The Bases of Human Behaviour Class 11 Psychology Notes


  • The uniqueness of individuals results from the interaction of their genetic endowments and environmental
  • Biologists believe that these species were not always like this; they have evolved to their present form from their pre-existing forms.
  • It is estimated that the characteristics of modern human beings developed some 2,00,000 years ago as a result of their continuous interaction with the environment.
  • Evolution refers to gradual and orderly biological changes that result in a species from their pre-existing forms in response to the changing adaptational demands of their environment.
  • Physiological as well as behavioural changes that occur due to the  evolution process are so slow that they  become visible after hundreds of generations
  • Evolution occurs through the process of natural selection.
  • The traits or characteristics that are associated with high rate of survival and reproduction of those species are the most likely ones to be passed on to the next generations.
  • Fitness is the ability of an organism to survive and contribute its genes to the next generation.
  • Three important features of modern human beings differentiate them from their ancestors:
  • (i) a bigger and developed brain with increased capacity for cognitive behaviours (ii) ability to walk upright on two legs, and (iii) a free hand with a workable opposing thumb.
  • Our behaviours are highly complex and more developed than those of other species because we have got a large and highly developed brain.
  •  the weight of the brain is about 2.35 per cent of the total body weight, and it is the highest among all
    species (in elephant it is 0.2 per cent).
  • the human cerebrum is more evolved than other parts of the brain.
  • The biological and behavioural qualities, which are helpful in meeting these objectives, increase an organism’s ability to pass it on to the future generation through its genes.
  • The environmental demands lead to biological and behavioural changes over a long period of time


  • An important determinant of our behaviour  is the biological structures that we have inherited from our ancestors in the form of developed body and brain.
  • The importance of such biological bases becomes obvious when we observe cases in which brain cells have
    been destroyed by any disease, use of drug or an accident. Such cases develop various kinds of physical and behavioural disabilities.
  • Many children develop mental retardation and other abnormal symptoms due to transmission of a faulty gene from the parents.
  • cultural systems are quite varied across human populations.
  • All of us negotiate our lives with the culture in which we are born and brought up.
  • Culture provides us with different experiences and opportunities of learning by putting us in a variety of situations or placing different demands on our lives.
  • besides biological bases, there are cultural bases of behaviour also.



  • Neuron is the basic unit of our nervous system.
  • Neurons are specialised cells, which possess the unique property of converting various forms of stimuli into electrical impulses and are also specialised for reception, conduction and transmission of information in the form of electrochemical signals.
  • They receive information from sense organs or from other adjacent neurons, carry them to the central nervous system and bring motor information from the central nervous system to the motor organs .
  • They are of many types and vary considerably in shape, size, chemical composition, and function.
  •  three fundamental components, i.e. soma, dendrites, and axon.


  • The soma or cell body is the main body of the nerve cell.
  • It contains the nucleus of the cell as well as other structures common to living cells of all types.
  • The genetic material of the neuron is stored inside the nucleus and it becomes actively engaged during cell reproduction and protein synthesis.
  • The soma also contains most of the cytoplasm of the neuron.


  • Dendrites are the branchlike specialised structures emanating from the soma.
  • They are the receiving ends of a neuron.
  • Their function is to receive the incoming neural impulses from adjacent neurons or directly from the sense organs.
  • On dendrites are found specialised receptors, which become active when a signal arrives in electrochemical or biochemical form.
  • The received signals are passed on to soma and then to axon so that the information is relayed to another neuron or to muscles.


  • The axon conducts the information along its length, which can be several feet in the spinal cord and less than a millimeter in the brain.
  • At the terminal point the axon branches into small structures, called terminal buttons.
  • These buttons have the capability for transmitting information to another neuron, gland and muscle.
  • Neurons generally conduct information in one direction, that is, from the dendrites through soma and axon to the terminal buttons.


  • The conduction of information from one place to another in the nervous system is done through nerves, which are bundles of axons.
  • Nerves are mainly of two types: sensory and motor.
  • Sensory nerves, also called afferent nerves, carry information from sense organs to central nervous system.
  • motor nerves, also called efferent nerves, carry  information from central nervous system to muscles or glands.
  • A motor nerve conducts neural commands which direct, control, and regulates our movements and other responses.
  • There are some mixed nerves also, but sensory and motor fibers in these nerves are separate.

Nerve Impulse

  • Information travels within the nervous system in the form of a nerve impulse.
  • When stimulus energy comes into contact with receptors, electrical changes in the nerve potential start.
  • Nerve potential is a sudden change in the electrical potential of the surface of a neuron.
  • When the stimulus energy is relatively weak, the electrical changes are so small that the nerve impulse is not generated, and we do not feel that stimulus.
  • If the stimulus energy is relatively strong then electrical impulses are generated and conducted towards the central nervous system.
  • The strength of the nerve impulse does not depend on the strength of the stimulus that started the impulse.
  • The nerve fibers work according to the “all or none principle”, which means that they either respond completely or do not respond at all.
  • The strength of the nerve impulse remains constant along the nerve fiber.


  • Information is transmitted from one place to another within the nervous system in the form of a neural impulse.
  • A single neuron can carry a neural impulse up to a distance covered by the length of its axon.
  • When the impulse is to be conducted to a distant part of the body, a number of neurons participate in the process.
  • The axon tip of a preceding neuron make functional connections or synapse with dendrites of the other neuron.
  • A neuron is never physically connected with another neuron; rather there is a small gap between the two.
  • This gap is known as synaptic cleft.
  • The neural impulse from one neuron is transmitted by a complex synaptic transmission process to another neuron. T
  • he conduction of neural impulse in the axon is electrochemical, while the nature of synaptic transmission is chemical.
  • The chemical substances are known as neurotransmitters


The Nervous System

  • Human nervous system is the most complex and most developed of all living creatures.
  • Central Nervous System (CNS) and Peripheral Nervous System (PNS).
  • The part of the nervous system found inside the hard bony cases is classified as CNS.
  • Brain and spinal cord are the organs of this system.
  • The parts of the nervous system other than central nervous system are placed in the PNS.
  • PNS can be further classified into Somatic and Autonomic nervous system.
  • Somatic nervous system is concerned with voluntary actions, while the autonomic nervous system performs functions on which we have no voluntary control.

The Peripheral Nervous System

  • The PNS is composed of all the neurons and nerve fibers that connect the CNS to the rest of the body.
  • The PNS is divided into Somatic Nervous System and Autonomic Nervous System.
  • The autonomic nervous system is further divided into Sympathetic and Parasympathetic systems.
  • The PNS provides information to the CNS from sensory receptors and relays back motor commands from the brain to the muscles and glands.

The Somatic Nervous System

  • This system consists of two types of nerves, called cranial nerves and spinal nerves.
  • There are twelve sets of cranial nerves which either emanate from or reach different locations of the brain.
  • There are three types of cranial nerves – sensory, motor, and mixed.
  • Sensory nerves collect sensory information from receptors of the head region and carry them to the brain.
  • The motor nerves carry motor impulses originating from the brain to muscles of the head region.
  • movements of the eyeballs are controlled by motor cranial nerves.
  • Mixed nerves have both sensory and motor fibers, which conduct sensory and motor information to and from the brain.
  • The sensory fibers of the spinal nerves collect sensory information from all over the body and send them to the spinal cord from where they are then carried out to the brain.

The Autonomic Nervous System

  • This system governs activities which are normally not under direct control of individuals.
  • The Autonomic Nervous System has two divisions: Sympathetic division and Parasympathetic division.
  • Although the effect of one division is opposite to the effect of the other, both work together to maintain a state of equilibrium.
  • The sympathetic division deals with emergencies when the action must be quick and powerful, such as in situations of fight or flight.
  • The Parasympathetic division is mainly concerned with conservation of energy.
  • It monitors the routine functions of the internal system of the body.
  • When the emergency is over, the parasympathetic division takes over
  • it decelerates the sympathetic activation and calms down the individual to a normal condition

The Central Nervous System

  • The central nervous system (CNS) is the centre of all neural activity.
  • It integrates all incoming sensory information, performs all kinds of cognitive activities, and issues motor
    commands to muscles and glands.
  • The CNS comprises (a) brain and (b) spinal cord.

The Brain and Behaviour

  • It is believed that the human brain has evolved over millions of years from the brains of lower animals, and this evolutionary process still continues.
  • The limbic system, brain stem and cerebellum are the oldest structures, while Cerebral Cortex is the latest development in the course of evolution.
  • The brain is organised into structures and regions that perform specific functions.
  • Brain scanning reveals that while some mental functions are distributed among different areas of the brain, many activities are localised also.

Structure of the Brain


  • 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 regulate basic life supporting activities
  • This is why medulla is known as the vital centre of the brain.
  • It has some centres of autonomic activities also.


  • It is connected with medulla on one side and with the midbrain on the other.
  • A nucleus 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.


  • 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.
  • the motor commands originate in the forebrain, the cerebellum receives and coordinates them to relay to the
  • 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.


  • 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.


  • It is considered to be the most important part of the brain because it performs all cognitive, emotional, and motor activities.


  • The hypothalamus is one of the smallest structures in the brain, but plays a vital role in our behaviour.
  • It regulates physiological processes involved in emotional and motivational behaviour,
  • It also regulates and controls the internal environment of the body and regulates the secretion of hormones from various endocrine glands.


  • It consists of an egg-shaped cluster of neurons situated on the ventral 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
  • It has close links with the 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,
  • The cerebrum makes two-third of the total mass of the human brain.
  • 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.
  • The two hemispheres appear identical, functionally one hemisphere usually dominates the other
  • 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.


  • 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.
  • 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.
  • 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.
  • The spinal cord plays the role of a huge cable, which exchanges innumerable messages with the CNS.
  • it carries sensory impulses coming from the lower parts of the body tothe brain; and motor impulses  riginating from the brain to all over the body.
  • it performs some simple reflexes that do not involve the brain.

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
  • Reflexes serve to protect the organism from potential threats and preserve life.

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 to send their secretions to specific places.
  • Hormones are circulated by the bloodstream.
  • This system works in conjunction with different parts of the nervous system.
  • The whole system is thus known as neuroendocrine 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 hormonal 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”.

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.
  • The steady secretion of this hormone maintains the production of energy, consumption of oxygen and elimination of wastes in body cells.
  • 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.
  • The secretion of adrenal cortex is controlled and regulated by Adrenocorticotrophic Hormone (ACTH) secreted by anterior pituitary gland.
  • The adrenal cortex secretes a group of hormones, called corticoids, which are utilised by the body for a number of physiological purposes
  • . Any disturbance in its function seriously affects the functions of the nervous system.
  • Adrenal medulla secretes two hormones, namely epinephrine and norepinephrine
  • Sympathetic activation take place through the secretion of these two hormones.


  • 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 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.
  •  The ovaries in females produce estrogens and progesterone.
  •  Estrogens guide the sexual development of the female body.
  • Progesterone has no role in sexual development.
  • Its function is related with preparation of uterus for the possible reception of fertilised ovum.
  • Testes in males produce sperm continuously and secrete male sex hormones called androgens.
  • 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 secretion of hormones at specific times in our lives, we would not be able to grow, mature and reproduce.


  • 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.
  • 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
  • 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 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 have 23 chromosomes but not in pairs.
  • A new generation results from the fusion of a sperm cell and an egg cell
  • Chromosomes are composed mainly of a substance called Deoxyribonucleic Acid (DNA).


  • Every chromosome stores thousands of genetic commands in the form of genes.
  • These genes dictate much of the course of an organism’s development.
  • 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.
  • Change of a gene from one form to another is called mutation.
  • 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.


Concept of Culture

  • Human behaviour is fundamentally social.
  • culture refers to “the man-made part of the environment”.
  • It comprises diverse products of the behaviour of many people, including ourselves.
  • culture shapes our behaviour in a significant manner.

What is Culture?

  • culture is an idea created and shared by a group of people.
  • culture includes behavioural products of others who preceded us.
  • It indicates both substantial and abstract particulars that have prior existence in one form or another.
  • It contains a way of life that will be followed by most of us who grow up in that context.
  • Culture provides meaning by creating significant categories like social practices and roles as well as values, beliefs and premises.
  • It allows us to categorise and explain many important differences in human behaviour that were previously attributed to biological differences.
  • Social and cultural contexts within which human development takes place vary widely over time and place.
  • A society is a group of people who occupy a particular territory and speak a common language not generally understood by neighbouring people.
  • A society may or may not be a single nation, but every society has its own culture, and it is culture that shapes human behaviour from society to society.
  • Culture is the label for all the different features that vary from society to society.
  • It is these different features of society whose influences psychologists want to examine in their studies of human behaviour.

Cultural Transmission

  • We have seen earlier that as human beings we are both biological and socio-cultural creatures.
  • We have a highly developed capacity to benefit from experiences of our own and those of others.
  • No other creature has learning capacity to the same extent as we have.
  • The processes of enculturation and socialisation make us cultural beings.


  • Enculturation refers to all learning that takes place without direct, deliberate teaching.
  • We  learn certain ideas, concepts, and values simply because of their availability in our cultural context.
  • concepts are transmitted, both directly and indirectly, and are learned very well because they are an integral part of the life of a cultural group, and are never questioned.
  • enculturation refers to all learning that occurs in human life because of its availability in our socio-cultural context.
  • The key element of enculturation is learning by observation.
  • Whenever we learn any content of our society by observation, enculturation is in evidence.


  • Socialisation is a process by which individuals acquire knowledge, skills and dispositions, which enable them to participate as effective members of groups and society.
  • It is a process that continues over the entire life-span, and through which one learns and develops ways of effective functioning at any stage of development.
  • Socialisation forms the basis of social and cultural transmission from one generation to the next.
  • The probability of our behaving in a particular way is greatly affected by people who relate to us.
  • Any one who possesses power relative to us can socialise us are called “socialisation agents”.
  • The process of socialisation is not always a smooth transition between the individual and the socialisation agent.
  • In the case of socialisation, the learning involves deliberate teaching. In the case of enculturation, teaching
    is not necessary for learning to take place.
  • Enculturation means engagement of people in their culture.

Socialisation Agents


  • Parents have most direct and significant impact on children’s development.
  • Children  respond in different ways to parents in different situations.
  • Parents encourage certain behaviours by rewarding them verbally or in other tangible ways
  • They also discourage certain behaviours through non-approving behaviours.
  • They also arrange to put children in a variety of situations that provide them with a variety of positive experiences, learning opportunities, and challenges.
  • parents adopt different strategies, which are generally known as parenting styles.
  • The conditions of life in which parents live influence the styles they adopt in socialising children.
  • Grandparental proximity and network of social relationships play considerable role in child socialisation directly or through parental influences.


  • School is another important socialising agent.
  • If the transaction has been successful, the skills and knowledge children acquire in schools either through curriculum or interaction with teachers and peers also get transferred to other domains of their life.
  • researchers believe that a good school can altogether transform a child’s personality.
  • That is why we find that even poor parents want to send their children to good schools.

Peer Groups

  • Friendship acquires great significance in this respect.
  • It provides children not only with a good opportunity to be in company of others, but also for organising
    various activities collectively with the members of their own age.
  • Children also learn to assert their  own point of view and accept and adapt to those of others.
  • Development of self-identity is greatly facilitated by the peer group.
  • communication of children with peer group is direct, process of socialisation is generally smooth.

Media Influences

  • In recent years media has also acquired the property of a socialisation agent.
  • children learn about many things from these sources, adolescents and young adults often derive their models from them, particularly from television and cinema.
  • The exposure to violence on television is a major issue of discussion, since studies indicate that observing violence on television enhances aggressive behaviour among children.
  • There is a need to use this agent of socialisation in a better way in order to prevent children from developing undesirable behaviours.


  • Acculturation refers to cultural and psychological changes resulting from contact with other cultures.
  • Whenever Acculturation occurs, it requires re-learning of norms, values, dispositions, and patterns of behaviour.
  • Changes due to acculturation may be examined at subjective and objective levels.
  • At the subjective level, changes are often reflected in people’s attitudes towards change. They are referred to as acculturation attitudes.


  • It refers to an attitude in in which there is an interest in both, maintaining one’s original culture and identity, while staying in daily interaction with other cultural groups.
  • There is some degree of cultural integrity maintained while interacting with other cultural groups.


  • It refers to an attitude, which people do not wish to maintain their cultural identity, and they move to become
    an integral part of the other culture.
  • there is loss of one’s culture and identity.


  • It refers to an attitude in which people seem to place a value on holding on to their original culture, and wish to avoid interaction with other cultural groups.
  •  people often tend to glorify their cultural identity.


  • It refers to an attitude in which there is little possibility or interest in one’s cultural maintenance, and little interest in having relations with other cultural groups.
  • In this case, people generally remain undecided about what they should do, and continue to stay with a great deal of stress.
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