Introduction
 

Cholesterol is a derivative of the cyclopenta more thin, is human body cell membrane phase structure and an important component of nerve myelin, weig is 70 kg of normal person, containing about 140 grams of cholesterol in the body, as early as the 18th , people have found cholesterol in bile stone chemists the herschel in 1816 will be a name to this with the nature of the lipid material cholesterol cholesterol widely exists in animals, especially in the most abundant in the brain and nerve tissue in the liver and kidney and spleen skin bile content is high also its solubility is similar to fat, insoluble in water, soluble in ether choroform solvent, etc.

1. Cholesterol functions as an insulating cover for the transmission of electrical impulses in the nervous tissue.
2. Cholesterol is required to build and maintain membranes; it modulates membrane fluidity over the range of physiological temperatures. The hydroxy group on cholesterol interacts with the polar head groups of the membrane phospholipids and sphingolipids, while the bulky steroid and the hydrocarbon chain are embedded in the membrane, alongside the nonpolar fatty-acid chain of the other lipids.
3. Cholesterol contributes to the decreased fluidity of the cell membrane as the molecule is in a trans conformation making all but the side chain of cholesterol rigid and planar. In this structural role, cholesterol reduces the permeability of the plasma membrane to neutral solutes, hydrogen ions, and sodium ions.