACTH) secreted by anterior pituitary gland. When the secretion of adrenal cortex goes down, anterior pituitary gets the message and increases the secretion of ACTH, which stimulates the adrenal cortex to secrete more hormones. The adrenal cortex secretes a group of hormones, called corticoids , which are utilised by the body for a number of physiological purposes, e.g., regulation of minerals in the body, particularly sodium, potassium, and chlorides. Any disturbance in its function seriously affects the functions of the nervous system.

Pituitary Gland This gland is situated within the cranium just below the hypothalamus. The pituitary gland is divided into anterior pituitary and posterior pituitary. The anterior pituitary is directly connected with hypothalamus, which regulates its hor monal secretions. The pituitary gland secretes the growth hormone and many other hormones, which direct and regulate the secretions of many other endocrine glands found in our body.

This is why the pituitary gland is known as the “master gland”. Fig. . : Major Endocrine Glands Thyroid Pancreas Adrenal glands Ovary (in female) Testes (in male) Pituitary Adrenal medulla secretes two hormones, namely epinephrine and norepinephrine (also known as adrenaline and noradrenaline, respectively).

Sympathetic activation, such as increased heart rate, oxygen consumption, metabolic rate, muscle tone, etc., take place through the secretion of these two hormones. Epinephrine and norepinephrine stimulate the hypothalamus, which prolongs emotions in an individual even when the stressor has been removed. Pancreas The pancreas, lying near the stomach, has a primary role in digestion of food, but it also secretes a hormone known as insulin . Insulin helps the liver to break down glucose for use by the body or for storage as glycogen by the liver.

When insulin is not secreted in proper amount, people develop a disease, called diabetic mellitus or simply diabetes. Gonads Gonads refer to testes in males and ovaries in females. The hormones secreted by these glands control and regulate sexual behaviours and reproductive functions of males and females. Secretion of hormones of these glands is initiated, maintained and regulated by a hormone, called gonadotrophic hormone (GTH) secreted by the anterior pituitary.

The secretion of GTH starts at the age of puberty ( to years in human beings) and stimulates gonads to secrete hormones, which in turn stimulates development of primary and secondary sexual characteristics. The ovaries in females produce estrogens and progesterone. Estrogens guide the sexual development of the female body. Primary sexual characteristics related with reproduction, such as development of ovum or egg cell, appear on every days or so in the ovary of a sexually mature female.

Secondary sexual characteristics, such as breast development, rounded body contours, widened pelvis, etc., also depend on this hormone. Progesterone has no role in sexual development. Its function is related with preparation of uterus for the possible reception of fertilised ovum. The hormonal system for reproductive behaviour is much simpler in the male because there is no cyclic pattern.

Testes in males produce sperm continuously and secrete male sex hormones called androgens. The major androgen is testosterone. Testosterone prompts secondary sexual changes such as physical changes, growth of facial and body hairs, deepening of voice, and increase in sexually oriented behaviour. Increased aggression and other behaviours are also linked with testosterone production.

The normal functioning of all hormones is crucial to our behavioural well-being. Without a balanced secretion of hormones, the body would be unable to maintain the state of internal equilibrium. Without the increased secretion of hormones during the times of stress, we would not be able to react effectively to potential dangers in our environment. Finally, without the secretion of hormones at specific times in our lives, we would not be able to grow, mature and reproduce.

H EREDITY : G ENES AND B EHAVIOUR We inherit characteristics from our parents in the form of genes. A child at birth possesses a unique combination of genes received from both parents. This inheritance provides a distinct biological blueprint and timetable for an individual’s development. The study of the inheritance of physical and psychological characteristics from ancestors is referred to as genetics .

The child begins life as a single zygote cell (mother’s ovum fertilised by father’s sperm). Zygote is a tiny cell with a nucleus in its center containing chromosomes. These chromosomes with all genes are inherited from each parent in equal numbers. Chromosomes Chromosomes are the hereditary elements of the body.

They are threadlike-paired structures in the nucleus of each cell. The number of chromosomes per nucleus is distinctive, and is constant for each living organism. The gametic cells (sperm and ovum) have chromosomes but not in pairs. A new generation results from the fusion of a sperm cell and an egg cell.

At the time of conception, the organism inherits chromosomes from parents, from the mother and from the father. Each of these chromosomes contains thousands of genes. However, the sperm cell (fathers’) differs from the egg cell (mother’s) in one important respect. The 23rd chromosome of the sperm cell can be either the capital X or Y type of the English alphabet.

If the X type sperm fertilises the egg cell, the fertilised egg will have an XX 23rd chromosome pair, and the child will be a female. On the other hand, if a Y type sperm fertilises the egg, the 23rd chromosome pair will be XY, and the child will be a male. Chromosomes are composed mainly of a substance called Deoxyribonucleic Acid (DNA). Our genes are composed chiefly of DNA molecules.

The two genes that control the development of each trait are situated at the same locus, one on each chromosome of a particular pair. The exception is the sex chromosomes, i.e. the pair of chromosomes that determines an individual’s sex. other behavioural traits).

The traits, which can be passed on to the offspring through genetic material are called its genotype. All biological and psychological characteristics that a modern man possesses are the result of genotype inheritance with phenotypical variations. A given gene can exist in several different forms. Change of a gene from one form to another is called mutation .

The type of mutation that occurs spontaneously in nature provides variation in genotypes and permits the evolution of new species. Mutation permits recombination of new genes with the genes already present. This new combination of genes structure is then put to test in the environment, which can select out those genotypes that turn out to be best fitted for the environment. C ULTURAL B ASIS : S OCIO -C ULTURAL S HAPING OF B EHAVIOUR After reading the biological basis of behaviour you may have developed an idea that many of our behaviours are influenced by hormones and many others occur as reflexive responses.

However, hormones and reflexes do not explain all of our behaviour. The hormones play an important role in regulating human physiology, but they do not completely control human behaviour. Similarly stereotype (fixed pattern), which is the most distinguishing feature of a reflex, does not appear with most human responses. We can draw examples from several domains of our life to argue that our behaviour is more complex than the behaviour of animals.

A major reason for this complexity is that unlike animals, human beings have a culture to regulate their behaviour. Let us consider the basic need of hunger. We know that it has a biological basis, which is common among animals and human beings, but the way this need is gratified by human beings is extremely complex. For example, some people eat vegetarian food, while others eat non- vegetarian food.

How have they become vegetarians and non-vegetarians? Some vegetarians take eggs; others do not. Why is Divide the class in two groups and have a debate on the topic “Psychologists should leave the study of neurons, synapses and the nervous system to biologists”. One group should speak in favour and the other group against the motion.