Describe the change that takes place in the long bones of an adult that no longer allow growth in height.Why are myocardial cells able to maintain high levels of energy synthesis? 2. What is the significance of the myocardial cells possessing more T tubules? 3. The SA node is the usual pacemaker of the heart. How many action potentials does it produce per minute? How is this different than the rate in the structures further along the activation pathway? What is the relevance of this?