Explain how an action potential is propagated down an axon in continuous conduction. Why is saltatory conduction faster than continuous conduction?

Verified step by step guidance

1. Understand that an action potential is a rapid change in membrane potential that travels along the axon of a neuron. Continuous conduction occurs in unmyelinated axons, where the action potential is propagated step-by-step along the entire length of the axon.
2. In continuous conduction, the action potential begins at the axon hillock. Sodium (Na⁺) channels open in response to a stimulus, allowing Na⁺ ions to enter the neuron, causing depolarization. This depolarization triggers adjacent voltage-gated Na⁺ channels to open, propagating the action potential down the axon.
3. As the action potential moves, the previously depolarized region undergoes repolarization. Voltage-gated potassium (K⁺) channels open, allowing K⁺ ions to exit the neuron, restoring the resting membrane potential. This ensures the action potential moves in one direction.
4. Saltatory conduction, in contrast, occurs in myelinated axons. The myelin sheath insulates the axon, preventing ion exchange along the myelinated segments. Action potentials 'jump' between the nodes of Ranvier, which are gaps in the myelin sheath where voltage-gated Na⁺ and K⁺ channels are concentrated.
5. Saltatory conduction is faster than continuous conduction because the action potential only needs to be regenerated at the nodes of Ranvier, rather than along the entire axon. This reduces the time and energy required for ion exchange and propagation, making the process more efficient.

Key Concepts

Action Potential

An action potential is a rapid, temporary change in the electrical membrane potential of a neuron, allowing it to transmit signals. It occurs when a neuron reaches a threshold potential, leading to the opening of voltage-gated sodium channels, resulting in depolarization. This is followed by repolarization as potassium channels open, restoring the resting membrane potential.

Continuous Conduction

Continuous conduction refers to the slow propagation of action potentials along unmyelinated axons. In this process, the action potential is regenerated at every segment of the axon, leading to a gradual wave of depolarization. This method is less efficient and slower compared to saltatory conduction, as it requires more time for the ion channels to open and close along the entire length of the axon.

Saltatory Conduction

Saltatory conduction is the rapid transmission of action potentials along myelinated axons, where the action potential jumps between nodes of Ranvier. This occurs because myelin sheaths insulate the axon, preventing ion flow except at these nodes. As a result, saltatory conduction is significantly faster than continuous conduction, as it reduces the time and energy required for the action potential to propagate.