Action Potentials Flashcards
(25 cards)
What are the 3 electrical properties of excitable cells?
Resistance; current and voltage
Why do all cell have membrane potential
Have varying concentration of ions in cells and are selectively permeable to some of them hence some ions move out of membrane and some cannot and vice versa.
What happens when a state of electrochemical equilibrium is reached?
When electrical repulsion forces equals chemical attraction forces(due to diffusion).
What is equilibrium potential?
Potential when electrochemical equilibrium is reached
In the Nernst Equation, what is the value of RT/F
And z
-61
Z= charge of ion
In the Nernst equation what is represented by concentration on the numerator of log
Intracellular concentration
What are the extracellular and intracellular concentration of sodium ions
Extra- 150mM
Intra- 10mM
What are the extracellular and intracellular concentration of potassium ions
Extra- 5mM
Intra- 150mM
Na- 72mV; K= -90mV; why doesn’t the membrane potential rest at either values?
The cells have varying amount of sodium and potassium channels that are open; more potassium channels that are open than odium
What does the Goldman-Hodgkin-Katz equation describe
Membrane potential of cells taking account of channels that are open and closed
In the GHK equation, what are the conditions for which normal resting potential is reached?
K channels- always open
Cl- channels- always closed
Na+ channels - open 5% of the time
What are the 4 different types of changes in membrane potential?
Depolarisation- potential moves towards zero
Repolarisaiton- more negative towards resting potential
Overshoot- above zero
Hyperpolarisation - more negative below resting potential
What causes graded potentials?
Caused by stimulation-
Occurs in synapses and sensory receptors
Contribute to initiating/ preventing action potentials
Why is there a decremental spread in action potential down the axon
Charge leaks out
Leakage depends on size of axon and stimulus
What determines the permeability of ion channels in an action potential
Permeability depends on conformational state Depolarisation - opened Sustained depolarisation - inactivated Hyperpolarisation- closed Repolarisation?
Apart form neurones and muscle cells where else can action potential be generated
In some endocrine tissue
Compare the permeability of both VG channels during upstroke
VGNa+ open quickly
VGK+- open slowly
Describe what happens during repolarisation
VGNa+ - closed-
More VGK+ open quickly
What else happens at the start of Repolarisation
Absolute refractory period
Activation gate open
Inactivation plug (gate)- closed
What happens at the end of repolarisation
Absolute refractory period continue
Activation and inactivation gate closed
What happens after hype-polarisation
Relative refractory period
Activation gate closed
Inactivation plug open; strong stimulus can trigger action potential.
What restores resting potential after AP; compare speed
NORMAL (NOT VG)ion channels (fast)
Ions pumps - slow
What occurs during passive propagation of action potential
ONLY resting K+ channels are open.
Resistance alters propagation distance.
Where are VG channels located in myelinated axons
At Nodes of Ranvier
