Lecture 6 - Membrane Potentials Flashcards
Which of the following can cross the cell membrane via simple diffusion?
- steroids
- Na+
- glucose
- proteins
steroids
describe active transport
The direct expenditure of energy (via hydrolysis of ATP) to pump Ca2+ out of the cell against its concentration gradient
Na⁺ in found in high concentration outside the cell ([Na⁺]ₒ) while K⁺ is found in high concentration inside the cell ([K⁺]ᵢ). Which of the following explains the uneven distribution of these ions across the cellular membrane?
The presence of Na+/K+ ATPase in the cellular membrane
Active transport of Na+ and K+ against their individual concentration gradients
Which are the two most prominent anions inside the cell?
proteins and phosphate (HPO4-)
what does not explain why the presence of K+ leak channels in the cell membrane leads to a negative membrane potential?
the K+ leak channel allows bidirectional flow of K+ ions
summary of RMP
The action potential is divided into three phases. Initially the membrane potential will explosively rise to above 0mV (often between +20 and +40mV). This phase of the action potential is called the depolarization phase. Once the action potential peaks, the repolarization phase begins, as the membrane potential falls back towards the resting membrane potential. However, during the action potential, the membrane potential will typically overshoot the resting membrane potential and enter the third phase of the action potential called the hyperpolarization phase – where the membrane potential is more negative than the resting membrane potential. The hyperpolarization phase of the action potential is due to the excess efflux of K+ from the cell.
Why does increasing permeability to K+ hyperpolarize the membrane?
The reversal potential and equilibrium potential are the same concept. The reversal potential is the sum of the impact of the concentration gradient and the electrical charge difference across the membrane
The reverse potential is potassium (Ek) is at a more negative potential then RMP
summary of Nernst Equation
The equilibrium potential is also known as the reversal or Nernst potential. Each ion has two sources of energy that will drive its movement these are the concentration gradient and the electrical potential across the cell membrane. The equilibrium potential can be used to predict the direction of movement of each ion. The Ek is typically more negative than the RMP. This means that if the conductance across the membrane for K+ increases, K+ will leave the cells and the membrane will hyperpolarize. Similarly, since the Ena is typically more positive than the RMP, increasing conductance for Na+ will result in Na+ entering the cell, depolarizing the membrane.
at RMP, which cation has thye greater driving force?
Na+
Consider a scenario in which a ligand-gated monovalent cation channel is opened. Which ions is this channel permeable to?
K+ and Na+
does the ion with the greater DF move the fastest?
Yes
Since Na+ is moving into the cell more rapidly than K+ is exiting, Vm (membrane potential) will:
depolarize
The nicotinic acetylcholine (nACh) receptor is an ionotropic receptor. This mean when a ligand binds to the receptor it opens an ion channel. The nACh is a monovalent cation channel. Typically, the nACh depolarizes the membrane when activated. This is because:
the DF on Na+ is higher than for K+
the RMP is further away from Ena than from Ek
Which best explains why the reversal potential for Cl⁻ (ECl) is close to resting membrane potential but significantly positive to the reversal potential for K+ (EK)
The presence of the Na/K ATPase pump but the absence of a Cl⁻ pump.
Which best explains why increasing membrane permeability to K⁺ hyperpolarizes the membrane?
The reversal potential of potassium (EK) is at a more negative potential than RMP.
