IB Biology: C2.2-Propagation of an action potential

How does an action potential propagate along an unmyelinated nerve fiber?

• It jumps from one insulated segment to the next.

• It travels continuously as depolarization spreads to adjacent regions.

• It moves backward towards the point of stimulation.

• It requires active transport of ions across the entire membrane.

Why does an action potential typically travel in only one direction along a nerve fiber?

• The nerve fiber is only excitable at one end.

• The voltage-gated sodium channels are only present at one end.

• The area where the action potential has just passed becomes refractory.

• The myelin sheath prevents backward propagation.

What is the primary function of the myelin sheath in a myelinated nerve fiber?

• It actively transports ions to generate action potentials.

• It acts as an electrical insulator, decreasing ion flow across the membrane.

• It provides structural support to the axon.

• It contains a high density of voltage-gated sodium channels.

What happens when an action potential reaches a node of Ranvier?

• Potassium (K⁺) ions diffuse into the axon, causing depolarization.

• The myelin sheath opens channels for ions to cross the membrane.

• The action potential skips the node completely, traveling only under the myelin sheath.

• Sodium (Na⁺) ions diffuse into the axon, depolarizing the membrane and regenerating the action potential.

What happens when sodium ions diffuse from a region that has just had an action potential to another region with a node of Ranvier close by?

• The sodium ions remain trapped at the first node, preventing further conduction of the impulse.

• The adjacent node of Ranvier is depolarized to threshold, triggering a new action potential.

• The sodium ions move under the myelin sheath and cause continuous depolarization along the entire axon.

• The sodium ions directly stimulate neurotransmitter release at the next synapse.

What is saltatory conduction of nerve impulses?

• The back-and-forth movement of ions across the axon membrane to maintain resting potential.

• The continuous flow of ions along the entire length of an unmyelinated axon.

• The jumping of action potentials from one node of Ranvier to the next along a myelinated axon.

• The transmission of nerve impulses across a synapse using neurotransmitters.

What are the primary advantages of saltatory conduction in myelinated nerve fibers compared to continuous conduction in unmyelinated fibers?

• It is slower but more energy-efficient.

• It is faster and more energy-efficient.

• It allows for bidirectional signal transmission.

• It requires more voltage-gated sodium channels.