Dr. Dre is investigating reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish's neurons. What is a likely explanation?

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The scenario describes two animals, a crab and a fish, with the fish showing faster action potential conduction along its neurons. To determine which explanation best accounts for this, examine each option in turn.
Option 1: 'The fish's axons are not myelinated. The crab's axons are myelinated.' If this were true, we would expect the crab to conduct impulses faster due to myelination, not the fish. Since the observation is the opposite (the fish conducts faster), this option contradicts the reported data and is inconsistent with the established role of myelin in speeding conduction.
Option 2: 'There is a higher percentage of ion channels in the axons of the crab compared with the percentage of ion channels in fish axons.' Merely having more ion channels does not automatically translate to faster conduction along axons. The speed of conduction is more directly influenced by insulation (myelination) and axon diameter, while channel density affects excitability and signaling dynamics, not the fundamental speed of saltatory conduction. This makes the statement unlikely to explain the observed difference in conduction velocity.
Option 3: 'The fish's axons are myelinated. The crab's axons are not myelinated.' This aligns with the well-established principle that myelination accelerates nerve impulse travel by enabling saltatory conduction, which reduces membrane capacitance and increases conduction velocity. If the fish’s axons are myelinated and the crab’s are unmyelinated, the fish would logically show faster conduction, matching the scenario.
Option 4: 'The fish's axons are smaller in diameter than the axons in the crab.' In general, smaller-diameter axons conduct more slowly because internal resistance to current is higher. This would predict slower conduction in the fish, not faster. Therefore, this option would not explain the observed faster conduction in the fish and is inconsistent with the data.
Overall, evaluating each choice against known neurophysiological principles—myelination speeding conduction via saltatory conduction, diameter affecting internal resistance, and channel density influencing excitability—helps separate the plausible explanation from the implausible ones. The third option directly matches the mechanism that would produce the described outcome, while the others introduce contradictions or less direct factors that don’t fit the observation.

Bio 93 Section CDE 2025 Final Exam Practice, Part 1

Dr. Dre is investigating reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish's neurons. What is a likely explanation?

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Bio 93 Section CDE 2025 Final Exam Practice, Part 1

Dr. Dre is investigating reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish's neurons. What is a likely explanation?

View Explanation

Log in for full answers

Similar Questions

True or False: In brain development, myelination starts occurring at the end of infancy and continues throughout childhood but then becomes complete at the end of adolescence.

Question at position 32 Schwann cells primarily:Wrap around axons to form myelin sheathsCover axons without gaps for continuous insulationInsulate the central nervous system axonsRegulate the extracellular environment of neuron cell bodies

The axons of peripheral system neurons are surrounded by cells called ______ They wrap the axon in many layers of a whitish, non-conductive protein called ______. Without this coating, the electrical impulse that propagates the nerve signal can be lost to the surrounding tissue.

Schwann's cells form myelin sheaths around axons in the central nervous system.

What allows the action potential to pass quickly and efficiently down the axon?

What involves an increase in the speed and efficiency with which information travels through the nervous system during brain development in children between the ages of 3 and 5.

What is myelination?

Which of the following is not true about myelination?

More Practical Tools for Students Powered by AI Study Helper

Making Your Study Simpler

The axons of peripheral system neurons are surrounded by cells called They wrap the axon in many layers of a whitish, non-conductive protein called . Without this coating, the electrical impulse that propagates the nerve signal can be lost to the surrounding tissue.