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Chapter 3
THE BIOLOGICAL BASIS OF
BEHAVIOUR
Learning outcomes to keep in mind whilst studying this chapter
What is the biological basis of behaviour and why is it
important?
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Describe the role of genetics in human behaviour
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Discuss the significance of the nervous system in human behaviour
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Discuss the endocrine system and its contributions to the promotions
of effective human behaviour
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Explain the importance of muscle system in the executions of human
behaviour.
Genetics
Cells
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Basic functional units comprised in all living organism
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DNA molecules (genes) control heredity from one generation to
generation
Mitosis
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23 Chromosomes constant
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New cells 23 pairs of chromosomes
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Continuous split and reproduction of new cells throughout the entire
body to sustain life
DNA
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Deoxyribo-nucleic acid – contains genetic origins
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Thousands of DNA molecules combine to form a chromosome.
Meiosis ... simplified
Genes
Twins
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Identical genes (monozygotic)
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Non-identical genes (dizygotic)
Sex determination
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Certain attributes only carried by X-chromosomes – e.g. gender and certain
illnesses
Genotype
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All genes
Phenotype
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Some genes, observable features, environment influence
Multiple determination (polygenic heredity)
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Combined influence of various genes, most human characteristics
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Examples – Intelligence, temperament, personality, etc.
The structure of the neuron
Cell membrane
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Surrounds the entire neuron and it is semi permeable
Dendrites
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Bushy, branch-like extensions of a neuron
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Receive and conduct information toward the cell body
Axon
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Terminal branches form junctions with other cells
Myelin sheath
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Fatty tissue increasing speed of transmission
Nodes of ranvier
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Gaps on the axon which the myelin does not enclose
A synaptic cleft
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Space between the axon of one neuron and the dendrite of another (spatial or
temporal summation).
The structure of a neuron
A synapse
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The nerve synapse
transfers nerve impulse
information from a pre-synaptic
membrane to a postsynaptic
membrane neurotransmitters
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The synapse operates as an
on/off switch and as a filter for
information flow.
How the neuron functions
Arousal threshold
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The minimum intensity which a stimulus must have in order to trigger a
nervous impulse
Neurotransmitters
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A chemical that accumulates in the synapse from presynaptic neurons and
stimulates the postsynaptic neuron to produce nerve impulses
Action potential
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Electrochemical potential of the neuron resulting in a selective influx of
positively charged ions
Spatial summation
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Impulses from a number of neurons combine to provide a stimulus strong
enough to exceed the threshold of the post synaptic neuron
Temporal summation
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Successive impulses from one axon collectively activate the post synaptic
neuron.
Classifying neurons
Receptor neurons
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Vision, sound, smell, taste, cold, heat, pressure, touch
Sensory neurons
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Conduct information from the receptors to the Central Nervous
System
Motor neurons
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Conduct information from the Central Nervous System to the effectors
(muscles and glands)
Association neurons
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Connect sensory and motor neurons.
“ Hi Mate. Hang in there! It will all become easier with more revision …
The central nervous system
The spinal cord
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Situated in the spinal column and enclosed by 31 vertebrae
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Connecting structure enables
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sensory impulses from the body to reach the brain
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motor impulses from the brain to descend to control motor activities of the
body
The brain
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Enables humans to think, plan and process all sensory information
gained from the environment
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Composed of some 10 billion nerve cells
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Cerebral activity is sustained by oxygen and nutrients
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Electrical activity of the brain is measured by an
electroencephalograph (ECG).
The cerebral cortex and cerebrum
Cerebral cortex (grey
matter)
•
•
•
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The outer layer of the brain
Comprises 80% of the brain
capacity
Processes complex mental
processes
Surrounds the Cerebrum –
constituting its outer part
Cerebrum
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Two cerebral hemispheres
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Left
• Logical, serial, order, maths,
language
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Right
• Spatial, imagination, intuition,
emotions.
The four lobes of the cortex
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Frontal cortex – control of information processing by sending information
to other parts of the body
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Parietal cortex – receipt of sensory input from various parts of the body
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Occipital cortex – controls visual perception
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Temporal cortex – controls hearing and visual perception.
Subcortical areas
The thalamus
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Processes all sensory impulses, except sense of smell
The hypothalamus
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Unconscious activities of various organs
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Body temperature, appetite and feeding behaviour
The limbic system
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Electric stimulation evokes emotional responses
Reticular activation system (RAS)
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Coordinating centre with diffused cells, inhibitory/facilitating functions that
include activation, sleep and wakefulness
Medulla oblongata
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Respiration and blood pressure
Cerebellum
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Coordination of muscle activity, muscle tone and balance.
Peripheral nervous system
The autonomic nervous system
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Responsible for regulation of visceral organ activities
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Sympathetic Nervous System ─ Activation functions
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Parasympathetic Nervous System ─ Inhibitory functions
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The two sub-systems work together to maintain the homeostasis of
the autonomic nervous system
Somatic nervous system
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Connected to receptors in skin, inner tissue, joints and skeletal
muscles (voluntary muscles)
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Somatic reflexes generally do not involve the autonomic nervous
system.
Endocrine system
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Consists of glands
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Ovaries, testes, adrenals, pancreas, pineal gland, parathyroid and
pituitary
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Secrete hormones which are transmitted via the bloodstream to brain
and other parts of the Central Nervous System
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Pituitary gland (master gland) determines numerous behavioural
aspects through direct release of its own hormones as well as its
effects on other glands
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Neuroendocrine functions also affect and are affected by the immune
system
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Stress.
The muscle system
Structure and functioning of muscles
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Connected to both motor and sensor nerves
Dynamic and static muscle activity
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Dynamic (rhythmic activity)
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Static (fixed position)
Repetitive strain
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Repetitive use of certain body elements
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Carpal Tunnel Syndrome (CTS) – over-use
Working body posture
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Body size, standing, sitting and lying down.
The muscle system (continued)
Loss of muscle power
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Measured on a scale of zero to
five
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Complete loss of muscle power
– plegia (paralysis)
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muscle weakness affecting
movement in limbs – paresis
Work station design
•
Ergonomics recommendation
for work station design.
Well done! You have completed chapter 3.
Remember to complete the assessment activities.
Thank you.