Section 2 - Membrane and action potentials Flashcards
What is the resting membrane potential?
Electrical potential difference across the membrane
If the membrane is only permeable to K+ then K+ would diffuse down its ______ gradient until the electrical potential across the membrane ____ the K+ diffusion
concentration
counters
What is the name of the electrical potential that counters net diffusion of K+?
The k+ equilibrium potential or Nernst potential of K+
Explain the Nernst potential
It’s the electrical potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane
T or F: the sign of the potential is positive if the ion diffusing is positive and it is negative if the ion is negative
False, positive if the ion is negative and negative if the ion is positive
What is the formula to calculate the Nernst potential?
EMF (mV) = ± 61 log (concentration inside/concentration outside)
EMF = electromotive force
Is it the extracellular or intracellular fluid that is high in Na+, Ca2+ and Cl- and positively charged?
The extracellular fluid
The intracellular fluid is high in ____ (3)
K+, Mg2+ and proteins
Negatively charged
How do we call the electrical potential that counters net diffusion of Na+?
The Na+ equilibrium potential of Nernst potential of Na+
Name the three factors that influence the Goldman equation (equilibrium potential of membrane permeable to several different ions)
- Concentration (C) of respective ions on the inside (i) and outside (o) of the membrane
- Permeability (P) of membrane (P) to each ion
- Polarity of the electrical charge of ions positive or negative
T or F: The membrane is far more permeable to K+ than to Na+
True see p.15
Leak channels are much more permeable to ___ than ___ (100 times)
K+
Na+
What is the resting membrane potential for large nerve fibers vs small neurons of nervous system
- 90 mV for large nerve fibers
- 70 mV for small neurons
Name the three factors that influence the resting membrane potential
- Diffusion of potassium and sodium ions
- Permeability of ions through leak channels
- Na+/K+ pump (creates more negativity inside because transports 3 Na+ ions out vs 2 K+ ions in)
T or F: the resting membrane potential is closer to the equilibrium for the ion with the highest permeability (i.e. K+)
True
What are the other names for action potential (AP)?
Spike
Impulse
Firing
T or F: AP is a all-or-non event: it occurs fully or it does not occur at all
True
T or F: the amplitude of an AP can change
False (all-or-none)
What are the three functions of action potentials?
- Transmitting nerve signals
- Rapid transmission over distance
- Encoding information (neuronal language)
In which of these examples the AP will travel at the
highest speed?
A)Twisting your ankle…ouch! It hurts!!!
B)Feeling the position of my limbs in space
C)Feeling a pressure on my skin
B) see p.22 for image of axons
Name the 5 sequence of events of the action potential
- Resting stage
- Depolarization (overshoot)
- Repolarization
- Afterpotential (undershoot)
- Back to resting stage
What is the voltage related to the resting stage?
-90mV
What is the voltage related to depolarization?
-90mV to +35mV
What is the cause of the depolarization?
Sudden opening of Na+ channels, Na+ ions flow inside the cell
What is the voltage related to repolarization?
+35mV to -90mV
What is the cause of the repolarization?
Na+ channels begin to close so the Na+ ions stop to flow inside
K+ channels open slowly so K+ ions start to flow outside
What is the related voltage for the afterpotential stage?
less than -90mV
What is the cause of the afterpotential?
K+ channels that remain open for a few milliseconds after repolarization of membrane is completed so excess K+ flows out of membrane
What is the cause of back to resting stage?
The closing of K+ channels
What are to two special types of protein channels on the nerve membrane that cause the activation of action potentials?
Voltage-gated Na+ channels
Voltage-gated K+ channels
T or F: Action potential is a facilitated diffusion because voltage-gated channels are sensitive to the change in membrane electrical potential
False, it is a simple diffusion
Voltage-gated Na+ channel : is the activation gate on the exterior or the interior side of the membrane?
exterior side
Name the three states of the voltage-gated sodium channel (see p.31-32)
- resting stage (activation closed & inactivation open
- activated stage (both open)
- inactivated stage (activation open & inactivation closed)
T or F: the voltage-gated K+ channels only have one gate
True
Name the two states of the voltage-gated potassium channel
- resting stage (gate close)
2. slow activation state (gate open) see p.34-35
Because of the function that mirror neurons
play, Dr. Ramachandran referred to them as:
a) Sympathy neurons
b) Harmony neurons
c) Empathy neurons
d) Affinity neurons
e) Compatibility neurons
C) empathy neurons
When does the threshold for initiation of an action potential occurs?
When the number of Na+ ions entering the nerve becomes greater than the number of K+ ions leaving the nerve
What is the voltage related to the threshold?
-65mV for a nerve with a resting potential of -90mV
What are the three causes of initial increase in membrane potential?
- electrical stimulation (current)
- mechanic stimulation (ex: needle on the skin)
- chemical stimulation (neurotransmitters)
T or F: the frequency of firing (number of Aps) is independent on the intensity of the stimulus
False, it is dependent
Name this process : period during which a new AP cannot occur as long as the membrane is still depolarized from the preceding AP
Absolute refractory period
Why does an absolute refractory period happens?
Because Na+ channels are inactivated (no entry) and the membrane has to return near original resting potential to allow inactivation gates to reopen
Name this process : period that follows the absolute refractory period during which a new AP can occur in response to a strong stimulus (greater than normal)
Relative refractory period
Why does a relative refractory period happens?
Some Na+ channels start to go back to resting state and others are still inactivated and K+ channels are still open and the membrane is hyperpolarized (during the undershoot)
What offers the best transmission between myelinated and unmyelinated nerve fibers? explain
Myelinated because the nerve fibers are insulated from the passage of ions + node of Ranvier increase the speed
When the nerve fibers are unmyelinated, what happens to the action potential?
The neuron has to create a new AP every step of the way to create the adjacent propagation (see p.46)
Explain the concept of saltatory conduction
Saltatory conduction conserves energy for axon (from 0,25m/s in unmyelinated axon to 120 m/s in myelinated axon)
What is the name of the blockage of AP conduction?
Multiple Sclerosis (Ms)
Explain MS
MS is an immune-mediated inflammatory disease that causes the demyelination of the central nervous system
What are the effects of MS on the body? (3)
- Muscle weakness
- Loss of sensation
- Death
