PHysiology questions plz help

(1)/(2) Nerve cells communicate to each other by acting as "transducers:" creating electrical signals (very small voltages and currents) in response to the input of certain chemical compounds called neurotransmitters, and releasing neurotransmitters when stimulated by electrical signals. So when an electric stimulus is used, say in a neuron, an action potential is initiated whereby voltage-gated channels (proteins) located within the plasma membrane of the cell open, and in turn, allow the flow of ions (Na+) into the cell increases until the cell reaches its threshold.

Go through these tutorials, it will become crystal clear (the two bottom ones should also explain part (2)):

- http://www.sumanasinc.com/webcontent/animations/content/action_potential.html

- http://www.learn.ppdictionary.com/resources/ActnPtnlPropagation.htm

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- Voltage-Gated Channels & the Action Potential: http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/anim0013.swf::Voltage%20Gated%20Channels%20and%20the%20Action%20Potential