Final answer:
Myelin acts as an insulator that decreases resistance and increases the conduction speed of action potentials. The nodes of Ranvier contain ion channels that regenerate the action potential, allowing it to 'jump' from node to node in a process called saltatory conduction, which speeds up the transmission significantly.
Step-by-step explanation:
Myelin's Role in Action Potential Propagation
Myelin is a fatty substance that insulates axons, the long fibers of neurons that transmit electrical signals. In the context of an action potential, which is a brief electrical impulse by which information is transmitted along the axon of a neuron, myelin plays a critical role. It acts as an electrical insulator, preventing the current from leaking out of the axon. This insulation property effectively decreases resistance to the flow of electrical current, allowing the action potential to be conducted more rapidly along the axon.
Nodes of Ranvier and Saltatory Conduction
Nodes of Ranvier are small gaps in the myelin sheath where the axon membrane is exposed. These nodes regenerate the action potential as sodium (Na+) and potassium (K+) ions flow through their respective voltage-gated channels located at these nodes. This process of action potential 'jumping' from one node to the next is known as saltatory conduction, which is much faster compared to the transmission in unmyelinated axons, where the action potential would have to be continuously generated along the entire length of the axon. Thus, the nodes of Ranvier play a vital role in this process by refreshing the signal at specific intervals, allowing for rapid and efficient transmission of the action potential.
Considering the options provided in the question, the correct answer is: c) Myelin increases the speed of transmission, nodes of Ranvier refresh the signal.