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 …

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.