Chapter 3 THE BIOLOGICAL BASIS OF BEHAVIOUR
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.
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).
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.
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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.