Flashcards in Resting Membrane Potential (3) Deck (32)
Why is membrane potential important in cells?
- Provides basis of signalling in nervous system and cells.
How is membrane potential measured?
- Microelectrode penetrates cell membrane
- Microelectrode contains conducting solution
- Circuit set up with voltmeter to read potential difference
What is the membrane potential?
- Potential inside cell relative to extracellular solution
What are the ranges of resting potentials in the following?
- Animal cells
- Cardiac/skeletal cells
- Nerve cells
- Animal: -20 to 90mv
- Cardiac/skeletal: -80 to -90mv
- Nerve: -50 to -75mv
Compare the intra/extra cellular concentrations of the following:
- Na+ 10/145mM
- K+ 160/4.5mM
- Cl- 3/114mM
- A- 167/40mM
Give examples of other anions that are transported across cellular membranes.
- Amino acids
- Charged groups on proteins
When at resting potential what movement is there of K+?
- K+ from inside to out via chemical gradient
- K+ from out to inside via electrical gradient
- Balanced so no net movement.
What is the Nernst equation and state it.
- Allows calculation of membrane potential at which X is at equilibrium given intra and extracellular X concentrations
- Ex = 61/Z log ((X outside)/(X inside))
How much K+ is need to set up resting potential?
- V. small
In cardiac and skeletal cells why is their resting potential not exactly Ek?
- Cells are never perfectly selective for K+
What is depolarisation?
- Decrease in size of membrane potential from its normal value
- Cell interior is less negative
- e.g. -70mv to -50mv
What is hyperpolarisation?
- Increase in size of membrane potential from normal value
- Cell interior becomes more negative
- e.g. -70 to -90mv
How do membrane potentials arise?
- Result of selective ionic permeability.
- Changing selectivity will change membrane potential
What does increasing the permeability to certain ions result in?
- Moves membrane potential towards the equilibrium potential for that ion
What is the equilibrium potential for the following?
- K+ -95mv
- Na+ +70mv
- Cl- -96mv
- Ca2+ +122mv
Which ions' movement can result in hyperpolarisation and why?
- K+ as moves out of cell making it more negative inside the cell
- Cl- as moves into the cell making inside more negative
Which ions' movement can result in depolarisation?
- Na+ and Ca2+ as both move into the cell making it less negative
What are the 3 types of gating?
What are ligand gated channels?
- Channels that open/close in response to binding of chemical ligand
- e.g. Channels at synapses that respond to extracellular transmitters/Intracellular messengers
What are voltage gated channels?
- Channels that open/close in response to a change in membrane potential
- e.g. AP related channels
What are mechanical gated channels?
- Opening/closing in response to membrane deformation
- e.g mechanorecepotors.
Where can synaptic connections occur between?
- Nerve: nerve/muscle/gland/sensory
What is fast synaptic transmission?
- Receptor is also on ion channel
- Transmitter binding causes channel to open
What do excitatory transmitters do?
- Open ligand gated channels causing membrane depolarisation
What are excitatory synapses permeable to?
- Na+ and Ca2+
What is the resulting change in membrane potential known as?
- Excitatory post-synaptic potential (EPSP)
How are excitatory synapses controlled?
- Amount of transmitter
What do inhibitory synapses do and what are they permeable to?
- Opening of ligand gated channels to cause hyperpolarisation
- K+ and Cl-
What types of transmitters regulate inhibitory synapses?
- Gamma-aminobutyric acid (GABA)