The Resting Membrane Potential Flashcards
What do all cells have?
An electrical potential difference (voltage) across their plasma membrane
What does the membrane potential provide?
The basis of signalling in the nervous system, as well as in many other types of cells
How is the resting membrane potential expressed?
As the potential inside the cell relative to the extracellular solution
What is the membrane potential of animal cells?
They have negative membrane potentials, that range from -20 to -90mV
What is the resting potential of nerve cells?
-50 to -75mV
What is resting membrane potentials of smooth muscle cells?
~ -50mV
What is the resting membrane potential of skeletal and cardiac muscle cells?
-80 to -90 mV
What is the cell membrane selectively permeable to?
Different ions
How does the permeability of the membrane to ions occur?
By way of channel proteins
What makes the whole cell membrane selectively permeable to ions?
The selectivity of ion channels and the types of channels that are open
What dominates the membrane ionic permeability at rest for most cells?
Open K+ channels
When is there no net movement of K+?
When the chemical and electrical gradients for K+ are equal and opposite
What is true when there is no net movement of K+?
There will be a negative membrane potential
What does the resting membrane potential arise because of?
The membrane being selectively permeable to K+
What is the intracellular concentration of Na?
~10mM
What is the extracellular concentration of Na?
145mM
What is the intracellular concentration of K?
160mM
What is the extracellular concentration of K?
4.5mM
What is the intracellular concentration of Cl?
4mM
What is the extracellular concentration of Cl?
114mM
What is the intracellular concentration of anions (other can Cl)?
167mM
What is the extracellular concentration of anions (other than Cl)
40mM
What anions other than Cl are involved in the gradient across the cell membrane?
Phosphate
Bicarbonate
Amino acids
Charged groups on proteins
In what direction is the K concentration gradient?
From the inside of the cell to the outside of the cell
In what direction is the K electrical gradient?
From the outside of the cell to the inside of the cell
What is the equilibrium potential for an ion?
The membrane potential at which there is no net movement of the ion across the membrane (the concentration gradient = the electrical gradient)
What can be used to calculate the equilibrium potential?
The Nernst Equation
What happens in depolarisation?
Membrane potential decreases in size
Does depolarisation cause an action potential?
Not necessarily- it may only be a few mV
What happens to the cell interior in depolarisation?
It becomes less negative
What causes depolarisation?
Opening of Na or Ca channels
What happens in hyperpolarisation?
The membrane potential increases in size, falling below resting
What happens to the cell interior in hyperpolarisation?
It becomes more negative
What causes hyperpolarisation?
Cl or K channels opening
What do cells have in reality?
Channels open for more than one type of ion
What does the contribution of each ion to the membrane potential depend on?
How permeable the membrane is to that ion
What can change a cells membrane potential?
Changes in the cells permeability to a single ion
How can be used to cells membrane potential be calculated?
The GHK equation
What does the GHK equation show?
That membrane potential depends on the number of open channels open for each ion
Where can synaptic connections occur?
Between nerve, muscle, sensory cells and glands
How can synaptic transmission be categorised?
Into fast and slow
What is the receptor protein in fast synaptic transmission?
A ion chanel
What happens in fast synaptic transmission?
The binding of transmitter causes the channel to open
What happens in slow synaptic transmission?
The receptor protein and ion channel are separate proteins, that may be linked by G-proteins or intracellular messengers
What are the two basic patterns of slow synaptic transmission?
Direct G-protein gating
Gating via an intracellular messenger
What are the characteristics of direct G-protein gating?
Localised
Quite rapid
How does gating via an intracellular messenger work?
The G-protein activates an enzyme, which initiates a signalling cascade, through an intracellular messenger or protein kinase which activates the channel
What are the characteristics of gating via an intracellular messenger?
Occurs throughout the cell
Amplification by cascade
What do excitatory transmitters do?
Open ligand-gated channels, causing membrane depolarisations
What can ligand-gated channels opened by excitatory transmitters be permeable to?
Na, Ca, and sometimes cations in general
What is the membrane depolarisation caused by excitatory transmitters called?
Excitatory Post-Synaptic Potential (EPSP)
How does EPSP differ from an AP?
It is graded with the amount of transmitter
Give two examples of excitatory transmitters
Acetylcholine
Glutamate
What do inhibitory transmitters do?
Open ligand-gated channels, causing hyperpolarisation
What are ligand-gated channels opened by inhibitory transmitters permeable to?
K or Cl
What is the hyperpolarisation caused by inhibitory transmitters called?
Inhibitory post-synaptic potential (IPSP)
Give 2 examples of inhibitory transmitters
Glycine
γ-aminobutyric acid (GABA)
