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POLARIZED
RESTING MEMBRANE POTENTIAL
IV. Conduction of a Nerve Impulse
Resting Potential (Membrane Potential)
IV. Conduction of a Nerve Impulse
2
GRADED POTENTIAL VS ACTION POTENTIAL> Local membrane potential > Propagated change in change (depol. or hyperpol.) membrane potential
> Magnitude changes due to > Same strength stimulus strength
> Magnitude decreases with > Unstoppable distance
Events at a Chemical Synapse
IV. Conduction of a Nerve Impulse cont'd Synapse
Graded Potential Mechanism
Graded Potential Description Summation (EPSPs & IPSPs)
IV. Conduction of a Nerve Impulse cont.
Resting neuron is "polarized".
1. Threshold stimulus is received
2. Na+ ligand-gated channels in a local region of the membrane open
3. Na+ diffuse in, depolarizing the membrane (can lead to an action potential)
> Graded Potential (in dendrite or cell body area)> Triggering voltage-gated Na+ channels to open...further
depolarizing (in axon)
4. This results in an action potential causing a bioelectric current that stimulates adjacent portions of the membrane
5. Wave of action potential travels the length of the nerve fiber as a nerve impulse
6. Na+ voltage-gated channels close> K+ channels in the membrane open
7. K+ diffuses out, repolarizing the membrane.> Refractory Period = neuron cannot conduct another
impulse until repolarization occurs!
8. Role of Na+/K+ Pumps:> Restore ion concentration
• "All or None" Law: Once a threshold stimulus is met; a nerve impulse is conducted/propagated.... all impulses are the same strength. A greater intensity of stimulus does NOT produce a stronger impulse, but rather produces more impulses per second.
ECF Na+
ICF K+
+ + + + + + + + + +
Following Depolarization: