Chapter 3: Neural Conduction and Transmission Flashcards
How does information flow within a neuron?
Through electrical signals known as Action Potential.
How does information flow between neurons?
Through chemical signals known as Neurotransmission.
What is Resting Membrane Potential?
A difference in electrical potential across the membrane of a nerve cell during an inactive period.
The inside of the cell (intercellular fluid) is negatively charged in comparison to the the outside of the cell (extracellular fluid).
Identify and describe the 3 important aspects of Resting Membrane Potential.
1. Electrochemical Equilibrium (Concentration Gradient and Electrostatic Pressure) As anions (-) move to the outside of the cell due to the concentration gradient, there is an opposing force from electrostatic pressure that pushes them back in - thus keeping the RMP negative.
- Selective Permeability of the Cell Membrane
Ions move through Ion Channel Proteins according to the concentration gradient.
a) Leak Channels are always open, leading to passive transport of ions through the cell membrane.
b) Gated Channels only open by voltage, mechanical or ligand stimulus.
3. Sodium/Potassium Ion Pumps Active transport (needs energy) of sodium and potassium occurs through the Na+/K+ ion pump.
What is Electrochemical Equilibrium Potential?
Voltage difference across the cell membrane to counterbalance the movement of molecules down their concentration gradient and the opposing electrostatic pressure.
What’s a Ligand gated channel protein?
Needs neurotransmitter to bind to it for it to open.
How much Na+ to the outside of the cell and K+ to the inside of the cell respectively are displaced by a Sodium Potassium Pump during RMP?
The pump displaces 3 Na+ molecules out of the cell, and brings 2 K+ molecules into the cell.
What’s the mV of RMP?
Around -65mV.
True or false; there is more K+ inside the cell than Na+, Cl- and Ca+ during RMP.
True.
True or false; neurons have far more K+ leak channels than Na+ leak channels.
True.
What causes a neuron at rest to be slightly negative compared to the surrounding fluid?
The movement of K+ ions out of the cell through Leak channel proteins.
How is RMP achieved? (3)
1) Na+ and K+ freely move in and out of the cell and aim to maintain a balanced concentration gradient through Leak Channel proteins on the cell membrane. The cell has more K+ leak channels and as a result K+ flows out of the cell faster than Na+ flows in, making the charge negative.
2) Through Active Transport, Sodium potassium pump proteins displace 3 Na+ out and 2 K+ molecules into the cell, maintaining the net charge as negative.
3) This is how a RMP of -65mV is maintained.
What is Action Potential?
The propagated electrical message of a neuron that travels along the axon to the presynaptic axon terminals.
What’s the difference between Depolarization and Polarization?
Depolarization: Membrane potential decreases (the difference between the charge on the inside of the cell and outside of the cell decreases), thus the cell has a more + value.
Polarization: Membrane potential increases, thus the cell has a more - value.
At what part of the neuron does the decision to fire or not occur?
the Axon Hillock.
Identify and describe the 0/5th stage of the Action Potential process.
5) Resting Stage: neuron is at RMP.
There is more K+ in the cell than Na+ due to difference in number of leak channels on cell membrane.
Identify and describe the 1st stage of the Action Potential process.
1) Stimulus: Initial depolarization of neuron due to stimuli.
Here, Na+ enters the cell through Gated channels that open due to the stimuli.
If the influx of ions is enough to cause an AP (if it reaches the Threshold mV) then the cell will fire moving to the next stage, if not, it fails.
Identify and describe the 2nd stage of the Action Potential process.
2) Depolarization: AP fires.
If stimulus-provoked depolarization brings cell potential to -55 mV threshold, action potential fires.
Voltage-gated Na+ channels open. Na+ moves down its concentration gradient into the cell, further depolarizing the cell.
What’s the Threshold potential mV for an AP to occur?
-55 mV
Identify and describe the 3rd stage of the Action Potential process.
3) Repolarization: membrane potentials falls after a peak.
Depolarization reaches peak of +40 mV. This triggers Voltage-Gated Na+ channels to CLOSE and become temporarily inactivated.
At the same time, voltage-gated K+ channels OPEN.
What’s the peak potential mV before repolarization?
+40mV
Identify and describe the 4th stage of the Action Potential process.
4) Hyperpolarization: potential overshoots below resting to about -90mV.
Voltage-gated Na+ channels remain CLOSED.
Voltage-gated K+ channels remain OPEN, driving membrane potential closer to the electrochemical equilibrium of K+.
Identify and describe the 5th and final stage of the Action Potential process.
5) Resting State: neuron returns to resting membrane potential.
All Voltage-gated ion channels CLOSE.
K+ and Na+ Leak channels remain OPEN. Remember, Number of K+ leak channels»_space;> number of Na+ leak channels.
Identify at which stage there is an Absolute Refractory period.
The 2nd and 3rd stages where the potential reaches its peak.
