downward curve, since Na+ currents are inward, whereas the relationship for K+ would be upward. c) The graph for Na+ conductance would rise rapidly and fall rapidly, reflecting fast activation and inactivation of Na+ channels, whereas the graph for K+ would rise more slowly to a maintained plateau. d) Would, respectively, show that the Na+ and K+ conductances were zero at the Na+ and K+ equilibrium potentials. e) Both follow Ohm's law (in other words, the conductance to both Na+ and K+ would increase linearly with voltage)

Action potentials 1. Membrane is depolarized past threshold 2. Voltage gated Na+ channels open, Na+ rushes in – Positive feedback – Membrane potential very positive 1. Voltage gated Na+ channels inactivate 2. Voltage gated K+ channels open in response to original stimulus, K+ rushes out – Negative feedback – hyperpolarization 1. Voltage gated K+ channels close slowly 2. Na+/K+ pumps actively transport Na+ out of the cell and K+ into the cell 7. Voltage gated Na+ channels close

When your brain is deprived of oxygen, mitochondria in neurons stop producing ATP. What effect would this have on action potentials?

True or False? Action potentials are considered to be “all-or-none” events. a) True b) False

True or False? Action potentials are considered to be “all-or-none” events. a) True • This means that once there’s a strong enough stimulus above threshold, an action potential is initiated. If the stimulus isn’t strong enough and doesn’t reach above threshold, you have no AP.

Propagation of Action Potentials • Na+ channels open in response to a depolarizing stimulus (generates an AP) • Some depolarizing current passively flows down the axon • Local depolarization causes neighboring Na+ channels to open (generates AP) • Refractory period ensures transmission in one direction • Nodes of Ranvier + myelin sheath = saltatory conduction

PART 2 Lectures 4-6

Patch Clamp • Capable of measuring currents flowing through single channels (microscopic currents) • Main findings – voltage sensitive Na+ and K+ channels are responsible for the macroscopic conductances and currents that underlie the action potential

Which of the following statements is NOT a correct description of the voltage clamp as used by Hodgkin and Huxley to study the action potential in the squid giant axon? • A. The voltage clamp involves threading two fine wires inside a squid axon. • B. The voltage clamp allows measurement of the ionic currents that flow across the axon membrane in response to changes in membrane potential • C. The voltage clamp amplifier compares the actual voltage across the axon membrane with a command voltage set by the experimenter. • D. The voltage clamp records currents through single sodium channels. • E. The voltage clamp injects an electrical current back into the axon which is equal and opposite to the current flowing across the axon membrane.

Which of the following statements is NOT a correct description of the voltage clamp as used by Hodgkin and Huxley to study the action potential in the squid giant axon?