1)Concentration Gradient in Vs out of Given Ion

SI Wednesday October 14, 2009 Membrane Physiology Glossary of Terms and Useful Info Efflux: Flow of ions out of the cell Influx: Flow of ions into the cell

Resting EM: Resting Membrane Potential: -70mV

Eion: Ionic Equilibrium Potential for a given ion. AKA the value of the membrane potential if cell is only permeable to the given ion. Based on: 1)Concentration Gradient IN vs OUT of given ion 2)Electrical Gradient + EK: Ionic Equilibrium Potential for K : approx -90mV

ENa: approx +66mV

ECl: approx -42mV Voltage/Potential: Measure of the charge difference across a membrane (IN with respect to OUT) Permeability: Extent to which certain ions can flow across a membrane → Dictated by how many channels are open for that ion Depolarization: Membrane potential becomes closer to zero (less negative) Hyperpolarization: Membrane potential becomes farther from zero Review Exercises: Identify a couple of physiological examples where establishing concentration gradients does some sort of work in the body. What is the “work” that can be accomplished by the electrochemical gradients built into the neuron at rest and why is this essential for the nervous system?

Recall the three important properties of ion channels. What are the four major categories of ion channels? Identify which “potential” each is associated with.

What are the three most important transmembrane proteins in maintaining the resting membrane potential?

What would happen to the Resting Membrane Potential if the extracellular concentration of potassium ions suddenly became abnormally low.

1 SI Wednesday October 14, 2009 Membrane Physiology Short Answer Exercises: Describe the four basic characteristics of graded potentials. In what anatomical regions of the neuron are graded potentials typically generatedl?

We all have our thresholds. What does it mean for a neuron to have a threshold?

Label the following on the image below Graded EPSPs Absolute Refractory Period Begins (and why) Threshold Value Absolute Refractory Period Ends (and why) VGNaC Activation Gate Opens Relative Refractory Period Begins VGNaC Activation Gate Closes Relative Refractory Period Ends VGNaC Inactivation Gate Closes Rising Phase / Depolarization VGNaC Inactivation Gate Opens Falling Phase / Repolarization VGKC Opens Undershoot and Overshoot VGKC Closes

2 SI Wednesday October 14, 2009 Membrane Physiology At the top of the rising phase (when voltage gated K+ channels open) in what direction do the electrical and chemical gradients point respectively for K+ ?

If an action potential was engaged in a debate with a graded potential, what would it assert as the fundamental differences between the two parties? (see attached table)

If you experimentally depolarized a resting axon beyond threshold half-way along the axon, an action potential would propagate bidirectionally….both towards the soma (backpropagation) and towards the synaptic terminal(s). Under actual physiological conditions, when an action potential is initiated at the initial segment of the axon, there is no backpropagation observed despite the fact that influx of sodium ions at that same point in the axon would theoretically depolarize all adjacent regions of the membrane. Why? (Be brief but specific).

What is the difference between continuous vs. saltatory conduction?

What is the evolutionary significance of myelination?

Bonus Fun Activity: Go to www.nernstgoldman.physiology.arizona.edu Click ‘launch now’. Set to ‘Goldman Equation’ at the upper right corner. Manipulate the permeability as well as the intracellular and extracellular concentrations of the various ions to observe the effect on the membrane potential and the equilibrium potential for that ion. You can restore the default settings at the bottom right hand corner.

Multiple Choice Fun: 1. The activation of ligand-gated ion channels is always associated with: A. Generation of action-potentials B. Change in the permeability to an ion C. Depolarization D. Hyperpolarization

2. If you were an axon establishing a new connection with another neuron, where would you want to establish that synapse to have to most profound impact on the frequency with which that neuron fires action potentials? A. Dentritic Branches B. Dentritic Spines C. The Axon Hillock D. The point at which dendrites branch from the soma

3. The absolute refractory period is due to: A. Inactivation of voltage-gated sodium channels B. Prolonged opening of voltage-gated potassium channels C. Prolonged opening of potassium leakage channels D. Inactivation of sodium leak channels

4. During an action potential, activity at which type of channel is responsible for the rapid restoration of the resting membrane potential after depolarization has occurred? A. Potassium leak channels B. Voltage-gated sodium channels C. The Na+/K+ ATPase D. Voltage-gated potassium channels