Changing Membrane Potentials Flashcards
What is the main purpose of changes in membrane potential?
It underlies many forms of signalling between and within cells
Give 3 examples of signalling involving changes in membrane potential
- Action potentials is nerve and muscle cells
- Triggering and control of muscle cells
- Control of hormone and neurotransmitter secretion
- Transduction of sensory information
- Postsynaptic actions of fast synaptic transmitters
- Regulation of smooth muscle tone
What is depolarisation and what is its effect?
- Decrease in the size of the membrane potential from its normal value
- Cell interior becomes less negative
What is hyperpolarisation and what is its effect?
- Increase in the size of the membrane potential from its normal value
- Cell interior becomes more negative
How are membrane potentials created?
Result of selective ionic permeability
What is an equilibrium potential in terms of ions and membranes?
Membrane potential of an ion when there is no net movement of ions
What is the effect of increasing membrane permeability on equilibrium potential?
Moves the membrane potential towards the ion’s equilibrium potential
Which channels open during hyperpolarisation?
K+ and Cl- Channels
Which ion channels open during depolarisation?
Na+ or Ca2+
What does the GHK equation represent?
- Contribution of each ion to the membrane potential
- Depends on membrane permeability to the ion
Give an example of a membrane potential channel that is less selective
- Nicotinic Acetylcholine Receptors
- Ion channels for Na+ and K+ open
What 3 types of gated ion channels contribute to membrane potential?
- Ligand gating
- Voltage gating
- Mechanical gating
What is the mechanism of an ion ligand gated channel? Give an example
- Channel that opens or closes in response to a chemical ligand binding
- Synapse channel responding to extracellular transmitters
What is the mechanism of an ion voltage gated channel? Give an example
- Charged gates that sense depolarisation
- Channels open or close in response to membrane potential changes
- Channels involved in action potentials
What is the mechanism of an ion mechanical gated channel? Give an example
- Channel opens or closes in response to membrane deformation (stretch/shrink)
- Mechanoreceptors in hair cells/carotid sinus stretch receptors
Name 3 cell to cell synaptic connections
nerve cell > nerve cell
nerve cell > muscle cell
nerve cell > gland cell
sensory cell > nerve cell
What is fast synaptic transmission?
- Receptor protein is also an ion channel
- Transmitter binding causes the channel to open
What is an excitatory synapse?
A synapse where transmitters open ligand-gated channels that cause membrane depolarisation
What is an excitatory post-synaptic potential (EPSP)?
A change in membrane potential
What is a characteristic and a transmitter involved in excitatory synapses?
- Longer time course than an action potential
- Graded with amount of transmitter
Transmitters - Acetylcholine, Glutamate
What is the mechanism of an inhibitory synapse?
Transmitters open ligand-gated channels that cause hyperpolarisation
What ions are involved in inhibitory synapses and what is the effect?
- Permeable to K+ or Cl-
- Moves membrane away from the activity threshold
Give an example of a transmitter involved in an inhibitory synapse
- Glycine
- GABA
What is slow synaptic transmission?
The receptor and channel are separate proteins
What are the 2 mechanisms involved in slow synaptic transmission?
- Direct G-Protein gating
- Gating via an intracellular messenger
What are the steps involved in slow synaptic transmission using intracellular messengers?
Receptor > G-Protein > Enzyme > Signalling Cascade > Intracellular Messenger > Channel
Which 2 factors influence membrane potential?
- Changes in Ion concentration
- Electrogenic pumps
What is the effect of extreme ion concentration changes on membrane potential?
Can alter membrane excitability in vital organs such as the heart
Give an example of an electrogenic pump and its mechanism
- Na+/K+ ATPase
- 3 Na+ out for every 2 K+ in
- Makes membrane potential slightly more negative
What is responsible for the entire membrane potential and what does it set up?
- Active transport of ions
- Sets up and maintains the ionic gradient
