Self-study
Although severing a motor nerve kills part of the nerve, it can regenerate, growing about 1 millimeter per day from the point of damage toward the muscle the nerve controlled. ███ ███ ████████ █ ███████ █████ █████ ████ ██████████ █ ████ ██████ ████████ █ ████ ██████ ████ ██ ██████████ ██ ████ █████ ██ ███████ ██ ███ ████████ ██████ ████ ██ ███ ██████ ████████████ ███ ███████ █████ ███████ ███ ████████ █████ ██████ ██ █████ ████ ██ ███ ████ ████ ███ ████ █████████ ███ ████ ██████ ██████ ██ ████████████ █████ █████ █████ ██████ ██████ █████ ██ ██████ █████ ██████ ██████ ███
Summary
Severing a motor nerve kills part of the nerve. However, the nerve can regenerate. When regenerating, a nerve grows about 1 millimeter every day from the point of severing toward the muscle the nerve controlled. For example, a severed nerve controlling a hand would take longer to regenerate if the nerve was severed at the shoulder compared to the wrist.
Growing nerve cells also require the original nerve sheath to guide them to the muscle. However, the original nerve sheath disintegrates after three months unless living nerve tissue exists within it.
Strongly Supported Conclusions
If a severed motor nerve would take more than three months to regenerate, it is unlikely to reconnect to its muscle.
If an severed motor nerve's original sheath contains living nerve tissue, then the likelihood that the nerve can successfully regenerate even after three months increases.
22.
The statements above, if true, ████ ████████ ███████ █████ ███ ██ ███ ██████████
a
Doubling the speed ██ █████ ███ █████ █████ ████ ████ ██████ ███ ██████████ ████ █ ███████ █████ █████ ████ █████ ███ ██████ ██ ███ ███████████
This answer is unsupported. We don’t know if the speed at which nerve cells grow is directly proportional with the likelihood it will reach the original muscle.
b
It is sometimes █████████ ████ █ █████ ██████ ███ █████ ██ █████████████ ██ ███████ ██ ████ ███ ███████ ██ ███████████████
This answer is unsupported. We don’t know whether it’s possible to reverse or slow the process of disintegration.
c
If a severed █████ █████ ████ ███ ██████████ ████████████ ██████ █████ ██████ █████ █████ ████████ ███████████ ██████ ██ ████████ ██ ███ ██████ ████ ███ █████ ███ ███████████
This answer is unsupported. We don’t know if the original nerve's regeneration is necessary for a muscle’s function to be restored. There may be another way to restore function that the stimulus just doesn't mention.
d
If living nerve ██████ █████ ██ █████████ ███ █████████ ██████ ███ ████████ ██████ ██ █ ███████ █████ ██████ ███ ██████████ ████ ███ █████ ████ ██████████ █████ ████████ ██ ████ ██████
This answer is the best supported. Without living nerve tissue, the nerve sheath would disintegrate after three months. So having living nerve tissue at least gives the nerve sheath a chance of surviving after three months. In addition, the nerve sheath is necessary for the original nerve to successfully regenerate. So, implanting living nerve tissue into a nerve sheath provides something that's necessary for survival of the nerve sheath beyond three months, which in turn provides something that's necessary for a nerve to regenerate. This supports the claim that by implanting living nerve issue, the chances a nerve regenerates could increase in at least some cases (cases in which nerve regeneration would take longer than three months).
e
Without surgical intervention, █ ██████ ████ ███ ████ ████████ ███████ ██ █ ███████ █████ █████ ██ ████████ ██ ██████ ████ █████████
This answer is unsupported. We don’t know if surgical intervention is necessary, or even helpful to restore function to a muscle severed from a motor nerve.