Synaptic transmission

• Define synaptic transmission.


  The process in which neurons communicate with one another via neurotransmitters.
• Outline the first step of synaptic transmission.

  An action potential arrives at the axon terminal of a neuron which causes vesicles to fuse with the cell membrane and release neurotransmitters into the synaptic gap.
• Outline the second step of synaptic transmission. 


  Neurotansmitters diffuse (move from areas of high to low concentration) across the synaptic gap before binding to their specialised receptors on the post-synaptic neuron.
• Outline the third step of synaptic transmission. 


  When excitatory neurotransmitters bind, they produce an EPSP which increases the positive charge of the neuron. This makes the post- synaptic neuron more likely to fire.

  When inhibitory neurotransmitters bind, they produce an IPSP which increases the negative charge of a post-synaptic neuron. This makes the post-synaptic neuron less likely to fire.
• Outline the fourth step of synaptic transmission. 


  For the post-synaptic neuron to decide whether to fire or not, the EPSPs and IPSPs are summed through the summation process i.e. if the net effect is excitatory (more EPSPs) the neuron will fire or if the net effect is inhibitory (more IPSPs) the neuron will not fire.
• Outline the fifth step of synaptic transmission.

  Once neurotransmitters have exerted their effects, they detach from the receptor and are either re-uptaken back into the presynaptic neuron through re-uptake transporters or they are broken down by enzymes.
• Explain what is meant by ‘excitation’ as part of the synaptic transmission process.


  Excitation refers to when excitatory neurotransmitters bind to the receptors and produce an excitatory post-synaptic potential (EPSP). This increases the positive charge of the post-synaptic neuron, making it more likely to fire.
• Explain what is meant by ‘inhibition’ as part of the synaptic transmission process.


  Inhibition refers to when inhibitory neurotransmitters bind to the receptors and produce an inhibitory post-synaptic potential (IPSP). This increases the negative charge of the post-synaptic neuron, making it less likely to fire.
• Explain why synaptic transmission can only happen in one direction.


  The vesicles containing neurotransmitters are only located in the pre-synaptic neuron. This means that neurotransmitters can only be released from the pre-synaptic neuron.
• Explain why synaptic transmission can only happen in one direction


  The process of diffusion means that neurotransmitters travel from areas of high concentration to areas of low concentration. This means they can only travel from the pre-synaptic neuron (where they are initially highly concentrated) to the post-synaptic neuron (initially a low area of concentration).
• Explain why synaptic transmission can only happen in one direction.


  Receptors for neurotransmitters to bind to are only located on the post-synaptic neuron. This means that neurotransmitters can only bind on the post-synaptic neuron, not the pre-synaptic.
• Explain how drugs can impact the process of synaptic transmission.


  Drugs can increase the process of synaptic transmission by blocking re-uptake transporters. This prevents neurotransmitters from being re-uptaken out of the synaptic gap. In turn, they can continue to bind and exert their effect on the post-synaptic neuron.
• Explain how drugs can impact the process of synaptic transmission.

  Drugs can decrease the process of synaptic transmission by blocking receptors. This prevents neurotransmitters from binding to the receptors. As a result, they cannot exert their excitatory or inhibitory effects.