Final answer:
A synaptic current evokes a larger excitatory postsynaptic potential (EPSP) in the postsynaptic neuron, potentially leading to an action potential if the membrane depolarization reaches threshold through the summation of EPSPs.
Step-by-step explanation:
The synaptic current evokes a larger excitatory postsynaptic potential (EPSP) in the postsynaptic neuron. An EPSP is a depolarization of the postsynaptic membrane which moves the membrane potential toward the threshold for an action potential. When neurotransmitters bind to receptors at excitatory synapses, they typically result in the opening of Na+ channels, allowing Na+ ions to enter the postsynaptic neuron and depolarize the membrane. If this depolarization is sufficient, it may reach the threshold and trigger an action potential.
Conversely, release of neurotransmitters at inhibitory synapses leads to an inhibitory postsynaptic potential (IPSP), which is a hyperpolarization that makes the postsynaptic neuron less likely to fire an action potential. An example of an inhibitory neurotransmitter is GABA, which causes Cl- channels to open, leading to an influx of Cl- ions and membrane hyperpolarization.
The process of summation involves multiple presynaptic inputs creating EPSPs around the same time. This can sufficiently depolarize the postsynaptic cell, allowing it to reach the threshold and fire an action potential. Integration of both EPSPs and IPSPs determines the net change in postsynaptic membrane voltage and whether an action potential will occur.