Lecture Notes on Electrical Properties and Neurology Basics
Introduction
- Start with a quote by Bertrand Russell emphasizing the paradox of knowledge giving power despite its limitations.
- Key message: The more we learn, the more we realize how little we know, promoting humility.
Focus of Lecture
- Understanding electrical properties of cells.
- Discussion on action potentials and their stages.
- Introduction to ionic channels, particularly voltage-dependent channels.
- Exploration of membrane potential and its determinants.
Key Concepts
Membrane Potential
- Measured as the difference in electrical potential between the inside and outside of a cell.
- Example: If interior is -50mV and exterior is +10mV, the membrane potential is -60mV.
Ionic Currents
- Currents are caused by the movement of positive charges (e.g., sodium, potassium ions).
- Convention: Inward currents are negative, and outward currents (e.g., potassium leaving the cell) are positive.
Ohm's Law in Biology
- Current (I) = Voltage (V) / Resistance (R).
- High resistance = low current; low resistance = high current.
Cell Membrane as Circuit
- Composed of capacitors (lipid bilayer) and resistors (channels, transporters).
- Channels regulate ion flow to maintain membrane potential.
Action Potentials
Stages
- Resting State: Membrane potential is negative.
- Depolarization: Sodium channels open, sodium ions rush in, making the inside more positive.
- Repolarization: Potassium channels open, potassium ions leave, restoring negativity.
- Late Repolarization: System resets to resting state.
Importance of Sodium and Potassium
- Sodium influx causes depolarization; potassium efflux causes repolarization.
- The inactivation of sodium channels is crucial for repolarization.
Refractory Period
- Time required for sodium channels to transition from inactivated to deactivated state.
- Determines the rate of action potential firing.
Ionic Channels and Drugs
- Sodium channels are crucial for action potentials.
- Drugs like lidocaine stabilize inactivated sodium channels, used in treating epilepsy and arrhythmias.
Cellular and Molecular Diversity
- Variability in action potentials due to different types of sodium and potassium channels.
- Channels distributed differently within various parts of a neuron (dendrites, soma, axon).
Types of Action Potentials
- Neuronal: Fast repolarization in cerebellum, slow in thalamus.
- Cardiac: Long durations, essential for heart rhythm.
- Pancreatic: Involved in insulin release, slow potentials.
Review and Summary
- Review of various channel types and their localization.
- Importance of understanding the molecular basis for drug targeting.
- Key sodium channels: Nav1.4 (skeletal muscle), Nav1.5 (heart).
Conclusion
- Encouragement to use summaries and review questions to grasp concepts better.
- Reminder of additional resources and materials available for further study.
These notes encompass the fundamental aspects of electrical properties in cells, focusing on action potentials and their implications in neurology and pharmacology.