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37 Cards in this Set
- Front
- Back
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What are the two types of synapses?
Most abundant? |
Chemical and electrical
Chemical most abundant |
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How does a synaptic current form?
What is it transformed into? |
Synaptic current results from post-synaptic receptors opening their channels in response to NT binding to receptors
This causes a postsynaptic potential |
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What is an excitatory postsynaptic potential (EPSP)?
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Depolarization of postsynaptic neuron --> AP
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What is an inhibitory postsynaptic potential (IPSP)?
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Decreases membrane potential of postsynaptic neuron --> decreases APs
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How is the 'strength' of the connection between 2 neurons measured?
What affects this? (2) |
Strength = amplitude of PSP
Depends on... 1. Number of synapses 2. Strength of each individual synapse |
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What does the neuromuscular junction connect?
What is special about the signal transmission across this synapse? |
Synaptic terminals of motorneurons and skeletal muscle endplate
Transmission is one-to-one: each arriving AP always triggers a postsynaptic event |
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How is transmission at the NMJ different from that of the CNS?
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NMJ = one to one transmission; each AP always triggers a postsynaptic event
CNS = probability of NT release is variable, differs between cells |
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What are the steps of the excitation-secretion coupling phase? (10 steps)
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1. AP invades pre-synaptic terminal
2. Depolarization, opens voltage-gated Ca channels 3. Influx of Ca 4. Synaptic vesicles exposed to Ca 5. Ca binds to synaptotagmin 6. Conformational change --> vesicle fusion 7. NT released via exocytosis 8. NT binds to post-synaptic receptors 9. Ligand-gated NT receptors in post-synaptic membrane open 10. EPSP or IPSP |
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What is synaptotagmin and what does it do?
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Synaptic vesicle protein that senses Ca --> changes conformation of vesicle --> vesicle binds to presynaptic membrane for NT release
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How long does the excitation-secretion coupling phase last?
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less than 1 ms
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What are the steps of the recovery phase of synaptic transmission (4)?
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1. Presynaptic potential returns to resting
2. Presynaptic Ca channels close 3. NT molecules cleared by breakdown or reuptake 4. Synaptic vesicles docked near presynaptic Ca channels |
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How long does the recovery phase take?
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less than 1 sec
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What steps are involved in the recycling phase of synaptic transmission? (2)
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1. Synaptic vesicles retrieved via endocytosis (if they underwent exocytosis before)
2. Vesicles re-filled with NT, added to reserve pool |
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How long does the recycling phase last?
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less than 1 min
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What is the frequency of acute myelid leukemias ?
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Acute Myelogenous Leukemia (M2) 30-40% Acute Promyelocytic (M3) 5-10%, Acute Monocytic (M5) 10%
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How are olfactory bulb cells and amacrine cells different in synaptic transmission?
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Release NT from dendrites because they lack an axon
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How is presynaptic Ca related to NT release?
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Presynaptic Ca concentration from voltage-gated Ca channels is necessary and sufficient for NT release
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What is synapsin?
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Links vesicle to cytoskeleton
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What is synaptobrevin/VAMP?
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Important for vesicle docking
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What is synaptotagmin?
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Ca sensor --> changes conformation to allow fusion of vesicle to presynaptic membrane
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What are some cytosolic proteins involved in vesicle release and what are their functions? (3)
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1. SNAP-25 - docking
2. NSF - ATPase 3. munc-18/n-sec1 - regulation of docking |
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What are some presynaptic membrane proteins and what are their functions? (3)
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1. Syntaxin (docking)
2. Ca channels 3. Neurexins (neuronal adhesion) |
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What is the SNARE complex made up of and what is it used for?
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SNARE = syntaxin, synaptobrevin, SNAP-25
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How are botulism and tetanus formed?
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Cleavage of SNARE components by proteases
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What are the steps of vesicle-membrane fusion? (4)
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1. Vesicle docks on presynaptic membrane
2. SNARE complexes (on presynaptic membrane) bring membranes together 3. Ca binds to synaptotagmin 4. Catalyzes membrane fusion |
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What are miniature end plate potentials (MEPPs)?
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Spontaneous fusion of single presynaptic Ach vesicle -->activate AchR --> opening of postsynaptic channels --> spontaneous synaptic potential, even when AP is blocked
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What is a quantum?
What is the quantum of AP-dependent synaptic transmission |
Smallest unit of something
Miniature end plate potentials |
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What is the relationship between EPP and mEPP?
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mEPP is the smallest unit of an EPP
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How much increase in EPP amplitude is each mEPP responsible for?
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0.4 mV
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What are the 4 steps of vesicle recycling?
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1. Coated pits --> coated vesicles --> endocytosis by dynamin
2. Uncoating by synaptojonin, Auxillin, HSC 3. NT enters endosomes 4. NT goes into vesicles |
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What happens in Lambert-Eaton Myasthenic Syndrome?
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Antibodies to voltage-gated Ca channels --> decreased Ca influx --> decreased Ach release --> muscle weakness
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What happens at the NMJ in LEMS?
(What is decreased, what stays the same?) |
Reduced number of quanta (MEPPs)
Amplitude of MEPPs that do arrive is the same (each vesicle still holds the same amount of Ach) |
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What forms electrical synapses?
What are these made from? |
Gap junctions
2 Hemichannels in pre- and post-synaptic vesicles |
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How does a pore of a gap junction compare with that of an ion channel?
What are the implications? |
Gap junction pore much bigger than ion channel
All ions equally permeable, as well as metabolites |
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What type of current flow is only possible in electrical synapses?
Which direction does current flow? |
Bi-directional current flow
Current flows away from the cell with higher potential |
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How does the timing of electrical synapse transmission differ from chemical synapse transmission?
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Electrical = no delay
Chemical = some delay |
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What are the 2 functions of electrical synapses?
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1. Exchange of metabolites and 2nd messengers - among coupled cells in a neuronal population
2. Excitation signal - rods in retina excite ganglia cells |
