Co-ordinated functioning of the endocrine and nervous system.
Behaviour - Biological bases
Biological Bases of Behaviour.
1. Human Anatomy and physiology- Brief
2. Biosocial Aspects
3. The Evolutionary Perspective
4. Genes and Behaviour
5. Receptor-effector-connector mechanisms-
the Neural Bases of behaviour.
6. Endocrine System and Behaviour
• The nature of psychology is bio-social.
• It thrusts upon the behavioral events of
• MAN CONSTANTLY INTERACTS
WITH THE ENVIRONMENT
• Man consistently engages in interaction with
• Sensory nerve impulses are transducted to
• Brain sends motor impulses to the organs of
• The effector organs produce a response
which is called behaviuor.
• This brain mediated receptor effector
mechanisms which produce a behaviour is
called physiological or biological basis of
• BILOGICAL BASES OF BEHAVIOUR
• Human beings (Homo sapiens) are the most
developed species among the millions of
organisms on earth.
• Organisms show variations among themselves
• These variations are the main cause Evolution
• Evolution refers to gradual and orderly biological
changes that results in species from the
preexisting forms in response to the changing
adaptational demands of the environment.
• EVOLUTION 6
Comparison of evolutionary change in human
The largest brains are those of sperm whales, weighing about 8 kg (18 lb).
An elephant's brain weighs just over 5 kg (11 lb), a bottlenose dolphin's 1.5 to 1.7
kg (3.3 to 3.7 lb), whereas a human brain is around 1.3 to 1.5 kg (2.9 to 3.3 lb)
Evolution follows natural selection.
Natural selection leads to survival of the
Fitness refers to the ability of the
organism to survive and contribute its
genes to the next generation
Landmark features in the evolutionary history
• Ability to walk upright on two legs.
• Hands became free to operate tools and
explore the environment.
• Human beings became better adapted to the
• Refers to evolutionary change in structure
and size of brain
• Weight of human brain is 2.3% of the body
weight.(1.3 TO 1.4 Kg)
• Due to this specialized brain tissue human
beings became capable of complex activities.
• Language made human interactions much
more effective than any other animal.
• Lead to cultural evolution.
• Tool and medium for effective communication
• Through the biological process of evolution human
beings stand at the top of the evolutionary ladder
• Evolution is a continuous process
ENVIROMENTAL INFLUENCE ON EVOLUTIONARY
• There used to gender
based division of labor
in the early human
• Now the gender based
human society is
deteriorating day by day
as part of the survival of
• Sex determination is based on the ‘x’ or ‘Y’ sex
chromosomes present in the sperm
• The ovum contains two ‘X’ chromosomes as
the sex chromosomes.
• Sex of the child entirely depend on the
chromosome of the sperm cell.
GENES AND BEHAVOIUR
• The development of human
being…. Is the climax of all
wonders -Conkun EG
• Human beings with all these
potentials have developed
from tiny threads of life
• Gametic cells unite to form
Zygote which contains 23
pairs of chromosomes
• Chromosomes contain
DNA in them.
• James Watson Francis
crick, and Maurice
extensively on DNA.
• DNAs contain Genes
which are the bearers
• Genes are also called
the “master code”
• They contain the blue
print of life.
• Sometimes there will be
abnormalities in the
• During gamete formation meiotic division
• During this process there is exchange genetic
• In the Zygote the genes function in a chance
selection method leading to Character
difference in offsprings.
Genotype and Phenotype
• The genetic make up of an organism is called
• The observable characteristics of an organism
is called ‘phenotype’.
• The given gene can exist in several different
• Change of gene from one form to another
form also can occur ,called mutation.
• Mutation also leads to variation and at last
speciation Movie 1 19
The science that focuses on the genetic bases of
behavioral traits such as intelligence, mental
disorders etc .is called
NATURE AND NURTURE
• Despite similarities in
inheritance ,children differ
from their parents in
• Heredity (nature) and
have significant role to
play in the development
• Socio-biology is the systematic study of the
biological basis of social behavior.
• The central assumption of sociobiology is
that the key purpose of human life is to pass
along genes in future generation.
• The evolutionary history evidences the fact
that human beings posses built in
programmed behavioral predispositions. Eg.
Competition, Aggression, Altruism etc.
• Under the guidance of heredity, organisms
living in a normal environment, undergoes a
process of growth involving three major sets
of structures .
1. The Nervous system
2. The Endocrine glands
3. The Muscles
First two systems are intensively studied to
understand the Biological bases of behavior
THE NERVOUS SYSTEM
• Behavior of an organism involves the
coordination of receptors, effectors and
• Nervous system plays the role of the
• So it is important to know nervous system in
detail to understand more clearly about
The basic structural and functional unit of the nervous system is called a
nerve cell or neuron.
Each nerve cell consists of a central portion containing the nucleus, known
as the cell body, and one or more structures referred to as axons and
The dendrites are rather short extensions of the cell body and are involved
in the reception of stimuli.
The axon, by contrast, is usually a single elongated extension; it is
especially important in the transmission of nerve impulses from the region
of the cell body to other cells. 27
Types of neurons
Sensory or Afferent neuron
Motor or efferent or efferent
Interneuron or connector neuron
• A specialized cell designed to transmit
information to other nerve cells, muscle, or
gland cells, the neuron is the basic working
unit of the brain.
• The brain is what it is because of the
structural and functional properties of
• It contains between one billion and one
trillion neurons, depending on the species.
• The neuron consists of a cell body containing
the nucleus, cytoplasm, and an electrically
excitable output fiber, the axon.
• Most axons also give rise to many smaller
branches before ending at nerve terminals.
• Neurons signal by transmitting
electrical impulses along their axons,
which can range in length from a tiny
fraction of an inch to three or more
• A neuron is a long cell that has a thick
central area containing the nucleus; it
also has one long process called an
axon and one or more short, bushy
processes called dendrites.
• Dendrites receive impulses from other
• These impulses are propagated
electrically along the cell
membrane to the end of the axon.
• At the tip of the axon the signal is
chemically transmitted to an
adjacent neuron or muscle cell.
• Two types of phenomena are involved
in processing nerve signals
Electrical and Chemical
• Electrical events propagate a signal
within a neuron, and chemical
processes transmit the signal from one
neuron to another neuron or to a
• Like all other cells, neurons contain charged
ions: potassium and sodium (positively
charged) and chlorine (negatively charged).
• Neurons differ from other cells in that they
are able to produce a nerve impulse
• Nerve impulse generation has three stages
• Resting potential
• Generation of action potential
• Propagation of action potential
Law governing propagation of action
Propagation of action potential is governed by a law
called ‘All or None law’.
The intensity of the stimulus which is adequate to
produce an impulse is called ‘Threshold stimulus’.
All or none law states that if cell responds it responds
fully provided the stimulus is just above the threshold
Once a nerve fiber is fired it cannot fire for
a brief period of time – absolute refractory
period (1/1000 sec)
It is followed by a relative refractory period
during which a very strong stimulus is
required to produce a new impulse.
• When the electrical signal reaches the tip of
an axon, it stimulates small presynaptic
vesicles in the cell.
• These vesicles contain chemicals called
neurotransmitters, which are released into
the microscopic space between neurons (the
• The neurotransmitters attach to specialized
receptors on the surface of the adjacent
• This stimulus causes the adjacent cell to
depolarize and propagate an action
potential of its own.
• The duration of a stimulus from a
neurotransmitter is limited by the
breakdown of the chemicals in the
synaptic cleft and the reuptake by the
neuron that produced them.
• Synapse is a case of contiguity without continuity.
In the case of week signals there are two types of
facilitating summation taking place at the synapse.
1) Special summation: Nerve impulses from two
presynaptic neurons combine together
2) Temporal summation: two nerve impulses at some
intervals from same presynaptic neuron combine
within the life period of the weaker signal.
Excitatory Post Synaptic Potential (EPSP) -
depolarises post synaptic neuron
• In addition to facilitating functions at synapse
,inhibitory functions also takes place .
• Inhibitory substances hyperpolarize the post
synaptic neuron, making it more negative.
neuron Inhibitory Neuron
Division of nervous
1.PERIPHERAL NERVOUS SYSTEM.
2.CENTRAL NERVOUS SYSTEM.
3. AUTONOMIC NERVOUS SYSTEM
Anatomy of PNS
• PNS include cranial and spinal nerves that connect CNS with
receptors and effectors of the body.
• Cranial nerves
12 pairs of cranial nerves arise from brain ( 4 pairs sensory, 4
pairs motor and 4 pairs mixed).
• Spinal nerves
31 pairs of mixed type arise from the spinal cord
Cervical 8 pairs
Thoracic 12 pairs
Lumbar 5 pairs
sacral nerves 5pairs
Cocceageal nerve 1 pair
Central Nervous System -CNS.
The Central Nervous System is that
part of the nervous system which lies
within the bony case formed by the
skull and the spine.
The central nervous system, which
includes the brain and spinal cord,
processes and coordinates all incoming
sensory information and outgoing
motor commands, and it is also the
seat of complex brain functions such as
memory, intelligence, learning, and
The brain and the spinal cord consists
of this system. 46
THE SPINAL CORD
It is that part of the Central neurons
system which lies within the back bone .
It is composed of the grey matter and the
The grey matter consists of nerve cells
nerve cells lying inside and the white
matter consisting of nerve fibers lying
outside completely covering the grey
Spinal cords function is two fold.
In the first place it functions as a channel
of communication from the brain and to
the brain. Secondly it works as an organ
for effective reflex action.
Spinal cord cross
• Sudden involuntary response to stimulus is
called reflex action
• The stimulus response pass through a ‘reflex
• Reflex arch is a simple nervous pathway
connecting a receptor and an effector. It
consists of the following parts
• A) The receptors
• (b) Afferent or sensory neuron
• (c) Association neuron or interneuron
• (d) Efferent or motor neuron
• (e) Effector organ
Some examples of common
human reflex actions
• (a) Knee jerk reflexes
• (b) Ankle jerk reflexes
• (c) Blinking reflexes
• (d) Sneezing reflexes
• (e) Salivation or watering of mouth on sight,
smell or thought of food.
• (f) Withdrawal reflexes, viz. withdrawal of
hand or finger on touching a hot plate surface
Central Nervous System.
• The Central Nervous System is that part of the
nervous system which lies within the bony case
formed by the skull and the spine.
• The central nervous system, which includes the brain
and spinal cord, processes and coordinates all
incoming sensory information and outgoing motor
commands, and it is also the seat of complex brain
functions such as memory, intelligence, learning, and
• The brain and the spinal cord consists of this system.
THE MEDULLA OBLONGATA
• The Medulla oblongata is a continuation of
the brain on the one hand and a spinal cord
on the other.
• There fore its nerve tissues form a
connection between the two paths of central
nervous system. It is both a conductor as
well as an integrating center.
• It regulates the highly complex process like
digestion, respiration and circulation which
are necessary for preservation of life.
– Provides pathways for sensory and motor
impulses to and from hemispheres.
– It also connects other parts of the brain
with cerebrum and cerebellum
• Cerebellum or
hindbrain is situated
behind and beneath
• It helps to maintain
the equilibrium of
the body and keeps
• Mid brain connects cerebellum with
• Connected to the midbrain , there is a
complex mass of network of nerve fibres.
• This is called reticular activating system – RAS
or ascending reticular activating system.
• This is critically concerned with various
degrees of arousal – from deep sleep to alert
The reticular formation is a collection of neurones in
the core of the brain stem, surrounded by neural
pathways that conduct ascending and descending
nerve impulses between the brain and the spinal
It has a vast number of synaptic links with other parts
of the brain and is therefore constantly receiving
'information' being transmitted in ascending and
The reticular formation is involved in:
1. coordination of skeletal muscle activity associated
with voluntary motor movement and the
maintenance of balance .
2. Coordination of activity controlled by the autonomic
nervous system, e.g. cardiovascular, respiratory and
gastrointestinal activity selective awareness that
functions through the reticular activating system
(RAS), which selectively blocks or passes sensory
information to the cerebral cortex, e.g. the slight
sound made by a sick child moving in bed may
arouse his mother but the noise
• The mid brain is divided into two main parts:
The roof or tectum :
- superior colliculi – vision
- inferior coliiculi - auditory
The floor : provides connection between
lower and higher centres of brain
The limbic system is a group of brain structures that play a role in emotion,
memory, and motivation. For example, electrical stimulation of the amygdala in
laboratory animals can provoke fear, anger, and aggression. The hypothalamus
regulates hunger, thirst, sleep, body temperature, sexual drive, and other
• The hippocampus is the largest of limbic
structure. It has significant role to play in
memory, particularly in the storage of long-
• The amygdala has important role to play in
aggression. It is also involved in memory,
emotion, and certain basic motives.
• The hypothalamus is the smallest structure in
brain with a vital role to play in behaviour.
• It is concerned with regulation of
physiological processes relating to emotional
and motivational behaviours-eating,
drinking, temperature regulation and sexual
• It is also concerned with regulation of
endocrine system. Basically, hypothalamus
involves in the maintenance of homeostasis
in the body
SPECILIZATION OF CEREBRAL
Cerebrum is divided into two equal halves by
a deep grove.
The left hemisphere is responsive to the right
side of the body, while the right side is
responsive to the left side of the body.
Yet the two halves function in unison with
each other with the help of the thick fibres
called Corpus callosum .
• Left and Right Brain Functions
Although the cerebrum is
symmetrical in structure, with two
lobes emerging from the brain stem
and matching motor and sensory
areas in each, certain intellectual
functions are restricted to one
• A person’s dominant hemisphere is
usually occupied with language and
logical operations, while the other
hemisphere controls emotion and
artistic and spatial skills.
• In nearly all right-handed and many
left-handed people, the left
hemisphere is dominant
Left hemisphere is often called the language
Stroke on the left side of the brain affects
SODIUM AMYTAL –a sedative- test on the
brain also indicates the localization of speech
area n the left half.
Left HS is specialized for language function in
95% of the right handed people and 65% in
left handed people 74
Upper temporal lobes and lower
frontal lobes are main localized
centres for language function
Temporal lobe language centre is
called Wernicke’s area.
The frontal lobe centre is called
• Wernike’s area is mainly involved in
understanding of spoken and written
• Other language problems related to Wernike’s area:
Impaired ability to repeat spoken words.
Reading and writing problem.
Difficulty in naming a common object.
Intrusion of incorrect sounds or words into the flow
• Symptoms of Broca’s area is different from
• Damage to Broca’s area causes non fluent
and ungrammatical speech.
• Eg. “he go.....school...yesterday...8 o’clock”
(He went to school yesterday at 8 o’clock ).
Anatomy of language
Wernicke’s Geschwind model
• This model explains how an individual listens,
speaks and understands written words.
W- Wernike’s area
A- Arcuate fasciculus
B- Broca’s area
• This theory states that each anatomical area
plays a particular role in various aspects of
• Spontaneous speech originates in Wernike’s
area . But to speak it out ,the activity pattern
of the Wernike’s area is sent to Broca’s area
through Arcuate fasciculus.
• The Broca’s area programmes are then sent to
the motor cortex region fore xpression.
centres for language.
Spatial relation, colour,
size and shape
• The right hemisphere is also concerned with the
1. Anatomical method
2. Extirpation and ablation
3. Action potential method
5. Chemical method
6. Selective breeding
1. C T Scanning
2. PET Scanning
3. MRI Scanning
Methods can be classified into two
METHODS EMPLOYED IN STUDYING BRAIN
• Tissue of the
posthumous body is
treated in such a way
that nerve tracks can be
viewed with the help of
a microscope .
Lesion,extirpation and ablation
• A lesion is the destruction or
functional disruption of an area of
the brain. An ablation is the removal
of a part of the brain. Both of which
produce behavioral deficit indicating
the role of that part of the brain in
developing the lost character.
• Extirpation refers to cutting out.
• A small window on the skull is cut to
remove the brain or part either by
cutting or suction. 83
• Investigators some times wish to
study the effect of stimulating or
damaging or recording the activity of
deeper part of the brain of animals.
The Stereotaxic instrument is
provided with scale and electrodes.
Researchers refer to a previously
formed map called Stereotaxic atlas
to help this process of study.
Stimulation and recording
from the brain
• In this method electrode are
implanted in the brain and briefly
stimulated certain areas. The
resultant behaviour is studied and
their relation is established between
the stimulated area.
• Eg stimulating the lateral
hypothalamus increases eating 86
Action potential method
• Sensitive electrical recording devices are used to
detect the electrical changes in the neurons of the
• Chemical crystals, drugs or hormones are
inserted to the brain nuclei helps to study the
type of transmitter substances employed in
• The resultant reactions are observed to
identify the type of brain chemical involved
• In this method the experimenter raises a
number of generation of plants or animals
and systematically sort out each generation
to study the hereditary genesis of behaviour.
• (ie. Transfer of characters/behaviour from
parents to offsprings are studied)
• Owing to modern advances in and
developments of modern sophisticated
techniques it is possible to know and
understand the functions of brain without
causing any harm to it .
• These techniques are called Brain Imaging
• X- rays are passed
through the brain
at every one
degree of the
brain till 1800
• MRI reveals
Positron Emission Tomography
• In this method, a patient is injected with
glucose treated with radioactive tracers.
• As the body metabolizes the glucose, the PET
scan monitors the radioactive particles
emitted by the tracers in the glucose.
• Images are produced that show metabolic
reactions, making this method useful to
diagnose brain tumors and
Single photon emission computed
• Single photon emission computed
tomography (SPECT), developed in the 1950s
and 1960s, uses radioactive tracers to visualize
the circulation and volume of blood in the
• Electroencephalography, procedure for obtaining a
record of the electrical activity of the brain by
means of electrodes attached to the surface of the
Normal Seizure 98
THEORIES OF BRAIN FUNCTIONS
• According to this theory each part of the
cerebrum is specialized to perform a particular
function. Eg. Sensory function.
• Three major localized functions are as follows:
I. Sensory functions
II. Motor functions
III. Association functions
• Most of the sensory functions
have specific areas in the
cerebral cortex called Primary
Categorization of sensory function
Specified areas in
brain to perform
1 Taste and smell Tongue
cortex buried in the
2 Kinesthetic/somesthetic Skin Parietal lobe
3 Visual Eye Occipital lobe
4 Audition Ear
A portion of
• Primary area- controls some
• Secondary motor area – less
• Supplementary motor area –
Muscle tone and postural control
Three areas in
the brain has
• Decision making
• Emotionally charged activities
• (ie. Higher order brain functions)
Problems associated with damage to areas
Frontal lobe Delayed response , blunted expression
Association area Affects learning, thinking, memmory, reasoning, emotionally
charged activities etc
Asteriognosis Loss of ability to recognize solid objects through touch
Alexia Inability to recognize printed words
Sensory aphasia Inability to recognize spoken words
Mass action theory
According to this theory different areas or parts of the brain
area are more or less functionally interchangeable.
It has been observed that impairment or injury in a particular
area though cause disturbance or almost complete loss of
function, gradually , owing to practice, the lost function recurs
Also the living structures in the nearby area take over to
discharge the lost function.
• Though the rationale put forward by
equipotential or mass action theorists
are tenable. However modern studies
show that various parts of the brain
are responsible for different functions .
• Therefore a compromising position
appears to be more tenable
Autonomic Nervous System
• Autonomic Nervous System, in vertebrate
anatomy, one of the two main divisions of
the nervous system, supplying impulses to
the body's heart muscles, smooth
muscles, and glands.
• Two antagonistic divisions make up the
autonomic nervous system:
1. the sympathetic, or thoracicolumbar, division,
which stimulates the heart, dilates the bronchi,
contracts the arteries, and inhibits the digestive
system, preparing the organism for physical
2.The parasympathetic, or craniosacral, division,
which has the opposite effects, and prepares the
organism for feeding, digestion, and rest
• The sympathetic division consists of a
chain of interconnected ganglia (groups of
nerve cells) on each side of the vertebral
column, which send nerve fibers to several
large ganglia, such as the coeliac
• They, in turn, give rise to nerves passing
to the internal organs. The ganglia of the
sympathetic chains are connected to the
central nervous system by fine branches
connecting each ganglion with the spinal
• Fibers of the parasympathetic system
arise in the brain and, with the cranial
nerves, especially the vagus and
accessory nerves, pass to ganglia and
plexuses (networks of nerves) within the
• The lower part of the body is innervated by
fibers arising from the lowest (sacral)
segment of the spinal cord and passing to
the pelvic ganglion, which gives rise to
nerves for such organs as the rectum,
bladder, and genital organs.
DUCTLESS GLANDS OR
• There are several glands in our body,
which secrete several bodily chemicals
both internally as well as externally.
• They can be grouped into two distinct
categories namely duct glands and
ductless glands or endocrine glands.
•The under activity or over activity of these
glands caused by the deficiency or excess of the
hormones secreted by them as well as well as by
the co acting influence of other glands like
Thyroid, Pituitary and Adrenal affects not only
the sexual growth and development of an
individual but also his entire behaviour and
• A slight imbalance of these glands causes
restlessness, anxiety and weakness.
• Our physical strength, morale thinking and
reasoning power and decision-making
ability – all depend upon the health of the
• In short, these glands are found to play a
dominant role in the life of a person.
• Without their proper functioning a man or
woman finds difficulty in leading a happy
NERVOUS SYSTEM AND
• Our behaviour to a great extend is
controlled by our nervous system.
• How we will behave in a particular
situation depends upon the judgment
of our brain.