Download membrane potential

BBio 351 – November 10, 2015
Outline for this week
• Finish Hasuwa (2013)
• Start neurophysiology – review/extend knowledge of…
• Membrane potential
• Ion distributions
• Electrochemical gradients
• Nernst equation
• Action potential
• Synapses
• Post-synaptic potentials
• Summation
Overall course flow
• How will we tackle the nervous system?
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How neurons fire and communicate (this week)
Neural circuits and integration
Nervous system evolution
Central nervous system (brain & spinal cord)
SENSORY systems: intro, mechanical, taste/smell, vision
• Review: endocrine system vs. nervous system?
Mini-meta-POGIL from Brown A&P workbook
1. Place a large plus sign on the side of the membrane with the most
positive charges and a large minus sign on the side of the membrane
with the fewest positive charges.
Patrick J.P. Brown (2016)
2. Where are most of the sodium ions – inside the cell, or outside the
cell?
3. If the channel were to open, which way would sodium travel
through the channel?
4. What effect would this have on the membrane potential (the
difference in charge across the membrane)?
Patrick J.P. Brown (2016)
5. This chart shows the resting membrane potential of a nerve cell.
Notice that the line is running at around -70 millivolts.
a. The resting membrane potential has a negative value. Based
on what we’ve already learned – is this measuring the inside
or the outside of the cell?
Patrick J.P. Brown (2016)
b. If a sodium channel opens, will the inside of the cell become more
positive or more negative as the sodium ions come in along their
concentration gradient?
c. Based on your answer to A and B, extend the line in the chart to
show what might happen to the potential when sodium channels
open.
d. Before the sodium channel opened, the membrane was polarized,
like a battery (a positive and negative side). After opening the sodium
channel, is the cell going to be polarized anymore?
Patrick J.P. Brown (2016)
Misleading aspects of this POGIL exercise?
Draft of a potential jingle
• Is this at all helpful?
• Can you supply a catchy melody or otherwise make it
better?
“Potential” means that something just might happen;
That something always needs a driving force….
That force could be a gradient,
And a gradient is a difference,
And a difference is a potential – yes, of course!
Crowther, unpublished
What are electrochemical gradients?
Ion
Na+
K+
Chemical gradient
Electrical gradient
Electrochemical
gradient
The Nernst equation shows how 1 ion would
balance its electrical and chemical potentials.
“…At the voltage you have found [said Walther Nernst],
There’s no flux in or out [said Walther Nernst]!”
Nernst equation: example
There is 0 net flux at the Nernst potential (E).
Which way does the flux go at OTHER
membrane potentials?
• Example 1
Note: chemical concentrations
& gradient remain constant.
There is 0 net flux at the Nernst potential (E).
Which way does the flux go at OTHER
membrane potentials?
• Example 2
Note: chemical concentrations
& gradient remain constant.
There is 0 net flux at the Nernst potential (E).
Which way does the flux go at OTHER
membrane potentials?
• General rule?
Why is the membrane potential what it is
(about -70 mV at rest)?
From 1 ion to many: from the Nernst equation to
the Goldman-Hodgkin-Katz equation