Ion channels are pores that allow specific charged particles to cross the membrane in response to an existing electrochemical gradient. The Na +/K + ATPase pump maintains these important ion concentration gradients. Therefore, this pump is working against the concentration gradients for sodium and potassium ions, 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 pump. Figure 12.5.1 – Cell Membrane and Transmembrane Proteins: 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 uses energy to move 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. Specific transmembrane channel proteins permit charged ions to move across the membrane. Charged particles, which are hydrophilic, cannot pass through the cell membrane without assistance ( Figure 12.5.1). The cell membrane is a phospholipid bilayer, so only substances that can pass directly through the hydrophobic core can diffuse through unaided. Both muscle and nerve cells make use of a cell membrane that is specialized for signal conduction 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. For skeletal muscles to contract, due to excitation–contraction coupling, they require input from a neuron. In a prior chapter, we described how muscle cells contract based on the movement of ions across the cell membrane. Most cells in the body make use of charged particles ( ions) to create electrochemical charge across the cell membrane. The basis of this process is the action potential. An action potential is a predictable change in membrane potential that occurs due to the open and closing of voltage gated ion channels on the cell membrane. To understand how neurons are able to communicate, it is necessary to describe the role of an excitable membrane in generating these signals.
The functions of the nervous system-sensation, integration, and response-depend on the functions of the neurons underlying these pathways.
Describe the changes that occur to the membrane that result in the action potential.Describe the components of the membrane that establish the resting membrane potential.By the end of this section, you will be able to:ĭescribe how movement of ions across the neuron membrane leads to an action potential
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