The immediate source of energy for muscular contraction is the high-energy phosphate compound called adenosine triphosphate (ATP). Although ATP is not the only energy-carrying molecule in the cell, it is the most important one, and without sufficient amounts of ATP most cells die quickly. The three main parts of an ATP molecule are: an adenine portion, a ribose portion, and three phosphates linked together. The formation of ATP occurs by combining adenosine diphosphate (ADP) and …showed first 75 words of 3405 total…

…showed last 75 words of 3405 total…slow movements. The premotor cortex operates in conjunction with the motor cortex to refine complex motor actions and may be important in acquisition of motor skills. The autonomic nervous sytem is responsible for maintaining the constancy of the body's internal environment and can be separated into two divisions: the sympathetic division and the parasympathetic division. In general, the sympathetic portion tends to excite an organ, while the parasympathetic portion tends to inhibit the same organ.