Chapter 11.7 Anatomy

24 July 2022
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presynaptic neuron
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in a synapse, neurotransmitters are stored in vesicles located in the _________. Yes, neurotransmitters are stored in the axon terminals of the presynaptic neuron.
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voltage-gated Ca+2 channels
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an action potential releases neurotransmitter from a neuron by opening which of the following channels? Yes, opening of these channels causes calcium to move into the axon terminal. Calcium inside the neuron causes the vesicles to merge with the membrane and release the neurotransmitter via exocytosis into the synaptic cleft.
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chemically gated; postsynaptic
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binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane. Yes, the neurotransmitter is a chemical released from the presynaptic membrane, so it would open chemically gated channels on the postsynaptic membrane.
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either depolarize or hyperolarize
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binding of the neurotransmitter to its receptor causes the membrane to _______________. Yes, the neurotransmitter can cause the postsynaptic membrane to either depolarize or hyperpolarize, depending on which ion channels are opened.
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acetylcholine
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The mechanism by which the neurotransmitter is returned to a presynaptic neuron's axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned? Yes, acetylcholine is broken down by acetylcholinesterase before being returned to the presynaptic neuron's axon terminal.
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the amount of neurotransmitter released and the amount of calcium that enters the axon terminal
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at a chemical synapse, the intensity of the stimulus is coded by __________.
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no neurotransmitter was released
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when the calcium was removed from the extracellular solution ________.
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the amount of neurotransmitter released decreased
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when magnesium was added to the extracellular solution ________.
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divalent cations
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calcium and magnesium are both ____________.
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all of these
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a syapticcleft, or synaptic gap, can be found between a neuron and ______________.
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a postysnaptic potential
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the membrane potential that occurs when neurotransmitters bind to their receptors is called _________.
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at the axon terminal
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the release of neurotransmitter occurs _________________.
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an acti potential arrives at the axon terminal
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which of the following occurs first?
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neuron
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a postsynaptic cell can be neuron, a muscle cell, or a secretory cell. wha is an example of a presynaptic cell? A neuron is the only type of presynaptic cell. Neurons release neurotransmitters, effectively changing an electrical signal or action potential into a chemical signal that can communicate across the synaptic cleft to the postsynaptic cell.
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chemically gated channels
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which component has a role in the postsynaptic cell during synaptic activity? Neurotransmitter binds to receptors on the postsynaptic cell. These chemically gated channels open, allowing the transfer of the "signal" from a presynaptic neuron to the postsynaptic cell.
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calcium influx into the synaptic terminal causes vesicle fusion.
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what is the role of calcium in synaptic activity? When an action potential reaches the synaptic terminal, voltage-gated channels open and calcium enters the cell. Calcium causes vesicles to fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft.
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neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane.
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what is the direct role of neurotransmitter at a chemical synapse? neurotransmitter leaves the presynaptic neuron by exocytosis and binds receptors on the postsynaptic cell membrane, opening the channels. When ions enter the postsynaptic cell, a graded potential takes place.
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exocytosis
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neurotransmitter is released from presynaptic neurons through what mechanism? Neurotransmitter molecules are released from vesicles that fuse with the plasma membrane through exocytosis. Note that "exo-" means "outside" and "cytosis" means "cell." Once released, neurotransmitter diffuses across the synaptic cleft.
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a chemically gated channel
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what type of channel on the postsnaptic membrane binds neurotransmitter? Chemically gated channels bind a specific chemical, which causes the channel to open. At chemical synapses, neurotransmitter molecules are released by the presynaptic neuron and bind to chemically gated channels on the postsynaptic cell membrane. The opening of these channels allows ions to diffuse across the membrane, causing a graded potential in the postsynaptic cell.
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reuptake and degradation
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in addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity? To terminate neurotransmitter effects, neurotransmitter molecules must be removed from the synaptic cleft. Reuptake does this by moving neurotransmitter back into the presynaptic neuron. Diffusion causes neurotransmitter to drift away from the synaptic cleft. Degradation occurs when enzymes break down neurotransmitter. As long as neurotransmitter molecules remain in the synaptic cleft, the chemically gated channels on the postsynaptic cell will continue to bind them and cause graded potentials.
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(c) Action potential arrives at axon terminal (a) Voltage-gated calcium channels open (e) Neurotransmitter released into synaptic cleft (b) Neurotransmitter binds to receptors (f) Graded potential generated in postsynaptic cell (d) Neurotransmitter is removed from the synaptic cleft
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Events that occur during synaptic activity are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Voltage-gated calcium channels open (b) Neurotransmitter binds to receptors (c) Action potential arrives at axon terminal (d) Neurotransmitter is removed from the synaptic cleft (e) Neurotransmitter released into synaptic cleft (f) Graded potential generated in postsynaptic cell The correct sequence starts with a neural signal at the presynaptic cell, followed by the release of neurotransmitter, the creation of a graded potential in the postsynaptic cell, and degradation of the neurotransmitters. Neurotransmitters transfer information between a neuron and a postsynaptic cell. This process gets a "message" across a physical separation much like sending a text to your friend who is across town.
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dendrite cell body axon hillock axon presynaptic terminal
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arrange the parts in order, from left to right, of a successful direct depolarization path within one neuron. Incoming messages to the dendrites or cell body pass through neuroplasm to the axon hillock. If a threshold stimulus value is reached at the axon hillock, depolarization passes down the axon to the presynaptic terminal containing synaptic vesicles.
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small, consecutive steps of Na+ penetration into the axon along its length
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which of the best characterizes depolarization? The direction of flow for the Na+ ion is from the extracellular fluid into the cytoplasm (ICF). This occurs in small, consecutive steps.
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voltage-gated membrane channels open, and Ca+2 enters the cytoplasm, increasing intracellular calcium.
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when an action potential arrives at the end of the axon termi, a series of events take place that result in the release of neurotransmitter from the presynaptic axon. select the answer that correctly describes the primary stimulus for vesicles to move toward the cell membrane and eventually release their contacts. Calcium enters the cytoplasm as a result of changes in the gated channel protein, increasing cytoplasmic content of Ca+2.
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membrane organelles fuse with the membrane and release contents out of the cell
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which statement best describes exocytosis? The rise in intracellular Ca+2 binding with receptor proteins triggers the synaptic vesicles to fuse with the membrane and release contents out of the cell.
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an increase in the amount of neurotransmitter exocytized by the presynaptic axon
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what condition will increase the diffusion of molecules, such as neurotransmitters? Increased differences in concentrations, or increased gradients, will increase diffusion.
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bound at postsynaptic receptors to open postsynaptic ion channels
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if the membrane of a postsynaptic dendrite is setting up a graded potential, what must have happened after neurotransmitter was released by the presynaptic terminal? Diffusion carries the transmitter from higher to lower concentration. The transmitter binds to a receptor on the postsynaptic membrane and effects a cascade of events, resulting in the opening of ion channels. These lead to graded potentials, which may set up an action potential.
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1) action potential sweeps down presynapatic axon 2) calclium channels open in axon terminal 3) synaptic vesicles fuse and exocytize neurotransmitter 4) diffusion of neurotransmitter into extracellular fluid separating two neuron's membranes 5) graded potential at postsynaptic membrane
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drag and drop the descriptie labels of events into the correct sequence at the chemically synapse
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presynaptic axon to synapse to dendrite or postsynaptic cell body
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which of the following choices best represents snaptic transmission? Synaptic transmission uses a synapse and, therefore, two cells. Incoming messages are dendritic or somatic; outgoing messages are axonal.
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local graded potential and action potential transmission is blocked, and there is no response by the postsynaptic cell, the muscle
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Predict the possible effect of a drug that totally blocks the neurotransmitter receptor on the postsynaptic membrane. For example, curare is a neurotoxin used by several South American cultures. The primary effect of curare is that acetylcholine, a major neuromuscular neurotransmitter, cannot bind at its receptor because curare is blocking it. Predict the possible effects of curare on the postsynaptic membrane and muscle. No ion channel or graded potential can be initiated; therefore, there is no subsequent action potential.
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Ca2+, which then causes release of neurotransmitter from the axon terminal
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what ion entering the axon terminal at A, and what effect does it have? Calcium ion channels open when the membrane is depolarized, and the inflow of Ca2+ leads to the release of neurotransmitters from synaptic vesicles.
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exocytosis
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by which nethod does the structure B release neurotransmitter? The influx of Ca2+ triggers the release of neurotransmitters stored in synaptic vesicles (B) by exocytosis.
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chemically gated
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how would the receptors at C best be classified? the receptors at C are affected by the binding of a chemical neurotransmitter.
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the membrane potential of the postynaptic membrane changes
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which of the following statements most accurately describes the effects caused by binding of the neurotransmitter (green dots) to the structure labeled C? Binding of the neurotransmitter to the receptor at C causes the opening of receptor-associated ion channels. Depending on the particular types of channels that open, diffusion of certain ions (typically Na+, K+, or Clรขห†') will cause a depolarizing or hyperpolarizing effect on the postsynaptic membrane.
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reuptake of the neuroransmitter by transport into the postynaptic cell
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the box labeled D illustrates three mechanisms by which the effects of a neurotransmitter may be terminated. which of the following mechanisms is NOT included in the figure? Neurotransmitters are generally not transported into the postsynaptic cell upon which they exert their effects.
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direct signaling involves the activiation of G Proteins
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which description fo synapses is NOT correct? Indirect signaling involves G Proteins. Direct signaling involves opening ion channels that affect the polarization of the membrane.
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inability to destory and remove acetylcholine from the synaptic cleft.
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loss of function in the enzyme acetylcholinesterase would result in which of the following?
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the synaptic cleft transmits a chemical signal to the post synaptic cell through diffusion of neurotransmitters across the cleft.
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select the correct statement regarding chemical synapses.
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true
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a stimulus traveling toward a synapse appears to open calciium ion channels at the presynaptic end, which in turn promotes fusion of synaptic vesicles to the axonal membrane
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Na+ entering the cell
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During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving? During the depolarization phase of the action potential, open Na+ channels allow Na+ ions to diffuse into the cell. This inward movement of positive charge makes the membrane potential more positive (less negative). The depolarization phase is a positive feedback cycle where open Na+ channels cause depolarization, which in turn causes more voltage-gated Na+ channels to open.
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Na+ channels are inactivating, and K+ channels are opening.
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what is happening to voltage-gated channels at this point in the action potential? As voltage-gated Na+ channels begin to inactivate, the membrane potential stops becoming more positive This marks the end of the depolarization phase of the action potential. Then, as voltage-gated K+ channels open, K+ ions rush out of the neuron, following their electrochemical gradient. This exit of positively-charged ions causes the interior of the cell to become more negative, repolarizing the membrane.
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at the end of the depolarization phase, as the membrane potential approaches its peak value
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During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)? Voltage-gated Na+ channels are opened by depolarization and then quickly inactivated. Once inactivated, these channels cannot pass Na+ ions. At the peak of the action potential, a large number of Na+ channels are open, but they are rapidly inactivating. As the action potential enters the repolarization phase, the number of open Na+ channels continues to decrease because more and more inactivation gates close. The number of inactivated Na+ channels is greatest towards the end of the repolarization phase.
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K+ ions leaving the cell through voltage-gated channels
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The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________. The opening of voltage-gated K+ channels allows K+ ions to exit the cell, repolarizing the membrane. In other words, the exit of K+ ions makes the membrane potential more negative. K+ also exits through leakage channels during this phase because leakage channels are always active. However, most of the membrane permeability to K+ during this phase is due to voltage-gated channels. Voltage-gated K+ channels make the action potential more brief than it would otherwise be if only leakage channels were available to repolarize the membrane.
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K+ ions diffusing through voltage-gated channels
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During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________. The large number of voltage-gated K+ channels opening during the repolarization phase quickly makes the membrane potential more negative as positively-charged K+ ions leave the cell. K+ ions continue to leave through open channels as the membrane potential passes (becomes more negative than) the resting potential. This hyperpolarization phase of the action potential is therefore due to K+ ions diffusing through voltage-gated K+ channels. The membrane potential remains more negative than the resting potential until voltage-gated K+ channels close. This period of hyperpolarization is important in relieving voltage-gated Na+ channels from inactivation, readying them for another action potential.
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K+ channels close. Na+ channels go from an inactivated state to a closed state.
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During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels? Voltage-gated K+ channels are opened by depolarization. This means that as the membrane potential repolarizes and then hyperpolarizes, these K+ channels close. With the closing of voltage-gated K+ channels, the membrane potential returns to the resting membrane potential via leakage channel activity. Resetting voltage-gated Na+ channels to the closed (but not inactivated) state prepares them for the next action potential.
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The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time.
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Tetraethylammonium (TEA) blocks voltage-gated K+ channels such that K+ cannot pass even when the channels are open. However, TEA leaves K+ leakage channels largely unaffected. How would you expect the action potential to change if you treated a neuron with TEA? The passage of K+ ions through open voltage-gated K+ channels is an important component of the repolarization phase of the action potential. However, repolarization would still occur (albeit more slowly) in the presence of TEA. Once voltage-gated Na+ channels open during the depolarization phase, those same Na+ channels quickly inactivate. In other words, open Na+ channels inevitably inactivate regardless of whether K+ channels open or not. This means that the depolarization phase of the action potential stops on its own. Once Na+ channels inactivate, the membrane potential is set by other open channels. If voltage-gated K+ channels are blocked by TEA, then the membrane will be (slowly) set, by leakage channels, to the resting membrane potential.