Action potential
axon hillock
concentration gradient
depolarized
electrical gradient
electrical polarization
hyperpolarized
membrane
nerve impulses
nodes of Ranvier
positive
presynaptic terminal(s)
propagation
resting potential
saltatory conduction
selective permeability
sodium
threshold of excitement
voltage

Instructions: Fill in the blanks with the terms listed above.
The neuron has a _1) of -70mV on average. When the neuron’s membrane becomes _2) , its _3)_electrical polarization__ shifts in a positive direction. The neuron becomes _4) when the neuron membrane becomes even more negative. When enough depolarizing messages are received by the neuron to reach the _5), voltage-gated channels in the membrane open and allow _6) ions to rush into the cell. Sodium rushes into the cell due to a feature of the cell membrane called __7), which allows some elements to pass through the cell membrane freely while limiting the movement of ions such as sodium and potassium until these voltage-gated channels open. Once the channels open, sodium is attracted to the negative interior of the cell due to a force called the _8), because the sodium ion carries a positive charge and is attracted to its opposite. Another force, called the _9), attracts sodium ions to the area inside the cell where fewer sodium ions are located while the neuron is in its resting state. All of these influences that make sodium rush into the cell contribute to the electrical charge inside of the neuron becoming much more _10), resulting in a/an _11). This rapid and massive depolarization of the membrane travels from the _12) of the cell body to the 13), causing _14)-gated ion channels to open in a sequential fashion along the axon. This movement along the axon is called _15) of the action potential. If the axon is wrapped in segments of myelin sheath with pieces of exposed axon called _16) located in between them, the depolarization of the _17) will occur at each exposed piece of axon membrane, greatly speeding the rate at which the action potential travels down the axon. This speedy conduction of 18) along the axon is called _19).