| Define equilibrium potential | Equilibrium potential occurs when: The chemical and electrical gradients for an ion are equal in magnitude, the ion is in electrochemical Equilibrium, and the net movement of this ion species across the membrane is zero. |
| State the equilibrium potential of Na+ and K+ | At resting membrane potential K+, Na+ and Ca2+ ions are not at equilibrium |
| Explain the significance of the Nernst Equation | The Nernst Equation states that at equilibrium the chemical gradient and the electrical gradient of an ion species are equal in magnitude and opposite in direction |
| Explain the action potential as a sequence of changes in driving force and permeability | Permeability is a measure of how easily an ion can cross the membrane. It depends on the number of open channels and the number of ions passing through each channel. |
| Explain the significance of the Goldman Hodgkin Katz (GHK) equation | When more than one ion channel is present in the membrane, the membrane potential can be calculated using the Goldman-Hodgkin-Katz equation (GHK equation): |
| Describe negative and positive feedback loops in action potential | Positive feedback loop: membrane depolarisation opens more Na+ channels and accelerates further depolarisation (Ensures fast excitation) Negative feedback loop: membrane depolarisation opens more K+ channels which slows down depolarisation and promotes membrane repolarisation (Ensures recovery from excitation) |
| Describe the all-or-nothing law of action potentials | V threshold – membrane potential that opens voltage gated Na+ channels Hyperpolarising and subthreshold depolarising stimuli cause graded changes in membrane potential Depolarising stimuli of any amplitude above the threshold cause identical action potentials |
| State the effects of Tetrodotoxin (TTX) blockers on the amplitude and duration of the action potential | TTX is a poison produced by symbiotic bacteria that blocks the pore of the voltage-gated Na+ channels It is found in species such as blue ringed octopus and puffer fish. |
| State the effects of Tetraethylammonium (TEA) blockers on the amplitude and duration of the action potential | TEA is a blocker of voltage gated KV channels |
| State the effects of Tetraethylammonium blockers on the amplitude and duration of the action potential | KV channels blockers increase the duration of action potentials With all KV channels blocked, only Na V channels inactivation allows the downstroke of AP. No hyperpolarization (undershoot) occurs. |
| State the effects of local anesthetics (LA) on the amplitude and duration of the action potential | Local anaesthetics cross the lipid bilayer in an uncharged form and bind to the intracellular part of the Na V channels in the inactivated state LA creates an absence of pain sensation in a specific location of the body |
