Question

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what happens when an action potential reaches a node of ranvier?
the depolarization of the cell membrane triggers the opening of voltage - gated ion channels, allowing negative ions to flow in and positive ions to flow out
the action potential is blocked at the node of ranvier
the depolarization of the cell membrane triggers the opening of voltage - gated ion channels, allowing positive ions to flow in and negative ions to flow out
reaching a node of ranvier causes the cell membrane to repolarize
the node of ranvier becomes hyperpolarized instead of depolarized

Explanation:

When an action potential reaches a node of Ranvier, the depolarization of the cell - membrane triggers the opening of voltage - gated ion channels. Sodium ($Na^+$) ions, which are positive, flow into the cell and potassium ($K^+$) ions, also positive, flow out initially during the rising phase of the action potential. But mainly, positive ions flow in to further depolarize the membrane. The action potential is not blocked, and repolarization or hyperpolarization do not occur at this initial stage of reaching the node.

Answer:

The depolarization of the cell membrane triggers the opening of voltage - gated ion channels, allowing positive ions to flow in and negative ions to flow out