What initiates an action potential on a muscle cell?
a. acetylcholine binding to receptors on the sarcolemma within the neuromuscular junction
b. acetylcholinesterase
c. myosin cross bridges binding to actin
d. atp?

Which of these is true of the cytoplasm of an unfertilized egg? a. it is an unevenly distributed mixture of mrna, proteins, organelles, and other substances. b. it does not contain substances that are important in directing development. c. these substances are supplied by the sperm. d. it does not contain substances that are important in directing development. e. development is directed solely by the surrounding cells. f. it is a homogeneous mixture of mrna, proteins, organelles, and other substances. g. it does not contain substances that are important in directing development. h. these substances are produced by the dna of the fertilized zygote.