NEU Exam 1 Flashcards
What are the four principles of action potentials?
- The All-or-None Phenomenon: An AP either happens completely, or it does not happen at all
- Refractory Periods: Refractory periods are caused by: potassium continuing to leave the cell, and voltage-gated sodium channels unable to open again
- Forward Movement: once an action potential is initiated→ it will travel in a ONE-WAY direction (axon hillock→the axon terminal).
- Rate Code: Coding for Stimulus Intensity
- No strong or weak APs, all the same regardless of stimulus strength
- Strong stimuli cause action potentials to occur more frequently
- CNS determines stimulus intensity by the frequency of impulses
Higher frequency means stronger stimulus
The All-or-None Phenomenon:
An AP either happens completely, or it does not happen at all
Refractory Periods:
Refractory periods are caused by: potassium continuing to leave the cell, and voltage-gated
Forward Movement:
once an action potential is initiated→ it will travel in a ONE-WAY direction (axon hillock→the axon terminal).
Rate Code:
Coding for Stimulus Intensity
- No strong or weak APs, all the same regardless of stimulus strength
- Strong stimuli cause action potentials to occur more frequently
- CNS determines stimulus intensity by the frequency of impulses
Higher frequency means stronger stimulus
What is the threshold the membrane potential needs to reach to fire an action potential?
-55mV
For the following steps of the action potential
Resting state:-70mV, the inside of the cell is NEGATIVELY charged relative to the outside
Action potential begins when a depolarization increases the membrane potential so that threshold is reached→-55mV
At threshold: VG Na+ channels open, Na+ flow into the cell
This influx of Na+ makes the membrane potential INC (LESS NEG/MORE POS) → +40mV
This is DEPOLARIZATION
SODIUM channels self-inactivate (close), ABSOLUTE REFRACTORY PERIOD (ABSOLUTELY CANNOT GENERATE AN AP, impossible to generate AP)
Potassium channels open→ K+ leaves the cell→going down its concentration gradient→ REPOLARIZATION→RMP decreases→bringing it back towards the normal RMP
The continual K+ leaving the cell→ causes cell to be MORE AND MORE negative→hyperpolarization
RELATIVE REFRACTORY PERIOD (another AP can be generated but would require a stronger stimulus to reach threshold).
Back to resting membrane potential: -70mV
Sodium/Potassium Pump: restores electrical conditions
3Na+ OUT: 2K+ IN (remember KIN)
Nernest Equation
One ion can cross
concentraion of in and out
K+
In 150
Out 5
GHK Equation
more than one can cross
concentration of ion and peremabiilty of an ion
Na+
In 10
Out 145
Establishing RMP
membrane more permeibale to K+
Rmp is closer to GHK than Nerenst
What affects action potential conduction velocity?
*Axon diameter (THICKNESS): larger axon diameter→faster conduction. This is because a larger diameter reduces the resistance to ion flow→enables the AP to propagate more quickly.
- *Myelation: is a fatty substance, wraps around the axon, protecting the sheath.
— Myelinated axons have a SALTATORY CONDUCTION: where the AP jumps from one node of Ranvier to the next→ speeding conduction velocity.
— This is because myelin insulation PREVENTS LEAKAGE and allows for a RAPID propagation at the nodes.
Temperature: higher temperature generally increases the speed of AP conduction
– This is due to the increased kinetic energy of ions→leading to faster movement through ion channels.
Axon length: longer axons experience a DECREASE in conduction velocity due to increased resistance along the length of the axon
— Please note: this effect is relatively small compared to the influence of the axon diameter & myelination
Ion channel properties: opening & closing kinetics. Faster opening & closing if Na+ channels→ FASTER CONDUCTION.
Explain the difference between action potential propagation in unmyelinated versus myelinated neurons
Unmyelinated Neurons:
- Continuous conduction
- Depolarization occurs step by step, throughout the axon
- VG Na+ channels are distributed along the entire length of the axon
- The action potential is regenerated at each step
Myelinated Neurons:
- Saltatory Conduction
- Depolarization: only happens at NODES OF RANVIER
- VG Na+ channels are concentrated at nodes of ranvier
- The action potential is regenerated only at the nodes of ranvier
Which statement correctly differentiates between the passive and active current in a myelinated axon?
The active current flows only in the nodes of Ranvier, unlike the passive current
- Passive flow is just movement of sodium ions that is passive depolarization
- Active when voltage gated channels are open and sodium is rushing in
Nodes of Ranvier represent
gaps in myelin wrapping
Changes in membrane potential
way to receive, integrate, send information
Changes produce two types of signals
Graded potentials - Incoming signals operating over SHORT distances
Action potentials - Long-distance signals of axons
Action Potentials (AP)
Principal way neurons send signals
Occur only in axons of neurons, and muscle cells (skeletal, cardiac, smooth)
Brief reversal of membrane potential
Make predictions on what you think might happen if a toxin were to bind to and stop the activity of the sodium-potassium pump?
RMP will get depolarized and during AP reset ionic conditions → might affect refractory period
The refractory period is responsible for what other principle of action potentials?
Forward movement
Recent research has explored whether myelin thickness can change over time based on experience, and emerging evidence indicates this is possible. If an axon for a neuron important for motor learning increases the number of layers of myelin, thus increasing myelin thickness, what will happen to capacitance, internal resistance, membrane resistance, and propagation velocity?
Capacitance (charges are further apart) - less
Internal - same bc diameter hasn’t changed
Membrane - same
Prop - increases
A neuron has increased its production of Na+ leak channels, increasing the permeability of the membrane so that it is now twice as permeable to Na+ as it is to K+ RMP is now +14.5mV. Which direction will Na+ move with the above RMP?
In, primarily due to concentration gradient - only changed permeability not ions
A newly discovered species of lizard is found to have a unique central nervous system. The neurons of this lizard have a resting membrane potential that is -83 mV. Why might the RMP of these neurons be so much more negative than in a human neuron?
The membrane is more permeable to potassium than in a human neuron
