Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad Electrical Properties of Cells Physiology page 1

Physiology page 2 Content Resting membrane potential Detour to physics Other excitable cells (a list) Action potential in neurones Muscle cells Electrical Properties of Cells Receptor cells 1780 Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad Luigi Galvani

Electrical Properties of Cells Physiology page 3 Hudgkin-Huxley experiment 1939 Under normal resting physiological conditions there is an electrical potential difference between the outside and inside of a cell (i.e., cell = ‘battery’) The inside is usually negative relative to the extracellular fluid. Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 4 Resting membrane potential All living cells have it Typical values: -40 to -90 mV 0 mV -70 mV Sources of negativity: proteins phosphates Cl - inside X + outside Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 5 Resting membrane potential Molar concentrations of ions in different environments [mmol/l] IonSeaE. coliAnimal cellSerum K Na (free) (bound) Mg (bound) 10 (bound) 0.6 (free) Ca Cl Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 6 Physics recap Newton’s law of gravitation Potential energy (gravitational) Coulomb’s law Electrical potential energy Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 7 Physics recap Voltage = electric potential U E = U E (r) / q [V or J/C] where U E is potential energy q is affected charge m 2 with charge q is under the influence of m 1 that creates an electric field around itself. I.e., voltage is el. potential energy per Coulomb Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page We measure electric potential (voltage) with a voltmeter. Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 9 Atoms Anion of carbon Cation of nitrogen Cation of carbon Isotope of carbon Ion (anion, cation) Isotope, nuclide Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page Ions exert force on free electrons which move the voltmeter pointer. Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 11 Resting membrane potential All living cells have it Typical values: -40 to -90 mV 0 mV -70 mV Sources of negativity: proteins phosphates Cl - inside X + outside Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 12 How is the resting membrane potential created? Key points: Plasma membrane is permeable to K + [K + i ] = 140 mmol/l [K + e ] = 4 mmol/l Negative proteins are mainly inside the cell K + is forced out down its concentration gradient This is not a closed circuit Electrostatic force drops to 0 after 2 nm Bulk volumes are electro-neutral Plasma membrane Is a ‘capacitor’ Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 13 How is the resting membrane potential created? The uncompensated positive charges outside the cell and the uncompensated negative charges inside the cell physically line up on the membrane surface and attract each other across the membrane. Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 14 How is the resting membrane potential created? U E = Q/C where U E is voltage Q is total charge C is capacitance C = 1 µF/cm 2 To produce U E = 100 mV, approx ions have to be deposited on 1 µm 2 of the membrane Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 15 How is the resting membrane potential created? Nernst equation Goldman equation [K + ] o = 4 mmol/l [K + ] i = 140 mmol/l E eq,K+ = -90 mV E m = 0.95*(-90) + 0.3*(67) + 0.2*(-86) = mV Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 16 How is the resting membrane potential created? Nernst equation [K + ] o and [K + ] i are ‘bulk’ molar concentrations, not the numbers of ions attracted to plasma membrane that eventually create the membrane potential. Those conc. almost do not change. Membrane phenomena (that account for notable shifts of U m ) do not affect them. Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 1 Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 2 A temporary reversal in the electrical potential difference across plasma membrane that occurs when a cell has been activated by a stimulus. Action potential definition Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 3 Tsunami (action potential travels like a wave) Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 4 Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 5 Where can we see action potential? Neurones: -70 to +40 mV 3 ms Cardiac muscle cells: -60 to +10 mV 300 ms Neuromuscular junction: -95 to +20 mV 5 ms Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 6 Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 7 Action potential Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 8 Sodium-potassium pump (Na + /K + -ATPase) reinstates the resting potential 3 Na + 2 K + 1 K + 90 Na + 20 K + 10 Na + 1 ATP -70 mV Voltage-gated Na + and K + ion channels Na + K+K+ K+K+ Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 9 Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 10 Sodium-potassium pump Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 11 Conduction in myelinated vs. non-myel. neurones 10 – 120 m/s m/s Schwann cell (myelin) Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 12 Saltatory conduction Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Introduction To Action Potential Physiology page 13 5 m 18 m Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad

Electrical Properties of Cells Physiology page 17 Excitable cells Neurones Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2013 Ludek Nerad Muscle cells: skeletal, cardiac, smooth Receptor cells (belonging to sensory organs) Photoreceptors in the retina Mechanoreceptors in auditory and vestibular systems, in the skin, joints, muscles, and other tissues Chemoreceptors in the olfactory and gustatory systems and in parts of the CNS Thermoreceptors in the skin