Q: What is membrane potential?
A: The electrical charge difference across a cell’s plasma membrane (inside vs outside), measured in millivolts (mV).
Q: Typical resting membrane potential of a neuron?
A: Approximately −70 mV (inside negative relative to outside).
Q: What ionic distributions primarily determine resting potential?
A: High Na⁺ and Cl⁻ outside; high K⁺ and large anionic proteins (A⁻) inside.
Q: What is the electrochemical gradient?
A: The combined effect of concentration and electrical (voltage) gradients driving ion movement.
Q: What does the Nernst equation calculate?
A: The equilibrium potential for a single ion species given concentration difference across membrane.
Q: What is the Goldman–Hodgkin–Katz (GHK) equation used for?
A: Calculating membrane potential while accounting for multiple ions and their permeabilities.
Q: What creates most of the negative resting potential?
A: K⁺ leak channels allowing K⁺ efflux plus intracellular anions and Na⁺/K⁺ pump activity.
Q: How does the Na⁺/K⁺ pump affect membrane charge?
A: It expels 3 Na⁺ and imports 2 K⁺ per ATP, contributing a small net outward positive current (helps maintain negativity inside).
Q: What are graded potentials?
A: Local, variable-amplitude voltage changes that decay with distance and time (e.g., EPSPs/IPSPs).
Q: What are action potentials?
A: All-or-none regenerative electrical impulses that propagate along axons without decrement.
Q: What is the threshold potential for AP initiation?
A: Around −55 mV (varies by neuron); when enough Na⁺ channels open to trigger regenerative depolarization.
Q: Describe the sequence of ion channel events during an action potential.
A: Depolarization opens voltage-gated Na⁺ channels → rapid Na⁺ influx (rising phase) → Na⁺ channels inactivate near +30 mV → voltage-gated K⁺ channels open → K⁺ efflux repolarizes membrane.
Q: What is the absolute refractory period?
A: Time during which no new AP can be fired because voltage-gated Na⁺ channels are inactivated.
Q: What is the relative refractory period?
A: Period after an AP when a stronger-than-normal stimulus can elicit another AP (K⁺ channels still open, membrane hyperpolarized).
Q: How does myelination speed conduction?
A: Myelin insulates axon segments, reducing capacitance and letting depolarization leap between Nodes of Ranvier (saltatory conduction).
Q: Compare conduction velocities for myelinated vs unmyelinated axons.
A: Myelinated can reach ~120 m/s; unmyelinated much slower (~0.5–30 m/s depending on diameter).
Q: What is saltatory conduction?
A: APs “jump” node to node along myelinated axons, regenerating at Nodes of Ranvier.
Q: How does axon diameter affect conduction speed?
A: Larger diameter lowers internal resistance and increases conduction velocity.
Q: What is capacitance in neuronal membranes?
A: The membrane’s ability to store charge; lower capacitance speeds voltage changes.
Q: What are EPSPs and IPSPs?
A: EPSP = excitatory postsynaptic potential (depolarizing); IPSP = inhibitory postsynaptic potential (hyperpolarizing).
Q: Which ions commonly mediate EPSPs and IPSPs?
A: EPSPs often via Na⁺ influx; IPSPs via Cl⁻ influx or K⁺ efflux.
Q: What is temporal summation?
A: Rapid succession of inputs from one synapse summating to influence membrane potential.
Q: What is spatial summation?
A: Simultaneous inputs from multiple synapses at different locations summating.
Q: Where is the “decision” point for generating an AP?
A: Axon initial segment (AIS) — integrates summed inputs and has high density of voltage-gated channels.
