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Lecture 5

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Physiology 2130
Anita Woods

Physiology Lecture 5 – Action Potential  Resting Membrane Potential o The uneven distribution of ions across the cell membrane o Caused by selective permeability of the membrane to certain ions o The cell membrane is 40x more permeable to potassium than sodium o Resting = present in all living cells, even those without electrical activity o Potential = a form of stored or potential energy  Role of Sodium/Potassium + ATPase in RMP o Moves sodium OUT of the cell o Moves potassium INTO the cell o Overall: maintains concentration gradients  Excitable Cells o Excitable Cells: generate and respond to electrical signals. Includes neurons and muscle cells (cardiac, smooth, skeletal) o Neurons use electrical signals (in the form of action potentials) to receive, process, initiate, and transmit messages  Ion Movement Creates Electrical Signals o Also, at rest, the cell is only slightly permeable to sodium o Therefore, if we change the permeability of the cell to sodium we can change its electrical potential  Gated Channels o In neurons, gated channels control the ion permeability of the neuron o Mechanically gated ion channels: open in response to mechanical stimulation (change in pressure) o Chemically gated ion channels: open in response to a chemical/ligand binding (acetylcholine binding) o Voltage gated channels: open in response to a change in voltage of the cell (-70mV to - 55mV)  Action Potential o At the axon hillock, if the threshold is reached (-55mV), then an action potential will be propagated down the axon o 3 important things about action potentials
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