Lecture 20:Action Potentials

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An action potential is a trnasient, regenerative electrical impulse in which the membrane potential(Vm) rapidly rises to a peak about 100 mV more positive than the normal, negative resting voltage.

True

What cells does an action potential occur in?

electrically excitable; communicates action (correct)

electrically exhausted; communicates loss of energy

physically active

physically exhausted

The key to action potentials is voltage-gated channels that open and close based on changes in Vm.

True

What kind of action potential do nerve and skeletal muscle have?

rapid transmission Signup and view all the answers

What kind of action potential does the heart have?

prolonged repolarization phase to give heart muscle extra time to contract and push blood Signup and view all the answers

A stimulus is small ion movements across the membrane that depolarize Vm.

True Signup and view all the answers

What causes an AP to be triggered?

if Vm reaches threshold level-threshold voltage causes voltage gated channels to open Signup and view all the answers

What phase is Vm decaying back to resting potential?

repolarizing Signup and view all the answers

Threshold triggers action potential!!!!!!!

True Signup and view all the answers

What are the action potential phases controlled by?

voltage gated ion channels Signup and view all the answers

Changes in what opens and closes specific channels?

Vm Signup and view all the answers

What is an absolute refractory period?

A second response is not possible regardless of strength or duration of the stimulus. Signup and view all the answers

Relative Refractory Period

a second response can be elicited, but at a greater "cost"(strength and/ or duration) Signup and view all the answers

What is the voltage gated structure like?

6 TM helices, voltage pore, voltage sensor, 4 units form 1 channel Signup and view all the answers

What is special about the voltage-sensor?

-S4(helix 4) has multiple charged residues(+, lys, or arg) -S4 helix changes position as Vm changes: voltage sensor -induces conformational change in channel -affects open probability -highly conserved feature of voltage-gated channels Signup and view all the answers

What "S" helix makes up part of the P-region(pore)?

S6 Signup and view all the answers

The pore region is where inhibitors block and bind. They provide selectivity for ion type.

True Signup and view all the answers

How many units come together to form a channel?

4 Signup and view all the answers

What is electrotonic conduction?

sub-threshold changes in Vm weaken with distance due to loss of energy to the medium Signup and view all the answers

Active Zone

position of AP initiation Signup and view all the answers

What could cause a decrease in the probability of firing an AP?

increase in distance from the active zone Signup and view all the answers

What are the two strategies to fix resistance and leaks in membrane ion channels?

<ol> <li>increase the diameter of the axon to decrease resistance of axon 2)add insulation on the membrane to stop ion leaks(prevents passive current flow across membranes)</li> </ol> Signup and view all the answers

The membrane and distance are resistors.

True Signup and view all the answers

Myelination

-myelin acts as an insulator -current only flows at nodes of Ranvier -density of channels very high at nodes -nodes become active zone for AP propagation -AP goes node to node called saltatory conduction -very rapid propagation Signup and view all the answers

MS

-membranes of nerve cells lose resistance -membrane capacitance increases -changes in Vm cannot be effectively transmitted -action potentials fail to propagate -loss of nerve function:paralysis, lost sensation Signup and view all the answers