What is the Plasma Membrane?

[Audio] Hello and welcome to the A & P corner, where all things anatomy and physiology rules and so do you! If you're new here, don't forget to hit that like button and don't forget to subscribe so you can stay up to date with the posted content. Alright, now that we got that out of the way, let's get into it. In this video we're going to learn about the plasma membrane: what it is, what it does, and what it is made up of..

[Audio] The fluid mosaic model shows the plasma membrane as a double layer of phospholipids with proteins embedded in it. The plasma membrane is extremely thin – 7-10 nanometers. The proteins scattered in the plasma membrane act like gates, allowing only certain molecules or ions to enter and exit the cell. You could say these proteins are the crossing guards of the plasma membrane! Many of the proteins that float in the lipid bilayer form a constantly changing pattern. The model was aptly named after this characteristic..

[Audio] The plasma membrane serves five functions: it serves as a mechanical barrier, seperating the intracellular fluid from the extracellular fluid. Its selective permeability allows only certain substances to enter and exit. The electrochemical gradient creates and helps maintain the electrochemical gradient necessary for muscle and neuron function. It aids in communication, allowing cells to recognize one another and interact. Lastly, the plasma membrane aids in cell signaling, as the protein in the membrane interacts with certain chemical messengers and relays info to the cells' interior..

[Audio] There are three lipids, or fats, found in the plasma membrane. Those are phospholipids, glycolipids, and cholesterol. Let's get into more detail on these three membrane lipids that form the basic fabric of the membrane..

[Audio] Phospholipids have a "head" and a "tail". The head is charged, polar, and hydrophilic, or water loving. This means it likes to be by water molecules. Both the intracellular and extracellular fluids contain water. The tail, however, is uncharged, nonpolar, and hydrophobic,or water fearing. This means it doesn't like to be by water molecules. The two layers of phospholipids line up tail to tail, just like you see in the picture. This encourages the membranes to assemble into generally spherical shapes, and when torn reseal itself..

[Audio] Glycolipids are one of the other lipids found in the plasma membrane. Glycolipids are nonpolar fatty acid tails attached to polar sugar groups. They are only found in the outer plasma membrane, and account for 5% of the total membrane lipids..

[Audio] Cholesterol is the other lipid found in the cell plasma membrane. It makes up 20% of the membrane lipids. Like phospholipids, it has a polar region and a nonpolar region. Its polar region is its hydroxyl group. Its nonpolar region is its fused ring system. Wedging itself between the phospholipid tails, it stabilizes the membrane and keeps the phospholipids from moving around so much..

[Audio] Alright now remember the fluid mosaic model and those protein gates? We're going to discuss the two different types of proteins found in the plasma membrane: integral proteins and peripheral proteins. Stick with me now..

[Audio] Integral proteins are stuck in the lipid bilayer. Some stick out from only one side of the membrane, but most are called transmembrane proteins – meaning they span the entire cell membrane and stick out on either side. Regardless if it's transmembrane or not, integral proteins have hydrophobic regions and hydrophilic regions. Being structured this way allows for interactions between the nonpolar lipid tails in the membrane and the water inside and outside the cell. Channels, or pores, are clusters or transmembrane proteins and are involved in transporting small water-soluble molecules or ions. Carriers are other transmembrane proteins that bind to substances first, and then move through the membrane. Some transmembrane proteins are enzymes, and some use signal transduction and act as receptors for hormones and other chemicals..

[Audio] Unlike integral proteins, peripheral proteins are not embedded in the lipid bilayer and are instead loosely attached to the integral proteins. They can be easily removed and do not disrupt the membrane. They help support the membrane from its cytoplasmic side using a network of filaments. Like integral proteins, some peripheral proteins are enzymes while others are motor proteins that assist in changing cell shape during division and muscle cell contractions. Others link cells together..

[Audio] Made up of glycoproteins and glycolipids, the glycocalyx, or sugar covering, forms a fuzzy, sticky, carb rich area on the cells surface. Yes, you heard that right! Our cells are basically sugar coated! These glycoproteins and glycolipids are secreted by the cell and are the membrane proteins that come in contact with the extracellular fluid. Every cell type has a different pattern of sugars in the glycocalyx – this helps cells recognize one another. When a cell becomes cancerous its glycocalyx may change constantly, allowing it to stay ahead of the immune system and avoid being destroyed..

[Audio] The last feature of the plasma membrane we'll cover in this video are cell junctions. Junctions are the most important way cells are held together. There are three types of junctions: tight junctions, desmosomes, and gap junctions. Tight junctions are impermeable junctions that encircle cells. It helps keep things from passing through the extracellular space between adjacent cells. Despite being called impermeable, some of these junctions allow certain ions to pass. Desmosomes, name meaning binding bodies, are anchoring junctions. They're commonly found in tissues that are subjected to great mechanical stress, such as skin and heart muscles. These junctions fit together like the teeth of a zipper in the intercellular space. Gap junctions, or nexus, are communicating junctions between adjacent cells. They're found in electrically excitable tissues like heart and smooth muscle. Gap junctions allow ions, sugars, and other small molecules to pass through. The passing of ions from cell to cell helps synchronize electrical activity and contraction..

[Audio] Now, that did get a little technical and hairy, but if you stuck with it this far and found any part of this video helpful, hit that like button and don't forget to subscribe to stay up to date with all the posted content. As always, credit is given where credit is due. This video is brought to you by the sixth edition of Pearson educations anatomy and physiology book. Images were downloaded from freepik.com. For more A&P information, head back to the channel page and check out the other videos. Thanks for watching. Stay learning!.