Question

q4.3. which ion channel is responsible for the rising phase of the action potential, and why?
na⁺ channels, because positive na⁺ ions are at higher concentration outside the axon than inside, and so they enter the axon and raise (v_m)
na⁺ channels, because positive na⁺ ions are at higher concentration inside the axon than outside, and so they leave the axon and raise (v_m)
k⁺ channels, because positive k⁺ ions are at higher concentration outside the axon than inside, and so they enter the axon and raise (v_m)
k⁺ channels, because positive k⁺ ions are at higher concentration inside the axon than outside, and so they leave the axon and lower (v_m)

Explanation:

During the rising phase of an action potential, voltage - gated Na⁺ channels open. There is a higher concentration of Na⁺ outside the axon compared to inside. When these channels open, Na⁺ ions flow into the axon down their electrochemical gradient, depolarizing the membrane and raising the membrane potential ($V_m$).

Answer:

Na⁺ channels, because positive Na⁺ ions are at higher concentration outside the axon than inside, and so they enter the axon and raise $V_m$