Isaac observed a sample of motor units in which single neurons innervated fibers of the same type. This led Isaac to conclude that
A) neural input probably determines the identity of muscle fibers as slow- or fast-twitch.
B) the organism that supplied the samples had probably suffered a spinal cord injury.
C) the organism that supplied the samples was very old.
D) his sample was not representative, and he needed to obtain more samples before reaching a conclusion.

Question

Quizplus · Accepted Answer

Isaac's observation suggests that the type of muscle fiber (slow- or fast-twitch) is determined by the neural input from the motor neuron that innervates it. This is supported by studies showing that different types of motor neurons innervate fibers with different properties. Therefore, choice A is the best answer. Choices B and C are not supported by the information provided and choice D is unlikely as Isaac's observation is based on a sample of motor units which may be representative of the overall population.

Isaac Observed a Sample of Motor Units in Which Single