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Membrane & Resting Memberane Potential of Nerves

🧠 Explore Neuron Physiology, Membrane Potentials, Action Potentials, and Nerve Conduction with Dr Faiza 🧠 Develop a strong understanding of how neurons generate, conduct, and regulate electrical signals. This comprehensive lecture connects membrane physiology with nerve structure, glial function, graded potentials, action potentials, conduction, nerve injury, and important clinical correlations. It is designed to strengthen core concepts for undergraduate and postgraduate medical students and support preparation for professional and licensing examinations including USMLE, PLAB, FCPS, NEET PG, and similar exams worldwide. 🎓 Speaker 🎓 Dr Faiza is a physiology educator with qualifications including MBBS as Best Graduate from Allama Iqbal Medical College, FCPS Physiology, MHPE from Riphah International University Islamabad, ICMT, CHPE, DHPE from STMU, MPH from Government College University Faisalabad, and MBA from Virtual University of Pakistan. Her academic expertise includes medical physiology, neurophysiology, and health professions education. 🎯 Learning Objectives 🎯 Explain the physiological basis of membrane potential. Describe diffusion potentials of sodium and potassium. Define Nernst potential and apply the Nernst equation. Explain the effects of changes in Na+, K+, Ca2+, and Cl− concentrations on equilibrium potentials. Describe the normal distribution of major ions across the cell membrane. Explain the physiological basis and role of the Goldman equation. Describe the generation and maintenance of the resting membrane potential. Describe the physiological anatomy and functional zones of neurons. Explain axonal transport and myelination in the CNS and PNS. Classify neurons and peripheral nerve fibers. Describe the functions of major neuroglial cells. Explain the physiological basis and properties of graded potentials and action potentials. Describe the ionic basis and phases of the action potential. Explain absolute and relative refractory periods. Compare graded potentials with action potentials. Explain impulse conduction in myelinated and unmyelinated nerve fibers. Describe the significance of saltatory conduction. Explain the effects of hyperkalemia, hypokalemia, and hypocalcemia on neuronal excitability. Explain the mechanism of action of local anesthetics. Describe nerve injury, Wallerian degeneration, and peripheral nerve regeneration. Discuss the physiological basis of multiple sclerosis and Guillain–Barré syndrome. 🔬 Topics Covered 🔬 Membrane potential and diffusion potential Potassium and sodium equilibrium potentials Nernst potential and Nernst equation Goldman equation Electrochemical driving force Measurement of membrane potentials Voltage clamp method Resting membrane potential Electrical dipole layer Na+/K+ ATPase pump Potassium leak channels Contribution of Na+ and K+ to resting membrane potential Structure and functional zones of the neuron Soma, dendrites, axon, axon hillock

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Physiology of Neuron, Nerve, Glia, Membrane Potentials and Action Potentials Dr Faiza MBBS (Best Graduate, AIMC Lahore) FCPS Physiology, MHPE (Riphah Int University, Islamabad) ICMT, CHPE, DHPE (STMU) MPH (GC University, Faisalabad) MBA (Virtual University of Pakistan)
Membrane Potentials
3 Learning Objectives • Explain the Physiological basis of membrane potential. • Explain diffusion potentials of Na & K Potentials. • Define Nernst potential. • Explain Physiological Basis of Nernst potential. • Write the Nernst equation. • Calculate Nernst potential for Na & K. • Explain the effects of altering the concentration of Na+, K+, Ca on the equilibrium potential for that ion. • Describe the normal distribution of Na+, K+, Ca and Cl- across the cell membrane. • Explain physiological basis of Goldman equation. • Clarify the role of Goldman equation in generation of Resting Membrane Potential (RMP).
Introduction to Membrane Potentials • Potential across the cell membrane due to the differential distribution of ions across it • Electrical potentials exist across almost all cell membranes
Diffusion Potential Potential difference generated across a membrane because of a concentration difference of an ion
Diffusion Potential • Potential difference generated across a membrane because of a concentration difference of an ion • Size of the diffusion potential • Depends on the size of the concentration gradient. • Sign of the diffusion potential • Depends on whether the diffusing ion is positively or negatively charged.
Potassium Diffusion Potential • High potassium concentration inside the nerve fiber • Membrane is selectively permeable only to potassium • Potassium ions diffuse outward down concentration gradient • Outward movement carries positive charges to the exterior • Non-diffusible anions remain, creating internal negativity • Diffusion blocked when potential opposes concentration gradient • Mammalian potential -94 mV (negative inside)
Sodium Diffusion Potential • High sodium concentration outside the nerve fiber • Membrane is selectively permeable only to sodium • Sodium ions diffuse inward carrying positive charges • Creates electropositivity inside and electronegativity outside • Diffusion blocked when potential opposes concentration gradient • Mammalian potential +61 mV (positive inside)
Nernst Potential • The diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane
The Nernst Equation • Calculates Nernst potential for selectively permeable membrane • "z" represents the electrical charge of the ion (e.g., +1 for K+) • Resulting sign is negative for positive ions diffusing outward
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The Goldman Equation • Calculates potential when membrane is permeable to multiple ions
The Goldman Equation • Factors • Ion polarity • Membrane permeability (P) • Concentration difference (C) • Involves three key ions • sodium, potassium, and chloride • Ion importance is proportional to its specific membrane permeability
Electrochemical Driving Force • Difference between membrane potential (Vm) and equilibrium potential (Veq) Vdf = Vm - Veq • Positive Vdf for cations predicts movement out of the cell • Negative Vdf for cations predicts movement into the cell
Electrochemical Driving Force • Difference between membrane potential (Vm) and equilibrium potential (Veq) Vdf = Vm - Veq • Direction of diffusion may alter when Vm changes • Veq is also referred to as the reversal potential
Measuring Membrane Potentials • Uses a small electrolyte-filled micropipette (microelectrode) • Micropipette tip is impaled through the cell membrane • Indifferent electrode placed in extracellular fluid • Voltmeter measures potential difference between electrodes • Oscilloscope used for recording rapid potential changes
The Voltage Clamp Method • Used to measure ion flow through specific channels at set voltages • Two-Electrode System: • One measures voltage • One injects current • Injects current to hold voltage at a steady level • Injected current equals membrane current of opposite polarity
The Voltage Clamp Method • Squid Giant Axon: • Used for study due to its large diameter (up to 1 mm) • Selective Analysis: • Ions or blockers used to isolate Na+ or K+ flow
Resting Membrane Potential Dr Faiza MBBS (Best Graduate, AIMC Lahore) FCPS Physiology, MHPE (Riphah Int University, Islamabad) ICMT, CHPE, DHPE (STMU) MPH (GC University, Faisalabad) MBA (Virtual University of Pakistan)
20 Learning Objectives • Describe the Physiological basis of generation of RMP.
Resting Membrane Potential Potential at rest when nerve fiber is not conducting an impulse
The Electrical Dipole Layer • Negative charges align along the inside membrane surface • Positive charges align along the outside membrane surface
Resting Membrane Potentials • Quiescent period where stable voltage can be measured • Skeletal muscle -85 to -95 mV • Neurons -60 to -70 mV • Smooth muscle -50 to -60 mV • Erythrocytes -8 to -12 mV • Resting state is often a brief, transient state for many cells
The Na+ -K+ Pump • Mechanism: • Transports three Na+ ions to the extracellular fluid • Transports two K+ ions to the interior of the cell • Functions: • Classed as an electrogenic pump due to net positive ion loss • Maintains large concentration gradients across the nerve membrane • Essential for establishing the negative internal potential
Resting Ion Concentrations • Na+ • Outside 142 mEq/L • Inside 14 mEq/L • Inside / Outside ratio = 0.1 • K+ • Outside 4 mEq/L • Inside 140 mEq/L • Inside / Outside ratio = 35 • High internal potassium and high external sodium are maintained • These gradients provide the energy for diffusion potentials
Potassium "Leak" Channels • Protein channels that allow K+ to escape even at rest • Also known as tandem pore domain potassium channels • Highly selective for potassium over sodium ions • Approximately 100 times more permeable to K+ than Na+ • Key factor in determining the resting membrane potential level Each permeable ion attempts to drive the membrane potential toward its equilibrium potential.
Potassium's Contribution to Resting Potential =- 94 mV
Sodium's Contribution to Resting Potential = +61 mV
Sodium + Potassium's Contribution to Resting Potential • Goldman equation used to calculate combined Na+ and K+ effect K+ permeability is 100x greater ↓ thus it dominates the potential • Combined diffusion potential for Na+ and K+ is -86 mV
Establishing Total Resting Membrane Potential • Combined potential of Na & K: -86mV • Contribution by Na-K pump: -4mV • Total net resting potential in large nerve fibres : -90 mV
Maintenance of Resting Membrane Potential • Na-K ATPase pump • Maintains the conc gradient of Na and K
Thank You References: • Guyton, A. C., & Hall, J. E. (2021). Textbook of Medical Physiology (15th ed., Chapter 5: Membrane Potentials and Action Potentials). Philadelphia, PA: Elsevier. • Barrett, K. E., Barman, S. M., Brooks, H. L., & Yuan, J. X.-J. (2019). Ganong’s Review of Medical Physiology (26th ed., Chapter 4: Excitable Tissue: Nerve). New York, NY: McGraw-Hill Education. • Sherwood, L. (2015). Human Physiology: From Cells to Systems (9th ed., Chapter 4: Principles of Neural and Hormonal Communication ). Boston, MA: Cengage Learning.