Lt5 Membrane Potentials Review +MCQs PDF

Physiology School of Medicine Founded in 1845 Course: MD137 2024-2025 Introduction to Physiology Lecturer: Lecture 4:...

Physiology School of Medicine Founded in 1845 Course: MD137 2024-2025 Introduction to Physiology Lecturer: Lecture 4: Dr. Leo Quinlan Membrane potentials review [email protected] RMP review 2 Sodium (Na+) and potassium (K+) play a dominant role in RMP. Various negatively charged intracellular proteins and organic phosphates that cannot cross the cell membrane are also contributory. To understand how the resting membrane potential is generated and why its value is negative, it is crucial to understand equilibrium potentials, permeability, and ion pumps. How and why ion move ? Gradients ! 3 Two important concepts central for the understanding of ion movement: 1. The difference in [gradient] across the membrane drives the direction of movement of the ions. The gradient is maintained by the use of energy, either primary or secondary active transport, and creates a force for movement of that ion across the membrane. 2. There is an ion channel (leak channel) that allows for the ions to pass through the membrane. Ions move down the concentration gradient from high to low, in this case for K+ from the inside (intracellular region) to the outside (extracellular region). Note: permeability is the capability of ions to ow across the membrane. Conductance measures the movement of charge across the membrane. How and why ion move ? Charge ! 4 Positive and negative ions tend to pair up in an ionic solution, as opposites attract !!! 1. The movement of only a cation from the inside of the cell to the outside of the cell leaves behind a negative anion, and thus the inside of the cell becomes more negative, while the outside of the cell becomes more positive. This generates an electrostatic gradient that builds up over time. 2. Eventually the negative charges inside the cell start to exert a force to keep the positively charged K+ ions inside the cell, a force that opposes the movement of the ions down the concentration gradient. When this negative electrostatic charge is opposite the force of the concentration gradient, there is no movement of the ions. This is called the equilibrium potential for that ion, which is calculated by the Nernst equation. Equilibrium potential 5 Equilibrium potential is calculated using the Nernst equation: Vm = RT/zF * ln([ion outside the cell]/[ion inside of the cell]). Vm= membrane equilibrium potential R = gas constant = 8.314472 J · K-1 T = temperature (Kelvin) F = Faraday's constant = 9.65 x 10^4 C mol-1 Z = 1 for a monovalent ion such as K+ (=2 for a divalent Ca2+). Equilibrium potential 6 The equation can be simpli ed: RT/F can be simpli ed to 61.5 at normal body temperature (37oC). RT/F can be simpli ed to 58 at room temp temperature (18oC). fi fi fi RMP in different cells and its different roles 7 What kind of neurons carry signals exclusively towards the brain? 8 A. Interneurons B. Motor neurons C. Sensory neurons D. Multipolar neurons E. All neurons The part of the neuron that sends electrical signals over large distances is the 9 A. Soma B. Axon C. Dendrites D. Microtubules E. synapse Which neuroglia are responsible for forming the myelin sheath around axons in the peripheral nervous system? 10 A. Microglia B. Astrocytes C. Schwann cells D. Oligodendrocytes E. Ependymal cells Ionic gradients across membranes are maintained by: 11 A. Leak channels B. Proton pumps C. Voltage gated ion channels D. Sodium exchangers E. Sodium/potassium pumps The Nernst potential for potassium is 12 A. Positive in reasting neurons B. The potential at which potassium leaves the cell C. The threshold for opening voltage gated K+ channels D. Is the equlibrium potential for a K+ gradient E. Concentration dependent effect of K+ on RMP The entry of chloride ions into resting neuron 13 A. Triggers an action potential B. Is not possible as neurons do not have chloride channels C. Will cause a depolaralisation D. Will cause a hyperpolarisation E. Is not possible as chloride can only leave cells due to concentration gradient effects Which of the following values is unnecessary when finding the equilibrium potential of an ion using the Nernst equation? 14 A. The temperature B. The ratio of external and internal ion concentrations C. The charge of the ion D. The permeability of the ion channel E. Faradays constant What is the primary ion responsible for the depolarization phase of an action potential? 15 A. Calcium (Ca²⁺) B. Sodium (Na⁺) C. Potassium (K⁺) D. Chloride (Cl⁻) E. Magnesium (Mg2+) During the repolarization phase of an action potential, which ion moves out of the neuron? 16 A. Calcium (Ca²⁺) B. Sodium (Na⁺) C. Potassium (K⁺) D. Chloride (Cl⁻) E. Magnesium (Mg2+) What is the typical threshold potential that must be reached for an action potential to be initiated? 17 A. -90 mV B. -70 mV C. -55 mV D. 0 mV E. -40 mV Which of the following statements about action potentials is true? 18 A. Action potentials can vary in amplitude depending on the strength of the stimulus. B. Action potentials can travel in both directions along an axon. C. Action potentials are initiated by the in ux of potassium ions. D. Action potentials are all-or-nothing events. E. Action potentials occur only in the dendrites of neurons. Which of the following best describes the role of voltage- gated sodium channels during the action potential? 19 A. They open in response to hyperpolarization and allow sodium ions to exit the cell. B. They open in response to depolarization and allow sodium ions to enter the cell. C. They close during the depolarization phase to prevent sodium ion entry. D. They are responsible for the repolarization phase by allowing sodium ions to exit the cell. E. They are in an inactive state at resting membrane potential What is the primary reason for the refractory period following an action potential? 20 A. To allow the neuron to return to its resting membrane potential. B. To prevent the backward propagation of the action potential. C. To ensure that the action potential travels at a constant speed. D. To allow the neuron to recover from ion depletion. E. to facilitate potasium exit Which of the following factors does NOT affect the conduction velocity of an action potential along an axon? 21 A. Axon diameter B. Myelination C. Temperature D. Length of the axon E. Ion channel density During the after potential or hyperpolarization phase of an action potential, which of the following occurs? 22 A. Voltage-gated sodium channels are fully open. B. The membrane potential becomes more positive than the resting potential. C. Voltage-gated potassium channels remain open longer than necessary. D. The sodium-potassium pump is inactive. E. Chloride ions enter the cell to restore the resting potential.