The Cell Membrane

The external membrane or plasmalemma of a neuron (Fig. 23) has the general composition of all biological membranes: a bimolecular layer of opposing phos-pholipid molecules, with hydrophilic phosphorylated heads at the external and internal membrane surfaces and hydrophobic chains in the water-free interior. Cholesterol, proteins, glycoproteins, and glycolipids are interspersed in the phospholipid bilayer. The lipids form a barrier to prevent ions and water-soluble molecules from entering and to retain the cytoplasm. They also provide a fluid matrix in which protein molecules lie in a fluid mosaic manner. The proteins permit selective passage of certain materials through pores, as carrier enzymes, antigens, and receptor sites for bonding neuroactive substances. The apparent uniformity of the plasmalemma is misleading. Regional peculiarities in the distribution of membrane proteins and lipids are known. The apical, lateral, basolateral, and basal domains of the columnar epithelial cell noted previously are good examples.

All About Alzheimers

All About Alzheimers

The comprehensive new ebook All About Alzheimers puts everything into perspective. Youll gain insight and awareness into the disease. Learn how to maintain the patients emotional health. Discover tactics you can use to deal with constant life changes. Find out how counselors can help, and when they should intervene. Learn safety precautions that can protect you, your family and your loved one. All About Alzheimers will truly empower you.

Get My Free Ebook


Post a comment