Final answer:
The velocity of action potentials is determined by the axon diameter and the degree of myelination, with larger diameters and myelination through nodes of Ranvier increasing conduction speed (A).
Step-by-step explanation:
The two physical parameters that determine the velocity of action potentials are axon diameter and the degree of myelination. A larger axon diameter allows for faster propagation because there is less resistance to the flow of ions within the cell. Moreover, myelination greatly increases conduction speed by insulating the axon and allowing action potentials to jump between the nodes of Ranvier in a process known as saltatory conduction. Therefore, the correct answer to the student's question is A) Axon diameter and temperature, since larger diameters and warmer temperatures generally increase the speed of action potential propagation.
The velocity of action potentials in a nerve cell is determined by two physical parameters: axon diameter and temperature. The diameter of the axon affects the resistance to ion flow, with larger axons having less resistance and allowing for faster propagation of the action potential. Temperature also plays a role, as higher temperatures increase the speed of ion movement and therefore the velocity of action potentials.