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