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Introduction to physiology. Your colleague , Firas alkhalayleh A 3’rd year medical student. Nerve and Muscle Physiology. Plasma Membranes of Excitable tissues Ref: Guyton, 12 th ed: pp: 57-69. 11th ed: p57-71 ,. Resting membrane potential. {NA+} inside = 14 mEq/L

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Introduction to physiology

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Introduction to physiology

Introduction to physiology

Your colleague , Firas alkhalayleh

A 3’rd year medical student

Nerve and muscle physiology

Nerve and Muscle Physiology

  • Plasma Membranes of Excitable tissues

  • Ref: Guyton, 12th ed: pp: 57-69. 11th ed: p57-71,

Introduction to physiology

Resting membrane potential

Introduction to physiology

  • {NA+} inside = 14 mEq/L

  • {Na+} outside = 142 mEq/L

  • {K+} inside = 140 mEq/L

  • {K+} outside = 4 mEq/L

Introduction to physiology

  • The diffusion potential for K+ only is found to be -94 millivolte

  • The diffusion potential for Na+ only is found to be +61 millivolte

Nernest equation

Nernest equation

  • E (mV) = - 61.log (Ci/Co)

  • E = Equilibrium potential for a univalent ion .

  • Ci = conc. inside the cell.

  • Co = conc. outside the cell.

Introduction to physiology

  • The greater the ratio {I}/{o} , the greater tendency to diffuse in one direction .

  • At normal body tempreture

    EMF=+/- 61 * log {I}/{O}

    EMF= electromotive force .

Introduction to physiology

  • Nernst equation means ……. !!!!

  • If EMF is + the moving ions are –

  • If EMF is - the moving ions are +

Multiple ions involvement

Multiple ions involvement

  • Depends on :

  • Polarity of the electrical charges .

  • Permeability of the membrane .

  • The {I} + {O}

Goldman hodgkin katz equation

Goldman-Hodgkin-Katz equation

EMF (mV) =

- 61. log [( CiNa+. PNa+ + CiK+. PK+ + CoCl- .PCl- )

(CoNa+ PNa+ + CoK+ PK+ + CiCl- PCl-)]

Ci = Conc. inside

Co = Conc. outside

P = permeability of the membrane to that ion.

Introduction to physiology

  • During transmission of nerve impulses , permeability of the Na+ and K+ undergoes rapid change , whereas that of Cl- doesn't change greatly .

Introduction to physiology

  • K+ leak channels are 100 times more permeable to K+ than Na+ .

Action potential

Action potential

  • A rapid change in the membrane potential.

  • Resting stage .

  • Depolarization stage .

  • Repolarization stage .

Voltage gated channels

Voltage-gated channels

Introduction to physiology

  • When the membrane potential becomes less negative than during the resting state , rising from -90 toward 0 , it finally reaches a voltage – usually between -70 and -50 – that cause a sudden conformational change in the activation gate , flipping it all the way to the open position.This is called the activated state , during this state , Na+ ions pour inward through the channel increasing the Na+ permeability of the membrane as much as 500-to 5000-fold .

The inactivation state

The inactivation state

  • The same increas in the voltage that open the activation gate also closes the inactivation gate . The inactivation gate , however, closes a few 10,000ths of a second after the activation gate opens . That is, the conformational change that flips the inactivation to the closed state is a slower process than the conformational change that opens the activation gate . Therefore after the Na+ channel has remained open for a few 10,000ths of a second, the inactivation gate closes, and the Na+ no longer can pour to the inside of the membrane . At this point, the membrane potential begins to recover back toward the resting state, which is repolartization state .

Voltage gated k channels

Voltage –gated K+ channels

Introduction to physiology

  • During the resting state, the gate of the K+ channel is closed and K+ are prevented from passing to the exterior. When the membrane potential rises from -90 toward 0 , this voltage causes a conformational opening of the gate . However, because of the slight delay in the opening of the K+ channel, for the most part, they open just at same time that the Na+ channels are beginning to close because of inactivation. Thus, the decrease in Na+ entry to the cell and the simultaneous increase in K+ exit from the cell combine to speed the repolarization process, leading to full recovery of the RMP .

The plateau in some aps

The plateau in some APs

Introduction to physiology

Thank you ….

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