Membrane potentials 膜电位 Xia Qiang, PhD Department of physiology Zhejiang University School of Medicine Tel:88206417 Email: xiagiangazju. edu.cn
Membrane potentials 膜电位 Xia Qiang, PhD Department of Physiology Zhejiang University School of Medicine Tel: 88206417 Email: xiaqiang@zju.edu.cn
W YORK NE NmN、d三 Describe the maintenance of resting potential in a cell Explain how a cell is induced exciting Contrast graded potentials and action potentials Describe how a cell has refractory phase
LEARNING OBJECTIVES Describe the maintenance of resting potential in a cell Explain how a cell is induced exciting Contrast graded potentials and action potentials Describe how a cell has refractory phase
Copyright o The McGraw-Hill Companies, Inc. Permission required for reproduction or display Distribution of major Mobile Ions TABLE 6-2 Across the Plasma Membrane of a Typical Nerve cell Concentration, mmol/L ION EXTRACELLULAR INTRACELLULAR Na 150 15 110 K 150 A more accurate measure of electrical driving force can be obtained using mEq/L, which factors in ion valence. Since all the ions in this table have a valence of 1, the mEq/L is the same as the mmol/L concentration
E NEW YORK s raIn 10己 A potential difference across Potential difference/mV the membranes of inactive cells, with the inside of the cell negative relative to the outside of the cell 60 Ranging from -10 to-100 mV 0 1 3 Time/ms
Resting membrane potential （静息电位） A potential difference across the membranes of inactive cells, with the inside of the cell negative relative to the outside of the cell Ranging from –10 to –100 mV
Overshoot refers to the development of a charge reversal +60 A cell is polarized Repolarization is(复极化) because 50> movement back its interior toward the Is more resting potential negative than its E9g exterior gSN o0 70 a Resting potential Depolarization occurs Hyperpolarization is when ion Time the development of movement even more negative reduces the charge inside the cell charge imbalance
Depolarization occurs when ion movement reduces the charge imbalance. A cell is “polarized” because its interior is more negative than its exterior. Overshoot refers to the development of a charge reversal. Repolarization is movement back toward the resting potential. Hyperpolarization is the development of even more negative charge inside the cell. （极化） （去极化） （超极化） （复极化） （超射）
E NEW YORK s 10己 Intracell chemical driving force K Na electrochemical Na balance Na Na++++++++十中+Mat electrical Na Na Na driving force Na Na Extracellular
chemical driving force electrical driving force ++++++++++++++++ - - - - - - - - - - - - - - - - - electrochemical balance
≡NEwY Equal 8 ②②②团团sdg oooOooOO Cytoplasmic Equal Source: Barrett KE, Barman SM, Boitano S, Brooks HL: Ganong'sReviewofMedicalpHysiologywww.accessmedicine.com Copyright (o The McGraw-Hill C s, Inc. All rights reserved A membrane potential results from separation of positive and negative charges across the cell membrane. The excess of positive charges (red circles) outside the cell and negative charges(blue circles) inside the cell at rest represents a small fraction of the total number of ions present
A membrane potential results from separation of positive and negative charges across the cell membrane. The excess of positive charges (red circles) outside the cell and negative charges (blue circles) inside the cell at rest represents a small fraction of the total number of ions present
E NEW YORK s raIn 10己 The Nernst Equation: rT lon o R=Gas constant e=relog T=Temperature Z=Valence K equilibr ZF lon 4 F=Faraday s constant (钾离子平衡电位) K o E=60o%(K+y
The Nernst Equation: K+ equilibrium potential (EK) (37oC) i o Ion Ion ZF RT E [ ] [ ] = log R=Gas constant T=Temperature Z=Valence F=Faraday’s constant ( ) [ ] [ ] 60log mV K K Ek i o + + = （钾离子平衡电位）
Begin Compartment 1 Compartment 2 0.15M 0.15M K+ in Compartment 2, Nat in Compartment 1 Nacl 工 KCI BUT only K+ can move K Na lon movement: K crosses into K Compartment 1 Nat Nat stays in Compartment 1.(d) K Nat At the potassium K equilibrium potential: Na buildup of positive charge in Compartment 1 produces an electrical potential that exactly offsets the K chemical concentration gradient
Begin: K+ in Compartment 2, Na+ in Compartment 1; BUT only K+ can move. Ion movement: K+ crosses into Compartment 1; Na+ stays in Compartment 1. buildup of positive charge in Compartment 1 produces an electrical potential that exactly offsets the K+ chemical concentration gradient. At the potassium equilibrium potential:
Begin: Compartment 1 Compartment 2 K in Compartment 2, 0.15M 0.15M Nat in Compartment 1; BUT only Nat can move. Nacl KCI lon movement Nat crosses into Na+一 Compartment 2: but K stays in K Compartment 2 Na Nat At the sodium K equilibrium potential buildup of positive charge in Compartment 2 produces an electrical potential that exactly offsets the Nat chemical concentration gradient
Begin: K+ in Compartment 2, Na+ in Compartment 1; BUT only Na+ can move. Ion movement: Na+ crosses into Compartment 2; but K+ stays in Compartment 2. buildup of positive charge in Compartment 2 produces an electrical potential that exactly offsets the Na+ chemical concentration gradient. At the sodium equilibrium potential: