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human physiology qu please help

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human physiology qu please help

Postby grainne89 » Tue Dec 15, 2009 11:44 am

can anyone help me answer this qu : explain how an action potential in a presynaptic nerve cell may initiate graded potentials in dentrites of post-synaptic nerve cells
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Postby MrMistery » Sat Dec 19, 2009 1:20 am

do you know how a synapse works?
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Postby jwalin » Sat Dec 19, 2009 2:23 am

look up synapses.

but the rough guidline is

Ca 2+ enter the first
Ach moves out of the first
goes into the cleft
binds to receptors on the second
change ion receptor shape.
a part also acts as Na + channel.
Na+ flood in

note this is a rough guideline. google synapsis. this mechanism has been outlined for Ach. other chemicals could also play a role.
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Re: human physiology qu please help

Postby LeslieSamuel » Thu Dec 24, 2009 2:38 am

The example listed above is a great one. Just to fill in SOME of the details: When there is an action potential in a presynaptic neuron, it results in Neurotransmitter release from the axon terminals. The neurotransmitter (for example Acetylcholine) binds to receptors of the postsynaptic nerve cell. This then causes Sodium channels to open.

Because Sodium is highly concentrated outside the neuron (relatively speaking), this causes Sodium ions to rush into the cell. Depending on how much sodium rushes in, that will determine the size of the potential change in the postsynaptic cell. The more NT that are released, the bigger the EPSP. The longer the ACH stays around before breaking down, the bigger the EPSP.

Hope that makes sense.
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