Membrane potential Flashcards
What are the 2 types of membrane potentials?
Resting and Action potentials
Resting membrane potential
Both voltage gated Na+ and K+ channels are closed
Ranges from -40 ~ -90 mv
Why is the voltage always negative?
Because more positive charge is moving out of the cell than going in
What part of the body has -40 mV?
heart
What part of the body has -90 mV?
Neurons and muscles
What are the major determinants of RMP?
- Na+, K+ ATPase pump
- Ions moving towards a dynamic equilibrium
- Differential permeability of the membrane
Resting membrane potential depends on what?
The equilibrium of K+
Equilibrium Potential
When the uneven K+ charge (more inside) produces a voltage across the membrane
Resting membrane is more permeable to ______ than to ______
- K+
- Na+ ions
Why is resting membrane more permeable to K+ than to Na+
There are more K+ leak channels –> K+ reach equilibrium and equilibrium potential easier
What does the equilibrium potential for the more permeant K+ determine?
RMP than the EP of Na in more neurons
What does disturbance in Na and K levels lead to?
Disturbances in the membrane potential (nerves and muscles)
Nernst Equation
Ex= RT / zF In [Xoutside] / [Xinside]
Ex= -60 mV / z log [Xinside] / [Xoutside]
Action Potential
A regenerative electrical signal that begins at the axons initial segment resulting from competing EPSP and IPSP and spreading down the length of the axon without decreasing magnitude
What happens if the cell doesn’t reach threshold potential?
Action potential won’t occur
Depolarization
Cells will bring in + charge –> in the plasma membrane it’s +, attracting + ions from ECF –> when the cell goes from -70 to -50 the voltage- gated sodium channels will open –> if enough channels are open then the threshold is surpassed -> action potential initiated
Repolarization
The membrane potential goes toward the resting potential
Na+ channels self-inactivated, K+ channels are open
Membrane potential move temporarily below its resting level to a hyperpolarized state
Postsynaptic potential
RMP in muscles and neurons changed by synaptic signals from presynaptic cells
Synaptic Signals
Electrical, mechanical and chemical
What will synaptic signals change?
The permeability of the membrane sodium
For post synaptic potential to generate an action potential, what does it have to do?
It has to reach a threshold potential
Why is the action potential essential?
To transmit information between neurons
EPSP
Excitatory postsynaptic potential
It’s “excitatory” because such a synaptic transmission increases the chances for an AP at the initial segment of the postsynaptic cell’s axon
How is a membrane depolarized?
When an presynaptic signal changes the postsynaptic membrane potential to a more positive value
Na+ channels open, this allows Na+ ions to diffuse into the neurons moving the membrane potential towards the more positive sodium equilibrium potential
When is a membrane hyperpolarized?
When an EPSP changes the postsynaptic membrane potential to a more negative value
IPSP
Inhibitory Postsynaptic potential
It’s “inhibitory” because usch a synaptic transmission decreases the chances for an AP at the initial segment of the postsynaptic cell’s axon
______ drives the membrane potential toward the threshold for an action potential
EPSP
_____ drives the membrane potential away from the threshold for an action potential
IPSP
EPSP and IPSP characteristics
Transient
Magnitude of PSP is small and decreases with distance from the originating synapse
Greatest at the synapse
Why are PSP’s transient?
The chemical transmitted is quickly removed from the synapse
Hyperpolization
Due to the flow of K+ ions out through the voltage gated K+ channels, in addition to the flow out through K+ leak channels, and the membrane potential is closer to the K+ equilibrium potential
AP time
Takes about 2-3 msec in neurons, longer in muscle cells
AP path
Generated in the axon’s initial segment –> moves down the unmyelinated axon as positive charges passively migrate to the immediately adjacent membrane to trigger an action potential there
AP characteristics
All or none
Always the same size
Either not triggered at all or triggered completely
Speed of AP
Varies and is affected by internal diameter and myelination state of the axon
Small: unmyelinated, slow (0.5 m/s)
Large: heavily myelinated, fast (> 90 m/sec)
Where can AP and ion exchange occur?
Only in the nodes of Ranvier and jumps from one node to the next (Saltatory conduction)
What does an AP cause?
At the neuromuscular junction, it causes a muscle fiber to twitch (contract)
Local Anesthetics (lidocaine)
Blocks voltage gated Na channels –>
Prevents permeability –>
Prevents AP –>
Somatosensory info not transmitted
Clinical Significance: Local Anesthetics
Tetrodoxin
Lidocaine
