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38 Cards in this Set

  • Front
  • Back

Nernst Equation in Words

Equilibrium Potential (Volts) =




[ Diffusion / ( Ion Charge x F ) ] ln ( out / in )

Ohm's Law

Voltage = Current X Resistance

Capacitance

The amount that can be stored in a capacitor.

Capacitance =

Charge / Voltage

Series capacitors make capacitance...

go down.

Parallel capacitors make capacitance...

go up.

Higher Veq is caused by...

more force (higher resistance).


1/G(ion)

What is G?




How we talk about resistance of membrane to ions.

Goldman Equation Simplified

Vm = Equilibrium Potential / Conductance




We can measure these to determine membrane potential.

Lower the membrane resistance and...

more current leaks out, so it decays faster resulting in a shorter length constant.



First Action Potential Experiment

Took Sodium out of water surrounding (neuron?). Saw the action potential decreased. Concluded Sodium must be critical to the AP.




Read more about this in book.

What does a voltage clamp let you measure?

How much current you inject to maintain voltage helps you figure out resistance with Ohm's Law.

Results of the Voltage Clamp Experiment




(2)

1. Shows there is 2 parts to the action potential.



2. Sodium and Potassium are involved.


Some Qualities of APs (4)

1. They are all or none




2. They are always the same in the same neurons




3. You can do lots of them in a row (regenerative)




4. The are unidirectional (unless initiated non-physiologically in the middle of the axon and then they shoot both ways).

What do passes 1-4 do?

This is where the voltage sensor is. When the inside gets positive, it pushes pass 4 up which pulls at 5 and 6 causes them to twist open.

What do the intracellular loops do in ion channels?

They cause inactivity.





Quantal Yield

Different synapses release different numbers of vesicles.




Example: neuromuscular junction synapses have huge quantal yields.




Different kinds of neurons can also have different vesicle sizes. Vesicle size often depends on the neurotransmitter type.

RIM Proteins

Scaffolding that brings calcium channels towards snares.

What kind of molecule is Botox?

Protease

Calcium & the Time Window

Adding calcium to cause an endplate potential only works in a very narrow time window. If there is no calcium in the area and you add calcium it only makes the synapse functional if you add the Calcium at the exact right moment where depolarization is happening in the terminal.

Vesicle Fusion Observations

Timing is important (for voltage gated calcium channel opening and vesicle fusion and end plate potential triggering; both occur in less than 2 ms).




Therefore vesicles need to be docked near or on target membrane and primed to fuse with membrane quickly (all slow ATP dependent processes have to have already happened).

Specifics of the Patch Clamp Workings

Patch pipette seals onto surface of ion channel and forms a high resistance seal.




It measures voltage.




It injects current into feedback circuit so that the pipette voltage matches the command voltage. The amount of current needed to keep the two voltages equal is what is recorded.




This allows you to see ion flow.

Patch Clamp Student Video Take Homes

1. Patchclamp recording began in the late 1970’sand is also reffered to as cell-attached patch. This technique uses a patchpipette (electrode) into a plasma membrane of a cell and the high resistancecreated is measured in ohms. This prevents ion flow between a pipette andmembrane.




2. The clamp corresponds to the extracellularpotential of a small patch underneath isolation. For example, TTX was found inbacteria of pufferfish and showed how voltage gated Sodium channels areblocked. The importance of a patch pipette is the voltage and current injectedthrough feedback and the response during a depolarization step.




3. The experiments show how not all channels openimmediately after membrane potential occurs and the driving force getsinfluenced by the different ionic components in the cell.

Metabotropic Receptors

GPCR, G-proteins, secondary messengers.




No direct change in membrane potential.




Slow.

Two ways to use Voltage Clamp

1. Set command voltage to elicit currents




2. Use presynaptic stimulation to observe currents

Structure of Ligand-Gated Ion Channels

5 subunits. Each subunit has many transmembrane amines. Ligand binding site. Some gates that can swing open to let ions in.

How did we figure out the structure of Ligand-Gated Ion Channels?

Blow darts with Curare. Paralyzed animals.


This toxin blocked acetylcholine receptors.




Examining this in frog eggs let them examine different potential candidates for this channel: over express candidates in the egg. Add acetylcholine to cause inward current. Add curare and inward current in inhibited. This let them find the channels.

Difference Between Current and Potential

Current on top and Potential on bottom.

Current on top and Potential on bottom.

Passive Parts of Neurons

Myelin sheath, membrane resistance, length and time constants

Factors for Strength (4)

# of postsynaptic receptors: more = stronger



Ca+ concentration




Receptor Affinity






# of Presynaptic Vesicles Released

How is excess NT taken up?

Via plasma membrane symporters (with Na) on presynaptic or glial plasma membranes.

Synaptic Vesicle Recycling Article Takeaway

Synaptic vesicle retrieval is critical to continuous synaptic transmission.




In flies there was a high temp mutation that caused paralysis because vesicles could not be recycled because of a dynemin mutation.

Scaffolding Proteins in the Presynaptic Density

Actin binds to CamK2 which binds to PSD-95 which holds neuroligands and key receptors in place.




Neuroligands and neurexin bind to each other.


Cadherins bind to each other.


How did researchers discover functions of PSD-95 and other receptors?

Antibody affinity purification: isolate protein antigens of interest, but into column with suspected antibodies, and if you get a match not much will come out of column.

When do action potentials arise?

After supra-threshold depolarization, which opens voltage gated sodium channels.

What sets the time of integration as well as the attenuation of more distal synaptic inputs?

Cable properties.

What increases the size and speed of the PSP and where is it located?

Active properties in the dendrites.

What does backpropagation do?

It can allow for stronger integration for specifically timed inputs.