Membrane Resting Potential & Action Potential Flashcards
What is resting membrane potential?
It is the electrical potential difference across a membrane
What is the name of the electrical potential that counters the net diffusion of K+
The K+ equilibrium potential or the Nernst potential for K+
What is the Nernst Potential?
It is the electrical potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane.
What is the Nernst Potential Equation?
EMF (millivolts): +/- 61 log (concentration inside/concentration outside)
The sign of the potential is positive if the ion is negative and negative if the ion is positive
What are the three factors that affect the equilibrium potential of membrane permeable to several different ions (Goldman equation)?
1) Concentration of the different ions on both the inside and outside of the cell
2) Permeability of the membrane to each ion
3) Polarity of the electrical charge of ions positive or negative
Why is Vm (-86 mV) so close to Ek (-94 mV) compared to Ena (+61)?
The membrane is far more permeable to K+ than Na+
What is the resting membrane potential for large nerve fibers (motoneurons)?
-90mV
What is the resting membrane potential for small neurons of the nervous system?
-70 mV
What factors affect the resting membrane potential? (3)
1) Diffusion of K+ and Na+
2) Permeability of ions through leak channels (more permeable to K+)
3) Na+/K+ Pump: creates more negativity inside
What is an Action Potential?
It is a very rapid change in the membrane potential from “-“ to “+” values and returns back to the initial resting potential level.
It is an “ all-or-none” event, either it happens fully or not at all.
It propagates along the nerve fiber until it comes to the end of the fiber
What are the functions of an Action potential? (3)
1) Transmitting Nerve signals: sensory info goes from periphery to CNS and motor info goes from CNS to the periphery
2) Rapid transmission over distance: speed of transmission depends on fiber size and whether or not it is myelinated
3) Encoding Information (neuronal language): The frequency of AP encodes info ( amplitude cannot change)
How many stages are there to an action potential?
5, resting stage depolarization repolarization afterpotential (undershoot) back to resting stage
At what membrane potential is the resting stage?
-90mV
Define depolarization stage
-90 to 35 mV, 0.1 ms period (very fast)
Caused by the sudden opening of Na+ channels and the flow of Na+ ions into the cell
Define Repolarization stage
35 mV to -90 mV
Na+ channels begin to close, Na+ ions stop flowing into the cell.
K+ channels begin to open, and K+ ions start to flow outside
Re-establishes the negative resting potential of the cell
What is Afterpotential (hyperpolarization, undershoot)?
Less than -90 mV which is cause by K+ channels that remain open for a few milliseconds after repolarization of the membrane is reached.
Define Back to resting stage
K+ channels close
How many gates does the voltage-gated sodium channel have?
2 gates: activation gate (exterior side of the membrane) Inactivation gate (interior side of membrane)
What are the three states of the voltage-gated sodium channels?
Resting state: inactivation gate open, activation gate closed (no Na+)
Activated state: both gates open (opening threshold -70 mV to -50mV) (Na+)
Inactivated state: inactivation gate closed, activation gate open (happens when membrane potential increases over 0 mV (overshoot)) ( No Na+)
How many gates do the voltage-gated potassium channel have?
1, on the interior side of the membrane
How many states do the voltage-gated potassium channels have?
2, resting state ( gate closed)
slow activation state (gate open)
Explain the Slow activation state (repolarization)
K+ channels are activated when the membrane potential increases above 0 mV, gates open slowly while the Na+ channels start to close. Potassium ions flow outside the cell which accelerates repolarization toward resting potential
How did Dr. Ramachandran refer to mirror neurons?
He called them empathy neurons
What is the threshold for initiation of an Action Potential?
it is the level of membrane potential at which the positive-feedback cycle is created (point of no return). Occurs when the number of sodium ions entering the nerve becomes greater than the number of potassium ions leaving the nerve
about - 65mV for a nerve with Vm= -90
What can cause the initial increase in membrane potential to reach the threshold?
Mechanical stimulation
Chemical stimulation
Electrical stimulation
True or False. The amplitude of an AP is dependent on the intensity of the stimulus that evokes it.
False, it is independent.
The frequency of firing however is dependent on the intensity of the stimulus
What is the Absolute refractory period?
It is a period during which another AP cannot occur as long as the membrane is still depolarized from the preceding AP
Why does the Absolute refractory period occur?
Because Na+ channels are inactivated and the membrane has to return near original resting potential to allow inactivation gates to reopen
What is the Relative Refractory Period?
It is the period that immediately follows an absolute refractory period during which a new AP can occur if the stimulus is strong enough.
Why does the relative refractory period happen?
Some Na+ channels start to go back to their resting state and others are still inactivated. K+ channels are still open and the membrane is hyperpolarized
Myelin is produced as an extension of what cells?
Schwann cells in PNS
Oligodendrocytes in CNS
What is a myelinated nerve fiber?
Nerve fiber whose axon is surrounded by myelin sheaths. Ions cannot significantly flow through myelin sheaths which thus insulates the nerve fiber
What is saltatory conduction?
APs can only occur at the node of Ranvier and are conducted from node to node. It conserves energy for axons. Conduction velocity varies from 0.25 m/s in unmyelinated fibers to as great as 120 m/s in large myelinated fibers.
What is Multiple Sclerosis (MS)?
It is an immune-mediated inflammatory disease that causes the demyelination of the CNS
symptoms include muscle weakness, loss of sensation, death
