Resting membrane potential Flashcards
What is the role of neurons/nerve cells?
They are the building blocks of the nervous system
What are the structures of a neuron?
Dendrites, Cell body, Axon, Axon terminal
What is the flow of electrical signals through a neuron?
From the dendrite, to the cell body along the axon and transferred to other cells by axon terminals
What kind of electrical signal flows from the dendrite to the cell body?
Synaptic potential
What kind of electrical signal flows from the cell body to other cells? What does the signal move through?
Action potential
Moves through axon
What does the cell body do?
Integrates the synaptic potentials and makes a decision whether to respond or not respond
If a cell body decides to respond to a synaptic potential, what does it produce?
An action potential
How is information received and transferred between nerve cells? What structure is involved in this?
By chemical signals
Synapses
How is information transferred through a nerve cell? What structures are involved in this?
Electrical signals
Dendrites, cell body and axon
What is the resting membrane potential of a neuron? Where is the voltage difference within the cell?
50-70 mV
It is in the cytoplasm
How was the rest membrane potential first discovered?
By getting a squid giant axon and an electrode and measuring the voltage difference between the squid giant axon and the reference node (in the air FYI)
Why was a squid giant axon used?
Because most animals have an axon with a diameter of 20-30µm which is too small for an electrode, squid giant axon is 500µm so electrode can fit much easier
Do all cells in the body have a negative membrane potential?
The vast majority of cells do
What happens when the electrical potential of the cell changes? Explain
It depends on the cell type. Only neurons, muscle cells and some endocrine cells can suddenly respond with a short change of this potential
If a cell is able to respond to a short/transient change in potential, what does this make it?
It makes the cell excitable
What does being excitable mean? What is the difference between an excitable and unexcitable cell?
It means that the membrane potential can change
Excitable = membrane potential can change and produce an action potential
Unexcitable = resting membrane potential is stable so no action potential
What are the two method for measuring the intracellular potential of cells?
Microelectrode recording and patch-clamp
How does the microelectrode recording technique work? What information does it record?
A glass microelectrode, with a tip size of less than 1 micron with a hole in it is filled with a salt solution to conduct electricity, is inserted inside the cell and the voltage difference between a reference electrode is measured
Measure the resting membrane potential, action potential, synaptic potentials etc.
What does the patch clamp technique? what does it measure?
A glass microelectrode, with a tip size of 2-3 micron with a hole in it filled with a salt solution to conduct electricity, are attached to the cell membrane and is broken by using a negative pressure creates a bridge between the inside of the cell and the pipette
Voltage changes and current
When we talk about charge moving in a cell, what is physically moving? How is this different from a copper wire?
Ions are moving in solution
In wire it is electrons moving
By convention, what is the potential outside the cell?
Defined as zero
What creates the resting membrane potential to be lower than the extracellular fluid?
Unequal concentration of Na+ and K+
Unequal permeability of the cell membrane to these ions
Electrogenic action of the Na-K pump (smaller contribution FYI)
Outside and inside the cell, what is the concentration of Na+ and K+?
Outside: Na+ = 150mM, K+ = 5mM
Inside: Na+ = 15mM, K+ = 100mM
How are the concentration gradients (i.e. the different concentration) of K+ and Na+ maintained?
By the Na+/K+ pump
How does the Na+/K+ pump contribute to the overall negative charge of the RMP?
It pumps out 3 Na+ for 2K+ pumped in. This results in a net loss of 1+ charge
What are the two main types of ion channels?
Non-gated channels (i.e. leak channels) and gated channels (voltage-gated, chemically-gated, mechanically-gated etc.)
What is the difference between an non-gated and a gated ion channel?
Non-gated ion channel are always open (therefore there are always particles moving through them) but gated ion channels only open when stimulated
What is unique about the cell membrane of neurons that contributes to the RMP? How does this influence the permeability of these ions?
There are many leak K+ channels but very few leak Na+ channels
K+ is 40 times more permeable through the cell membrane than Na+
How does the unequal concentrations and unequal cell membrane permeability to Na+ and K+ affect ion movement? What does this result in?
Na+ has a very low permeability so its new ion flow is very low
However K+ moves with its electrical gradient into the cell and then moves out with it concentration gradient (i.e. concentration and electrical gradient work in opposite directions)
Creates an equilibrium potential
What is an equilibrium potential?
It is where the net flow of ions is zero
How is the net flow of ions zero if there are concentration and electrical gradients?
Na+ have very low permeability so it does not move into the cell, it is only pumped out by Na+/K+ pumps
K+ diffuses out of the cell at the same rate as it is electrically attracted into it therefore electrochemical gradient is net zero
How can the equilibrium potential be calculated for each ion?
Using the nernst equation
What is the nernst equation?
61.5mV * (log[conc_ion_outside])/conc_ion_inside
What are the equilibrium potential for Na+ and K+ in mammals?
K+ = -80mV Na+ = +60mV
Why is the potential for Na+ positive?
There are more Na+ ions inside the cell than outside
Why is the potential for the K+ negative?
There are less ions inside the cell than outside
What assumption does the nernst equation make?
That a cell membrane is only permeable to one ion (i.e. has only one type of leak channels)
Is the assumption the nernst equation makes normally valid? When is there an exception?
It is not normally true as neurons have both Na and K leak channel (40 times more K FYI)
However the Glia cells only have leak channels for K so it is valid then
What do the glia cells do?
Supporting cells to the neurons
What is the resting membrane potential of glia cells?
-80mV
What is the rule for how a cell can shift its equilibrium potential?
the higher the permeability of the cell membrane to a particular ion, the greater the ability of this ion to shift the RMP towards its equilibrium potential
What can the range of RMP of a cell be?
Between -80mV and +60mV
Knowing the range of the RMP and the rule for how a cell can shift it equilibrium potential, why is the RMP of nerve cells at rest somewhere closer to the equilibrium potential of K+?
K+ has a much higher permeability than Na+ therefore the RMP is closer to the K+ equilibrium potential. However because there are some Na+ leak channels there is a slight lower permeability of K+ so due to the equilibrium potential rule, the RMP is not quite at the K+ equilibrium potential
Why are the nerve cells more positive than the glia cells?
Because in nerve cells there is a small contribution of + charge from the Na+ therefore it is not at the K+ resting membrane potential but glia cells doesn’t have any Na+ therefore at the K+ resting potential
What is the equation that takes into account both the concentration gradients and the relative permeability of the resting cell membrane of both K+ and Na+?
The Goldman equation
What is the simplified Goldman equation?
permeability = p
o = outside
i = inside
61.5mV * log( { p[K+_o] + p[Na+_o] } / { p[K+_i] + p[Na+_i] } )
What property does the Goldman equation tell us about the cell membrane?
If the permeability ratio changes then the RMP changes
What does the concentration gradient depend on? What does the RMP depend on?
Na/K pump
non-gated (leak) Na and K channels
