Final answer:
The statement that at the Nodes of Ranvier, there is a high concentration of Na+ channels is true. These nodes are crucial for the rapid propagation of action potentials along myelinated axons. The concentration gradient of Na+ ions drives them to enter the cell, causing depolarization and allowing the electrical signal to jump from node to node efficiently.
Step-by-step explanation:
The statement is true: at the Nodes of Ranvier, there is a high concentration of Na+ channels, and this is indeed a site of inward current. During the transmission of an action potential, the Nodes of Ranvier are critical regions where depolarization occurs due to the influx of Na+ ions into the nerve cell. These ions flood into the cell due to a high concentration gradient, moving from an area where Na+ is in higher concentration outside of the cell to a lower concentration inside the cell. As a result, this causes a change in membrane potential leading to the propagation of the action potential along the axon of the neuron.
As the membrane depolarizes, the electrically driven movement of Na+ ions continues, pushing the membrane potential towards and even beyond zero, eventually reaching up to +30mV. This process is followed by the opening of voltage-gated channels.
Myelinated axons possess Nodes of Ranvier that allow action potentials to 'jump' from node to node, speeding up the electrical signal along the axon. Unmyelinated axons, in contrast, do not have these nodes and therefore, the action potential moves more slowly as it must travel along the entire length of the axon without these 'jumps'. The concentration of voltage-gated Na+ and K+ channels at the Nodes of Ranvier are crucial for this rapid propagation of nerve impulses known as saltatory conduction.