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77 Cards in this Set
- Front
- Back
What are the only two types of tissues that are considered to have excitable membranes? |
Nerve and muscle cells. |
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What experiment did Otto Loewi do and what did it demonstrate? |
Stimulated the vagus nerve of a frog heart… it slowed…. Then he took some of the saline that perfused that heart, and put it on another frog heart, and it slowed, too. This demonstrated that the signals from the neurons were being transmitted by chemicals that are released from the neuron. |
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What is a synapse? |
The gap between two cells into which the signaling cell releases chemicals to signal the second cell. |
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Where are they found? |
Between two neurons, or a neuron and its target cell, such as a muscle cell. |
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Is synaptic conduction considered to be an electrical or chemical event? |
Chemical. |
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Can a single neuron have both a presynaptic and a postsynaptic membrane? |
Yes, almost all do. |
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Where are presynaptic and a postsynaptic membranes found? |
The dendrites or cell body is considered to be postsynaptic, because it is receiving information… the axon terminal (or bouton) is considered presynaptic as it will transmit info across the synapse. |
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Where are synaptic vesicles found? |
Within presynaptic axon terminal (or boutons). |
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What do synaptic vesicles contain? |
Neurotransmitters. |
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What triggers the fusion of synaptic vesicles with the membrane and the consequent release of its contents? |
The influx of Ca++ through voltage-gated Ca++ channels that are opened when the AP's reach the axon terminal. |
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When neurotransmitter (NT) binds to its receptor on the postsynaptic membrane what type of change occurs in the postsynaptic cell? |
Ion channels open. |
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Is the change localized to the area of the receptor or does it spread? |
It spreads away; the stronger the stimulus, the longer the channel is open and the farther away it spreads. |
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At what location on a nerve cell are the neurotransmitter’s receptors found? |
Dendrites or cell body. |
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Does a neuron have more than one synapse? |
Yes, there are generally many, many synapses. |
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Can the binding of NT to its receptor cause a postsynaptic neuron to be closer to the threshold membrane potential? |
Yes… this is considered excitatory. |
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Can the binding of NT to its receptor cause a postsynaptic neuron to be farther from the threshold membrane potential? |
Yes… this is considered inhibitory. |
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What type of ion permeability change could depolarize a membrane? |
Positive ions move into the cells like, sodium (Na+) and calcium (Ca++). |
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What type of ion permeability change could hyperpolarize a membrane? |
Negative ions moving into cells like chloride (Cl-). Or movement of K+ out of the cell. |
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Can a brief change in a cell’s membrane potential be used as a communication signal from one cell to another? |
Yes. |
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Is there more than one type of NT? |
Yes... i.e. NE, ACh, etc. |
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Is it possible to have more than one type of receptor for a single type of NT? |
Yes….i.e. ACh has two types of |
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Can a neuron have more than one active synapse at the same time? |
Definitely, and most of the time it does. |
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To what does summation refer? |
The ability of EPSP's and/or IPSP's to add together. |
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How can summation increase the possibility of a neuron reaching threshold? |
The more excitatory signals coming in over a short period of time, the closer the membrane gets to threshold. |
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Does a graded potential have a threshold? |
No. |
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What causes a graded potential? |
The opening of ion channels in the cell body at the synapse. |
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Does a graded potential have a refractory period? Why? |
No. Because the channels can remain open as long as the chemicals (NT’s) are around. This allows the info, both excitatory and inhibitory, to be continuously processed and added together as needed. |
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Does a refractory period prevent summation? |
Yes, it would. |
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How does a synaptic transmission cease? |
First, the presynaptic neuron stops firing (no more AP's)… also the neurotransmitter in the cleft is quickly broken down by enzymes, either in the synapse itself or in the presynaptic neuron (and sometimes the postsynaptic neuron). |
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How is NT removed from the synaptic cleft? |
Re-uptake or degredation . |
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Is it important that the NT leave? Why? |
Yes. To stop the synaptic signal. |
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Do you think if a chemical were found that delayed the re-uptake of NT in the synapse, it could have any medical use? |
Yes, as an example, in depression, we have found out that patients neurons either aren’t making enough serotonin or it is removed too quickly (producing very short signals), so antidepressant like Zoloft or Paxil block the re-uptake of serotonin – this allows the signal to be longer and/or stronger and alleviates the depression. |
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Do you think if there was a chemical that delayed the re-uptake of NT in synapses of neurons which cause us to experience pleasure, that the chemical could become addictive? |
Absolutely! As an example, cocaine blocks the re-uptake of the monoamine NT's and is extremely addictive! |
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Which NT pathways does Prozac affect, and what does it do? |
Serotonin - it acts as an antidepressant. |
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What is a MAO, and what does it do? |
Monoamine oxidase… MAO is the enzyme that is responsible for degrading (breaking apart) the monoamine NTs once they are re-uptaken into the presynaptic neuron. |
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What are the symptoms and causes of Parkinson’s disorder? |
A tremor of the resting muscles… not enough dopamine producing neurons in the substantia nigra. |
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Why does treatment of Parkinson’s occasionally cause symptoms of schizophrenia? |
Parkinson's is treated by trying to increase |
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What is Alzheimer’s disease? |
The most common cause of senile dementia (including loss of memory)… brain lesions contain lots of deposits of beta-amyloid protein and degenerating nerve fibers, with the most extensive damage to cholinergic neurons (neurons which use ACh) in the hippocampus. |
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Synapse |
-a functional connection b/n a neuron (presynaptic) & another cell (postsynaptic) -Chemical synaptic transmission is via the release of neurotransmitters (NT) |
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Synaptic Potentials |
- |
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Graded potential |
- |
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EPSP (Excitatory Postsynpatic Potential) |
-the change in postsynaptci potential occurring at an excitatory synapse ( the receptor channgels to which the NT binds are nonspecific cation channels that permit simultaneous pasage of Na+ & K+ through them) -A single EPSP only depolarizes the membrane a little bit, not to threshold. |
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IPSP (Inhibitory Postsynaptic Potential |
-the small hyperpolarization of the postsynaptic cell |
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Neurotransmitter (NT) |
- specific chemical messenger that is packaged and synthesized by he presynaptic neuron to be received by the postsynaptic neuron |
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Presynaptic neuron |
-the neuron at the synapse sending the signal to the postsynaptic neuron |
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Postsynaptic neuron |
-The neuron at the synapse receiving the signal from the presynaptic neuron |
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Synaptic vesicles |
-Store neurotransmitters |
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Synaptic cleft |
-The space b/n the presynaptic & postsynaptic neurons -too wide for the direct spread of current from one cell to another, & therefore prevents APs from electrically passing b/n the neurons |
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Votage-gated channels |
-open/close in response to changes in membrane potential -have a 'timer': refractory period |
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ACh (acetylcholine) |
-Most widely used NT -at all neuromuscular junctions -used in brain -used in ANS: where can be excitatory/inhibitory |
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Nicotinic ACh channel receptors |
-Ligand-gated channels -Accept ACh or nicotine -ALWAYS DEPOLARIZE THE MEMBRANE= EXCITATORY SIGNAL |
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Muscarinic ACh receptors |
-Ligand-sensitive molecule;not a channel -Accept ACh or muscarine -GIVES EXCITATORY/INHIBITORY RESPONSE -activates G-protein, which activates the cell to make whatever it makes. |
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AChE (acetylcholinesterase) |
-Inactivates ACh, terminating its action; located in cleft -found in postsynaptic cell membrane
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NMJ (Neuromuscular Junction) |
- connects the nervous system to the muscular system via synapses between efferent nerve fibers andmuscle fibers -this is where ACh is passed from the presynaptic neuron to he postsynaptic neuron |
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Curare |
-found in snake venom or black widows -causes weak muscles and paralysis of diaphragm if extreme doses -Used in eye & hand surgeries to paralyze muscles. |
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Monoamine NT's |
-Include serotonin, norepinephrine & dopamine |
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Serotonin |
-derived from tryptophan -a monoamine NT -involved in regulation of mood, behavior, appetite, & cerebral circulation -associated w/depression; ppl w/depression don't have as much serotonin in their body as there should be. |
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Norepinepherine (NE) |
-Used in PNS & CNS -Sypathetic NT in PNS -in CNS, affects general level of arousal (being awake & alert to things) -Meth activates all pathway of brain that use NE. |
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Dopamine |
-Involved in motor control & emotional reward
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Catecholamines |
-NE, Dopamine, & Epinephrine |
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MAO (Monoamine Oxidase) |
-a presynaptic neuron that inhibits serotonin and catecholamines -destroys/degrades them |
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MAOI (Monoamine Oxidase Inhibitor) |
-inhibits MAO |
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COMT (catachol-o-methyl Transferase) |
-inactivates NE and dopamine |
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SSRI (serotonin-specific Reuptake inhibitors) |
-Antidepressants that prevent serotonin from being taken back into the cell from the junction; prolonging its action. |
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Prozac |
-an SSRI - |
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Zoloft |
-an SSRI |
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Paxil |
-an SSRI |
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Luvox |
-an SSRI |
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Parkinson's/Dopamine |
-Caused by not enough Dopamine in the motor control pathway of Dopamine. -treated by L Dopa in some cases, which can lead to Schizophrenia |
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Amphetamines |
-a potent central nervous system stimulant of the phenethylamine class that is used in the treatment of attention deficit hyperactivity disorder and narcolepsy |
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Amino acid NT’s |
-NTs that are amino acids -Including Glutamic acid, asparitic acid, glycine, & GABA |
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Glutamic aicd |
-major CNS excitatory NT |
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Aspartic acid |
-major CNS excitatory NT |
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Glycine- Inhibited by Strychnine |
-an inhibitory NT; opens Cl- channels which hyperpolarize -Strychnine blocks glycine receptors |
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GABA - gamma aminobutyric acid |
-inhibitory NT; opens Cl- channels -most common NT in brain |
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Schzophrenia |
-Caused by too much Dopamine in the emotional reward pathway of Dopamine. -treated by anti-dopamine drugs |
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Similarities b/n EPSPs & IPSPs |
-graded in magnitude -have no threshold (can stay open) -summate -have no refractory period |