The two sides of a nerve cell membrane have unequally distributed ions ( Na+ and K+). Sodium is inside, while potassium is outside. Carriers actively transport them. This active transport mechanism is called Sodium-Potassium Pump. Without stimulus, sodium channels are closed while some of the potassium channels are open.
Stimulus (depolarization) will cause the sodium channels to briefly open and the positively-charged ion diffuses into the nerve cell. The membrane potential becomes positive. The potassium channels open and positively-charged potassium diffuse out. With respect to the outside, the inside will become less positive again.
Sedimentary rocks, I think
Vertebrate striated muscle<span> contraction is controlled (regulated) by the action of the proteins troponin and tropomyosin on the actin filaments. Nervous </span>stimulation<span>causes a depolarisation of the </span>muscle<span> membrane (sarcolemma) which triggers the</span>release of calcium<span> ions from the </span>sarcoplasmic reticulum<span>.</span>
In cellular respiration, energy is converted from the nucleus. <span />