This lesson explores whether all cells have a membrane and includes an introduction to the cell membrane.
Additionally, it touches on some specialized cell membranes present in the body.
The Beauty of Nature
When sitting at a microscope watching the beautiful moving blobs that are cells dance around on the slide before you, it is natural to start to contemplate their design. Cells, the most basic unit of life, can exist on their own (as in the case of bacteria) or as part of a complex organism (like a human), and can be seen individually when viewed through a microscope. As you stare at the beautiful movement in the microscope, you may begin to wonder which characteristics all cells share and which characteristics are unique between cells. Cell membranes would be one example of a shared characteristic.
While cells are made of many components, one of the most basic is the cell membrane, which separates the inside of the cell from the outside of the cell.All cells have a cell membrane, although there are slight variations. Some cells also have cell walls. While these cell walls provide additional protection and support, they do not replace the function of the cell membrane.
The Cell Membrane
A cell membrane works to keep the inside of the cell and the outside of the cell separate. You can think of it as the skin of the cell. The cell membrane is selectively permeable. This means that only certain substances or molecules are allowed to move through the membrane. Substances that the cell needs will be allowed to enter, and substances that are no longer needed or are potentially harmful will be excreted from the cell through the membrane.Additional functions of the cell membrane include:
- Cell signaling – allows the cell to send messages to other cells
- Cell adhesion – allows the cell to connect to other cells or to other structures
- Cell structure – attachment point for other key pieces of the cell, such as the cell wall or cytoskeleton
Variations in Cell Membranes
Several types of cells have unique cell membranes. While they are still cell membranes, they have different names because they have unique adaptations.
The cell membrane in muscle cells (myocytes) is called a sarcolemma. The sarcolemma can help send and receive conduction signals from other muscles.The cell membrane in an egg cell (oocyte) is called an oolemma or the zona pellucida. It helps protect the oocyte and allows fertilization by a single sperm cell (while preventing multiple sperm cells from entering the cell).The axolemma is the cell membrane of an axon (the primary way the nervous system sends signals to the body).
Without the axolemma, the axon wouldn’t be able to communicate with other axons and the nervous system function as we know it would cease.
All cells have cell membranes. There are variations between cell membranes, but the same basic structure exists in all cells.
While some cells will also have a cell wall to provide additional support and protection, this does not replace the cell membrane.Cell membranes are selectively permeable. This allows for movement of select substances from the outside to the inside of the cell and from inside the cell to the outside of the cell. The most fundamental role of the cell membrane is to protect the cell. This includes protecting it from potentially harmful substances and molecules.Cell membranes do more than control the movement of substances in and out of cells.
They are also responsible for cell signaling, cell adhesion, anchoring cell structure, and more.Some types of cells have a different name for their cell membrane due to increased specialization, but the fundamental role is still the same.