An action potential is a regenerative spread of neuronal polarization that arise in the [[Axon hillock]] and move down the axons length. They are the fundamental way in which neuron cells signal to each other. ### How do they occur? Action potentials occur after a threshold is reached. The threshold differs for different cells but is usually somewhere between -55 and -40mV. This process occurs through the process of depolarization which is the change of charge in a cell that brings it closer to zero. ![[Pasted image 20220902100226.png]] Usually this occurs through the process of [[Inter-neuron signaling]] by the onset of a [[Excitatory postsynaptic stimulus (EPSP)]]. ### How do they Travel? Action potentials travel in a regenerative spread of neuronal polarization. As they go down the axon length, they cause the opening of voltage gated Na+ channels allowing positively charged Na+ ions to come into the cell flowing down the concentration gradient. This cluster of positively charged Na+ creates an area of positive charge which depolarizes the cell and causes the next subsequent Na+ channel to open creating a regenerative depolarization process. ^e08cd9 Once the action potential reaches the axon terminal, it activates voltage gated Ca2+ channels that cause the [[Inter-neuron signaling]] process. ### How fast do they go? The more myelin caused by [[Myelination]] the faster the action potential will spread down the axon length. They travel faster because of saltatory conduction. This is why some subconscious reactions are so fast. Your body has to react quickly to bring your hand away from a burner so you have an incredible amount of myelin around [[Neuronal circuits]] that control movements for things like that. In addition larger axons travel signals faster than smaller axons do. ### What happens after the onset of an action potential? After an action potential there is a [[Refractory]] period in which cells are less responsive to subsequent electrical signals. After the period of hyperpolarization the neuron cell experiences during the refractory period, it returns to it's resting potential around an average of -80 to -50 mV. ![[Pasted image 20220902095954.png]] ### Drugs That Can Stop Action Potentials There are many [[Neuropharmacology#^85999d|drugs]] that can alter the way neurons signal. One of the most famous is curare which interferes with the transmission of [[Neuron signaling|neuron signals]] by blocking Ach receptors making it difficult for muscular excitement. ^72e35c