Term
| Name 3 types of cells that synapses occur between |
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Definition
1. two neurons
2. Presynaptic neuron and postsynaptic target (ex. muscle cell)
3. Presynaptic sensory cell and postsynaptic neuron |
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Term
| Describe the differences between electrical and chemical transmission |
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Definition
1. Electrical has direct cell-cell contact via connexons, chemical invovles release into the synaptic cleft
2. Electrical has cytoplasmic continuity, chemical does not
3. No synaptic delay in electrical, there is one in chemical
4. Electrical is bi directional, chemical is uni directional |
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Term
| What is the neurotransmitter involved in neuromuscular junctions? |
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Definition
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Term
| Describe the steps in chemical transmission that involve the presynaptic cell |
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Definition
1. ACh (transmitter) is stored in vesicles
2. Docking of the vesicles
3. Depolarization of the cell
4. Ca influx via voltage gated ion channels
5. Vesicle fusion
6. Exocytosis |
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Term
| How can you determine which cells are the pre and post synaptic on a slide? |
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Definition
| Presynaptic cells have an abundance of vesicles visible in them as well as many mitochondria present |
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Term
| How can you determine if the junction you are looking at on a slide is neuron-neuron or neuron-muscle? |
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Definition
| In a neuron-neuron synapse, the membrane appears as a relative flat line. In neuron-muscle synapses there are folds in the membrane that go into the muscle cell |
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Term
| Describe the steps in chemical transmission that involve the post synaptic cell |
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Definition
1. Activation of transmitter receptors (nACh for ACh transmitter)
2. Depolarization of cell
3. Opening of ion channels
4. Ion influx (usually Ca)
5. Ca triggered release of Ca by sarcoplasmic reticulum
6. Inactivation of transmitter |
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Term
| What are the two major families of transmitters and describe differences in their creation and packaging. |
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Definition
1. small molecules vs. peptides and polypeptides
2. Small molecules are synthesized locally, whereas peptides are synthesized remotely and transported to the terminal
3. Small molecules are in small vesicles, peptides are in large dense core vesicles |
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Term
| What 2 compounds are acetylcholine synthesized from? |
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Definition
| Acetate and choline. Synthesizes is enzyme mediated. |
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Term
| What is the energy source that vesicles use to drive the filling of neurotransmitters? |
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Definition
ATP is utilized to create a proton gradient in the vesicle (vesicle acidification). The energy of this gradient is then harnessed to drive the filling of neurotransmitters.
Note: Vesicles can also fuse with neurotransmitter filled endosomes to fill |
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Term
| What is the kiss and run process and when does it happen? |
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Definition
1. Vesicles dock to the membrane surface
2. During the priming phase, Ca is needed for fusion to occur
3. Before Ca influx and fusion occurs, the vesicle breaks off the membrane and returns to the cytoplasm
This process commonly happens when the presynaptic terminal is very active |
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Term
| What proteins are used to mediate docking of the vesicles? |
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Definition
| SNARES (via coil-coil interactions) |
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Term
| What is the role of synaptotagmin and how does it accomplish this? What happens if you disable synaptotagmin? |
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Definition
1. Membrane protein that mediates fusion of the vesicle and calcium release
2. Does this by sensing calcium levels
3. Without synaptotagmin, you get binding to the membrane but no fusion and NT release |
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Term
| How does tetanus toxin work? |
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Definition
| It affects SNARES to block the function of inhibitory connections, leading to rigidity and convulsions |
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Term
| How does Botulin toxin work? |
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Definition
| Affects SNARES at the neuromuscular junction stopping muscle activity alltogether |
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Term
| What is an EPSP and how do they govern signal conduction? |
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Definition
1. EPSP is an excitatory postsynaptic potential caused by ACh locally, or a voltage change at the postsynaptic cell
2. If the EPSP reaches threshold for ion channels to open and Ca influx to occur, a signal will be transduced across the synaptic cleft into the postsynaptic cell |
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Term
| What 3 factors affect EPSP amplitude? |
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Definition
1. Quantity of NT released
2. Quantity of NT that reaches receptors
3. Number of activated receptors |
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Term
| What are miniature EPSP's and why do they occur? |
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Definition
| small transmembrane voltage changes that are unassociated with presynaptic stimulation. They are due to the spontaneous release of a single vesicle. |
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Term
| What is meant by "Postsynaptic potentials can be excitatory or inhibitory"? |
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Definition
Excitatory - increase the probability of an action potential
Inhibitory - decrease the probability of an action potential |
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Term
| What 3 factors determine whether a transmitter depolarizes or hyperpolarizes the postsynaptic cell? |
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Definition
1. Resting potential of the post membrane
2. Ion selectivity of the channels that open
3. Electrochemical driving force for that ion (combination of outside concentration vs. inside concentration as well as resting voltage) |
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Term
| Give estimates of the intracellular concentration, extracellular concentration, and nernst potentials for Na |
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Definition
| Intra: 12 Extra: 140 Nernst: 66 |
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Term
| Give estimates of the intracellular concentration, extracellular concentration, and nernst potentials for K |
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Definition
| intra: 140 extra: 4 nernst: -93 |
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Term
| Give estimates of the intracellular concentration, extracellular concentration, and nernst potentials for Ca |
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Definition
| intra: 10^-4 mM extra: 2.5 nernst: 135 |
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Term
| Give estimates of the intracellular concentration, extracellular concentration, and nernst potentials for Cl |
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Definition
| intra: 2.5-50 extra: 115 nernst: -42 |
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Term
| What are the two families of receptors and do they support fast or slow EPSP? |
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Definition
1. Ionotropic - fast
2. Metabolic - slow |
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Term
| What are the 3 methods of transmitter inactivation? |
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Definition
1. Diffusion out of cleft (slow)
2. Hydrolysis of the transmitter in the cleft
3. Re-uptake of transmitter into presynaptic cell |
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Term
| How is acetylcholine inactivated? |
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Definition
| Acetylcholinesterase cleaves ACh back into its original acetate and choline components, which are taken back up by the presynaptic cell by a sodium ion driven pump |
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Term
| Describe the reuptake of dopamine and how this is affected by cocaine |
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Definition
| Dopamine is not degraded in the cleft, but taken up in its NT state by a pump harnessing the energy of the sodium gradient. Cocaine blocks the activity of this pump, leaving the synaptic cleft flooded with dopamine. |
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Term
| What class of compounds blocks the reuptake of Serotonin and give an example of one |
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Definition
SSRIs (Selective Serotonin Reuptake Inhibitors)
Prozac |
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Term
| Name 5 examples of transmitters that are inactivated by reuptake mechanisms |
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Definition
1. Dopamine
2. Serotonin
3. GABA
4. Glycine
5. Glutamate |
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Term
| What is the main cause of Myasthenia Gravis and what are the symptoms? |
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Definition
1. An autoimmune disease against nAChR leading to a decrease in their number at the neuromuscular juncion
2. Patients become very tired or weak after little to moderate activity (ex. cant speak for long periods of time, droopy eyelids, etc.)
Also a decrease in EMG signal is observed with prolonged activity |
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Term
| What toxin is used to isolate and study nAChRs? |
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Definition
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Term
| What is the mechanism of nAChR decrease in MG? |
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Definition
1. Antibodies compete for and bind to the nAChRs
2. Antibodies cross link, serving as a signal for endocytosis
3. Endocytosed receptors get degraded |
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Term
| What are AChE Inhibitors and what effect do they have on signal transduction? |
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Definition
1. Acetylcholinesterase inhibitors
2. By stopping ACh from being degraded, an increased quantity of them exist in the synapse, leading to increased chance of the EPSPs crossing threshold for signal transduction |
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Term
| What is facilitation and what causes it? |
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Definition
1. Facilitation is a transient increase in synaptic strength when two or more action potentials occur in close succession (leads to an increase in EPSP amplitude)
2. The transient increase in [Ca] in the presynaptic terminal after the first stimulation leads to an increase in vesicle fusion and release in subsequent stimulations |
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Term
| What is heterosynaptic potentiation? |
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Definition
When one synapse's activity is altered by that of another synapse
ex. if you have both a calcium and a sodium receptor and both are activated, the resulting electrical signal in the post synaptic cell is a reflection of the sum of the two synapses' signals |
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