Rem rebound involves the
- tendency for rem sleep to increase following rem sleep deprivation.
- increase in rem sleep that characteristically follows intense learning episodes or stressful daytime experiences.
- unusual symptoms of tiredness and irritability that follow periods of rem sleep deprivation.
- tendency for rem sleep periods to become increasingly longer and more frequent as a normal night of sleep progresses.

The correct answer to the question: REM rebound involves the:___, would be: Tendency for REM sleep to increase following REM sleep deprivation.

Explanation:

REM sleep, also known as Rapid Eye Movement is one of the stages of sleep in which, depending on the depth of sleep, there is a loss of coordination of the muscle movement of the eyes. Usually, this stage of sleep requires a certain amount of time to happen, since it is a deep state, but in REM rebound  what we have is a person who has been deprived of REM sleep for a period of time, and who, after finally falling asleep will experience lenghtier and much more frequent episodes of REM sleep than those who haven´t. As the term "rebound" involves, it is like the body comes back from its forced lack of proper rest and as retribution prolongues these periods to accomplish the needed rest.

b) the heart is a pump made of muscle and that is difficult to grow in the lab.