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Flashcards in MR S3 Deck (18)
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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?

About -50mV


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


Define depolarisation

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


Define hyperpolarisation

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


Describe an inhibitory synapse

Transmitters include GABA and glycine
Inhibitory post synaptic potential
Permeable to K and Cl
Inhibitory transmitters open ligand gated channels, causing hyperpolarisation