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32 Cards in this Set
- Front
- Back
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What is the membrane potential?
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The difference in electrical charge between the inside and the outside of a cell
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What is resting potential?
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Steady membrane potential of about -70 mV charge built up across the membrane. In resting potential state, the neuron is polarized.
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Why does the unequal distributions occur?
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1) random motion: ions in neural tissue are in constant random motion
2) Electrostatic pressure: any accumulation of charges, positive or negative, in one area tends to be dispersed by the repulsion among the like charges in the vicinity and the attraction of opposite charges concentrated elsewhere 3) Neural membrane is passive: it does not involve the consumption of energy 4)membrane is active: mechanisms to counteract the influx of Na+ ions by pumping Na+ ions out sa rapidly as they pass in and to counteract the efflux of K+ ions by pumping K+ ions in as rapidly as they pass out |
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What is the tendency of particles in random motion?
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They are more likely to move down their concentration gradients than up them; they are more likely to move down their concentration gradients than up them...more likely to more from areas of high concentration to low and vice versa
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What are the four kinds of ions that contribute significantly to the resting potential?
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Sodium ions (Na+), Potassium ions (K+), Chloride ions (Cl-), and various negatively charged protein ions
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What are postsynaptic depolarizations and what do they do?
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Excitatory postsynaptic potentials (EPSPs) and they increase the likelihood that the neuron will fire
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What are postsynaptic hyperpolarizations called and what do they do?
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Inhibitory postsynaptic potentials (IPSPs), and they decrease the likelihood that the neuron will fire
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What are graded responses?
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Responses proportional to the intensity of the signals that elicit them
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What are two important characteristics for the transmission of postsynaptic potentials?
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1) It is rapid
2) Transmission of EPSPs and IPSPs are decremental: they decrease in amplitude as they travel through a neuron |
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What is the action potential?
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A massive but momentary reversal of the membrane potential from about -70 to about +50 mV. They are ALL-OR-NONE RESPONSES: They either occur to the full extent or not at all
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What is integration?
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Adding or combining a number of individual signals into one overall signal
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What does spatial summation show?
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*Local EPSPs that are produced simultaneously on different parts of the receptive membrane sum to form a greater EPSP
*Simultaneous IPSPs sum to form a greater IPSP *Simultaneous EPSPs and IPSPs sum to cancel each other out |
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What does temporal summation show?
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*Shows how postsynaptic potentials produced in rapid succsesion at the same synapse sum to form a greater signal
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How are action potentials produced ad how are they conducted along the axon?
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Voltage-activated ion channels: Ion channels that open or close in response to changes in the level of the membrane potential
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What is repolarization marked by?
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Outpouring of K+ ions
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What is the absolute refractory period?
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1-2 milliseconds after the initiation of an action potential during which it is impossible to elicit a second one
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What are the 2 ways action potentials along an axon differ from the conduction of EPSPs and IPSPs?
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1) The conduction of action potentials along an axon is nondecremental; action potentials do no grow weaker as they travel
2) Action potentials are conducted more slowly than postsynaptic potentials |
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What is the reason for differences between axonal and postsynaptic conduction?
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EPSPs and IPSPs are passive, whereas the axonal conduction of action potentials is largely active
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Where is the only place in myelinated axons that ions can pass through the axonal membrane?
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The nodes of Ranvier (gaps between adjacent myelin segments)
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What is the transmission of action potentials in myelinated axons called?
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Saltatory conduction
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What does myelination do to the speed of axonal conduction, and why?
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It increases the speed, because conduction is passive and the signal "jumps" along the axon from node to node
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What makes action potentials conducted along an axon faster?
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Larger diameter axons and ones that are myelinated
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What is conduction like typically in interneurons (neurons without axons)
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Decremental and passive
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What are directed synapses?
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Synapses at which the site of neurotransmitter reception are in close proximity
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What are nondirected synapses?
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Synapses at which the site of release is at some distance from the site of reception
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What do all large neurotransmitters have in common?
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They are all neuropeptides (short proteins)
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What is exocytosis?
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The process of neurotransmitter release
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When a neuron is at rest, where do synaptic vesicles that contain small-molecule neurotransmitters congregate?
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Near sections of the presynaptic membrane that are particularly rich in voltage-activated calcium channels
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How does the exocytosis of small-molecule neurotransmitters differ from the exocytosis of neuropeptides?
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Small-molecule neurotransmitters are typically released in a pulse each time an action potential triggers a momentary influx of Ca2+ ions through the presynaptic membrane; in contrast, neuropeptides are typically released gradually in response to general increases in the level of intracellular Ca2+ ions
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What is a ligand?
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Any molecule that binds to another
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What are ionotropic receptors?
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Receptors that are associated with ligand-activated ion channels
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What are metabolic receptors?
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Receptors that are associated with signal proteins and G proteins
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