CSB332H1 Lecture 4: Section 1- L4a
14 May 2018
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Lecture 4(a): Resting Membrane vs Action Potentials
Question –
• If a student wants to depolarize a cell that has leak channels, which one of the following would
allow for the cell’s depolarization?
a) Increase the extracellular K+ ion concentration
b) Increase the extracellular Na+ ion concentration
c) Increase the extracellular Cl- ion concentration
d) None of the above would cause the cell to depolarize
§ Answer: A
Resting Membrane Potential – Mainly K+
• As ions flow through the membrane, there is a change in charge (current) that is passing
through, therefore there must be channels that allowed ions to pass through
o Every system has a higher K+ concentration inside the cell than outside
ð Changing the extracellular K+ ion concentration the depolarizes the membrane slowly
(membrane become more positive in respect to the inside)
o At 450mM [K+] the membrane potential was 0 mV
• This is understandable as membranes have leak channels for K+
o Rate of K+ flow is dependent on electrochemical gradient:
§ Therefore, increasing the extracellular [K+] will lead to the depolarization of
the membrane by causing K+ ions to flow inside
ð This is NOT reproducible by increasing the extracellular Na+ ion concentration
o This is because we have very few Na+ leak channels (10% of K+ leak channels)
Action Potentials (AP):
• Action potential is an immediate change in electrical activity
(i.e. sudden change in the membrane potential => depolarization)
o APs are transported along an excitable cell such as nerve or muscle cells
Current Clamp:
• Control current injected into a neuron (i.e. can be 0) and measure membrane potential
o i.e. can inject (+) current into the neuron and watch it fire action potentials
Voltage Clamp:
• Control membrane potential of a neuron (i.e. hold it at -50 mV) and measure the current
(ions) flowing across the membrane
o i.e. can hold the neuron’s membrane potential at a depolarized state and measure the
activity of voltage-gated currents
Document Summary
Therefore, increasing the extracellular [k+] will lead to the depolarization of the membrane by causing k+ ions to flow inside. This is not reproducible by increasing the extracellular na+ ion concentration: this is because we have very few na+ leak channels (10% of k+ leak channels) Action potentials (ap): action potential is an immediate change in electrical activity (i. e. sudden change in the membrane potential => depolarization, aps are transported along an excitable cell such as nerve or muscle cells. Injecting small hyperpolarizing currents and passively measuring the change in membrane potential of the neuron: the larger the hyperpolarizing current, the more hyperpolarized the membrane becomes (more negative than the resting membrane potential) Large current = large change in mp: linear relationship (response) of v = ir. Follows" ohms law: the amount of current is directly related to the voltage change.
