Question

use the following information to answer question 28. in an experiment, two muscle fibres were electrically stimulated and their responses were noted. muscle fibre 1 was found to have a threshold of 18 mv. muscle fibre 2 was found to have a threshold stimulus of 32 mv. in a separate investigation, a student stimulated these same two neurons with an electrical probe starting with a strength of 5 mv and for each sequential test increase the probe strength by 10 mv. 28. which row identifies correctly the excitatory and inhibitory neurons? a. row a b. row b c. row c d. row d

Explanation:

Step1: Recall muscle - fibre response principle

A muscle fibre contracts when the stimulus voltage reaches or exceeds its threshold. Muscle fibre 1 has a threshold of 18 mV and muscle fibre 2 has a threshold of 32 mV.

Step2: Analyze each option

• Option A: 15 mV is below the threshold of both (18 mV for fibre 1 and 32 mV for fibre 2), so both should be relaxed, not one contracted and one relaxed.
• Option B: 25 mV is above the threshold of muscle fibre 1 (18 mV), so it will contract. 25 mV is below the threshold of muscle fibre 2 (32 mV), so it will relax. This is the correct combination.
• Option C: 35 mV is above the threshold of both muscle fibre 1 and muscle fibre 2, so both should contract, not one contract and one relax.
• Option D: 45 mV is above the threshold of both muscle fibre 1 and muscle fibre 2, so both should contract, not be relaxed.

Answer:

B. Row B