28 sept announcements pick up answer sheet for quiz 2 from front friday absentees: pick up quiz 1...
TRANSCRIPT
28 Sept Announcements
Pick up answer sheet for Quiz 2 from front
Friday absentees: pick up Quiz 1 & Andro Paper from Piano
Read & bring Androstenedione paper to lab this week
Test # 1 Oct 5
Today’s Topics
• Membrane potentials
• Ohm’s law
• The Nernst Equation
• The Goldman Equation
• Resting Membrane Potential
Fig. 06.07
From physics: Ohm’s Law Voltage = Current x Resistance
Fig. 06.08
Fig. 06.09
Fig. 06.10
Fig. 06.10a
There is a concentration gradient favoring the diffusion of Na+ and K+ through the selectively permeable membrane which has ion channels only for potassium.
Fig. 06.10b
With K+ channels open, K+ diffuses down its concentraiton gradient, leaving behind CL- ions which are not permeable through the membrane. As more and more K+ move to the left, the compartment they leave becomes more and more negatively charged.
Fig. 06.10c
Fig. 06.10d
Soon, the accumulation of negative charges seriously impeded the diffusion of K+ as the electrostatic force builds up in opposition to the concentration driving force.
Fig. 06.10e
Equilibrium potential = Nernst potential = diffusion potential
Eventually, the electrostatic force that impedes diffusion of K+ is exactly equal to the driving force favoring diffusion based on a concentration gradient. When these two driving forces are equal and opposite, the membrane potential reaches an equilibrium at which the voltage is called
So which compartment corresponds to intracellular fluid?
E ion+ = 61/Z log ([conc outside]/ [conc inside])
E K+ = 61/1 log (5/150)E K+ = -90 mV
The Nernst Equation
• Calculate the membrane potential if only one ion species is permeable and the concentrations are known on both sides of the membrane.
Fig. 06.11Now consider a situation in which only Na+ is permeable.
Fig. 06.11a
Fig. 06.11b
Fig. 06.11c
Fig. 06.11d
Fig. 06.11e
Equilibrium potential for Na+
E Na+ = 61/1 log (145/15)
E Na + = +60 mV
Electrical and concentration gradient driving forces for Sodium and Potassium
Graded potentials in dendrites and cell body, action potentials in axon because of the types of ion channels found in these membrane domains.
How does the membrane potential change if 1)permeability to sodium increases2) Permeability to potassium increases
Why is resting membrane potential closer to EK than ENa?
What would happen to membrane potential if suddenly PNa
became very great?
Which ion moving in which direction (into or out of cell) is responsible for depolarization and overshoot? Which ion moving in
which direction (into or out of cell) is responsible for repolarization and hyperpolarization?
Can the membrane potential go more negative than -90 mV?