🔑 Key Definitions
Resting Potential: Electrical charge difference across neuron membrane at rest; approximately -70 millivolts (inside negative)
Action Potential: Rapid depolarization and repolarization; brief reversal to approximately +50 millivolts
All-or-None Law: Action potentials fire completely or not at all; no partial firing
Na+/K+ Pump: Active transport mechanism that maintains ion gradients; pumps 3 Na+ out and 2 K+ in
Action Potential: Rapid depolarization and repolarization; brief reversal to approximately +50 millivolts
All-or-None Law: Action potentials fire completely or not at all; no partial firing
Na+/K+ Pump: Active transport mechanism that maintains ion gradients; pumps 3 Na+ out and 2 K+ in
📊 Action Potential Phases
- Resting State (-70mV): More Na+ outside, more K+ inside; maintained by Na+/K+ pump
- Depolarization: Na+ channels open, Na+ rushes IN, membrane becomes more positive
- Peak (+50mV): Inside becomes positive relative to outside
- Repolarization: K+ channels open, K+ rushes OUT, returns toward negative
- Hyperpolarization: Brief undershoot below -70mV; absolute refractory period
🧠 Postsynaptic Potentials
- EPSP (Excitatory): Makes membrane more positive (depolarizes); increases likelihood of action potential
- IPSP (Inhibitory): Makes membrane more negative (hyperpolarizes); decreases likelihood of action potential
- Spatial Summation: Multiple inputs from different locations combine
- Temporal Summation: Multiple inputs from same location arrive in quick succession
⚡ Key Principles
- All-or-None Law: Once threshold reached (~-55mV), action potential fires at full strength regardless of stimulus intensity
- Refractory Period: Brief time after AP when neuron cannot fire again; ensures one-way propagation
- Threshold: Critical voltage (~-55mV) that must be reached to trigger action potential
💡 Exam Tips
- Remember: Resting = -70mV, Peak = +50mV (roughly 120mV total change)
- Depolarization = Na+ IN (becoming more positive)
- Repolarization = K+ OUT (returning to negative)
- EPSP = Excitatory (increases firing), IPSP = Inhibitory (decreases firing)
- Na+/K+ pump uses ATP (active transport) - 3 Na+ out, 2 K+ in
- All-or-none: intensity coded by FREQUENCY of APs, not amplitude