Section 3 Flashcards
Describe the relationship between concentration and electrical gradients using an K+ as an example.
Define depolarization and hyperpolarization.
What are electrical gradients?
A difference in the concentrations of anions and cations across a barrier creates a separation of charge. Opposites charges attract, and this separation of charges creates an electrical potential across the membrane (aka membrane potential, measured in volts).
Define what is meant by an excitable cell.
Some cells such as nerves and muscle cells are what we call excitable cells and make use of the electrical potential for their functional role in the body.
What is Ohm’s Law?
The relationship between membrane potential and ionic currents
Equation:
V = IR
where V is voltage (the membrane potential), I is the current (ions moving across the membrane), and R is resistance (the ability of the plasma membrane to resist ion movement across it)
How do ions move across the plasma membrane?
Ion channels
What are the four main classes of ion channels?
Voltage-gated, chemically gated, mechanically gated, and thermally gated
Describe briefly how voltage gated ion channels work.
They open and close in response to changes in the membrane potential.
Describe briefly how chemically gated ion channels work. What is a common place they’re found?
They open when a specific chemical messenger (known as a ligand) interacts with it.
They can be found in the dendrites in neurons.
Describe briefly how mechanically gated ion channels work. Provide an example.
They open in response to mechanical deformations such as stretch.
Example is those in the cochlea of the ear.
Describe briefly how thermally gated ion channels work. Provide an example.
They respond to changes in temperature.
They are present in specialized neurons that project to the skin to act as temperature detectors.
What is the electrochemical gradient?
It is a combination of the concentration and electrical gradients. They can work together or in opposition.
What is the Nernst equation used for?
used to calculate the equilibrium potential (E) which is aka the reversal potential. This is the membrane potential at which there is no net flow of an ion across the membrane due to a balance between the electrical and chemical gradients
Know the equation for Nernst equation?
What are E values important for?
In determining if the net driving forces move ions into or out of a cell.
The net flow will always be in the direction that brings the membrane potential to its E. Because of this, the equilibrium potential of an ion can also be called its reversal potential
e.g, if the membrane potential is higher than the E value, this means the conc gradient is strong than the elec gradient and positive ions will flow out of the cell to make its membrane potential more negative.
The opposite is true as well
What is the resting membrane potential?
(RMP)
it is the electrical potential across its membrane
What is the resting membrane potential dependent upon?
the types of ions channels in a membrane, the concentration of ions on both sides of the membrane and their relative permeabilities at that time
When the cells RMP is negative, what does that mean in relation to the charges on the inside/outside of the cell.
If the RMP is negative, the inside of the cell is negative relative to the outside
When there are both K+ and Na+ channels present, will the RMP:
a) settle at the RMP for Na+
b) settle at the RMP for K+
c) settle at a RMP value between the two
c) And you would have to calculate this using the Goldman equation
Which one of the following can be calculated using the Nernst equation:
a) EP
b) RMP
EP
Which one of the following is dependant partly upon the types of ion channels in a membrane:
a) EP
b) RMP
RMP
Which one of the following applies to an ion:
a) EP
b) RMP
EP
Which one of the following is also called reversal potential:
a) EP
b) RMP
EP
Which one of the following is a measure of the electrical potential across the membrane:
a) EP
b) RMP
RMP
Which one of the followings value determines if the net driving forces move ions into or out of a cell:
a) EP
b) RMP
EP
Which one of the following can be calculated using the Goldman equation:
a) EP
b) RMP
RMP
What is depolarization?
When the magnitude of the polarization decreases (moves towards 0 mV)
What is repolarization?
After either a depolarization or a hyperpolarization, once the polarizing begins to return towards the RMP then it is said to be repolarizing
What is hyperpolarization?
When the magnitude of the polarization increases (moves even more negative than the RMP)
For excitable cells, if the membrane depolarizes enough it will fire what we call ___________.
an action potential
What are graded potentials?
Local changes in membrane potential that are used for short distance signalling.
Typically small in magnitude,
but can change in magnitude or strength.
The magnitude and duration of a graded potential depend directly on the strength and duration of the triggering stimulus.
What are graded potentials generally caused by?
Triggering events that make voltage-gated ion channels open
Why do graded potentials not move far along the membrane/not last long?
Because as the wave of depolarization moves along the membrane, there is a loss of charge. The magnitude of the graded potential decreases as it moves away from the site of the initial triggering event until it eventually disappears.
