I just finished fleshing out the action potential page. # Neuron Signaling Neurons communicate with each other using electrical signaling. To do this all cells have a negative electrical energy inside the cell compared to the outside. ## Intra-neuron signaling All cells at rest have a membrane potential around 50-80 millivolts (mV). To change this resting potential neurons use the [[Sodium Potassium Pump]]. By exchanging varying degrees of sodium, potassium, chloride, and calcium, neurons make their membrane potentials more positive ([[Depolarization]]), or more negative ([[Hyperpolarization]]). If the dendrites of a neuron reach sufficient depolarization of -40 mV and the signal makes it to the axon hillock, a threshold is reached and and an [[Action potentials|action potential]] is sparked. ## Inter-neuron signaling ### Presynaptic ###### What seven things happen when a action potential reaches the axon terminals to cause synaptic transmission? ==1.The action potential traveling down the axon arrives at the axon terminal.== ==2.This depolarization opens voltage-gated calcium channels in the membrane of the axon terminal, allowing calcium ions (Ca2+) to enter the terminal.== ==3.The Ca2+ activates synaptotagmin which fuses synaptic vesicles filled with neurotransmitter to the presynaptic membrane alongside the help of V-SNARE and T-SNARE proteins. The vesicles rupture releasing the neurotransmitter molecules into the synaptic cleft. ![[Pasted image 20220831102708.png]]== ==4. Neurotransmitter molecules cross the cleft to bind to special receptor molecules in the postsynaptic membrane, leading to the opening of ion channels in the postsynaptic membrane.== ==5.This ion flow creates a local EPSP or IPSP in the postsynaptic neuron.== ==6.Synaptic transmitter is either (a) inactivated (degraded) by enzymes or (b) removed from the synaptic cleft by transporters in a process called reuptake for reuse, so the transmission is brief and accurately reflects the activity of the presynaptic cell.== ==7.Synaptic transmitter may also activate presynaptic autoreceptors, regulating future transmitter release.== ### Post synaptic The postsynaptic potential is determined by how the post synaptic receptors are activated. If receptors activate that allow positively charged ions like Na+ to enter than depolarization will occur. This type of post synaptic potential is called a EPSP. However, if receptors activated allow more negatively charged Cl- ions to enter than hyperpolarization will occur. This is called a IPSP. But what if both excitatory and inhibitory receptors are activated? What determines if an action potential occurs or not? In this case the summation of PSPs is what matters. If there is a adequate summation of depolarizing PSPs on a postsynaptic neuron spatially than a action potential will occur. In addition, if there is an adequate summation of depolarizing PSPs temporally, than an action potential will occur. ![[Pasted image 20220913144514.png]] ###### What are the major differences between [[Action potentials]] and [[Post synaptic potentials]]? Action potentials are all or nothing and don't decay with time or distance where as PSPs get smaller with time and distance. PSPs can be either excitatory or inhibitory. ## How Does Synaptic Transmission Stop? ### Degradation The first way synaptic transmission stops is through degradation when the neurotransmitters are broken down by enzymes in the synaptic clefts stopping transmission. ### Reuptake The second way synaptic transmission is stopped is through reuptake caused by transmitter receptors on the axon terminal reuptaking neurotransmitters presynaptic neuron stopping transmission. Related: [[Synaptic Transition]] [[Neurophysiology]] [[Lecture 4 Neurophysiology]]