a. I band narrows as sarcomere contracts b. depolarization wave travels along sarcolemma and T-tubules c. myosin heads bind to actin fibers d. acetylcholine binds to receptors in the neuromuscular junction e. calcium is released into sarcoplasm

the abdomen (less formally called the belly, stomach, tummy or midriff) constitutes the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. the region occupied by the abdomen is termed the abdominal cavity. the stomach secretes acid and enzymes that digest food. ridges of muscle tissue called rugae line the stomach. the stomach muscles contract periodically, churning food to enhance digestion. the pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.

d. changes in climate and historical records

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answer; somatic;