Resting Membrane Potentials Potassium Determines Resting Membrane Potential -high permeability of membrane of K + relative to other Ions Excitable cells: Needs to be more positively generated action potentials Action Potentials Graph- The action potential +40 +20 Vm (mV) 0 - threshold -20 DEPOLARIZATION REPOLARIZATION -40 RMP > -70 AFTER-HYPERPOLARIZATION 0 1 stimulus 2 3 4 time (ms) . Action Potential is a Rapid and Transient Ā· Change in voltage across Membrane Action Potential depend on ionic gradient and relatively permeability to the membrane. . Generates excitable cells in response to the Pre-Synaptically neurotransmitter . Different tissues different Action Potentials
What Causes Rapid Depolarisation In The Cell Membrane? Ā· Caused by a Sodium Hypothesis ttHodgkin, and Katz, 1949) This is involved a rapid and highly specific increases of permeability of the membrane of Na+ ion ttENa) o This was done via a test. Reducing [Na] were used [70%,50%,33%] And plotted against the membrane potential. o Result: decrease in Action Potential in the membrane o decrease in Membrane Potential The "sodium hypothesis" (Hodgkin and Katz, 1949) Normal [Na+]. 70% [Na+]. Normal [Na+], 50% [Na+]. Normal [Na+]. 33% [Na+] 40 ENa+ = 60 log- 50 [Na+], 17 30 20 Membrane Potential (mV) 10 (Ā·) = Peak Amplitude of Action Potential Why the discrepancy? 0 -10- -20 -30-4A 15 20 30 40 50 70 100 120 Sodium Concentration (mM) What is the highest Action Potential Ion: o its EK o K+ Channel mediates repolarization phase of Action Potential.
o Voltage Gated channel Ions Na + /K + Channel generates Action Potentials. ttWhich closes and opens in the change in Action Potential) Voltage Clamping o Control membrane potential -so ionic current can be measured by investigating the mechanism of Action Potential generation Voltage Membrane: Keeps the membrane potential constant in response to membrane current Forces the membrane potential to change to voltage to specific value. This is done by changing the inwards and outwards current. o Positive ions + negative ions move inwards and outwards of the cell. To prevent this: Use blockers to see which ions can affect: Na blockers-completely losses inward current. o Proves Na+ causes depolarisation. K blockers-completely losses outwards current. o K causes Repolarisation What do we want for this? Na influx K Outflux. TABLE 8-4 Chemicals That Affect Electrical Signals in Neurons Name of Chemical Channel Blocked Tetrodotoxin (TTX) Voltage-gated Na+ Saxitoxin Procaine Tetraethylammonium chloride (TEA) Ethanol Voltage-gated Na+ Voltage-gated Na+ Voltage-gated K+ Ca2+ and assorted receptor-operated channels Comments Made in ovaries and liver of Japanese puffer fish Made by marine organism that causes "red tide" Local anesthetic Amine derivative Depresses action potentials and depolarizes the membrane; inhibitory in higher doses and excitatory in low doses