🧠Neurophysiology
Neurons are electrically excitable cells that process and transmit information through action potentials and synaptic transmission. Understanding the biophysics of neural signaling is fundamental to neuroscience and medicine.
⚡ Electrical Signaling in Neurons
Resting State
- • Vm ≈ -70 mV
- • K⁺ leak channels open
- • Na⁺/K⁺-ATPase active
- • High K⁺ inside, Na⁺ outside
Action Potential
- • All-or-none response
- • Threshold ≈ -55 mV
- • Peak ≈ +30 mV
- • Duration ≈ 1-2 ms
Synaptic Transmission
- • Chemical or electrical
- • Ca²⁺-dependent release
- • EPSPs and IPSPs
- • Synaptic plasticity
📈Phases of the Action Potential
1. Resting
-70 mV
K⁺ leak open
2. Depolarization
→ +30 mV
Na⁺ channels open
3. Peak
+30 mV
Na⁺ inactivating
4. Repolarization
→ -70 mV
K⁺ channels open
5. Hyperpolarization
-90 mV
K⁺ still open
⚡Hodgkin-Huxley Action Potential Simulator
Equivalent Circuit
Vm:-70.0 mV
Time:0.0 ms
m (Na act):0.05
h (Na inact):0.60
n (K act):0.32
Nobel Prize (1963): Hodgkin and Huxley received the Nobel Prize for this mathematical model that explains the ionic mechanisms of action potentials.
🔗Synaptic Transmission Simulator
Transmission Steps:
1. Action potential arrives
2. Voltage-gated Ca²⁺ channels open
3. Vesicle fusion & NT release
4. NT binds postsynaptic receptors
5. EPSP (depolarization)
Glutamate: Opens AMPA/NMDA receptors → Na⁺/Ca²⁺ influx → depolarization
💊Major Neurotransmitters
| Neurotransmitter | Type | Receptors | Functions |
|---|---|---|---|
| Glutamate | Amino acid | AMPA, NMDA, mGluR | Main excitatory NT, learning/memory |
| GABA | Amino acid | GABAA, GABAB | Main inhibitory NT, anxiety regulation |
| Acetylcholine | Ester | nAChR, mAChR | NMJ, autonomic, cognition |
| Dopamine | Catecholamine | D1-D5 | Reward, motor control, motivation |
| Norepinephrine | Catecholamine | α, β adrenergic | Arousal, attention, fight-or-flight |
| Serotonin (5-HT) | Indolamine | 5-HT1-7 | Mood, sleep, appetite |