1 Chemically, ATP is an adenine nucleotide bound to three phosphates. 2  There is a lot of energy stored in the bond between the second and third phosphate groups that can be used to fuel chemical reactions. 3  When a cell needs energy, it breaks this bond to form adenosine diphosphate (ADP) and a free phosphate molecule.
calf muscle pump. calf muscle pump. an action of the calf (soleus) muscles in which the muscles contract and squeeze the popliteal and tibial veins, forcing the blood in those veins to move upward toward the heart. Also called soleus pump.
Best Answer: Calcium flows through t-tubules. In response to stimulation, calcium channels in t-tubules open and allow calcium to flow down it's electro-chemical gradient into the cell. In skeletal muslce it contributes greatly to muscle contraction. The purpose of t-tubules is to allow depolarization to quickly penetrate to the interior of the cell. The t-tubules help to bring the extracellular environment to all parts of the muscle cell more quickly which better coordinates muscle contraction.