Excitable Cells

Question 1

Intracellular vs extra cellular recording techniques

Answer 1

Extra cellular- electrode outside the cell Intracellular - electrode inside of cell Patch clamping: pinched cell membrane to allow single pump to be measured

Question 2

Resting potential

Answer 2

More negative charged inside the cells 3Na our 2K in

Question 3

Events of action potential

Answer 3

1. Wave of depolarisation arrives and activates sodium and potassium gated channels. Potassium open slowly.
2. Sodium flows in and membrane potential rises
3. When it gets to +40 (close to sodium equilibrium potential), sodium channels innactivate, and potassium flows out of the cell, driving potential back down.
4. Potential falls almost to potassium potential (-90) before the potassium channels close and Na/K pumps restore the resting potential.

Question 4

Equilibrium potential

Answer 4

When Force of conc gradient pushing K out = electrical force pulling k+ back into the cell

Osmotic force = electrical force

Question 5

Driving force:

Answer 5

The electrochemical force generated by the ion causing to go down its electrochemical gradient

Question 6

What property is capacitors

Answer 6

The ability of the membrane to hold electrical charges on both sides

Question 7

Voltage

Answer 7

The work or energy needed to separate the charges across the membrane

Question 8

Nerst equation EZF = RT ln(concentration gradient)

Answer 8

Electrical work = osmotic work R,T,F are constants so with temperature and concentration gradient’ you can figure out what the equilibrium potential is. If you assume temp is 25 degrees, eaution can be simplified to E=58*log(concentration gradient) Concentration gradient = conc in over conc out

Question 9

Concentrations of N’a and K at rest

Answer 9

Outside: K 4mM. Na 140mM Inside: K 140mM Na 10mM

Question 10

Driving force

Answer 10

Membrane potential - equilibrium potential of an ion For sodium: -70Mv - (+50mV) = -120mV, so the driving force of -120 mV trying to get sodium into cell For potassium, +20 mV trying to get it out of the cell BUT easier to get potassium out so balances differences in driving force

Question 11

Properties of action potentials

Answer 11

Triggered by depolarization Threshold of depolarization must be reached At peak, Vm approaches Equilibrium Na Membrane is an excitable during refractory period

Question 12

Depolarization

Answer 12

Opening of Na channels, Na flows in Membrane voltage driven to Na equilibrium

Question 13

Repolarization

Answer 13

Opening of K channels, causing K to flow out. Membrane voltage driven to K equilibrium

Question 14

Absolute refractory period vs relative refractory period

Answer 14

Absolute refractory is during repolarization Relative is during hyperpolarization Because sodium gated channels are inactivated during repolarization

Question 15

Effect of thin axon, myelination on conduction velocity and why these effects.

Answer 15

Thin axon: conducts slower because axoplasmic (longitudinal) resistance to current in the axon decreases as axon gets wider.

Myelination: conducts faster because it reduces Rm, since there are less channels for the ions to flow out of.

Question 16

Events in synaptic transmission

Answer 16

Presynaptic action potential

Depolarization of synaptic terminal

Opening of voltage gated calcium channels

Fusion of ACh vesicles with membranes

Release of neurotransmitter (followed by reuptake of degradation)

ACh receptor-activated action channels open, causing activation of Na and K channels

Question 17

Miniature end plate potentials

Answer 17

Small depolarization of the postsynaptic terminals caused by the random release of a single vesicles of ACh. Sumation of these can cause action potentials.

Question 18

Excitatory and inhibitory post synaptic potentials

Answer 18

Excitatory: small potential that increases the chances of an action potential occurring in the post synaptic nerve

Inhibitory: small negative potential that causes slight hyperpolarisation and therefore makes it harder for an action potential to occur

Question 19

Spatial summation

Answer 19

when excitatory potentials from many different pre-synaptic neurons cause the post-synaptic neuron to reach its threshold and fire

Question 20

Temporal summation

Answer 20

when repeated excitatory potentials from a single neuron pre-synaptic neurons cause the post-synaptic neuron to reach its threshold and fire

Question 21

Explain how conductance along a channel is altered and how this related to permeabilty

Answer 21

Conductance is the a amount of current that flows through a membrane. Increasing permeability of a membrane to an ion (by opening channels) increases the conductance. Vise versa.

Question 22

Difference in Na and K conductance during an action potential

Answer 22

K channels open and close slower than Na channels do.

Question 23

Goldman Hodgking Katz equation (adapted Nerst) what extra factor does it consider?

Answer 23

It takes into account the relative permeability of the membrane to each ion, allowing for a more accurate membrane potential.

Question 24

Why is there a threshold?

Answer 24

At rest, the membrane is much more permeable to K than Na. Therefore an influx of Na can be counteracted by an outflux of k until a certain point (-50mv).

Question 25

Explain Rm and Rl

Answer 25

Rl: longitudinal resistance (along the axon)

Rm: resistance across the membrane (vertically through the channels)

Question 26

What channels help propagate the action potential in the muscle

Answer 26

acetylcholine gated receptors initiate the depolarisation at the neuromuscular junction, then it spreads via sodium and potassium voltage gated channels throughout the muscle.

Question 27

3 molecules than can cause reduced axonal vesicle release

Answer 27

Low calcium

high magnesium

curare