Why are action potentials usually conducted in one direction?
a. Ions can flow along the axon in only one direction
b. The brief refractory period prevents the reopening of voltage-gated Na⁺ channels
c. The axon hillock has a higher membrane potential than the terminals of the axon
d. Voltage-gated channels for both Na⁺ and K⁺ open in only one direction.

Verified step by step guidance

1. Understand the concept of action potentials: Action potentials are rapid electrical signals that travel along the axon of a neuron, allowing communication between neurons.
2. Learn about the refractory period: After an action potential occurs, there is a brief period during which the neuron is unable to fire another action potential. This is known as the refractory period.
3. Explore the role of voltage-gated Na+ channels: During the refractory period, the voltage-gated Na+ channels are temporarily inactivated, preventing the initiation of another action potential in the same region.
4. Consider the directionality of action potential conduction: Due to the refractory period, the action potential cannot travel backward because the Na+ channels behind the action potential are inactivated, ensuring one-way conduction.
5. Evaluate the options: Option b is correct because the brief refractory period prevents reopening of voltage-gated Na+ channels, ensuring that action potentials are conducted in one direction.

Key Concepts

Action Potential

An action potential is a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane, primarily in neurons. It is initiated when a neuron sends information down an axon, away from the cell body, and involves the opening and closing of ion channels, particularly sodium (Na+) and potassium (K+) channels.

Refractory Period

The refractory period is a short time after an action potential during which a neuron is unable to fire another action potential. This period is divided into the absolute refractory period, where no new action potential can be initiated, and the relative refractory period, where a stronger-than-normal stimulus is required. It ensures unidirectional propagation of the action potential along the axon.

Voltage-Gated Ion Channels

Voltage-gated ion channels are proteins in the cell membrane that open or close in response to changes in membrane potential. These channels are crucial for the generation and propagation of action potentials, as they allow the selective flow of ions like Na+ and K+, which alters the membrane potential and facilitates the transmission of electrical signals along neurons.