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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+
HIGHLOW
LOW
HIGH
Resting Membrane Potential
Figure 11.8
K+
Na+
HIGHLOW
LOW
HIGH
Resting Membrane Potential
Figure 11.7
Figure 11.8
K+
Na+
HIGH
LOW
LOW
HIGH
Resting Membrane Potential
3Na+
2K+
ATP
-70 mV
Silverthorn; Fig. 5-37
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+ Na+ Na+ Na+ Na+ Na+
Figure 11.13b
REPOLARIZATION
+ + + + +
- - - - -
Action Potential travelling and Repolarization chasing
Figure 9.9d
Na+ Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+ 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
