Electricity and neural function: resting membrane potential, action potential, synaptic transmission Flashcards
What is membrane potential?
Difference in charge between extracellular and intracellular fluid of the cell
What are the three main ionic contributors to membrane potential?
Na+, K+, A-
What is A-?
Organic anions
Can A- cross cell membranes?
No
Sodium concentration outside cell
150
Sodium concentration inside cell
15
Potassium concentration outside cell
5
Potassium concentration inside cell
150
A- concentration outside cell
0
A- concentration inside cell
65
Equation for equilibrium potentials
E = 61log (c0/ci) 61 = RT/zF
What is C0?
Outside concentration
What is Ci?
Inside cell concentration
What is R?
Gas constant
What is z?
Valence of ion
What is F?
Electrical constant
If the membrane was impermeable to Na+ and K+, what would the potential be?
-90mV
What is the resting potential?
-70mV
What is depolarisation?
Membrane becomes positively charged - caused by influx of sodium
What is repolarisation?
Voltage changes from +40mV to negative again - caused by efflux of potassium
What is the threshold potential?
-55mV
What happens to activation gates when the threshold potential is reached?
They open, allowing extracellular particles to enter
Very quickly reverses intracellular concentration of sodium so potential is now positive
When threshold potential reached, inactivation gate activated
Sodium leaks into cell
At what potential will voltage gated potassium channels open?
+30mV
In which direction does the sodium concentration gradient point?
Outside cell
When is inactivation of voltage-gated sodium channels activated?
-55mV
When do potassium channels open?
Activated at -55mV but open at +30mV
How does GABA work?
By triggering a hyper-polarization of the post-synaptic membrane when it binds to receptors. It does this by stimulating an efflux of K+
What is an ionotropic receptor?
Membrane bound receptor that contains an ion channel
What is temporal summation?
A single action potential in the presynaptic neuron releases low levels of neurotransmitter that are not high enough to trigger an action potential in the postsynaptic neuron. However, two or more action potentials in neuron 1 in quick succession release enough neurotransmitter to trigger an action potential in neuron 2
What is spatial summation?
Release of neurotransmitter from each of the presynaptic neurons does not trigger an action potential in the postsynaptic neuron. However, when neurons simultaneously release neurotransmitter, an action potential is triggered
In what direction does the electrical gradient for potassium go?
Into the cell
In what direction does the concentration gradient for potassium go?
Out of cell
In what direction does the electrical gradient for sodium go?
Out of the cell
In what direction does the concentration gradient for sodium go?
Into cell
