What happens when one inhibitory and two excitatory neurons fire?

The interaction between excitatory and inhibitory neurons plays a crucial role in determining whether an action potential is generated in a postsynaptic neuron. In the scenario described, one inhibitory neuron and two excitatory neurons are firing.

When neurons fire, they produce graded potentials—excitatory postsynaptic potentials (EPSPs) from the excitatory neurons and inhibitory postsynaptic potentials (IPSPs) from the inhibitory neuron. The excitatory inputs tend to depolarize the postsynaptic neuron, attempting to bring the membrane potential closer to the threshold required for firing an action potential. Conversely, the inhibitory input works to hyperpolarize the neuron, moving the membrane potential away from the threshold.

The overall effect on the postsynaptic neuron results from the summation of these graded potentials. If the total input from the two excitatory neurons is not sufficient to overcome the inhibitory input and reach the threshold potential, no action potential will be generated. This concept of summation is essential in neurobiology; it highlights how the balance of excitatory and inhibitory signals can modulate neuronal activity.

Therefore, the situation described where the summed excitatory and inhibitory influences can lead to either a firing or no firing of an action potential is accurately captured by the notion that