In response to being startled, an animal involuntarily contracts a skeletal muscle, causing it to shorten. what process is described by an animal's ability to involuntarily contract a skeletal muscle without receiving a direct signal from the brain, and which type of muscle contraction occurred as a result?

The answer is reflex action. Impulse that triggers a reflex action does not pass through the brain so as to shorten the time for response. It passes through a reflex arch and this is why the muscles are contracted even without time to think of what happened. The sensory and motor neurons only arch at the spinal cord.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.