Flashcards in MR S3 Deck (18)
What is a membrane potential?
A membrane potential is the voltage difference across a plasma membrane. This allows cell signalling across membranes.
Why do membrane potentials exist?
Because membranes are selectively permeable so may not let certain ions in/out and may actively transport ions in/out
This causes an electrochemical gradient to establish itself across the membrane of the cell
What is a normal resting membrane potential in an animal cell?
Between -20mV and -90mV
What is a normal resting membrane potential in a nerve cell?
About -50mV to -75mV
What is a normal resting membrane potential in smooth muscle cells?
What is a normal resting membrane potential in cardiac and skeletal muscle cells?
-80mV to -90mV
How is resting membrane potential set up?
In most cells, open K+ channels are responsible for most of the membrane potential
When electrical and concentration gradients for K+ are equal and opposite, there is no net movement of K+ ions but there is a negative potential
So potential relies on selective permeability of plasma membrane
What are the flaws of the Nernst equation?
It only works in model systems where the membrane is only selective to one ion
Therefore it gives the membrane potential lower than it would be in reality.
Name an equation that can be used to find the membrane potential for a membrane which is permeable to more than one ion
The GHK or Goldman Hodgkin Katz equation
Define 'Equilibrium Potential'
The equilibrium potential for an ion is the membrane potential at which there is no net movement of ions
Occurs when the electrical gradient is equal to the concentration gradient
Nernst equation can be used to work out the equilibrium potential
How may the potential of a cell be measured?
By using a micropipette/microelectrode connected to a voltmeter
Tip diameter >1μm
Membrane potential decreases in size
May only be a few mV, not necessarily an AP
Cell interior becomes less negative
Eg by opening Na and/or Ca channels
Membrane potential increases in size
Potential falls below resting
Cell interior becomes more negative
Eg by opening Cl or K channels
Where can synaptic transmissions occur?
Synaptic connections can occur between nerve, muscle, sensory cells and glands
Can be fast and slow
Describe fast synaptic transmission
In fast transmission, the receptor protein is also the ion channel
The binding of transmitter causes the channel to open
Describe slow synaptic transmission
In slow transmission, the protein receptor and the ion channel are separate proteins
They may be linked by either G-proteins or intracellular messengers
Describe excitatory synapses
Transmitters include acetylcholine, glutamate
Excitatory post synaptic potential
Lasts longer than AP
Graded with the amount of neurotransmitter
Excitatory transmitters open ligand gated channels, causing depolarisation
Can be permeable to Na, Ca and sometimes cations in general