EMG/NCSPhysiology of nerve conduction

EMG/NPhysiology of nerve conduction Membrane potential - ANS An electrical potential difference (voltage) across the membrane, resting =-70mV. Negative ions in cytosol. Positive ions in extracellular fluid. (ECF) Electrochemical gradient - ANS Ions move across membrane down gradient. More sodium outside, more potassium inside. Action potential - ANS Two phases depolarizing and repolarizing. Depolarizing - ANS Neg membrane potential becomes positive. Depolarizing phase - ANS 1. Stimulus causes membrane to depolarize to threshold -55mV. 2. Voltage gated sodium (Na^+) channel open. 3. Electrical and chemicals gradients favor inward movement of sodium which causes the Depolarizing phase. 4. The membrane potential goes to +30mV. Repolarizing - ANS The membrane potential is restored to the resting state. Repolarizing phase - ANS 1. Stimulus also opens voltage gated potassium (k+) channels. 2. These channels open more slowly and open when the sodium gates are closing. Potassium flows out of the cell. 3. The membrane potential goes from +30mV to -70mV. Refractory period - ANS The period of time after an action potential begins during which an excitable cell cannot generate another action potential. Two types of propaganation - ANS Depolarization and repolarization of entire axon membrane. Unmyelinated axons. Saltatory - ANS Myelination, faster. Depolarization And repolarization of axon membrane jumps from node to node. CS