NCERT Textbook - The Bases of Human Behaviour | Psychology for Grade 11 PDF Download

 Page 1


Chapter
3
The Bases of Human
Behaviour
The Bases of Human
Behaviour
• understand the evolutionary nature of human behaviour,
• relate the functions of nervous system and endocrine system to behaviour,
• explain the role of genetic factors in determining behaviour,
• understand the role of culture in shaping human behaviour,
• describe the processes of enculturation, socialisation, and  acculturation,
and
• relate biological and socio-cultural factors in understanding human
behaviour.
After reading this chapter, you would be able to
Introduction
Evolutionary Perspective
Biological and Cultural Roots
Biological Basis of Behaviour
Neurons
Structure and Functions of Nervous System and
Endocrine System and their Relationship with
Behaviour and Experience
The Nervous System
The Endocrine System
Heredity: Genes and Behaviour
Cultural Basis : Socio-Cultural Shaping of Behaviour
Concept of Culture
Biological and Cultural Transmission (Box 3.1)
Enculturation
Socialisation
Acculturation
Key Terms
Summary
Review Questions
Project Ideas
Contents
There are one hundred and
ninety-three species of monkeys
and apes. One-hundred and
ninety-two of them are covered with
hair. The exception is the naked
ape self-named, homo-sapiens.
– Desmond Morris
2022-23
Page 2


Chapter
3
The Bases of Human
Behaviour
The Bases of Human
Behaviour
• understand the evolutionary nature of human behaviour,
• relate the functions of nervous system and endocrine system to behaviour,
• explain the role of genetic factors in determining behaviour,
• understand the role of culture in shaping human behaviour,
• describe the processes of enculturation, socialisation, and  acculturation,
and
• relate biological and socio-cultural factors in understanding human
behaviour.
After reading this chapter, you would be able to
Introduction
Evolutionary Perspective
Biological and Cultural Roots
Biological Basis of Behaviour
Neurons
Structure and Functions of Nervous System and
Endocrine System and their Relationship with
Behaviour and Experience
The Nervous System
The Endocrine System
Heredity: Genes and Behaviour
Cultural Basis : Socio-Cultural Shaping of Behaviour
Concept of Culture
Biological and Cultural Transmission (Box 3.1)
Enculturation
Socialisation
Acculturation
Key Terms
Summary
Review Questions
Project Ideas
Contents
There are one hundred and
ninety-three species of monkeys
and apes. One-hundred and
ninety-two of them are covered with
hair. The exception is the naked
ape self-named, homo-sapiens.
– Desmond Morris
2022-23
Psychology
44
Evolution occurs through the process of
natural selection. You know that members of
each species vary greatly in their physical
structure and behaviour. 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. When repeated
generation after generation, natural selection
leads to the evolution of new species that are
more effectively adapted to their particular
environment. This is very similar to the
selective breeding of horses or other animals
these days. Breeders select the fittest and the
fastest male and female horses from their
stock, and promote them for selective breeding
so that they can get the fittest horses. 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
like perception, memory, reasoning, problem
solving, and use of language for
communication, (ii) ability to walk upright on
EVOLUTIONARY PERSPECTIVE
You must have observed that people differ
with respect to their physical and
psychological characteristics. The uniqueness
of individuals results from the interaction of
their genetic endowments and environmental
demands.
In this world, there are millions of different
species of organisms differing in a variety of
ways. 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
evolutionary process are so slow that they
become visible after hundreds of generations.
Human beings, the homo sapiens, are the most developed organisms among all
creatures on this earth. Their ability to walk upright, larger brain size relative to
body weight, and the proportion of specialised brain tissues make them distinct
from other species. These features have evolved through millions of years and have
enabled them to engage in several complex behaviours. Scientists have attempted
to study the relationship of complex human behaviour with the processes of the
nervous system, particularly the brain. They have tried to discover the neural
basis of thoughts, feelings, and actions. By understanding the biological aspects of
human beings, you will be able to appreciate how the brain, environment and
behaviour interact to generate unique forms of behaviour. In this chapter, we
begin with a general description of the nervous system in an evolutionary
perspective. You will also study the structure and functions of the nervous system.
You will learn about the endocrine system, and its influence on human behaviour .
Later in this chapter, you will also study the notion of culture and show its
relevance to the understanding of behaviour. This will be followed by an analysis
of the processes of enculturation, socialisation, and acculturation.
Introduction
2022-23
Page 3


Chapter
3
The Bases of Human
Behaviour
The Bases of Human
Behaviour
• understand the evolutionary nature of human behaviour,
• relate the functions of nervous system and endocrine system to behaviour,
• explain the role of genetic factors in determining behaviour,
• understand the role of culture in shaping human behaviour,
• describe the processes of enculturation, socialisation, and  acculturation,
and
• relate biological and socio-cultural factors in understanding human
behaviour.
After reading this chapter, you would be able to
Introduction
Evolutionary Perspective
Biological and Cultural Roots
Biological Basis of Behaviour
Neurons
Structure and Functions of Nervous System and
Endocrine System and their Relationship with
Behaviour and Experience
The Nervous System
The Endocrine System
Heredity: Genes and Behaviour
Cultural Basis : Socio-Cultural Shaping of Behaviour
Concept of Culture
Biological and Cultural Transmission (Box 3.1)
Enculturation
Socialisation
Acculturation
Key Terms
Summary
Review Questions
Project Ideas
Contents
There are one hundred and
ninety-three species of monkeys
and apes. One-hundred and
ninety-two of them are covered with
hair. The exception is the naked
ape self-named, homo-sapiens.
– Desmond Morris
2022-23
Psychology
44
Evolution occurs through the process of
natural selection. You know that members of
each species vary greatly in their physical
structure and behaviour. 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. When repeated
generation after generation, natural selection
leads to the evolution of new species that are
more effectively adapted to their particular
environment. This is very similar to the
selective breeding of horses or other animals
these days. Breeders select the fittest and the
fastest male and female horses from their
stock, and promote them for selective breeding
so that they can get the fittest horses. 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
like perception, memory, reasoning, problem
solving, and use of language for
communication, (ii) ability to walk upright on
EVOLUTIONARY PERSPECTIVE
You must have observed that people differ
with respect to their physical and
psychological characteristics. The uniqueness
of individuals results from the interaction of
their genetic endowments and environmental
demands.
In this world, there are millions of different
species of organisms differing in a variety of
ways. 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
evolutionary process are so slow that they
become visible after hundreds of generations.
Human beings, the homo sapiens, are the most developed organisms among all
creatures on this earth. Their ability to walk upright, larger brain size relative to
body weight, and the proportion of specialised brain tissues make them distinct
from other species. These features have evolved through millions of years and have
enabled them to engage in several complex behaviours. Scientists have attempted
to study the relationship of complex human behaviour with the processes of the
nervous system, particularly the brain. They have tried to discover the neural
basis of thoughts, feelings, and actions. By understanding the biological aspects of
human beings, you will be able to appreciate how the brain, environment and
behaviour interact to generate unique forms of behaviour. In this chapter, we
begin with a general description of the nervous system in an evolutionary
perspective. You will also study the structure and functions of the nervous system.
You will learn about the endocrine system, and its influence on human behaviour .
Later in this chapter, you will also study the notion of culture and show its
relevance to the understanding of behaviour. This will be followed by an analysis
of the processes of enculturation, socialisation, and acculturation.
Introduction
2022-23
Chapter 3 • The Bases of Human Behaviour
45
two legs, and (iii) a free hand with a workable
opposing thumb. These features have been
with us for several thousand years.
Our behaviours are highly complex and
more developed than those of other species
because we have got a large and highly
developed brain. Human brain development is
evidenced by two facts. Firstly, 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). Secondly,
the human cerebrum is more evolved than
other parts of the brain.
These evolutions have resulted due to the
influence of environmental demands. Some
behaviours play an obvious role in evolution.
For example, the ability to find food, avoid
predators, and defend one’s young are the
objectives related to the survival of the
organisms as well as their species. 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.
BIOLOGICAL AND CULTURAL ROOTS
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 a 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.
As human beings, we not only share a
biological system, but also certain cultural
systems. These 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.
Such experiences, opportunities and demands
also influence our behaviour considerably.
These influences become more potent and
visible as we move from infancy to later years
of life. Thus, besides biological bases, there
are cultural bases of behaviour also.  You will
learn about the role of culture in behaviour at
a later point in this chapter.
BIOLOGICAL BASIS OF BEHAVIOUR
Neurons
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. They 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 (brain and
spinal cord), and bring motor information from
the central nervous system to the motor organs
(muscles and glands).
Nearly 12 billion neurons are found in the
human nervous system. They are of many
types and vary considerably in shape, size,
chemical composition, and function. Despite
these differences, they share 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 (Figure 3.1). 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 (cell-
fluid) of the neuron. Dendrites are the branch-
like 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
2022-23
Page 4


Chapter
3
The Bases of Human
Behaviour
The Bases of Human
Behaviour
• understand the evolutionary nature of human behaviour,
• relate the functions of nervous system and endocrine system to behaviour,
• explain the role of genetic factors in determining behaviour,
• understand the role of culture in shaping human behaviour,
• describe the processes of enculturation, socialisation, and  acculturation,
and
• relate biological and socio-cultural factors in understanding human
behaviour.
After reading this chapter, you would be able to
Introduction
Evolutionary Perspective
Biological and Cultural Roots
Biological Basis of Behaviour
Neurons
Structure and Functions of Nervous System and
Endocrine System and their Relationship with
Behaviour and Experience
The Nervous System
The Endocrine System
Heredity: Genes and Behaviour
Cultural Basis : Socio-Cultural Shaping of Behaviour
Concept of Culture
Biological and Cultural Transmission (Box 3.1)
Enculturation
Socialisation
Acculturation
Key Terms
Summary
Review Questions
Project Ideas
Contents
There are one hundred and
ninety-three species of monkeys
and apes. One-hundred and
ninety-two of them are covered with
hair. The exception is the naked
ape self-named, homo-sapiens.
– Desmond Morris
2022-23
Psychology
44
Evolution occurs through the process of
natural selection. You know that members of
each species vary greatly in their physical
structure and behaviour. 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. When repeated
generation after generation, natural selection
leads to the evolution of new species that are
more effectively adapted to their particular
environment. This is very similar to the
selective breeding of horses or other animals
these days. Breeders select the fittest and the
fastest male and female horses from their
stock, and promote them for selective breeding
so that they can get the fittest horses. 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
like perception, memory, reasoning, problem
solving, and use of language for
communication, (ii) ability to walk upright on
EVOLUTIONARY PERSPECTIVE
You must have observed that people differ
with respect to their physical and
psychological characteristics. The uniqueness
of individuals results from the interaction of
their genetic endowments and environmental
demands.
In this world, there are millions of different
species of organisms differing in a variety of
ways. 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
evolutionary process are so slow that they
become visible after hundreds of generations.
Human beings, the homo sapiens, are the most developed organisms among all
creatures on this earth. Their ability to walk upright, larger brain size relative to
body weight, and the proportion of specialised brain tissues make them distinct
from other species. These features have evolved through millions of years and have
enabled them to engage in several complex behaviours. Scientists have attempted
to study the relationship of complex human behaviour with the processes of the
nervous system, particularly the brain. They have tried to discover the neural
basis of thoughts, feelings, and actions. By understanding the biological aspects of
human beings, you will be able to appreciate how the brain, environment and
behaviour interact to generate unique forms of behaviour. In this chapter, we
begin with a general description of the nervous system in an evolutionary
perspective. You will also study the structure and functions of the nervous system.
You will learn about the endocrine system, and its influence on human behaviour .
Later in this chapter, you will also study the notion of culture and show its
relevance to the understanding of behaviour. This will be followed by an analysis
of the processes of enculturation, socialisation, and acculturation.
Introduction
2022-23
Chapter 3 • The Bases of Human Behaviour
45
two legs, and (iii) a free hand with a workable
opposing thumb. These features have been
with us for several thousand years.
Our behaviours are highly complex and
more developed than those of other species
because we have got a large and highly
developed brain. Human brain development is
evidenced by two facts. Firstly, 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). Secondly,
the human cerebrum is more evolved than
other parts of the brain.
These evolutions have resulted due to the
influence of environmental demands. Some
behaviours play an obvious role in evolution.
For example, the ability to find food, avoid
predators, and defend one’s young are the
objectives related to the survival of the
organisms as well as their species. 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.
BIOLOGICAL AND CULTURAL ROOTS
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 a 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.
As human beings, we not only share a
biological system, but also certain cultural
systems. These 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.
Such experiences, opportunities and demands
also influence our behaviour considerably.
These influences become more potent and
visible as we move from infancy to later years
of life. Thus, besides biological bases, there
are cultural bases of behaviour also.  You will
learn about the role of culture in behaviour at
a later point in this chapter.
BIOLOGICAL BASIS OF BEHAVIOUR
Neurons
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. They 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 (brain and
spinal cord), and bring motor information from
the central nervous system to the motor organs
(muscles and glands).
Nearly 12 billion neurons are found in the
human nervous system. They are of many
types and vary considerably in shape, size,
chemical composition, and function. Despite
these differences, they share 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 (Figure 3.1). 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 (cell-
fluid) of the neuron. Dendrites are the branch-
like 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
2022-23
Psychology
46
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. On the other hand,
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, electrical impulses are
generated and conducted towards the central
nervous system. The strength of the nerve
impulse, however, 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.
Synapse
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.
In this process, one neuron faithfully relays
the information to a neighboring neuron. The
axon tip of a preceding neuron make
functional connections or synapse with
dendrites of the other neuron. A neuron is
Fig.3.1 : The Structure of Neuron
Nucleus
Terminal
buttons
Dendrites (receiving end)
Soma
Cytoplasm
Axon
(transmitting)
Myelin sheath
Nodes of ranvier
2022-23
Page 5


Chapter
3
The Bases of Human
Behaviour
The Bases of Human
Behaviour
• understand the evolutionary nature of human behaviour,
• relate the functions of nervous system and endocrine system to behaviour,
• explain the role of genetic factors in determining behaviour,
• understand the role of culture in shaping human behaviour,
• describe the processes of enculturation, socialisation, and  acculturation,
and
• relate biological and socio-cultural factors in understanding human
behaviour.
After reading this chapter, you would be able to
Introduction
Evolutionary Perspective
Biological and Cultural Roots
Biological Basis of Behaviour
Neurons
Structure and Functions of Nervous System and
Endocrine System and their Relationship with
Behaviour and Experience
The Nervous System
The Endocrine System
Heredity: Genes and Behaviour
Cultural Basis : Socio-Cultural Shaping of Behaviour
Concept of Culture
Biological and Cultural Transmission (Box 3.1)
Enculturation
Socialisation
Acculturation
Key Terms
Summary
Review Questions
Project Ideas
Contents
There are one hundred and
ninety-three species of monkeys
and apes. One-hundred and
ninety-two of them are covered with
hair. The exception is the naked
ape self-named, homo-sapiens.
– Desmond Morris
2022-23
Psychology
44
Evolution occurs through the process of
natural selection. You know that members of
each species vary greatly in their physical
structure and behaviour. 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. When repeated
generation after generation, natural selection
leads to the evolution of new species that are
more effectively adapted to their particular
environment. This is very similar to the
selective breeding of horses or other animals
these days. Breeders select the fittest and the
fastest male and female horses from their
stock, and promote them for selective breeding
so that they can get the fittest horses. 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
like perception, memory, reasoning, problem
solving, and use of language for
communication, (ii) ability to walk upright on
EVOLUTIONARY PERSPECTIVE
You must have observed that people differ
with respect to their physical and
psychological characteristics. The uniqueness
of individuals results from the interaction of
their genetic endowments and environmental
demands.
In this world, there are millions of different
species of organisms differing in a variety of
ways. 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
evolutionary process are so slow that they
become visible after hundreds of generations.
Human beings, the homo sapiens, are the most developed organisms among all
creatures on this earth. Their ability to walk upright, larger brain size relative to
body weight, and the proportion of specialised brain tissues make them distinct
from other species. These features have evolved through millions of years and have
enabled them to engage in several complex behaviours. Scientists have attempted
to study the relationship of complex human behaviour with the processes of the
nervous system, particularly the brain. They have tried to discover the neural
basis of thoughts, feelings, and actions. By understanding the biological aspects of
human beings, you will be able to appreciate how the brain, environment and
behaviour interact to generate unique forms of behaviour. In this chapter, we
begin with a general description of the nervous system in an evolutionary
perspective. You will also study the structure and functions of the nervous system.
You will learn about the endocrine system, and its influence on human behaviour .
Later in this chapter, you will also study the notion of culture and show its
relevance to the understanding of behaviour. This will be followed by an analysis
of the processes of enculturation, socialisation, and acculturation.
Introduction
2022-23
Chapter 3 • The Bases of Human Behaviour
45
two legs, and (iii) a free hand with a workable
opposing thumb. These features have been
with us for several thousand years.
Our behaviours are highly complex and
more developed than those of other species
because we have got a large and highly
developed brain. Human brain development is
evidenced by two facts. Firstly, 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). Secondly,
the human cerebrum is more evolved than
other parts of the brain.
These evolutions have resulted due to the
influence of environmental demands. Some
behaviours play an obvious role in evolution.
For example, the ability to find food, avoid
predators, and defend one’s young are the
objectives related to the survival of the
organisms as well as their species. 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.
BIOLOGICAL AND CULTURAL ROOTS
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 a 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.
As human beings, we not only share a
biological system, but also certain cultural
systems. These 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.
Such experiences, opportunities and demands
also influence our behaviour considerably.
These influences become more potent and
visible as we move from infancy to later years
of life. Thus, besides biological bases, there
are cultural bases of behaviour also.  You will
learn about the role of culture in behaviour at
a later point in this chapter.
BIOLOGICAL BASIS OF BEHAVIOUR
Neurons
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. They 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 (brain and
spinal cord), and bring motor information from
the central nervous system to the motor organs
(muscles and glands).
Nearly 12 billion neurons are found in the
human nervous system. They are of many
types and vary considerably in shape, size,
chemical composition, and function. Despite
these differences, they share 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 (Figure 3.1). 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 (cell-
fluid) of the neuron. Dendrites are the branch-
like 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
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Psychology
46
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. On the other hand,
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, electrical impulses are
generated and conducted towards the central
nervous system. The strength of the nerve
impulse, however, 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.
Synapse
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.
In this process, one neuron faithfully relays
the information to a neighboring neuron. The
axon tip of a preceding neuron make
functional connections or synapse with
dendrites of the other neuron. A neuron is
Fig.3.1 : The Structure of Neuron
Nucleus
Terminal
buttons
Dendrites (receiving end)
Soma
Cytoplasm
Axon
(transmitting)
Myelin sheath
Nodes of ranvier
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Chapter 3 • The Bases of Human Behaviour
47
functions. Based on location, the nervous
system can be divided into two parts: Central
Nervous System (CNS) and Peripheral Nervous
System (PNS). The part of the nervous system
found inside the hard bony cases (cranium
and backbone) 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 organisation of the nervous system
is schematically presented in Figure 3.3.
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. The
conduction of neural impulse in the axon is
electrochemical, while the nature of synaptic
transmission is chemical (Figure 3.2). The
chemical substances are known as
neurotransmitters.
STRUCTURE AND FUNCTIONS OF NERVOUS
SYSTEM AND ENDOCRINE SYSTEM AND THEIR
RELATIONSHIP WITH BEHAVIOUR AND
EXPERIENCE
Since our biological structures play an
important role in organisation and execution
of behaviour, we shall look at these structures
in some detail. In particular, you will read
about the nervous system and the endocrine
system, which work together in giving a shape
to human behaviour and experience.
The Nervous System
Human nervous system is the most complex
and most developed of all living creatures.
Though the nervous system functions as a
whole, for the ease of study, we can divide it
into many parts depending on its location or
Fig.3.2 : Transmission of Nerve Impulse through
Synapse
Terminal
button
Synaptic
vesicles
Synaptic cleft
Neurotransmitter
Dendrite
Fig.3.3 : Schematic Representation of the Nervous
System
Spinal Cord
(Ascending Pathways,
Interneurons, and
Descending Pathway)
Somatic Nervous
System (SNS)
(Sensory and Motor
Nerves, Voluntary)
Brain
(Hindbrain, Midbrain,
and Forebrain)
Sympathetic
Division
(Trouble Shooter)
Parasympathetic
Division
(Housekeeping)
Autonomic Nervous
System (ANS)
(Internal System,
Involuntary)
Nervous System
Central Nervous
System (CNS)
Peripheral Nervous
System (PNS)
(Neural Tissue outside
Brain and Spinal Cord)
Endocrine System
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
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