Synaptic Transmission


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•  Some neurotransmitters excite nerve impulses in postsynaptic neurons and others inhibit them

Presynaptic neurons release neurotransmitters that diffuse into the synapse and bind receptors on postsynaptic neurons

  • Some neurotransmitters generate excitatory post-synaptic potentials (EPSPs) by causing depolarisation (e.g. glutamate)
  • Some neurotransmitters generate inhibitory post-synaptic potentials (IPSPs) by causing hyperpolarisation (e.g. GABA)

If the combination of excitatory and inhibitory signals reaches a threshold limit, an action potential will be generated

Excitatory vs Inhibitory Neurotransmitters



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•  Nerve impulses are initiated or inhibited in postsynaptic neurons as a result of summation of all excitatory

    and inhibitory neurotransmitters received from presynaptic neurons


The combination of graded potentials (EPSPs and IPSPs) in the post-synaptic neuron is known as summation

  • Cancellation occurs when excitatory and inhibitory graded potentials cancel each other out (no threshold potential reached)
  • Spatial summation occurs when EPSPs are generated from multiple presynaptic neurons simultaneously to reach threshold
  • Temporal summation occurs when multiple EPSPs are generated from a single presynaptic neuron in quick succession

These summative effects determine which nerve pathways are activated and hence lead to alternate decision-making processes

Types of Summation