murik
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. At a particular chemical synapse, chloride (Cl-) channels open in the postsynaptic neuron whenever there is an action potential in the presynaptic neuron. In the postsynaptic neuron, the resting membrane potential is –70 mV, the Nernst equilibrium potential for chloride (ECl) is –65 mV, and the action potential threshold is –50 mV. If the postsynaptic neuron is at rest when the presynaptic neuron fires an action potential, the postsynaptic potential (PSP) will <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
A) be hyperpolarizing
B) be excitatory
C) involve a net influx of Cl-
D) all of the above
E) none of the above
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| doc179
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B
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| Musuq
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QS: At a particular chemical synapse, chloride (Cl-) channels open in the postsynaptic neuron whenever there is an action potential in the presynaptic neuron.
In the postsynaptic neuron, the resting membrane potential is –70 mV, the Nernst equilibrium potential for chloride (ECl) is –65 mV, and the action potential threshold is –50 mV. If the postsynaptic neuron is at rest when the presynaptic neuron fires an action potential, the postsynaptic potential (PSP) will?
will try 
Em=-70 ECl=-65 ... because they mention there is an action pot in the presyn ne, then the post syn ne should open Cl channels and so because Cl is not at equil with Em, the cl ions will have to efflux or leave the post syn neuron and the Ne goes from -70 to -65 so the cell becomes at equil for Cl thus it becomes more positive or less negative.
in that case...the choices:
A) be hyperpolarizing?, no because the cell is becoming more +, which will be depol instead
B) be excitatory, yes because it is aproaching its threshold which is -50
C) involve a net influx of Cl- ; i would say an eflux of Cl bec cell is becoming more positive
 that would be my guess, B
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