Assume you have isolated the motor neuron that innervates the calf muscle of a f

Question

Assume you have isolated the motor neuron that innervates the calf muscle of a frog and you can measure thefrequency and strength of contractions. You can generate action potentials in the motor neuron by stimulating the neuron electrically. As you increase the voltage of the stimulus, the number of motor neurons that show an action potential increases. A single 10V stimulus lasting 10msec causes all motor neurons innervating the calf muscle to contract but a 9V stimulus lasting 10 msec causes only 90% motor neuron to show an action potential.

(a) how would the strength of contraction in response to a 12 V, 10 msec stimulus compare to a 10 V, 10msec stimulus? (increase, decrease, no change)

(b) How would the strength of contraction in response to 50, 10 V, 10 msec stimulus compare to the response to a 10 V, 10 msec stimulus? (increase, decrease, same)

(c). How would the strength of contraction in response to a single 6 V, 10 msec stimulus compare to the response to a 10 V, 10 msec stimulus? (increase, decrease, same)

(d). In which of the three situations above would the distance between the z lines be the smallest? (A, b, c)
For all answers povide brief reasons

Explanation / Answer

a. The strength of contraction in response to a 12 V, 10 msec stimulus would not be different from the response of a 10 V, 10 msec stimulus. The reason for this is because the stimulus of 10 V for 10 msec is enough to stimulate all the neurons in the muscle. Once all the neurons have been stimulated, an increase in the stimulus produces no effect. ----------------------- b. The strength of contraction in response to a 50 V, 10 msec stimulus would not be different from the response of a 10 V, 10 msec stimulus. The reason for this is because the stimulus of 10 V for 10 msec is enough to stimulate all the neurons in the muscle. Once all the neurons have been stimulated, an increase in the stimulus produces no effect. ----------------------- ----------------------- c. The strength of contraction in response to a 6 V, 10 msec stimulus would be lesser than the response of a 10 V, 10 msec stimulus. The reason for this is because the stimulus of 10 V for 10 msec is enough to stimulate all the neurons in the muscle. A stimulus lower than 10V will not activate all the neurons. According to data, 60% of the neurons show an action potential. ----------------------- d. In A, B as all the neurons are activated, the distance between the z lines is shortest for all the neurons. In C as only 60% of the neurons are activated, the distance between the z lines is more. ----------------------- d. In A, B as all the neurons are activated, the distance between the z lines is shortest for all the neurons. In C as only 60% of the neurons are activated, the distance between the z lines is more.

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