Exam 2: Resting Membrane Potential and AP propagation

What causes conduction velocity to be higher?

The larger the diameter of the axon, the faster the speed. The more myelination (tightness of wrapping and how heavy) means higher speed.

What is conduction velocity?

the speed at which a signaling event moves down the cell.

What is resistance?

the ease in which ions can flow through the ion channel. At rest, the neuron is least resistant to K+(due to K+ leak)and more resistant to Na/Cl.

What is capacitance?

the ability of the membrane to store charges at the differential potential. The inside of the neuron us more negative than the outside. the - interior is attracted to + interior so charges line up.

What is the Nernst Equation?

a way to describe equilibrium potential for a single ion system. Takes into account concentration of ion inside and outside the cell, the temp of the solution and the valence of the ion. IS askin " at what electrical potential diff. does the flow of ions, based on the conc. gradient, have a net 0 movement?" Membrane potential and equilibrium potential are same here.

If the membrane potential becomes + relative to Ek (more + than -102mv) where does potassium go? More -?

If more +, potassium moves out of the neuron. More -, potassium will move into the neuron.

If the membrane potential becomes + relative to ENa (more + than +60mv) where does sodium go? More -?

If more +, sodium moves out of the neuron. More -, sodium will move into the neuron.

If the membrane potential becomes + relative to ECl(more + than -70mv) where does chloride go? More -?

If more +, chloride moves into the neuron. More -, chloride will move out of the neuron.

Does equilibrium potential for a given ion change when the ion permeability changes?

No, it does not change because very few ions actually move compared to the total number of ions present.

What is the Goldman equation?

it takes into account 3 permeant ions to determine membrane potential for a neuron at rest

how does myelin help create a faster action potential?

it reduces capacitance and increases resistance of the membrane, allowing for saltatory conduction.

How does decreasing capacitance help make AP faster?

the neuron membrane is made thicker, decreasing its ability to hold charge, and cations that come in are free to move to the next node and not go back to the membrane.

how does increasing resistance help make AP faster?

by creating areas where there are no charges (internode) charges cannot escape or leak out. charge movement is more efficient

Why are unmyelinated axons slower?

they have continuous conduction, capacitance is increased and resistance is decreased, so more ions want to stay by the membrane and are more likely to leak out.

Do unmyelinated axons have to change how they cluster ion channels to maintain speed?

Yes, the channels must be closer together. Trafficking and maintaining these channels is very costly so lipid raft clustering of ion channels might occur in these neurons to make up for lack of nodes. Lipid rafts allow for pumps and ion channels to cluster together, making it energetically more favorable.

What is the cable theory?

relies on two things; time constant and length constant. Used to describe how we put extent of myelination and axonal diameter together to determine axon potential speed.

What is the time constant?

how long it takes to change membrane potential, and is dependent on membrane resistance(Rm,myelination) and capacitance (Cm)

What is the length constant?

the length a potential will travel before it reaches 0 and is dependent on axonal diameter (Ri) and extent of membrane resistance (Rm, myelination)

If a neuron wants to increase its speed, what does it do?

Decrease internal membrane resistance by making axons bigger, increase membrane resistance in myelinated portion to prevent leak, decrease capacitance by increasing axonal membrane thickness

What disorders disrupt saltatory conducition/nodes?

ALS and MS

What is MS?

caused by immune cells attacking oligodendrocytes in the NS.

What does MS cause?

1. removal of nodes, too far apart for quick APs, 2. removal of boundaries that define nodes/PNJ/JXP/internode, 3. capacitance/resistance not appropriate, 4. energetically costly to myelinate/re-myelinate

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