11-2

LIGAND OR CHEMICAL GATE

Voltage-Gated Channel Example: Na + channel Figure 11.6b

Role of Ion Channels -Nongated Leakage channels – -Nongated pumps – –Chemically gated channels – –Voltage-gated channels –

Electrochemical Gradient chemical gradient = movement from high concentration to low concentration electrical gradient = when ions move toward an area of opposite charge

Figure 11.8 Arrows indicate movement along the electrochemical gradient K+ Na+ HIGH LOW HIGH Resting Membrane Potential

Figure 11.8 K+ Na+ HIGH LOW HIGH Resting Membrane Potential

Figure 11.7

Figure 11.8 K+ Na+ HIGH LOW HIGH Resting Membrane Potential 3Na+ 2K+ ATP -70 mV

Silverthorn; Fig RESTING MEMBRANE POTENTIAL

Voltage –gated channels during resting potential

Action Potential: Resting State Na + and K + channels are closed Each Na + channel has two voltage-regulated gates –Activation gates – closed in the resting state –Inactivation gates – open in the resting state Figure 11.12, part 1

DEPOLARIZATION

Action Potential: Depolarization Phase Na + gates ; K + gates Threshold – a critical level of depolarization At threshold, depolarization becomes self generating Figure 11.12, part 2

Action Potential travelling Figure 9.9d Na+

Figure 11.13b

REPOLARIZATION

Action Potential travelling and Repolarization chasing Figure 9.9d Na+ K

Figure 11.13c

Action Potential: Repolarization Phase Sodium inactivation gates voltage K + gates K + exits the cell and Figure 11.12, part 3

Action Potential: hyperpolarization Potassium gates CLOSE SLOWLY, This causes hyperpolarization of the membrane Figure 11.12, part 4

Phases of the Action Potential 1 – 2 – 3 – 4 – Figure 11.12

Ion redistribution by the sodium-potassium pump occurs after hyperpolarization The membrane reads -70mV again

Absolute and Relative Refractory Periods Figure 11.15