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Prot− negatively charged proteins
K+ potassium ions
Na+ sodium ions
Cl− chloride ions
neurotransmitter
A neuron adds up whatever change in membrane potential reaches the axon hillock, from every channel, from every direction, at that moment. Threshold is judged there and nowhere else.
Notice that the neuron keeps firing as long as the hillock stays above threshold. A stronger input doesn't make a bigger action potential. It makes more of them.
