Action Potential Flashcards
Where does an AP initiate?
in axon hillock
After initiation, where does an AP propagate?
AWAY from cell body/soma
What type of pumps establish and maintain membrane potential?
ATP dependent
Which postsynaptic potentials dictate what happens at the post synaptic membrane potential?
IPSPs and EPSPs
What is the Goldman equation?
Em = 58 log (Pk[Ko] + Pna[Nao] + Pcl[Clin] / Pk[Kin] + Pna[Nain] + Pcl[Clo])
What causes a change in Vm?
- by changing internal/external ionic conc.
- by changing relative permeability of ions across the plasma membrane
What conc. has the greatest permeability and influence on Vm?
K+
How are ionic permeabilities changed?
- ligand gated
- voltage gated
- nucleotide gated; 2nd messenger systems
- inward rectifier “leak” channels
- mechanosensitive gated (stretch)
What are examples of ligand gated channels?
(GABA, Glu, 5HT)
What are examples of voltage gated channels?
Na+ and K+
What are examples of nucleotide gated channels?
cAMP and cGMP
What are the 5 types of voltage gated channels?
- Na+
- Ca+
- K+
- Cl-
- H+
What types of ion channels play a major role in pH/homeostasis?
proton gated
What channel opens after depolarization and re-polarizes the membrane?
K+
What happens when Na+ channels open?
- membrane potential depolarizes
- increased flow of ions
What happens when K+ channels open?
membrane is repolarized
What happens AFTER K+ channels open?
- Na channels change conformation and inactivate
- increased Pna is shut down
What are the 3 conformational states following a depolarization?
- open: “a” or “m” gate
- inactive: “i” or “h” gate
- closed
When Pk remanis high, what happens to Vm?
becomes transiently more negative than the baseline resting Vm
What is the response of K+ relative to Na+ channel during an outward current?
delayed
What region has a voltage sensor on it and what is its function?
S4: sense changes in Vm and move in repsonse to the changes
Where is ion selectivity located in regards to the molecular structure of the channels?
within the pore itself
What is the trend of Pna and Pk in neuronal AP?
- rapid increase in Pna
- slower, more stable increase in Pk
Slower activation of what channel contributes to repolarization?
K+
What does the activation of K+ channels lead to?
- negative feedback loop
- hyperpolarization that decreases probability of activating more channels
AP will NOT fire if what?
Vm is under threshold
What type of phenomenon is AP?
all or none
Na channels can be blocked by what?
TTX and riluzole
What are the 2 factors influencing length constant?
membrane and internal resistance
What is high membrane resistance?
- very little ions are leaking out
- directly proportional to length constant
What is low internal resistance?
- less ions within the cell
- inversely proportional to length constant
What is the length constant?
distance it takes to reach 37% of Vmax
What is absolute refractory period?
2nd AP CANNOT fire because Na channels can’t be reactivated in open/inactivated state (peak in graph)
What is relative refractory period?
- greater depolarization is required for an AP to fire (flatter line in graph)
- active K+ channels move membrane away from threshold potential
What is the rate limiting event for AP propagation?
time needed to charge the membrane to change Vm
What is the formula to charge the membrane?
t= Rm * Cm
How does myelination increase the conduction velocity?
by increasing membrane resistance
What is the relationship between the myelination of an axon and its conduction velocity?
directly proportional
What can affect conduction velocity?
myelination and size of axon
What is capacitance?
ability to hold charges on the membrane
When does capacitance decrease?
when myelin membrane is added
What is saltatory conduction?
- propagation along myelinated axons
- AP jumps from one node to the next
What happens during saltatory conduction?
- myelination increases membrane resistance
- decreases membrane capacitance
- decreases membrane permeability
- increase conduction velocity
- length constant increased
How does increasing conduction velocity affect unmyelinated axons?
- slower conduction
- local current flow (electrotonic conduction)
How does increasing conduction velocity affect myelinated axons?
- faster conduction
- saltatory conduction
- AP jumps from node to node
What is multiple sclerosis?
autoimmune, degenerative disease of axon demyelination
What affect does axonal demyelination have on AP conduction velocity?
causes it to decrease
What are the key concepts of AP propagation?
- depolarization attenuates as it moves down the axon
- peak membrane potential during an AP remains consistently depolarized
- action propagation takes time to charge membrane
- myelination increases conduction velocity
As depolarization moves down the axon, this is caused by what?
membrane and interaxonal resistance
