SYNAPTIC TRANSMISSION

• WHAT ARE NEUROTRANSMITTERS?

  chemicals released from synaptic vesicles at presynaptic membrane that affect the neuron by increasing or decreasing the likelihood of it producing an action potential
• WHAT IS AN ACTION POTENTIAL?

  short lasting event produced when a neuron fires which is triggered by summation
• WHAT HAPPENS TO EXCESS NEUROTRANSMITTERS?

  excess reabsorbed into terminal buttons by reuptake
• WHAT ARE THE TYPES OF NEUROTRANSMITTER?

  excitatory or inhibitory
• EXCITATORY NEUROTRANSMITTERS?

  increase likelihood of neuron firing making it more positive
• INHIBITORY NEUROTRANSMITTERS?

  decrease likelihood of neuron firing making it more negative
• WHAT IS SUMMATION?

  process where inputs of all excitatory and inhibitory signals to one neuron are combined/ 'summed'
• PROCESS OF SUMMATION?

  1. Membrane of postsynaptic neuron has to reach a particular voltage to 'fire'
  2. Excitatory signals increase internal charge of neuron (depolarisation)
  3. Inhibitory signals decrease internal charge of neuron (hyperpolarisation)
  4. If sum is excitatory and the threshold value is reached an action potential is triggered
• WHY DOES TRANSMISSION ONLY OCCUR IN ONE DIRECTION?

  • synaptic vesicles containing neurotransmitters only released from presynaptic membrane
  • receptors for neurotransmitters only present on postsynaptic membrane
  • binding of neurotransmitter to receptor enables signal to be transmitted
  • diffusion of neurotransmitter -> can only go from high to low concentration
  • therefore can only travel from presynaptic to postsynaptic membrane
• HOW MAY DRUGS AFFECT SYNAPTIC TRANSMISSION?


  may increase/ decrease the number of neurotransmitters released

  -> can increase/ decrease the likelihood of an action potential