Action potentials and synaptic transmission Flashcards
Define threshold potential.
The level of polarization at which the chance of an action potential is 50%.
What are the steps of an action potential for voltage gated Na channel (start from closed)?
Closed:
Open: stimuli causes the channel to open (or not, for our case it opens) Opening of channels causes depolarization, causing more channels to open (positive feedback loop).
Inactivated: once the channel is open it’s binding site is exposed to the inactivator. This binds in less then a second. Inactivation ends after 1-2 ms spent at a more negative voltage.
Closed: After enough time at a more negative voltage, channels are in the closed configuration again.
Does every voltage gate fire in an action potential? How many gates does a nerve cell have?
no.
1000’s.
What is the Hodgkin Cycle and what does it describe?
Na+ influx causes membrane depolarization, which causes more gates to open increasing p(na) (permeability of na), which causes a Na+ influx.
It describes temporary transient positive feedback loop seen in action potentials.
Define non-decrementing propagation. Does it apply to action potentials?
as the signal is propagated it’s amplitude doesn’t decrease. Yes.
Name the three states of being for VGSCs.
Note: the pore is on the cytosolic side.
Closed: The pore is closed.
Open: the pore is open.
Inactivated: The pore is open, inactivation complex is blocking.
Where is the voltage sensing S4 segment in each of the three states for a VSGC?
Closed: The positive S4 segment is pushed away from the positive voltage outside of the cell.
Open: the S4 segment is drawn towards the more negative voltage outside of the cell.
Inactivated: the S4 segment is drawn towards the more negative voltage outside of the cell.`
Inactivation causes the unidirectional motion of an action potential. T or F?
T
To ‘recover’ from inactivation what must happen? What factor dictates speed of recovery?
in order for the channel to go from the inactivated to tthe close conformation the channel must enter a negative potential environment ~60 mV. The more negative the environment the faster the recovery will be.
About how long does recovery from inactivation take?
1-2 ms
Tetrodotoxin (ttx) does what? Is found where?
It blocks the Na channel by plugging the extracellular side of the pore.
It is found in many things, including blue ringed octopus, pufferfish, and rough-skinned newt.
What produces TTX?
Symbiotic bacteria, like psedoalteromonas tetradonis.
What is the Red tide caused by? What are its implications?
The red tide is caused by Dinoflagellates (marine plankton bloom). Dinoflagellates produce Saxitoxin (STX), which acts like TTX. It concentrates in shellfish because they are filter feeders. It also kills fish.
What does saltatory mean?
Latin for to hop to leap.
How are Schwann cells involved in signaling?
They wrap around the axon, and lay myelin an isolator. This insulation makes it so that if current from a voltage appears on one end of a myelin sheath it will travel through the insulated surface to the next node.
Schwann cells are the _____ cells of the peripheral nervous system.
Glial
How does a capacitor work?
Two conductors are separated by an insulator (dielectric). If charge builds up on one plate it will push away similar charges are the other plate. This causes a build up of opposite charges on the two plates.
How does capacitance effect action potentials in terms of sodium?
There are two way capacitance could be affecting action potentials. Either the negative resting membrane potential, pushes away negative ions on the other side, and sodium follows, to some degree, follows the flow of negative charge away from the plate, thus lowering extracellular sodium and consequently make it so action potentials are slower.
Myelination:
- ______ electrical capacitance
- ______ electrical resistance
- ______ membrane conductance
- ______ propagation velocity
- ______ the metabolic energy expenditure of the cell (from production of Na channels and from decreased need to use the Na/K pump.
Decreases capacitance Increases resistance Decreases conductors Increases propagation velocity Decreases metabolic expenditure
Multiple Sclerosis (MS) is caused by what?
It caused by the immune system attacking myelin sheaths.
Where do sodium channels exist in a myelinated cell?
At the Nodes of Ranvier exclusively.
Where do K+ channels predominate in the myelinated cell?
In the myelinated areas, with the exception of the point where the myelin attaches (which is immediately adjacent to the nodes of ranvier).
What is the extracellular protein named Caspr? Where might it be found?
Caspr is essentially a molecular glue to anchor the myelin to the membrane. It is found attaching the myelin to points adjacent to the nodes of ranvier
Given that K+ channels are found in areas myelinated by glial and schwann cells, what must these cells do?
These cells must absorb the K+ that comes from nerves K+ channels. (there is also some chance that they arrange the ions to be the correct concentration in this space, that’d be cool but I have no evidence)
