THE BIOLOGICAL BASIS OF BEHAVIOUR

Chapter 3

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 … 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 partCerebrum• 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. Well done! You have completed chapter 3. Remember to complete the assessment activities.Remember to complete the assessment activities.

Thank you.