ND1: Resting potentials Flashcards
What is a membrane potential?
The potential difference between the inside and outside of a cell
Conventionally, does the outside or the inside of a cell have a value of 0 mV?
Outside
How is the membrane potential of a cell measured?
A microelectrode filled with a conducting solution (usually KCl) penetrates the cell membrane and a voltmeter measures the potential difference
What is the unit of measurement of membrane potentials?
Millivolts (mV)
What is the range of membrane potentials of animal cells at rest?
–20 to –90 mV
What is the range of membrane potentials of cardiac and skeletal muscle cells at rest?
–80 to –90 mV
What is the range of membrane potentials of nerve cells at rest?
–50 to –75 mV
What are the five methods molecules can use to pass through the lipid bilayer of cells?
- Diffusion through the cell membrane
- Channels
- Carriers/exchangers
- Primary active transport
- Secondary active transport
What sets up the resting potential of the cell? How?
Na+/K+-ATPase
Actively transports 3 Na+ ions out of the cell and 2 K+ ions into the cell, against their respective concentration gradients
How much of the total energy consumption of a cell at rest is due to the Na+/K+-ATPase?
40%
How is the equilibrium potential for an ion calculated? Use K+ as an example.
Nernst equation
How does the resting membrane potential arise?
The membrane is more permeable to K+ at rest than it is to other ions
What are ion channels?
- Proteins that enable ions to cross cell membranes
- They have an aqueous pore through which ions flow by diffusion
What are the properties of an ion channel?
- Selectivity: for one (or a few) ion species
- Gating: the pore can open or close by a conformational change in the protein
- Rapid ion flow: always down the electrochemical gradient
What is depolarisation?
A decrease in the size of the membrane potential from its normal value, i.e. the cell interior becomes less negative
What is hyperpolarisation?
An increase in the size of the membrane potential from its normal value, i.e. the cell interior becomes more negative.
How can the membrane potential for an ion be changed?
By changing the membrane permeability to a particular ion
What are the three methods by which channel activity can be controlled?
- Ligand gating
- Voltage gating
- Mechnaical gating
How do ligand-gated ion channels work?
The channel opens or closes in response to the binding of a chemical ligand
e.g. channels at synapses that respond to extracellular transmitters (acetylcholine); channels that respond to intracellular messengers
How do voltage-gated ion channels work?
The channel opens or closes in response to changes in membrane potential
e.g. channels involved in action potentials
How do mechanical-gated ion channels work?
The channel opens or closes in response to membrane deformation
e.g. channels in mechanoreceptors (e.g. stretch receptors)
Between which types of cell do synaptic connections occur?
- nerve cell – nerve cell
- nerve cell – muscle cell
- nerve cell – gland cell
- sensory cell – nerve cell
What is the process of synaptic transmission?
- Information is passed down the axon of the neuron as an action potential
- Vesicles release their (neuro)transmitter at the presynaptic membrane in response to the action potential
- (Neuro)transmitters carry the signal across the synaptic gap
- (Neuro)transmitter binds to the receptor on the postsynaptic membrane and the receptor opens
How do excitatory synapses work?
Excitatory transmitters (e.g. acetylcholine, glutamate) open ligand-gated ion channels and cause membrane depolarisation
This results in an excitatory postsynaptic potential (EPSP)
How do inhibitory synapses work?
Inhibitory transmitters (e.g. glycine, γ-aminobutyric acid (GABA)) open ligand-gated ion channels that cause hyperpolarisation
This results in an inhibitory postsynaptic potential (IPSP)
