Final answer:
Two hyperpolarizing graded potentials that summate lead to a more negative membrane potential, making the neuron less likely to fire an action potential.
This is because summation of such inhibitory signals moves the potential further away from the threshold.
Step-by-step explanation:
When two hyperpolarizing graded potentials summate, they lead to an increase in the membrane's electrical charge's polarity. This means that the inside of the neuron becomes more negative compared to the outside.
Hyperpolarizing graded potentials are generally caused by potassium ions (K+) leaving the cell or chloride ions (Cl-) entering the cell. If these hyperpolarizations add together, they make it less likely for the neuron to reach the threshold necessary to trigger an action potential.
Instead of promoting neuronal firing, this summation acts as an inhibitory mechanism, moving the membrane potential further away from threshold and decreasing the likelihood of cell excitation.
Summation in neurons can be of two types: temporal summation and spatial summation. Temporal summation occurs when consecutive signals arrive at a synapse in rapid succession, where spatial summation occurs when signals arrive at multiple synapses at the same time.
The summation of graded potentials takes place at the initial segment of the axon or the axon hillock, which is densely populated with voltage-gated sodium channels that are crucial for initiating the depolarizing phase of an action potential.