Which of the following factors most directly influence the speed of nerve signal conduction along an axon?

• A. Number of dendrites on the neuron
• B. Diameter of the axon
• C. Presence of myelin sheath
• D. Type of neurotransmitter released

Answer: (C)

Verified step by step guidance

1. Understand the context: Nerve signal conduction refers to the transmission of electrical impulses along the axon of a neuron. The speed of this conduction is influenced by specific structural and physiological factors.
2. Factor 1: Diameter of the axon. Larger axon diameters reduce internal resistance to the flow of ions, allowing the electrical signal to propagate more quickly. This is due to the relationship between resistance and cross-sectional area.
3. Factor 2: Presence of a myelin sheath. Myelin is a fatty insulating layer that wraps around the axon. It facilitates faster signal conduction by enabling saltatory conduction, where the electrical signal 'jumps' between nodes of Ranvier (gaps in the myelin sheath).
4. Eliminate irrelevant factors: The number of dendrites on the neuron does not directly affect the speed of conduction along the axon, as dendrites are primarily involved in receiving signals, not transmitting them. Similarly, the type of neurotransmitter released affects synaptic transmission, not the conduction speed along the axon.
5. Conclude: The two factors that most directly influence the speed of nerve signal conduction along an axon are the diameter of the axon and the presence of a myelin sheath.