Physiology 3120 Lecture Notes - Lecture 3: Human Sexual Response Cycle, Gap Junction, Cardiac Muscle
20 Jan 2018
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Document Summary
Action potentials in other types of cardiac cells ventricular contractile cells. Duration = 300ms: much longer than neuronal ap. Membrane potential ranges from -90mv to +20mv: different from sa node (-60mv to +20mv) Ap spontaneously generates at the sa note and propagates outwards. Current flowing from a neighboring cell causes partial depolarization (gap junctions): ap propagates from ventricular cell to ventricular cell through intercalated discs that contain gap junction. Depolarizing wave opens fast na+ vg channels and. Na+ enters very rapidly (fast inward current): similar to fast vg na+ channels in neurons. At positive membrane potentials, na+ permeability decreases (fast na+ channels inactivate): fast na+ channels open and close rapidly. Cl- channels open and cl- moves in (only briefly). While k+ vg channels open and k+ leaks out. This inward ca2+ current almost balances the outward k+ current and as a result the membrane potential is relatively steady: more k+ exits than ca2+ enters.
