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This 4 page Class Notes was uploaded by Arielle Reiner on Wednesday September 16, 2015. The Class Notes belongs to 81.0 at University of Pittsburgh taught by Fanselow,Erika in Fall 2015. Since its upload, it has received 26 views. For similar materials see DRUGS AND BEHAVIOR in Neuroscience at University of Pittsburgh.
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Date Created: 09/16/15
Neurotransmission 09162015 How could neurons communicate with one another 0 We take for granted now that neurons are separate cells 0 We also take for granted that neurotransmitters exist and can be used to affect neurons Synapse structure Presynaptic v postsynaptic neurons 0 The word synapse is derived from the Greek word quotsynaptoquot which means quotto clapquot 0 Electron micrograph o The synaptic cleft is the space between the pre and postsynaptic cells It is about 1520 nm wide 1 nm 1 biionth of a meter 1 10quot9 meters 0 Axons can form synapses at different locations on the postsynaptic neuron Axodendritic v axosomatic v axoaxonic How do neurons release neurotransmitter When an action potential reaches the end of the axon the presynaptic terminal how can that release neurotransmitter 0 Things to know about neuronal membranes and neurotransmitter molecules Cell membranes are contiguous they form a surface all the way around the entire neuron and they cannot have open holes in them because things would leak in and out of the cell and this could not be well controlled So there must be a way to get the neurotransmitter out of the cell Neurotransmitter molecules are far too large to t through ion channels 0 Spheres of lipid bilayers form synaptic vesicles inside the presynaptic terminal The lipid bilayer in a neuron can be used to form spheres of membrane inside the neuron which are called vesicles Vesicles have uid on their inside and can contain molecules such as neurotransmitters o Synaptic vesicles gather on the presynaptic side of the synaptic cleft o Synaptic vesicle fusion causes exocytosis Because the outer surface of a vesicle is made of the same type of lipid bilayer as the cell membrane it can fuse with the cell membrane a A vesicle containing neurotransmitter is near the cell membrane n A group of molecules hold the vesicle right up next to the cell membrane and prime it to fuse n The arrival of an action potential triggers the vesicle to fuse with the membrane and thus release its neurotransmitter This is called exocytosis When an action potential depolarizes the presynaptic membrane this opens voltage gated calcium Ca2 channeb The Ca2 ions bind to the molecules holding the vesicle to the membrane and trigger fusion 0 Vesicle exocytosis and endocytosis cycle Once the vesicle has released its neurotransmitter it gets brought up into the neuron again a This is called endocytosis The lipid bilayer is then recycled and a new vesicle is formed Axon terminal membrane absorbs vesicle and it buds inside the axon endocytosis and the vesicle is then an endosome and from there it buds again and becomes an undocked synaptic vesicle which has clusters of proteins in the membrane and this lls with neurotransmitter which docks and primes back to the axon terminal exocytosis and the clusters of proteins fuse into the presynaptic membrane Neurotransmitter in the synaptic cleft Since the synaptic cleft is very narrow about 1520 nm the newly released neurotransmitter molecules are close to the postsynaptic receptors and can bind to them 0 But if the neurotransmitters stayed in the synaptic cleft there would be at least 2 problems 0 The postsynaptic cell would respond inde nitely to the signal from the presynaptic neuron 0 There would be no way to send a 2nCI separate signal because it would simply merge with the 1st 0 How are neurotransmitters removed from the synaptic cleft o 3 methods Degradation broken down by enzymes Reuptake brought back into the presynaptic neuron via transporters in the cell membrane Uptake by glial cells brought into surrounding glial cells also via transporters Neurotransmitters v neuromodulators 0 Some molecules that are released by neurons bind to receptors that are not necessarily or only in the synaptic cleft They can oat around in the CSF and bind to receptors on neurons other than the 1 directly postsynaptic to the neuron releasing the molecules 0 They are referred to as neuromodulators and tend to regulate neuronal activity over larger regions and on a slower time scale than classic neurotransmitters Some molecules can act as both a neurotransmitter and a neuromodulator depending on where the receptors are that they activate Receptor subunits Receptors are typically made of groups of proteins each of which is called a subunit 0 A single receptor can have multiple subunits that are identical or can contain multiple unique subunits Types of neurotransmitter receptors lonotropic o Directly open ion channels 0 Are not voltage gated or directly voltage dependent o Metabotropic Indirectly affects processes inside cell Acts via Gprotein activation 2 routes of action a Direct action of G protein on ion channels a Indirect action via 2ncl messenger action Neurotransmitter synthesis 0 Synthesis building blocks of a transmitter substance are imported into the terminal where the neurotransmitter is synthesized and packaged into vesicles Neurotransmitters are derived in 2 general ways and at 2 locations in the cell 0 Axon terminal building blocks from food are pumped into cell via transporters 0 Cell body proteins made via DNA and transported to the synaptic terminal 0 Enzymes can convert precursor molecules into neurotransmitters Possible sites of action for drugs 0 Drug serves as NT precursor 0 Drug inhibits NT synthesis 0 Drug prevents storage of NT in vesicles 0 Drug stimulates release of NT 0 Drug inhibits release of NT Drug stimulates postsynaptic receptors Drug blocks postsynaptic receptors Drug stimulates autoreceptors and inhibits release of NT Drug blocks autoreceotirs and increases release of NT Drug inhibits NT degradation Drug blocks reuptake
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