Neurotransmitters

• Neurotransmission


  1. Receives information from other neurons

  2. Neurotransmitters are stored in the axon end

  3. Neurotransmitters are released into the synaptic cleft

  4. Neurotransmitters bind to receptors on the postsynaptic neuron

  5. Receptors determine whether the signal is excitatory or inhibitory

  6. Enzymes or reuptake remove neurotransmitters from the synaptic cleft
• Neurons


  • Connect with other neurons at the synaptic cleft
  • Conduct impulses
• Myelin


  • Insulates the axon
  • Myelination continues from birth to adolescence
  • Certain diseases like MS destroy the myelin sheath leading to loss of coordination
• Receptors


  • Determine whether the signal is excitatory or inhibitory
  • A minimum number of neurotransmitters must attach to reach the threshold on the postsynaptic membrane to transmit the impulse
• Summation


  • Weak stimuli can be filtered out
  • Convergent neural pathways can release enough neurotransmitters to reach postsynaptic threshold and trigger an impulse
• Endorphins


  • Neurotransmitters that stimulate neurons involved in reducing the intensity of pain
  • Production increases in response to severe injury, prolonged exercise, stress and certain foods
  • Linked to feelings of pleasure from activities like eating, sex and exercise
• Dopamine


  • An example of an endorphin
  • Reinforces beneficial behaviours by activating the reward pathway
• Mode of action of drugs

  1. Agonist: Mimic the action of a neurotransmitter

  2. Antagonist: Block specific receptors

  3. Enzyme inhibitor: Enhanced effect

  4. Reuptake inhibitor: Enhanced effect
• Recreational drugs affect neurotransmission at synapses in the brain, altering mood, cognition, perception and behaviour
• Many recreational drugs affect neurotransmission in the reward pathway of the brain
• Drug Addiction


  Repeated use of antagonists leads to the nervous system increasing both the number and sensitivity of receptors, causing craving
• Drug Tolerance


  Repeated use of agonists leads to the nervous system decreasing both the number and sensitivity of receptors, needing more of the drug to get the same effect
• Many drugs used to treat neurotransmitter-related disorders are agonists or antagonists, and recreational drugs can act in the same way