00:00Welcome to Two Minute Neuroscience, where I simplistically explain neuroscience topics
00:04in two minutes or less.
00:05In this installment, I will discuss the action potential.
00:08The action potential is a momentary reversal of membrane potential that is the basis for
00:12electrical signaling within neurons.
00:14If you're unfamiliar with membrane potential, you may want to watch my video on membrane
00:18potential before watching this video.
00:21The resting membrane potential of a neuron is around negative 70 millivolts.
00:24When neurotransmitters bind to receptors on the dendrites of a neuron, they can have an
00:29effect on the neuron known as depolarization.
00:31This means that they make the membrane potential less polarized, or cause it to move closer
00:35to zero.
00:37This chart shows membrane potential on the y-axis, and time on the x-axis.
00:42When neurotransmitters interacting with receptors causes repeated depolarization of the neuron,
00:47eventually the neuron reaches what is known as its threshold membrane potential.
00:51In a neuron with a membrane potential of negative 70 millivolts, this is generally around negative
00:5555 millivolts.
00:57When threshold is reached, a large number of sodium channels open, allowing positively charged
01:02sodium ions into the cell.
01:04This causes massive depolarization of the neuron as the membrane potential reaches zero and
01:09then becomes positive.
01:10This is known as the rising phase of the action potential.
01:13The influx of positive ions creates the electrical signal known as the action potential, which
01:19then travels down the neuron.
01:21Eventually the action potential reaches its peak.
01:23Sodium channels close and potassium channels open, which allows potassium to flow out of
01:27the cell.
01:28This loss of positive potassium ions promotes repolarization, which is known as the falling
01:33phase of the action potential.
01:34The neuron returns to resting membrane potential, but actually overshoots it, and the cell becomes
01:40hyperpolarized.
01:41During this phase, known as the refractory period, it is very difficult to cause the neuron to fire
01:45again.
01:46Eventually the potassium channels close and the membrane returns to resting membrane potential
01:50ready to be activated again.
01:52The signal generated by the action potential travels down the neuron and can cause a release
01:56of neurotransmitter at the axon terminals to pass the signal to the next neuron.
