HH Flashcards
What is the general aim of this series of papers?
To determine the laws which govern movements of ions during electrical activity
Give a simplified overview of HH1
Resting and Action Potentials (1952): This paper explained how neurons maintain a resting state with a certain electrical charge and how they generate action potentials (electrical impulses) when stimulated.
What does HH1 deal with?
Deals with the experimental method and with the behavior of the membrane in a normal ionic environment
What does HH2 do?
It’s concerned with the effect of changes in sodium concentration and with a resolution of the ionic current into sodium and potassium currents. Permeability to these ions may conveniently be expressed in units of ionic conductance.
What does HH3 describe?
Describes the effect of sudden changes in potential on the time course of the ionic conductances
What does HH4 deal with?
Deals with the inactivation process which reduces sodium permeability during the falling phase of the spike
What does HH5 do?
Concludes the series and shows that the form and velocity of the action potential may be calculated from the results described previously
Give a simplified overview of HH2
Voltage Clamp Experiment (1952): They introduced a technique called the voltage clamp, which allowed them to control and measure the electrical currents in a neuron. This helped them understand how ions (charged particles) move across the neuron’s membrane during an action potential.
Give a simplified overview of HH3
Calcium and Potassium Currents (1952): This paper focused on the roles of calcium and potassium ions in generating and controlling the electrical activity of neurons. They studied how these ions flow across the neuron’s membrane during different phases of an action potential.
Give a simplified overview of HH4
Potassium Currents During an Action Potential (1952): They delved deeper into the specific role of potassium ions in the repolarization phase of an action potential, which is crucial for resetting the neuron’s electrical state after firing.
Give a simplified overview of HH5
Sodium Currents During an Action Potential (1952): This paper focused on sodium ions and their contribution to the depolarization phase of an action potential, which is the phase where the neuron’s electrical charge becomes more positive, leading to the firing of the action potential.
These papers laid the foundation for our understanding of how neurons communicate and paved the way for further research in neuroscience and biophysics.
HH - Papers Actions potentials
- passive spread decays
- not effective in long neurons
- active propagation
(Action potentials/spikes)
What is main advantage of voltage clamp?
Hold the membrane voltage of the cell at a fixed value
HH1 procedure
- Excitation synaptic output
- Depolarization of the membrane
- Na+ channels open
- Na+ flows INTO the cell
- Causes further Depolarization
- More Na+ channels open
- Vm = ENa ( = 50 to 55 mV)
- Na+ channels get inactivated
- K+ channels open
- Causes repolarization
- K+ flows out and continues a bit
- Causes hyperpolarization
- Membrane pumps become active
- Resting potential is restored
HH1: What happens first in procedure? Depolarization, hyperpolarization, or repolarization?
Depolarization and Na+ channels open and Na+ flows INTO cell.
Later Na+ channels get inactivated and K+ channels open instead and causes repolarization. K+ flows out and then causes hyperpolarization.
Then membrane pumps become active and resting potential is restored.
True or False: In the parallel conductance model, Na+ and K+ flow through SEPARATE and INDEPENDENT pathways.
True
HH2: Voltage and time dependence of conduction
- Currents are produced by proteins whose conformation is changed by voltage
- Currents increase with increases in voltage
- channels are proteins that undergo movements in response to changes in voltage
- protein movement opens the pore for the ion movement
HH2: What two ways does gating of the ion channels can occur?
- g is constant (0 or 1, binary, closed or open), pore size is FIXED
- g is a function of V (g(V)), a series of conformational changes. Pore size is a function of V.
Note: the increase in channels opening causes the slope instead of a step
Why is water attached to sodium more strongly (and harder to take out oxygen)?
- Coulombic attraction (where smaller distance has higher coulombic attraction)
- Switching reaction (distance larger, energy smaller, energy increasing for the system, not a favorable state)
True or False: Apply an electric field to lipids, creates Maxwell stress (stress laterally) and this gives rise to a pole.
Dipole in flat stress orientation (so not maxwell stress). Instead, water molecules experience the electric field. This led to pore formation due to water molecules puncturing the lipid membranes and creating pores.
HH3: HH attempted to distinguish the two mechanisms with a novel measurement called the BLANK.
Instantaneous current-voltage curve
HH3: What happens in depolarization and hyperpolarization?
Depolarization: Na channels get inactivated with time
Hyperpolarization: Waiting longer activates channels
HH3: Brief inhibitory synaptic input that hyperpolarizes neurons and momentarily blocks the spiking of the cell, actually makes the neurons more likely to what?
Fire an action potential when inhibitory input ceases
HH3: When an action potential has occurred, another spike can NOT be produced until the inactivation of Na+ channels is removed. What is the result?
As a result, each spike is followed by a brief period of time, called the Refractory period, before the axon can fire an additional spike.
