Complex sentence: If the neuron only gets excitatory impulses, it will also generate an action potential; but if the neuron gets as many inhibitory as excitatory impulses, the inhibition cancels out the excitation and the nerve impulse will stop there.
Split into simpler sentences: If the neuron only gets excitatory impulses, it will also generate an action potential. If instead the neuron gets as many inhibitory as excitatory impulses, the inhibition cancels out the excitation and the nerve impulse will stop there.