Question

19/40
which event produces the falling phase of an action potential?
opening na⁺ channels
opening ca²⁺ channels
increased myelin permeability
closing na⁺ channels, opening k⁺ channels

Explanation:

To determine the event for the falling phase of an action potential:

• Opening Na⁺ channels (first option) causes depolarization (rising phase), not falling.
• Opening Ca²⁺ channels (second option) is more relevant to synaptic transmission or other processes, not the falling phase of an action potential.
• Increased myelin permeability (third option) affects conduction speed, not the falling phase.
• During the falling phase, Na⁺ channels close (inactivation) and K⁺ channels open, allowing K⁺ to exit, repolarizing the membrane. This matches the fourth option: "Closing Na⁺ channels, opening K⁺ channels".

Answer:

D. Closing Na⁺ channels, opening K⁺ channels (assuming the options are labeled A - D in order: A. Opening Na⁺ channels, B. Opening Ca²⁺ channels, C. Increased myelin permeability, D. Closing Na⁺ channels, opening K⁺ channels)