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Action Potential

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MrWestbury

A nerve is composed of a bundle of neurons connected by synapses, with glial cells and blood vessels providing support. Action potentials travel along axons when a stimulus depolarizes the neuron's membrane enough to open voltage-gated sodium channels, flooding the intracellular space with sodium ions and causing a rapid increase in membrane potential. This wave of depolarization then propagates along the axon. Myelin sheaths allow the impulse to "jump" between nodes of Ranvier, increasing conduction velocity.

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Action Potential
A NERVE IS USUALLY COMPOSED OF A BUNDLE OF NEURONS WITH GLIAL CELLS AND BLOOD VESSELS TO SUPPLY NEEDED MATERIALS. NEURONS ARE NOT CONNECTED DIRECTLY TO ONE ANOTHER THERE ARE GAPS (SYNAPSES) BETWEEN THE NEURONS. ACTION POTENTIALS TRAVEL ALONG THE AXONS OF NEURONS
THE CELL MEMBRANE OF NEURONS HAVE AN UNEVEN DISTRUBTION OF CHARGES, WITH THE INSIDE MORE NEGATIVE THAN THE OUTSIDE (RESTING POTENTIAL -70mV) A CHANGE IN THIS BALANCE BY MOVING IONS CAUSES AN ELECTRICAL CHARGE ALONG THE LENGTH OF THE CELL THIS IS AN ACTION POTENTIAL. ACTION POTENTIALS START AT ONE SPECIFIC AREA AND THEN SPREAD OF PROPAGATE ALONG THE LENGTH OF THE AXON.
IF A STIMULUS OCCURS THAT IS STRONG ENOUGH TO REACH THE THRESHOLD LEVEL AN ACTION POTENTIAL RESULTS. THEY ARE ALL OR NOTHING EVENTS
Action Potential
A STIMULUS CAUSES Na+ LEAK CHANNELS TO OPEN IN THE CELL MEMBRANE IN A SMALL AREA. THIS DEPOLARIZES A SMALL AREA OF THE AXON AS Na+ RUSH INTO THE CELL (GRADED POTENTIAL). IF THIS REACHES THRESHOLD THE VOLTAGE GATED Na+ CHANNELS OPEN CAUSING MORE Na+ TO FLOOD INTO THE CELL. POSITIVE FEEDBACK MECHANISMS CAUSE MORE AND MORE Na+ GATED CHANNELS TO OPEN CAUSING THE MEMBRANE POTENTIAL TO BECOME MORE AND MORE POSITIVE. THE AMOUNT OF Na+ IN EXCEEDS THE AMOUNT OF K+ GOING OUT
ONCE THE MEMBRANE POTENTIAL INSIDE THE CELL BECOMES POSITIVE THE VOLTAGE GATED Na+ CHANNELS SNAP SHUT AND THERE IS NO INFLUX OF Na+ INTO THE CELL. THIS IS THE PEAK OF THE ACTION POTENTIAL GATES FOR K+ IONS OPEN THAT ALLOW K+ TO LEAK ACROSS THE CELL MEMBRANE. THIS IS A NEGATIVE FEEDBACK MECHANISM EVENTUALLY THE MEMBRANE RETURNS TO RESTING POTENTIAL (-70mV)
HOWEVER THE CONCENTRATIONS OF Na+ AND K+ ARENT WHERE THEY WERE BEFORE THE ACTION POTENTIAL. THE CONCENTRATIONS HAVE BEEN REVERSED! WE NOW HAVE MORE Na+ IN THE CELL AND MORE K+ OUTSIDE THE CELL. THE Na/K PUMP KICKS IN AND RESTORES THE ORIGINAL CONCENTRATIONS. UNTIL THIS OCCURS THE CELL IS HYPERPOLARIZED AND CANNOT FIRE ANOTHER ACTION POTENTIAL REFRACTORY PERIOD
THE MYELIN SHEATHS SECRETED BY SCHWANN CELLS INSULATE PORTIONS OF THE AXON, ALLOWING THE WAVE OF DEPOLARIZATION TO JUMP TO THE NEXT GAP (NODE OF RANVIER THIS INCREASES THE RATE TO AROUND 120 m/s

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Action Potential

  • 2. A NERVE IS USUALLY COMPOSED OF A BUNDLE OF NEURONS WITH GLIAL CELLS AND BLOOD VESSELS TO SUPPLY NEEDED MATERIALS. NEURONS ARE NOT CONNECTED DIRECTLY TO ONE ANOTHER THERE ARE GAPS (SYNAPSES) BETWEEN THE NEURONS. ACTION POTENTIALS TRAVEL ALONG THE AXONS OF NEURONS
  • 3. THE CELL MEMBRANE OF NEURONS HAVE AN UNEVEN DISTRUBTION OF CHARGES, WITH THE INSIDE MORE NEGATIVE THAN THE OUTSIDE (RESTING POTENTIAL -70mV) A CHANGE IN THIS BALANCE BY MOVING IONS CAUSES AN ELECTRICAL CHARGE ALONG THE LENGTH OF THE CELL THIS IS AN ACTION POTENTIAL. ACTION POTENTIALS START AT ONE SPECIFIC AREA AND THEN SPREAD OF PROPAGATE ALONG THE LENGTH OF THE AXON.
  • 4. IF A STIMULUS OCCURS THAT IS STRONG ENOUGH TO REACH THE THRESHOLD LEVEL AN ACTION POTENTIAL RESULTS. THEY ARE ALL OR NOTHING EVENTS
  • 6. A STIMULUS CAUSES Na+ LEAK CHANNELS TO OPEN IN THE CELL MEMBRANE IN A SMALL AREA. THIS DEPOLARIZES A SMALL AREA OF THE AXON AS Na+ RUSH INTO THE CELL (GRADED POTENTIAL). IF THIS REACHES THRESHOLD THE VOLTAGE GATED Na+ CHANNELS OPEN CAUSING MORE Na+ TO FLOOD INTO THE CELL. POSITIVE FEEDBACK MECHANISMS CAUSE MORE AND MORE Na+ GATED CHANNELS TO OPEN CAUSING THE MEMBRANE POTENTIAL TO BECOME MORE AND MORE POSITIVE. THE AMOUNT OF Na+ IN EXCEEDS THE AMOUNT OF K+ GOING OUT
  • 7. ONCE THE MEMBRANE POTENTIAL INSIDE THE CELL BECOMES POSITIVE THE VOLTAGE GATED Na+ CHANNELS SNAP SHUT AND THERE IS NO INFLUX OF Na+ INTO THE CELL. THIS IS THE PEAK OF THE ACTION POTENTIAL GATES FOR K+ IONS OPEN THAT ALLOW K+ TO LEAK ACROSS THE CELL MEMBRANE. THIS IS A NEGATIVE FEEDBACK MECHANISM EVENTUALLY THE MEMBRANE RETURNS TO RESTING POTENTIAL (-70mV)
  • 8. HOWEVER THE CONCENTRATIONS OF Na+ AND K+ ARENT WHERE THEY WERE BEFORE THE ACTION POTENTIAL. THE CONCENTRATIONS HAVE BEEN REVERSED! WE NOW HAVE MORE Na+ IN THE CELL AND MORE K+ OUTSIDE THE CELL. THE Na/K PUMP KICKS IN AND RESTORES THE ORIGINAL CONCENTRATIONS. UNTIL THIS OCCURS THE CELL IS HYPERPOLARIZED AND CANNOT FIRE ANOTHER ACTION POTENTIAL REFRACTORY PERIOD
  • 9. THE MYELIN SHEATHS SECRETED BY SCHWANN CELLS INSULATE PORTIONS OF THE AXON, ALLOWING THE WAVE OF DEPOLARIZATION TO JUMP TO THE NEXT GAP (NODE OF RANVIER THIS INCREASES THE RATE TO AROUND 120 m/s