Electric potential of cells Flashcards
What is the resting membrane potential of a cell?
-70 mV
What does the Goldman-Hodgkin-Katz (GHK) equation describe?
The diffusion potential when a membrane is permeable to several ions.
What is the GHK equation?
Add pic
The impact of each ion on membrane potential is ______ proportional to the membrane permeability for that ion.
Directly
Why is the Na/K ATPase considered to be electrogenic?
Each ATP hydrolyzed pumps 3 Na out of the cell and 2 K in. i.e. an additional + charge on the outside creating an internally negative membrane potential.
What ion is the primary contributor to resting membrane potential and how?
K+ due to passive diffusional efflux of K+ due to higher permeability and electric potential
What effect does adding + charge external cell have on the polarization?
None! The overall charge and electrostatic forces are so strong, the cell would not thus be considered hyperpolarized. Adding a neutral solution containing K+ to reduce the concentration gradient (and thus reduce efflux of K+).
What are receptor or generator potentials?
Small depolarizations originated by specialized structures in response to specific stimuli (e.g. heat, pressure, etc.)
What happens during voltage-gated sodium leak channels?
Na channels open and sodium floods into the cell. This brings K+ even further from its equilibrium potential, increasing the K+ driving force and creating an outward current though the leak K+ channels that tends to repolarize the cell.
What happens when the K+ driving force is increased due to sodium influx?
Na+ inward current exceeds K+, the cell is more depolarized activating additional Na channels to open…this is how you reach threshold!
What happens when threshold is reached?
A ton of sodium channels open (gNa), this drives towards ENa, and the driving potential for sodium (INa) decreases.
When sodium channels inactivate after threshold, there is a delay in…
Voltage-gated K+ channel is activated. This increase in K permeability moves K+ out, generating an outward K current (k), ultimately repolarizing the membrane.
As it approaches Ek, the cell is momentarily _______.
Hyperpolarized
The ________ of the action potential in any part of the axon acts as an electrical stimulus for the initiation of the action potential.
leading edge
_______ spreads beyond the local depolarization to initiate APs/depolarizations in other cells.
Current
Do large or small diameter axons conduct faster?
Large diameter
Each muscle fiber is controlled by a branch from _____ motor neuron(s).
One!!
What is a motor unit?
A motor neuron together with all of the individual muscle fibers it contacts.
A single muscle is composed of _____ motor units. How does this affect force of contraction?
Muscle fibers from different motor units. A more forceful contraction will activate more motor units of a single muscle.
When a motor neuron is activated, it generates and propagates an action potential, ___ the muscle fibers in that motor unit contract.
ALL
What happens when the action potential reaches the terminal of the muscle fiber axon?
Depolarization causes voltage-gated Ca2+ channels and Ca2+ enters the cytosol.
What does the influx of calcium in the cytosol do?
Cytosolic calcium promotes the fusion of vesicles containing acetylcholine (ACh) with the neuronal plasma membrane. Ach release in the cleft binds its receptor at the motor-end plate.
What happens when ACh binds at the motor-end plate?
Na and K-permeable channels open resulting in a larger Na influx than K influx…inward current depolarizes the motor end-plate producing local currents that bring the adjacent muscle PM to threshold and the signal is propagated.
ntraction called?What is a single muscle co
Twitch
End-plate potential/depolarization reaches into the interior of the muscle via numerous ______ in the form of transverse _________.
Surface invaginations, t-tubules.
What is Ek?
-96 mV
Which way do K+ leak?
Out of the cell (desire to reach Ek of -96).
If the Na/K pump stopped working, what would happen?
The cell would slowly depolarize to reach the ENa (+66mV).
As membrane potential approaches ENa, what happens?
Voltage-gated sodium channels close and voltage-gated potassium channels open (“delayed channels”). They close upon repolarization and only leak channels are open -> resting membrane potential achieved.
Conductance is ______ proportional to the number of open channels.
Directly
