Resting Cell Membrane -- Session 3 Flashcards
What is a membrane potential?
An electrical potential difference across a cell membrane
What is used to measure membrane potential?
Give the characteristics for the unique component of the measuring device/
Microelectrode with a micropipette
- one electrode measures the extracellular fluid & a micropipette measures voltage inside the cell membrane
- teh micropipette has a diameter of >1micrometres and is filled with a conducting solution (KCl/solution which is a s similar as possible to intracellular fluid to prevent excess disruption)
How is a membrane potential expressed?
A value which is relative to the outside of the cell
What is the range for membrane potential for animal cells?
-20mV to -90mV
What is the membrane potential range for cardiac muscle?
-80mV to -90mV
What is the membrane potential range for nerve cells?
-50mV to -75mV
Why do membrane potentials occur?
The membrane is selectively permeable to different ions due to transmembranous channel proteins.
What are the charactersitics of ion channels?
- Are specific to one/ a few ion species
- Gating – teh channel can be opened or closde by a conformational change in the protein molecule
- Ion flow always occurs down the electrochemical gradient
What is specific about potassium channels?
What movement of K+ ions occur at rest?
They are voltage insenstive and tend to open at resting potential
- Increased K+ inside cell so ions move out down chemical gradient
- Negative charge on the inside of the cell so ions are attracted bck into the cell down an electrical gradient
How is a membrane potential generated?
K+ channels are open so K+ can diffuse out down a conc. gradient
Anions cannot follow (cant diffuse through the membrane) so negative anions build up in cell.
Negative charge is present on inside in comparison to the outside.
Membrane potential opposes K+ outward diffusion so equilibrium arises.
What is an equilibrium potential?
The membrane potential where the electrical and diffusion forces balance each oter so there is no further net movement of an ion
What equation crayon use to calculate the potassium equilibrium potential?
Nernst equation
What are the two terms which can be used to describe changes of the membrane potential from its resting level and describe them.
HYPERPOLARISATION – an increase in the membrane potential so the inside becomes less negative
DEPOLARISATION – a decrease in the membrane potential so the inside becomes more negative
What will cause depolarisation of cells?
Opening Ca2+ or Na+ channels
What will causes hyperpolarisation of cells?
Opening K+ or Cl- channels
How can you determine how important each ion is to determining the membrane potential?
It depends upon how easily the ion can diffuse through the membrane relative to other ions
— depends on: the number of channels and how easily they let the ion through
How is ion channel opening determined?
Gating mechanisms which open and close the cells
What are the two main forms of hating mechanisms?
Ligand gating – channel is opened/closed by binding of a chemical ligand (can be extracellular transmitter or and intracellularly messenger)
Voltage gating – channel opens or closes in response to changes in membrane potential
What is a specific characteristic of a receptor in a fast synaptic transmission?
The receptor is also a ligand gated ion channel
What type of channels do depolarising transmitters open?
Channels with positive reversal potentials
– channels for Na+, Ca2+ or cations
What type of potential change do depolarising transmitters cause?
Excitatory postsynaptic potential
– causes excitation of cells
What type of channels do hyper polarising transmitters open?
Negative reversal potentials
– channels for K+ or Cl-
What type of change in potential do hyperpolarising transmitters cause?
Inhibitory postsynaptic potential
– lead to inhibition
What happens in slow synaptic transmission?
The receptor is not an ion channel It signals to the channel in one of two ways: 1. Within the membrane 2. By an intracellularly messenger --- both involve GTP-binding protein
What are the characteristics of channels signalling within the membrane?
Is localised
Very rapid
What are the benefits of signalling the ion channel by an intracellularly messenger?
It occurs throughout the cell
Is amplified by a cascade
What is responsible for the distribution of ions between the intra and extra cellular fluid?
The selective permeability of the membrane
Why is the value calculated for a resting membrane potential not often the value measured?
The membrane is not permeable to one ion only. Other ions ar Beale to diffuse in and out which has an effect on the actual resting potential value.
What contribution does Na+-K+-ATPase make to the maintainance of the resting membrane potential?
It generates the potential by removing Na+ bringing K+ into the membrane.
It helps to maintain the ion gradient.
