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POLARIZED

RESTING MEMBRANE POTENTIAL

IV. Conduction of a Nerve Impulse

Resting Potential (Membrane Potential)

IV. Conduction of a Nerve Impulse

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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:

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DEPOLARIZATION VS REPOLARIZATION

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DEPOLARIZATION VS REPOLARIZATION

Continuous Propagation vs Saltatory Progagation