PL6 BASIC OF BIOELECTRICITY Flashcards
(14 cards)
What is excitability, and what are excitable tissues?
• Excitability: The ability of cells to respond to a stimulus.
• Excitable Tissues: Nerve and muscle tissues that generate electrical responses by altering their membrane potential.
What is a stimulus, and how does it relate to excitability?
• A stimulus is any change (electrical, chemical, or mechanical) in the cell’s environment. It triggers ionic movements like:
• Influx: Movement of ions into the cell.
• Efflux: Movement of ions out of the cell.
What is the resting membrane potential (RMP)?
RMP is the electrical difference across the cell membrane at rest, with the inside being negative relative to the outside (-70 mV).
What factors contribute to the genesis of RMP?
• Na⁺-K⁺ ATPase pump: Pumps 3 Na⁺ out and 2 K⁺ in, creating a negative internal environment.
• K⁺ Efflux: Dominates over Na⁺ influx due to K⁺’s higher permeability.
• Non-diffusible anions (e.g., proteins, phosphates): Keep the inside more negative.
• Cl⁻ Movement: Opposed by electrical gradients, limiting influx.
• Direct Electrogenic Effect: The Na⁺-K⁺ pump loses one positive charge per cycle.
What is the role of ions in RMP?
• K⁺ Efflux: Drives the negative potential.
• Na⁺ Influx: Limited but counteracts some negativity.
• Cl⁻: Maintains stability between concentration and electrical gradients.
What happens during depolarization, repolarization, and hyperpolarization?
• Depolarization: Membrane potential becomes less negative (e.g., from -70 mV to -60 mV).
• Repolarization: Returns to RMP after depolarization.
• Hyperpolarization: Membrane potential becomes more negative (e.g., -70 mV to -80 mV).
What triggers an action potential, and what are its characteristics?
• Triggered when depolarization reaches a threshold (-55 mV).
• Characteristics:
• Obeys the all-or-none law.
• Monophasic (primarily in one direction).
What are the phases of action potential?
- Depolarization Phase:
• Rapid Na⁺ influx occurs through voltage-gated Na⁺ channels.
• Hodgkin’s positive feedback amplifies depolarization.- Repolarization Phase:
• Na⁺ channels inactivate, and voltage-gated K⁺ channels open, allowing K⁺ efflux. - After-depolarization Phase:
• Slower repolarization as K⁺ efflux decreases. - After-hyperpolarization Phase:
• Delayed K⁺ channel closure causes a slight overshoot in hyperpolarization.
- Repolarization Phase:
What are refractory periods, and how do they affect excitability?
• Absolute Refractory Period: No response to any stimulus.
• Relative Refractory Period: Requires a stronger stimulus for a response.
• Supernormal Period: Increased excitability.
• Subnormal Period: Reduced excitability.
How does excitability change during electrical responses?
• Depolarization: Increased excitability.
• Repolarization: Decreased excitability (absolute and relative refractory periods).
• Hyperpolarization: Reduced excitability (subnormal period).
What role do ion channels play on the cell membrane?
Ion channels regulate the selective movement of ions (Na⁺, K⁺, Cl⁻) to generate and maintain membrane potentials.
How do stimuli differ in their effects on cells?
• Subthreshold Stimulus: Produces local, non-propagated potentials (e.g., receptor or endplate potentials).
• Threshold Stimulus: Generates propagated action potentials in excitable tissues.
What is the importance of the Na⁺-K⁺ pump in bioelectricity?
• Maintains ionic gradients essential for RMP and AP generation.
• Directly contributes to the slight negativity of RMP by losing one positive charge per cycle.
Why is K⁺ movement more significant than Na⁺ in RMP?
The membrane is much more permeable to K⁺, leading to greater K⁺ efflux compared to Na⁺ influx.
