Session 4 Flashcards
(36 cards)
What is a resting membrane potential?
The electrical charge that exists across a membrane (mV, always expressed relative to the outside)
What is a microelectrode + what is it used for?
- thin glass pipettes, 1 micrometer in diameter
- measures membrane potential
- conducting solution of KCl
What contributes to the selective permeability of a membrane to an ion?
- Phospholipid bilayer (no ions through)
- Ion channels
- Channel protein - gating, selectivity, etc
What are the extracellular ionic concentrations?
Cl- = 123 mM Na+ = 145 mM K+ = 4.5 mM A- (anions) = 40 mM Ca2+ = < 0.0001 mM
What are the resting potentials of the main/relevant cells?
Cardiac myocytes = -80 mV
Skeletal myocytes = -90 mV
Smooth muscle myocytes = -50 mV
Neurones = -70 mV
How is the resting membrane potential set up?
Voltage-insensitive K+ channels are always open - they allow K+ ions to leave the cell down their concentration gradient and leave the negatively charged anions behind
How is the equilibrium created?
An electrical gradient is created after K+ ions leave the cell = will then re-enter the cell until an equilibrium is reached
How to calculate the equilibrium potential for a certain ion?
Nernst equation (Valency = according to charge, eg. Cl- = -1, Ca2+ = +2)
What happens when cations leak into the cell? (Na+ and Ca2+)
Membrane potential becomes more positive by depolarisation - will move away from EK+
What happens when anions (Cl-) leak into the cell?
- Cell becomes polarised
- Membrane potential moved closer to EK+
What does it mean when the cell has a lower membrane potential?
Lower selectivity for K+, more contribution from the leakage of other ions
What is depolarisation?
The interior of the cell becomes less negative/more positive compared to the resting value
What is hyperpolarisation?
Cell interior becomes more negative compared to normal value, membranes open for more than 1 ion
Why is there a need for changing membrane potentials?
- action potential generation
- controlling muscle contraction
- hormone/neurotransmitter secretion
- transduction
- postsynaptic action
What happens when a membrane is more selectively permeable to a particular ion?
The membrane potential will move closer towards the equilibrium potential for that ion
What ions cause hyperpolarisation?
K+ = -95 mV Cl- = -96 mV
What ions cause depolarisation?
Ca2+ = +122 mV Na+ = +70 mV
How do nicotinic acetylcholine receptors work?
They are LESS SELECTIVE
- ACh binds to the receptor in the neuromuscular junction
- let in predominantly K+ and Na+
- have 5 subunits
- 2 alpha subunits bind acetylcholine
What is ligand gating?
Channels open/close due to binding of a chemical ligand
What do ligand gated channels respond to?
- intracellular transmitters
- extracellular messengers
How do voltage gated ion channels work?
Open/close due to a change in the membrane potential (eg. When initiating an action potential)
What is mechanical gating?
Open/close due to membrane deformation (eg. Mechanoreceptors in carotid sinus)
What is synaptic transmission?
- pre-made neurotransmitter released in vesicles from the presynaptic cell
- binds to the receptors on the postsynaptic membrane
What is fast synaptic transmission?
The receptor serves as an ion channel as well, so binding of neurotransmitter to receptor will cause channel opening
