Biology Lecture Notes: Nerve Impulse
Introduction
- Topic: Nerve Impulse
- Focus: Resting Membrane Potential and Action Potential
- Importance: Action potential is essential in muscle contraction, sensory reception, gland secretion, and brain activity.
Key Concepts
Nerve Impulse
- Unidirectional flow (Orthodromic)
- Most excitable part of the neuron: Axon hillock
Resting Membrane Potential
- Polarized state: Inside is more negative than outside
- Potassium is the dominant ion inside the cell
- Sodium is the dominant ion outside the cell
- Resting potential typically around -90mV or -70mV
- Maintained by selective permeability and sodium-potassium pump
- Selective permeability: More potassium leaves the cell than sodium enters
- Sodium-potassium pump: Pumps 3 sodium out and 2 potassium in, resulting in net negative inside
Action Potential
- Activation (Depolarization): Sodium influx makes inside more positive
- Depolarization: Inside becomes more positive than outside
- Magnitude of action potential: 125mV (from -90mV to +35mV)
- Features rapid depolarization after reaching threshold stimulus
Return to Resting Potential
- Repolarization (Inactivation): Closing sodium channels, opening potassium channels, potassium efflux
- Hyperpolarization: Overshoot to -100mV, returns to -90mV via inward rectifier potassium channels
Key Players
- Depolarization Hero: Sodium (Na+) influx
- Repolarization Hero: Potassium (K+) efflux
- Resting Membrane Potential Hero: Potassium (K+) and sodium-potassium pump
Additional Concepts
All or None Law
- Action potential is either fully triggered or not at all
- Requires a threshold stimulus
Refractory Period
- Absolute and relative refractory periods prevent rapid, repetitive stimulation
Additional Resources
- Physiology playlist for in-depth knowledge
- CNS pharmacology course available on the website
- Topics include anti-epileptics, anti-depressants, etc.
Closing
- Encouragement to study, follow, and subscribe
- Website for more courses and content
- Sign-off: "Be safe, stay happy, study hard."
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