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Ion Pumps and Ion Channels

Ion Pumps and Ion Channels. Chapter 48 section 2. Overview. All cells have membrane potential across their plasma membrane Membrane potential is the difference in electrical charge between the inside and the outside of a membrane

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Ion Pumps and Ion Channels

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  1. Ion Pumps and Ion Channels Chapter 48 section 2

  2. Overview • All cells have membrane potential across their plasma membrane • Membrane potential is the difference in electrical charge between the inside and the outside of a membrane • The membrane potential of a resting neuron—one that is not sending signals—is its resting potential

  3. Formation of the Resting Potential • Potassium ions and sodium ions play critical roles in the formation of the resting potential. For each there is a concentration gradient across the plasma membrane of a neuron. • In mammalian neurons there is more potassium inside the cell and more sodium outside the cell. • Sodium-potassium pumps maintain these gradients • These pumps are used for ATP hydrolysis • These pumps use active transport • These pumps are ion channels

  4. Ion Channels • Ion Channels- pores formed by clusters of specialized proteins that span the membrane • The concentration gradients represent a chemical form of potential energy for the neuron • In order to change the chemical potential into electrical potential ion channels are needed • As the ions diffuse through the channels they carry with them an electrical charge • The net movement of positive or negative charge will generate a voltage, or potential, across the membrane

  5. Ion channels continued • Ion channels have selective permeability, meaning that they allow only certain ions to pass • A resting neuron has a lot of open potassium channels but few open sodium channels • The K+ ions can flow out of the cell but the ion channels do not allow anions such as Cl- into the cell, therefore there is a negative buildupinside the cell causing membrane potential • The negative charge keeps the positive ions inside the cell

  6. Modeling of Resting Potential • When the electrical gradient exactly balances the chemical gradient the model neuron has reached equilibrium • An ion’s equilibrium potential is the magnitude of the membrane voltage at equilibrium for that particular ion • To calculate equilibrium potential we use the Nernst equation • Eion= 62mV(log([ionoutside]/[ioninside]))

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