1. The biological perspective examines how the brain, genes, and evolution influence human behavior. Pioneers in this field include Karl Lashley, Donald Hebb, and Charles Darwin. 2. Neurons are the basic building blocks and communicate via electrical and chemical signals. The brain is divided into the forebrain, midbrain, and hindbrain. 3. The nervous system includes the central nervous system (brain and spinal cord) and peripheral nervous system. The peripheral system regulates involuntary and voluntary functions.

1. BIOLOGICAL BASES OF
HUMAN BEHAVIOUR
POORNIMA SINGH
M.A PSYCHOLOGY 2ND YEAR
ARYA MAHILA P.G DEGREE COLLEGE
,BHU

2. INTRODUCTION
• Biological perspective examines how brain
processes and other bodily functions regulate
behaviour .
• It focuses on : the Brain, Genes & Evolution.
• Pioneer in biological psychology are –
• 1.KARL LASHLEY (1890-1958) -
• was a pioneer of physiological psychology
(behavioral neuroscience). He examined how
damage to various brain regions affected rats
ability to learn and remember.

3. • 2. DONALD O. HEBB (1904-1985)
• He proposed that changes in the connection
between nerve cell in the brain provide the
biological bases for learning memory &
perception .
• His influential theory eventually led to the
discovery of neurotransmitter (which are
chemicals released by nerve cell that allow
them to communicate with one another).

4. • 3. Behavior Genetics – the study of how behavioral
tendencies are influenced by genetic factors (Plomin &
Haworth ,2009)
• For example :
• Identical human twins who result from splitting of
same fertilized egg therefore have the same genetic
makeup “are more similar to one another on many
behavioral traits” than are fraternal twins, who result
from two different fertilized egg & therefore are no
more similar genetically than are non twin siblings.
• Greater behavioral similarity found even when
identical twins have been reared in different homes &
dissimilar environment .(Lykken , 2006)

5. 4. CHARLES DARWIN (a British naturalist)
proposed a Theory of Evolution.
He noted that within a species some members
possess specific traits to greater extent than do
other members .
• Through a process he called NATURAL
SELECTION if an inherited traits gives certain
member an advantage over other ,these
members will be more likely to survive & pass
these characteristics onto their offspring .

6. • thus through natural selection a species
biology evolves in response to environmental
conditions .
• Evolutionary psychology seeks to explain how
evolution shaped modern human behavior .

7. NEURONS
• NEURONS - are the basic building blocks of
the nervous system.
• The estimated 100 billion nerve cells in our
brain & spinal cord are linked together .
• Each neuron has three main parts –
• 1. Cell body /SOMA
• 2. Dendrites
• 3. Axon

9. • 1.CELL BODY /SOMA – contains the
biochemical structures needed to keep the
neuron alive ,
• & its nucleus carries genetic information that
determine how cell develops & functions.
• 2. DENDRITES – emerging from cell body
branch like structure ,
• specialized receiving units like antennae that
collects information from neighboring neurons
& send them on to the cell body .

10. • 3. AXON- extending from the one side of the cell
body is a single axon ,
• which conducts electrical impulses away from
the cell body to other neurons ,muscles or
glands.
• The axon branches out at its end to form a
number of axon terminals (around 100 in some
cases)
• Each axon terminal may connect with dendrites
from numerous neurons , making it possible for
a single neuron to pass messages to as many as
50,000 other neurons (Simon, 2007)

11. • Neurons can vary greatly in shape and size.
• Basic function of neuron is receiving , processing
,& sending messages .
• Neurons are supported in their functions by Glial
cells.

12. • Function of Glial Cells –
• 1. they surrounds neurons & hold them in
place.
• 2. & also manufacture nutrient chemicals that
neurons need .
• 3. they absorb toxins & waste materials that
may damage or kill the neuron .
• 4. during prenatal brain development ,glial
cells send out long fibers that guide newly
divided neurons to their targeted places in the
brain (Fenichel,2006)

13. The MYELIN SHEATH :
• Some axons have a fatty whitish insulation
layer derived from glial cells during
development .
• Myelin sheath helps increase the speed of
nerve conduction.
• Myelin sheath is interrupted at regular
intervals by the Nodes of Ranvier.

14. • Damage to myelin coating can have tragic
effects
• For example :in people afflicted with multiple
sclerosis, the persons immune system attacks
the myelin sheath, disrupting the delicate
timing of nerve impulse to the muscles.
• This result in increasingly jerky &
uncoordinated movements & in the final
stages, paralysis(Toy,2007)

15. ELECTRICAL ACTIVITY OF NEURONS
• Neurons do two important things –
• 1. they generate electricity that creates nerve
impulses.
• 2. they also release chemicals that allow them
to communicate with one another .

16. • How nerve impulse occur ?
• The whereby a nerve impulse is created involves
the exchange of electrically charged atoms called
ions .
• In salty fluid outside the neuron are positively
charged sodium ions (Na+) & negatively charged
chloride ions(CI-)
• Inside the neuron are large negatively charged
protein molecules(anions or A-) & positively
charged potassium ions(K+)

17. • Nerve activation involve three basic steps-
• 1. RESTING POTENTIAL(at rest)
• The high concentration of sodium ions in the
fluid outside the cell ,
• together with the negatively charged protein ions
inside the neuron ,
• Results in uneven distribution of positive &
negative ions that makes the interior of the cell
negative compared to the outside
• This internal difference of around -70 mV is
called neuron’s resting potential.
• At rest neuron is said to be at state of
POLARIZATION

18. • 2.Nerve Impulse : The Action Potential
• Alan Hodgkin & Andrew Huxley ,neuroscientist
who won the Nobel prize in the research ,
• found that if they stimulated the neuron’s axon
with mild electrical stimulus ,
• the interior voltage differential shifted instantly
from – 70 mV to +40 mV,
• This electrical shift, which lasts about a
millisecond (1/1,000 of seconds )
is called action potential, or nerve impulse.

19. • What happens in the neuron to cause action
potential ?
• Hodgkin & Huxley found that the key
mechanism is the action of sodium &
potassium ion channels in the cell membrane.
• Attracted by the negative protein ions inside,
positively charged sodium ions flood into the
axon creating a state if DEPOLARIZATION (i.e
action potential)

20. • It’s all or nothing law – means that action
potential occur at a uniform & maximum
intensity ,or they do not occur at all.
• The action potential threshold has to be
changed from -70mV to about -50mV.

21. • 3. The ionic balance is restored ,& the neuron
is again at rest .
• In humans ,the limit seems to be about 300
impulses per second ( Kolb &Wishaw,2005).

22. – How neurons communicate : Synaptic transmission
– Neurons communicate through synaptic space &
neurotransmitters
• A tiny gap between the axon terminal and the
next neuron. Is known as synaptic space .
• Neurotransmitters, chemical substance that
carry messages across the synaptic space to
other neurons , muscles, or glands.

23. • The process of chemical communication involve five
steps :
• Synthesis stage
• Storage
• Release
• Binding
• & deactivativation
• In some instances , the deactivation mechanism is
reuptake , (in which the transmitter molecules are
taken back into the presynaptic axon terminals. )

24. The Nervous System
• The nervous system is the body's control
center.
• 3 major types of neurons carry out systems
input, output, & integration functions.
• 1. Sensory neurons –carry input messages
from the sense organs to the spinal cord &
brain.

25. • 2. Motor neurons – transmit output impulses
from the brain & spinal cord to the body’s
muscles & organs .
• 3. Inter neurons – perform connective or
associative functions within the nervous
system.
• The activity of interneurons makes possible the
complexity of our higher mental functions
,emotions & behavioral capabilities.

26. • For example,
interneurons would allow us to recognise
friend,
by linking the sensory input from the visual
system ,
with the memory of that persons
characteristics stored elsewhere in the brain .

27. • The 2 major divisions of nervous system are ,
• 1. the peripheral nervous system
• 2. the central nervous system

29. The Peripheral Nervous System (PNS)
• The PNS contains all the neural structure that
lie outside of the brain and spinal cord .
• Its specialized neurons help us carry out ,
• 1. the input functions that enable us to sense
what is going inside & outside our bodies,
• 2. the output function that enable us to
respond with our muscles & glands .

30. • The peripheral nervous system has two major
divisions –
• 1. the Somatic Nervous System
• 2. the Autonomic Nervous System

31. PNS
• 1. Somatic Nervous System (voluntary muscle activation)
• consist of sensory neurons that are specialized to
transmit messages from eyes , ear & other sensory
receptors
• and motor neurons that send messages from brain &
spinal cord to the muscles that control voluntary
movements .
• For example , as you read this slide ,sensory neurons in
your eyes are sending impulses into a complex network
of visual nerves that course through your brain .
• at the same time motor neurons are stimulating the eyes
movement that allow you to scan the lines .

32. PNS
• 2. Autonomic Nervous System
• which senses the body’s internal functions&
controls the glands & smooth muscles that form
the heart , the blood vessels & the lining of the
stomach & intestine .
• It is largely concerned with involuntary functions
such as respiration ,digestion ,& circulation ,also
involve many aspects of motivation ,emotional
behavior & stress responses.

33. PNS
• The autonomic nervous system consist of two
subdivisions
• 1.Sympathectic system – it arouses the body &
speed up its vital processes ,by activating many
organs at the same time .
• For example ,when you encounter a stressful
situation ,your sympathetic nervous system
helps you confront the stressor in several ways
,such as it speeds up heart rate , increase rate of
respiration etc.
• Sometime this is called fight or flight response.

34. PNS
• 2. Parasympathetic nervous system
• It slows down body processes & maintain state
of tranquility.
• It affects one or few organs at a time.
• Thus your sympathetic system speeds up your
heart & your parasympathetic slows it down.

35. The autonomic nervous system consist of two
subdivisions
• 1.Sympathectic system –
• it arouses the body & speed up
its vital processes ,by
activating many organs at the
same time .
• For example ,when you
encounter a stressful situation
,your sympathetic nervous
system helps you confront the
stressor in several ways ,such
as it speeds up heart rate ,
increase rate of respiration
etc.
• Sometime this is called fight or
flight response.
• 2. Parasympathetic
nervous system
• It slows down body
processes & maintain
state of tranquility.
• It affects one or few
organs at a time.
• Thus your sympathetic
system speeds up your
heart & your
parasympathetic slows
it down

36. The Central Nervous System
• The central nervous system contains the brain
& the spinal cord which connects most parts
of the peripheral nervous system with the
brain .

37. The Spinal Cord
• Spinal cord ,a structure of 16 to 18 inches long& about
1inch in diameter in human adult.
• Transmit information between brain &rest of body,
handles simple reflexes.
• Some stimulus –responses sequence are known as
spinal reflexes, &
Can be triggered at the level of spinal cord without any
involvement of the brain.
•

38. • For example ,if you touch something hot ,sensory
receptors in your skin triggers –nerve impulse in
sensory nerves –that flash into your spinal cord &
synapse inside within interneurons .
• The interneurons than excite motor neurons-that
send impulses to your hand ,so that it pulls away .
• Other interneurons simultaneously carry the
‘HOT’ message up the spinal cord to your brain.

39. The Brain

40. • The brain is divide into 3 divisons
• 1.forebrain
-thalamus
-hypothalamus
-cerebrum (cerebral cortex)
-limbic system
-corpus callosum

41. • 2.MID BRAIN
• receives it name from its resemblance under
microscope to a reticulum.
reticular formation act as
neural gating & cortical arousal system that
influences consciousness and attention

42. • 3. Hind brain
• -medulla
• -Pons
• -cerebellum
•

43. Methods to study Brain
• Methods that help in understanding the
functions of brain are :
• Neuropsychological test ( measure verbal &
nonverbal behavior of people who suffered
brain damage .
• Destruction & stimulation technique
• Electrical recording
• Brain imaging ( CT scan , MRI , PET scan)