Vertebrate striated muscle contraction is controlled (regulated) by the action of the proteins troponin and tropomyosin on the actin filaments. Nervous stimulation causes a depolarisation of the muscle membrane (sarcolemma) which triggers the release of calcium ions from the sarcoplasmic reticulum.
n. 1  Abnormally fast or deep respiration, which results in the loss of carbon dioxide from the blood, thereby causing a fall in blood pressure, tingling of the extremities, and sometimes fainting.
A rapid or fast heartbeat is when your heart is beating faster than normal. A normal heart rate is 60 to 100 beats per minute. Tachycardia is considered a heart rate of greater than 100 beats per minute.If you are exercising, or performing any kind of activity, your heart will normally beat faster.This allows your heart to pump blood through out your body, to provide oxygen to the tissues. For rapid heart rates that are caused by shortness of breath, you may have trouble lying flat in bed, and you may have to sleep on 2 or more pillows. 2  Your shortness of breath may cause you to wake up in the middle of the night. 3  If you have heart problems, your legs may be swollen, especially in your feet and ankles.