Chapter 4. Membranes and Transport
4.0 Introduction
Chapter Objectives
After studying this chapter, you will be able to:
- describe the structure and function of the cell membrane, including its regulation of materials into and out of the cell;
- compare and contrast mechanisms of active transport and passive transport across cell membranes; and
- describe the physiological basis of a cell’s resting membrane potential.
The plasma membrane (also known as the cell membrane or cytoplasmic membrane) is a biological membrane that separates the interior of a cell from its outside environment.
The primary function of the plasma membrane is to protect the cell from its surroundings. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells. Plasma membranes must be very flexible in order to allow certain cells, such as red blood cells and white blood cells, to change shape as they pass through narrow capillaries.
The plasma membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell and in attaching to the extracellular matrix and other cells to help group cells together to form tissues. The membrane also maintains the cell potential.
In short, if the cell is represented by a castle, the plasma membrane is the wall that provides structure for the buildings inside the wall, regulates which people leave and enter the castle, and conveys messages to and from neighboring castles. Just as a hole in the wall can be a disaster for the castle, a rupture in the plasma membrane causes the cell to lyse and die.
This work, Human Physiology, is adapted from Anatomy & Physiology by OpenStax, licensed under CC BY, and from Anatomy and Physiology by LibreTexts, licensed under CC BY-SA. This edition, with revised content and artwork, is licensed under CC BY-SA except where otherwise noted.
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