Electrical Signaling and Action Potentials Flashcards Preview

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Flashcards in Electrical Signaling and Action Potentials Deck (20):
1

Positive current

Positive ions moving out of the cell or negative ions moving into the cell

2


Ohm's Law


V = IR

I = gV

Ii = gi (Vm - Ei)

Note: (Vm - Ei) is driving force

3


Conductance (g)


Ease of current flow

(dependent on number of open channels)

4


Inward and outward current


Inward: positive flowing into cell, or negative flowing out of cell

Outward: positive flowing out of cell, or negative flowing into cell

5


Nernst Equation (at body temp)

Ek = (61.54mV)log10 ([K]o/[K]i)

Ek is equilibruim potential of K+

6


How does Na/K ATPase maintain a negative resting potential?


3 Na+ out

2 K+ in

Na+ moved out against conc gradient (ENa = +62mV)

K+ moved in against conc gradient (EK = -80mV)

Side note: in epithelial cells, Na/K ATPase on basolateral membrane (border of epithelial cell and blood)

7


Goldman-Hodgkin-Katz equation


Used when there is more than one ion channel

Erev = (61.54mV)log10 (Pk[K]o + PNa[Na]o.../Pk[K]i + PNa[Na]i...)

P = relative permeability

8


Voltage gated Na+ channel gates


m gate: in the middle; closed when channel closed, opens with voltage changes

h gate: at the bottom; closes when channel inactivates, otherwise is open

9

Voltage gated K+ channel


n gate: closed when channel closed, opens with change in voltage

Tetramer with pore loop in middle

Selective for K+ because selectivity filter of "surrogate water molecules" lining the pore draw K+ in (but not Na+ because Na+ is too small)

10


What causes depolarization/rising phase of action potential?


Increase in Na+ permeability, causing Na+ to flow into cell

11


What causes repolarization/falling phase of action potential?


Increase in K+ permeability causes K+ to flow out of the cell, and also inactivating Na+ channels which decreases Na+ permeability

12


Absolute refractory period


Impossible to trigger AP right away because all Na+ channels needed are inactivated

13


Relative refractory period


After the absolute refractory period

Harder to trigger AP because some Na+ channels inactivated, and also K+ conductance still kind of high so cell more hyperpolarized than usual

14


Accommodation


If cell depolarizes too slowly, no AP caused

Because: too much inactivation (via h gate) of Na+ channels, so sufficient number to cause AP is never available. Also, slow depolarization opened K+ channels so cell is slightly hyperpolarized.

15


Axon with small radius vs. large radius

Velocity of conduction of AP is faster when axon has larger radius

Larger stimulus pulse is needed to trigger AP when axon has larger radius (lower internal resistance)

16


Chemical synapse

Vesicles of NTs

NTs exit pre- and cross synaptic cleft to bind ligand on post-

More space between pre- and post-

17


Electrical synapse


No vesicles

Ions flow through gap junctions

Very close contact

18


Small molecule NTs


Enzymes that make NT are made in cell body and transmitted slowly down nerve terminal

Actual NT made locally and packaged/recycled in nerve terminal

Overall FAST transmission

Small clear vesicles

Ex: GABA, glutamate, Ach

(Low freq of APs causes less Ca2+ --> preferential release of small molecule NTs)

19


Peptide NTs


Made and packaged in cell body and vesicle sent down axon quickly to nerve terminal

Overall SLOW transmission

Large dark vesicles

Ex: Substance P

(High freq of APs causes lots of Ca2+ --> small molecule and peptide NTs released)

20


Why don't action potentials travel backwards?


Because the refractory period is occurring right behind the AP