Definition: Separation of charges across the plasma membrane.
Charge Distribution: More negative charge inside the cell than outside.
Contributing Ions: Chloride, sodium, potassium, and proteins.
Neurons: Unlike other cells, neurons can rapidly change their resting membrane potential in response to stimuli.
Voltage and Potential
Voltage: Measure of potential energy due to separated charges.
Resting Membrane Voltage: Potential difference across the membrane when the neuron is not transmitting signals.
Factors:
Greater charge difference leads to higher voltage.
Current and Resistance
Current: Flow of electrical charge (ions) between two points.
Resistance: Hindrance to charge flow (e.g., myelin sheath as insulator).
Ohm’s Law: Current (I) = Voltage (V) / Resistance (R)
Current is directly proportional to voltage and inversely proportional to resistance.
Membrane Ion Channels
Role: Establish and change resting membrane potential.
Types of Channels:
Leaking Channels: Always open.
Gated Channels: Open and close in response to signals (chemical, voltage, or mechanical).
Examples:
Chemically Gated: Open in response to neurotransmitters.
Voltage-Gated: Open in response to voltage changes.
Mechanically Gated: Open in response to physical deformation.
Ion Movement and Electrochemical Gradients
Electrochemical Gradient: Combination of electrical and chemical gradients.
Ion Flow and Voltage: Ion flow creates current and voltage changes across membranes.
Measurement: Voltage measured using a voltmeter.
Resting Membrane Potential (RMP)
Typical RMP: -70 millivolts.
Factors Influencing RMP:
Ionic composition differences between intracellular fluid (ICF) and extracellular fluid (ECF).
Plasma membrane permeability.
Key Ions:
Potassium (K+): Primary role due to its permeability.
Sodium (Na+): Balanced by chloride ions outside.
Sodium-Potassium Pump: Maintains concentration gradients by active transport.
Dynamic Changes in Membrane Potential
Graded Potentials: Short-distance signals that decrease over time and distance.
Action Potentials: Long-distance signals that maintain size.
Depolarization vs Hyperpolarization:
Depolarization: Voltage becomes less negative, increasing action potential likelihood.
Hyperpolarization: Voltage becomes more negative, decreasing action potential likelihood.
Summary: Resting membrane potential driven by ion concentration and permeability, with sodium and potassium leakage channels playing significant roles.