Session 4 Flashcards
What is a membrane potential
electrical charge that exists across a membrane
Animal cells negative membrane potential range
-20 to -90 mv
Cardiac and skeletal muscle cells resting potentials
-80 to -90
Nerve cells resting potentials
-50 to -75
How do you measure membrane potential
Microelectrode can penetrate cell membrane
Smooth muscle myocytes resting membrane potential
-50
Skeletal muscle myocytes resting membrane potential
-90
Neurones resting membrane potential -
-70
Cardiac myocytes resting membrane potential
-80
How does selective permeability arise
Phospholipid bilayer
Ion channels -Channel properties
Explain selective permeability of lipid bilayer
Hydrophobic interior, permeable to small uncharged molecules
What are ion channels
Proteins that enable ions to cross cell membranes, have an aqueous pore through which ions flow by diffusion
How do you set up the membrane resting potential
Open K+ channels dominate, equal and opposite so no net movement of K+ hence negative membrane potential
Membrane is selectively permeable to K+
What is equilibrium potential
Membrane potential at which something will be in equilibrium
Nernst equation
61 log10 concentration outside/inside
Characteristic of cells with lower resting potential
Lower selectivity for K+ due to increased contribution from other channels
Cardiac muscle and nerve cell characteristics
Resting potential close to Ek
Depolarization
Decrease in the size of the membrane potential, cell interior becomes less negative
Hyperpolarization
Increase in the size of the membrane potential, cell interior becomes more negative
What causes hyperpolarization
opening K+ or Cl- channels
What causes depolarization
Opening of Na+ or Ca+ channels
Changes in membrane potential are caused by
Changes in activity of ion channels
Example of a less selective channel
Neuromuscular junction, nicotinic acetylcholine receptors can be activated by ACh or nicotine
Nicotinic Acetylcholine Receptors mechanism
Intrinsic ion channel
Open by binding of acetylcholine
Let’s Na+ and K+ through
Membrane potential towards 0mv (intermediate between ENa and EK)
3 types of gating
Ligand gating, Voltage gating, Mechanical gating (membrane deformation e.g. mechanoreceptors)
Fast synaptic transmission
Receptor protein also ion channel
What do excitatory transmitters do
Open ligand gated channels that cause membrane depolarisation (Na+ and Ca2+)
E.g. acetylcholine, glutamate (longer time course than AP)
What do inhibitory transmitters do
Open ligand gated channels that cause hyperpolarisation (K+ and Cl-)
E.g. glycine, GABA
Features of slow synaptic transmission
Receptor and Channel are separate proteins
Direct G protein gating, or gating via an intracellular messenger
Other factors that influence membrane potential
Changes in ion concentration, Electrogenic pumps,
