Split reins are a piece of equipment used for communicating with a horse while it is being ridden. Split reins are actually two separate, individual reins that are used together, with one rein on each side of the horse's neck.
It is bounded by two sets of membranes, a smooth outer one and an inner one that is arranged in folds, or cristae, that extend into the interior of the mitochondrion, called the matrix. Mitochondria provide the principal source of cellular energy through oxidative phosphorylation and adenosine triphosphate synthesis. They also contain the enzymes involved with electron transport and the citric acid and fatty acid cycles.
The many functions of mitochondria include production of adenosine triphosphate (ATP) via the TCA Cycle (which is also as the Krebs Cycle and the Citric Acid Cycle). That process is an important metabolic pathway that is an essential part of carbohydrate and energy metabolism - see also what is metabolism.