Biological approach

• What are the main assumptions in the study of behavior from a genetic and evolutionary perspective?

  • Each person has around 100,000 genes.
  • Each individual (apart from identical twins) has a unique genotype.
  • The CNS generates most actions and reactions.
  • Neurotransmitters and hormones influence reactions to the environment.
  • Behaviors may have been adaptive in the past.
  • Natural selection passes on behaviors that ensure survival and reproduction.
• inheritance

  • the passing of characteristics from one generation to the next through genes
  • genes carry instruction for a characteristic - how it develops depends on how this gene reacts with other genes and how the environment reacts with them
• Genotype

  • an individuals genetic makeup
  • Occurs at conception and provides a unique genetic code for how each individual will develop
• Phenotype

  • how genes are expressed through physical, behavioural and psychological characteristics
  • Not all genes in the genotype will be expressed, this is because they are influenced by the environment
• Twins

  • Monozygotic - identical
  • Dizygotic - non identical
  • The more a trait is expressed by genes the greater the hereditability
  • scientists study the importance of genes through comparison of twins - expressed through a concordance rate
  • Concordance rate - % likelihood of the other twin getting something if one has it
• Natural selection

  • charles Darwin
  • Individuals within a species differ in characteristics and behaviour - some is inherited
  • Must compete with each other - those who win reproduce and pass characteristics to offspring
  • psychological characteristics such as intelligence would have been adaptive therefore survived the evolutionary process -
• Strengths

  • real world application - understanding of neurochemical processes in the brain has led to the use of psychoactive drugs that treat mental disorders (e.g antidepressants)
  • Uses scientific methods - precise and objective methods - includes scanning (mri)which assess biological processes in ways that are not open to bias
• Weaknesses

  • Antidepressant drugs do not work for everyone - suggests that brain chemistry may not account for all cases
  • Biological explanations are determinist - they see human behaviour is governed by internal, genetic causes over which we have no control. However, the way genotype is expressed is heavily influenced by environment. This suggests the biological view is too simplistic.
• Central nervous system

  • brain and spinal cord
  • Conscious awareness happens in the cerebral cortex - controls ‘higher order’ functions
  • Spinal cord - an extension of the brain and responsible for reflex actions
• 4 lobes

  • Frontal - functions (e.g thought and learning )
  • Temporal - hearing and memory
  • Parietal - sensory info (touch, temp and pain)
  • Occipital - processes visual info
• Peripheral nervous system

  • Autonomic nervous system - governs vital functions in the body (e.g breathing and heart rate)
  • Somatic nervous system - controls muscle movement and receives information from sensory receptors
• Endocrine system

  • Controls glands - releases hormones
  • Pituitary gland - key gland known as the master gland
  • it controls the release of hormones from all other glands, hormones are secreted into the bloodstream and affect any cell in the body that has a receptor for it
• Sympathetic nervous system

  • A stressor is received by the hypothalamus
  • Adrenaline is released from the adrenal medulla
  • Causes changes (increased heart rate, dilation if pupils)
  • Automatic response if a threat is percieved
• Parasympathetic nervous system

  • Once the threat has passed the parasympathetic nervous system takes over
  • Returns the body to resting state (heart rate slows down, stimulates digestion)
• Neurons

  • 100 billion in the nervous system - 80% in the brain
  • Signals are transmitted electrically and chemically
  • Sensory neuron, relay neuron and motor neuron
  • because a neuron is negatively charged, when activated it becomes positively charged for a split second, creating an electrical impulse
• Structure

  • cell body contains a nucleus
  • Dendrites - protrude from cell body and carry nerve impulses from neighbouring neurons
  • Axon - carries impulses away from the cell body down the length of the body
  • Fatty layer of myelin sheath - covers axon and protects it, also speeds electrical transmission
  • Myelin sheath is segmented by nodes of ranvier - they speed transmission up by forcing it to jump across the gaps
  • Terminal buttons - communicate with the next neuron in the chain across the synapse
• Synapse

  • Impulses reach the end of a neuron a chemical (neurotransmitter) is released and diffuses through the synapse to the next neuron
  • Exciatory neurotransmitters - trigger nerve impulses in the receiving neuron and stimulate the brain into action (e.g dopamine)
  • Inhibitory neurotransmitters - inhibit nerve impulses in order to calm the brain and balance mood (e.g serotonin)