In fact, the pump basically maintains those concentration gradients. That means that this pump is moving the ions against the concentration gradients for sodium and potassium, which is why it requires energy. As was explained in the cell chapter, the concentration of Na + is higher outside the cell than inside, and the concentration of K + is higher inside the cell than outside. The sodium/potassium pump requires energy in the form of adenosine triphosphate (ATP), so it is also referred to as an ATPase. The cell membrane is composed of a phospholipid bilayer and has many transmembrane proteins, including different types of channel proteins that serve as ion channels. Of special interest is the carrier protein referred to as the sodium/potassium pump that moves sodium ions (Na +) out of a cell and potassium ions (K +) into a cell, thus regulating ion concentration on both sides of the cell membrane. Several passive transport channels, as well as active transport pumps, are necessary to generate a transmembrane potential and an action potential. Transmembrane proteins, specifically channel proteins, make this possible. Charged particles, which are hydrophilic by definition, cannot pass through the cell membrane without assistance ( ).
The cell membrane is a phospholipid bilayer, so only substances that can pass directly through the hydrophobic core can diffuse through unaided. Both of the cells make use of the cell membrane to regulate ion movement between the extracellular fluid and cytosol.Īs you learned in the chapter on cells, the cell membrane is primarily responsible for regulating what can cross the membrane and what stays on only one side. For skeletal muscles to contract, based on excitation–contraction coupling, requires input from a neuron. Previously, this was shown to be a part of how muscle cells work. Most cells in the body make use of charged particles, ions, to build up a charge across the cell membrane.
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