Neurophysiology L3: Action Potential- Long Distance Communication Flashcards
Action potential require special, ______ ion channels
voltage gated
Dendrites have ______ potential
synaptic
What are 2 things that local potentials are produced by?
- Sensory stimulus
- Synaptic contracts (dendritic field)
What are synaptic contacts like?
- Most relatively silent- only some active (80% in reserve)
- Use stimulus to make others active
All neurons have ______ segment
initial
An AP can be triggered by a ________local potential reaching the ______segment (if large enough). This will have a (fast/slow) rise (fast/slow) drop (fast/slow) recovery
depolarizing; initial; fast; fast; slow
During -70mV (resting potential), the Na2+ channel is _______(open/closed/inactivated). This means that the activation gate is _______(open/closed) and the inactivation gate is _______(open/closed).
closed; closed; open
During -60mV, the Na 2+ channel is _______(open/closed). This means that the activation gate is _______(open/closed) and the inactivation gate is _______(open/closed).
open; open; open
During +30mV (ideal Na2+ voltage), the Na 2+ channel is _______(open/closed/inactivated). This means that the activation gate is _______(open/closed) and the inactivation gate is _______(open/closed).
inactivated; open; closed
Are local potentials graded or not graded?
Graded
Are action potentials graded or not graded?
Not graded (all or none)
- Once gates are open –> all open
Channels are either ____ or _____ (choose 2 out of the 3: opened/activated/inactivated)
open; inactivated (Can’t “activate” any gates)
Sequence of events that underpin an AP: Step 1
- Na2+ activation gate opens
- K+ gate closed
Sequence of events that underpin an AP: Step 2 (after Na2+ activation gate opens and K+ gate closed)
Na2+ flows in –> more positive (depolarization) –> towards +30mV
Sequence of events that underpin an AP: Step 3 (after depolarisation towards +30mV)
Reaches +30mV –> Na2+ inactivation gate closes –> K+ gate opens –> Na+2 can’t come in –> K+ goes out –> more negative (hyperpolarization) –> drives potential back to equilibrium (overshoot)
Sequence of events that underpin an AP: Step 4 (after hyperpolarisation towards equilbrium)
Back to equilibrium Na2+ inactivation gate open –> Na2+ activation gate closes –> less positive –> K+ gate opens –> more negative –> hyperpolarization to resting –> K+ gate closes
Influx- all channels are ____. Efflux- coming ____ of cell. Summary- Sequence of events that underpin an AP
open; out
What are the 2 AP refractory period(s)?
- Absolute refractory period (ARP)
- Relative refractory period (RRP):
What is the absolute refractory period (ARP)?
- Impossible to trigger an AP
- Na+ channel inactivation
What is the relative refractory period (RRP)?
- Larger than normal stimulus required
- Some residual Na channel inactivation
- High K+ permeability
What are the 2 steps of action potential propagation of unmyelinated axons? Is it fast or slow conduction?
- Slower conduction 0.1-2m/s
- AP at one point triggers AP in the next section
- Due to the refractory period, APs cannot “change directions”
What is step 1 of the action potential propagation of unmyelinated axons?
AP at one point triggers AP in the next section
What is step 2 of the action potential propagation of unmyelinated axons?
Due to the refractory period, APs cannot “change directions”
What are the 2 steps of action potential propagation of myelinated axons? Is it fast or slow conduction?
- Glial cells –> myelin sheaths to some axons –> duct tapes the channels = less leaky –> faster conduction 100m/s
- AP only occurs at Nodes of Ranvier: salutatory conduction
- Able to “jump”
- Due to the refractory period, APs cannot “change directions”
What is step 1 of the action potential propagation of myelinated axons?
AP only occurs at Nodes of Ranvier: salutatory conduction - Able to “jump”
What is step 2 of the action potential propagation of myelinated axons?
Due to the refractory period, APs cannot “change directions”
