Term
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Definition
| deviation from the normal resting potential; allowing cells to transmit information through the nervous system |
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Term
| affect of resting membrane potential |
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Definition
| determines whether solutes enter or leave the cell |
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Term
| resting membrane potential |
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Definition
| difference in electrical potential between inside and outside of the cell (inside negative to outside) |
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Term
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Definition
| says 1. solutions must have equal numbers of positive and negative charges; 2. biological membranes act as capacitors storing electrical charge with equal number of positive and negative charges on each side of membrane |
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Term
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Definition
| 1. permeable ion diffuses through the membrane; 2. electrical voltage difference arises that prevents further movement of ion |
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Term
| electrochemical potential equation |
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Definition
μK=μK°+RTln[K+]+zFE states how much energy is contained per mole of solute in a given solution |
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Term
| forces pushing on a solute from electrochemical potential |
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Definition
| 1. concentration gradient across the membrane; 2. voltage difference across the membrane; at equilibrium forces are equal on both sides |
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Term
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Definition
| calculates the equilbrium potential of an ion; E=(-61mV/z)log10(Cin/Cout) |
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Term
| Na+ and K+ equilibrium potentials |
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Definition
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Term
| non-equilibrium membrane potential |
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Definition
| causes a net driving force on the ion with the net energy difference and relevent voltage Em-Eion |
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Term
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Definition
| (g) is the reciprocal of resistance with units of Siemans; measure of how well something conducts electricity |
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Term
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Definition
| i=gΔV; where i is the current and V is the voltage |
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Term
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Definition
| proportional to number of specific channels of the type that are open |
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Term
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Definition
| i=g(Em-Eion; when the potentials are equal there is no flow of the ion even when channels are open |
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Term
| principles of the chord conductance equation |
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Definition
| 1. electroneutrality; 2. current into the cell must equal the current out of the cell; 3. allows us to find compromise value of membrane potential |
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Term
| chord conductance equation |
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Definition
| Em=[gk/(gk+gNa)]EK+[gNa/(gNa+gK)]ENa |
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Term
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Definition
| fraction of the total mebrane conductance that is due to the specific conductance of the ion: TK=gK/(gK+gNa) |
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Term
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Definition
substitutes the transferences into the chord conducatance equation: Em=TKEK+TNaENa ; membrane potential is weighted average of equilibrium potentials of the permeable ions w/ the transferences as the weighting factors |
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Term
| value of resting membrane potential |
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Definition
| conductance of K+ is~ 9 times greater at rest than Na+ so membrance potential will be about -75mV |
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Term
| role of Na/K pump in resting membrane potential |
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Definition
| not directly involved but indirectly involved by maintaining the ion concentrations |
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Term
| characteristics of an action potential |
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Definition
| 1. each successive one looks the same; 2. has a threshold (~-55mV);3. all or nothing;4. has refractory period where AP cannot be generated; 5. self-regenerating; 6. propogates without decrement |
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Term
| what happens in action potential |
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Definition
| 1. sudden and temporary increase in Na+ conductance; 2. transference increases; 3. Em moves closer to Ena+ (depolarizes) to overshoot |
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Term
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Definition
| when membrane potential becomes positive and moves closer to Ena+ |
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Term
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Definition
| at the peak the sodium conductance is at its peak |
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Term
| inactivation of sodium channels |
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Definition
| where sodium conductance spontaneously decreases and membrane potential begins to return to resting value |
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Term
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Definition
| gradual increase in K+ conductance and further returns membrane to resting potential and opens enough that causes a hyperpolarization |
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Term
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Definition
| voltage dependent sodium channels in nerve and skeletal muscle; have gates that move in response to electrical potential differences across cell membrane |
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Term
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Definition
| 1. m gate-gate on extracellular side that is activation gate; 2. h gate-gate on intracellular side that is called the inactivation gate; channel only opens if both are open |
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Term
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Definition
| gate of potassium channel |
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Term
| gates at normal resting potential |
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Definition
| m gate is closed and h gate is open and channel is closed but available for activation |
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Term
| gates during depolarization |
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Definition
| in less than 1 ms m gate rapidly opens and the h gate stays open and channel is open (only remains open for 1-2 milliseconds) |
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Term
| h gate during depolarization |
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Definition
| is caused to close but respond much slower and channel is inactivated (downstroke phase) |
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Term
| reactivation of sodium channel |
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Definition
| membrane potential must return to about -80mV and the m gate closes and the h gate opens and now available for activation |
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Term
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Definition
| voltage dependent closing of a channel; potassium channels deactivate as membrane potential returns to resting potential |
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Term
| absolute refractory period |
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Definition
| cannot trigger another action potential no matter how strong of a stimulus is used; due to not having enough sodium channels available to trigger another AP |
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Term
| relative refractory period |
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Definition
| can trigger another action potential but have to use a stronger stimulus; not as many sodium channels available as normal and many more potassium channels open so more difficult to depolarize the membrane to threshold |
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Term
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Definition
| potassium channels and act as activation gate; open when membrane is polarized but open much more slowly and stay open as long as membrane is depolarized |
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Term
| effect of low extracellular Ca2+ |
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Definition
| make nerve and muscle more excitable |
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Term
| mechanism of low Ca2+ extracellularly |
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Definition
| 1. makes it easier to open the m gate; 2. channels open at membrane potentials that are more negative than normal; 3. smaller than normal stimuli can activate action potential |
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Term
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Definition
| spontaneous contraction of skeletal muscle when the Ca2+ concentration is too low |
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Term
| effect of high extracellular K+ |
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Definition
| causes muscles and nerves to be less excitable than normal |
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Term
| mechanism of high extracellular K+ |
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Definition
| increasing concentration depolarizes the membrane; causing some h gates to close and n gates to open increasing the number of inactivated sodium channels makes it more difficult to open enough sodium channels to reach threshold; opening k+ channels makes it harder to depolarize by increasing the K+ transference |
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Term
| strength duration relationship of a nerve |
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Definition
| 1. w/ brief stimulation it takes a larger electrical current to cause an AP; 2. w/ longer stimulation, less electrical current is needed to cause an AP |
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Term
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Definition
| minimum current that can cause an action potential |
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Term
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Definition
| minimum stimulus time that will cause an AP using a current twice the rhoebase current |
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Term
| capacitive currents during action potential |
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Definition
| inward and outward currents do not exactly balance because some of the current is used to change the electric charge stored on the membrane; i(Na) is greater during the upstroke to make inside of the cell more positive and during downstroke the i(K) current is greater to make it more negative; the currents are only equal when when membrane potential is not changing |
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Term
| times when membrane potential is not changing |
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Definition
| 1. resting potential; 2. peak overshoot of the AP; 3. bottom of the undershoot of the AP |
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Term
| conduction of action potential |
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Definition
| AP is recreated at every point along the axon without decrement |
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Term
| local circuit of action potential |
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Definition
| 1. positive charge (Na+) enters the cell at x=0; 2. positive charge carried by K+ flows in both directions along lenth of axon; 2. positive charge carried by K+ flows out of axon through membrane K+ channels; 4. positive charge carried by Na+ flows through extracellular solution along axon back to x=0 |
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Term
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Definition
| AP is in its downstroke phase and g(K) is large and K+ can flow out through the open channels |
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Term
| ahead of the AP in the axon |
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Definition
| membrane is still at resting potential; g(K) is still low but i(K)=g(K)(Em-Ek); so to have a large outward current the Em-Ek must be postive and large and Ek can't change but Em can and it moves away from Ek in depolarizing direction |
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Term
| effect of myelin on local circuit currents |
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Definition
| increases the membrane resistance so no current flows out of the membrane and can only escape at nodes of Ranvier |
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Term
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Definition
| speed of an action potential explained by time constant and length constant; proportional to λ/tau |
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Term
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Definition
| how rapidly a voltage disturbance settles down; is a product of Rm and membrane capacitance Cm |
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Term
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Definition
| how far along the axon a voltage disturbance will be felt (where disturbance is only 37% of value at x=0) |
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Term
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Definition
| 1. myelinated axons-length constant and conduction velocity both directly proportional to the diameter; 2. unmyelinated axons- length constant and conduction velocity both directly proportional to square of the diameter |
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Term
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Definition
| synaptic transmission occurs from intercellular flow of current |
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Term
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Definition
| synaptic transmission is chemically mediated between most neurons) |
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Term
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Definition
| allow electrical current to pass directly between neighboring cells in electrical synapses |
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Term
| characteristics of gap junctions |
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Definition
| 1. normal state of channel is open; 2. spans two cell membranes; 3. both ends of the gap junction are intracellular; 4. both anions and cations can pass through same channel |
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Term
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Definition
| 1. high intracellular calcium in one of the coupled cells; 2. high intracellular H+ concentration; 3. depolarization of one of the cells |
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Term
| characteristics of transmission at electrical synapses |
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Definition
| 1. can be bi-directional; 2. faster transmission- no synaptic delay; 3. certainty that impulse from presynaptic cell will elicit one in postsynaptic cell; 4. allow cardiac and smooth muscle cells to contract synchronously; 5. allow neighboring cells to interact metabolically |
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Term
| processes of synaptic transmission |
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Definition
| 1. release of chemical transmitter from the presynaptic nerve terminal; 2. diffusion of transmitter to postsynaptic membrane; 3. binding of transmitter to receptor and response; 4. inactivation or removal of transmitter |
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Term
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Definition
| causes a conductance increase in the postsynaptic membrane |
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Term
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Definition
| causes other changes other than conductance changes in postsynaptic cell |
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Term
| structure of neuromuscular junction |
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Definition
| 1. synaptic vesicles containing transmitter accumulate around presynaptic dense bars; 2. cleft is filled with network of CT called basal lamina; 3. junctional folds located opposite of dense bars |
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Term
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Definition
| area where synaptic vesicles accumulate around presynaptic dense bars |
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Term
| synthesis of acetylcholine |
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Definition
| 1. synthesized from acteyl CoA and choline in cytoplasm; 2. choline made from serine or pumped into nerve terminal by sodium dependent, secondary active transport; 3. choline acetyltransferase is synthesized in the cell body and transported to the nerve terminal by axonal transport |
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Term
| formation of synaptic vesicles |
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Definition
| 1. formed within presynaptic nerve terminal; 2. transmitter loaded into vesicles by active transport (by H+ gradient created by ATP dependent pump) |
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Term
| miniature end plate potentials (MEPPs) |
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Definition
| under resting conditions, synaptic vesicles release their contents but do not excite muscle fiber to threshold |
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Term
| evoked transmitter release |
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Definition
| 1. depolarization of presynaptic terminal stimulate release of vesicles; 2. voltage sensitive calcium channels release calcium into cell when terminal depolarized and stimulates exocytosis |
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Term
| increasing extracellular magnesium |
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Definition
| reduces transmitter release by competing with calcium for entry into the calcium channels |
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Term
| excitatory postsynaptic potential (EPSP) |
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Definition
| end plate potential-caused by presynaptic action potential that releases many vesicles of ACh; about 300 vesicles release ACh causing EPP of 50mV (-80 to -30mV) |
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Term
| proteins on the synaptic vesicle |
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Definition
| 1. synaptoagmin-binds calcium that enters through the calcium channels; 2. synaptobrevin/VAMP |
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Term
| proteins on cell membrane |
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Definition
| 1. syntaxin; 2. SNAP-25; 3. Ca2+ channels |
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Term
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Definition
| time necessary for presynaptic depolarization to produce a postsynaptic conductance release; due to vesicle fusion and transmitter release |
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Term
| inactivation of transmitter |
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Definition
| ACh is hydrolyzed by acetylcholine esterase (AChE); drugs are used to block the action of AChE |
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Term
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Definition
| mimics effects of ACh but is not hydrolyzed by AChE |
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Term
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Definition
| ACh derivative used as a paralytic drug by binding to receptor and opens channel for a long time and depolarizes |
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Term
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Definition
| activated by nicotine and inhibited by curare; has binding site for transmitter and chemically gated ionic channel; ACh binds and channel permeable to both sodium and potassium flows and depolarizes the cell |
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Term
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Definition
| membrane potential that is the peak membrane depolarization |
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Term
| differences of NMJ and chemical synapse in the CNS |
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Definition
| 1. CNS postsynaptic cell receives input from many cells; 2. synaptic ending only 0.5-2 microns in diameter; 3. CNS only 3-5 quanta are released (vs. 200-300 ACh); 4. EPSP of single synapse not enough to cause an action potential (must be summed) |
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