Action Potential – Flashcards
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A simple nervous system __________
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Includes sensory information, an integrating center, and effectors
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Most of the neurons in the human brain are __________
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Interneurons
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The motor (somatic nervous) system can alter the activities of its targets, the skeletal muscle fibers, because ___________
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It signals bind to receptor proteins on the muscles
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The point of connection between two communication neurons is called the __________
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Synapse
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In a simple synapse, neurotransmitter chemicals are released by ___________
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The presynaptic membrane
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In a simple synapse, neurotransmitter chemicals are received by __________
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The postsynaptic membrane
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Although the membrane of a "resting" neuron is highly permeable to potassium ions, its membrane potential does not exactly match the equilibrium potential for potassium because the neuronal membrane is also _______________
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Slightly permeable to sodium ions
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The operation of the sodium-potassium "pump" moves __________
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Sodium ions out of the cell and potassium ions into the cell
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IN a resting potential, an example of a cation that is more abundant as a solute in the cytosol of a neuron than it is in the interstitial fluid outside the neuron is __________________
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K+
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The membrane potential in which there is no net movement of the ion across the membrane is called the ___________
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equilibrium potential
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Two fundamental concepts about the ion channels of a "resting" neuron are that the channels
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Open and close depending on stimuli, and are specific as to which ions can traverse them
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If you experimentally increase the concentration of Na+ outside a cell while maintaining other ion concentrations as they were, what would happen to the cell's membrane potential?
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The membrane potential would increase
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The concentration of ions are very different inside and outside a nerve cell due to __________
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Sodium-potassium pumps
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Which of the following ions is most likely to cross the plasma membrane of a resting neuron?
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K+
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For a neuron with an initial membrane potential at -70 mV, an increase in the movement of K ions out of the neurons cytoplasm would result in the ______
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hyper polarization of the neuron
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Opening all of the sodium channels on an otherwise typical neuron, with all other ion channels closed (which is an admittedly artificial setting), should move its membrane potential to ________
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+62 mV
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A graded hyper polarization of a membrane can be induced by ___________
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Increasing its membrane's permeability to K+
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Self-propagation and refractory periods (states) are typical of _________
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action potentials
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The "threshold" potential of a membrane is the ___________
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Minimum depolarization needed to operate the voltage-gated sodium and potassium channels
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Action potentials move along axons__________
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More rapidly in myelinated than in non-myelinated axons
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A toxin that binds specifically to voltage-gated sodium channels in axons would be expected to __________
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Prevent the depolarization phase of the action potential
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After the depolarization phase of an action potential, the resting potential is restored by ___________
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The opening of a voltage-gated potassium channels and closing of sodium channels
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The "undershoot" phase after hyper polarization is due to __________
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Sustained opening of voltage-gated potassium channels
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The fastest possible conduction velocity of action potentials is observed in ________
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Thick, myelinated neurons
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Action potentials are normally carried in only one direction: from the axon hillock toward the axon terminals. If you experimentally depolarize the middle of the axon threshold, using an electronic probe, then __________
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Two action potentials will be initiated, one going toward the axon terminal and one going back toward the hillock
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Why are action potentials usually conduction in one direction?
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The brief refractory period prevents reopening of voltage-gated Na+ channels
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If you experimentally increase the concentration of K+ inside a cell while maintaining other ion concentrations as they were, what would happen to the cell's membrane potential?
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The membrane potential would become less negative
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Which of the following statements about action potentials is correct?
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Action potentials are propagated down the length of the axon
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Why do Na+ ions enter the cell when voltage-gated Na+ channels are open in neurons?
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because the Na+ concentration is much higher outside the cell than it is inside, and the Na+ ions are attracted to the negatively charged interior
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What would probably happen if a long neuron had one continuous myelin sheath down the length of the axon with no nodes of Ranvier?
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The signal would fade because it is not renewed by the opening of more Sodium channels
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A neurophysiologist is investigating nerve reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish's neurons. What is the most likely explanation?
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Unlike the crab, the fish's axons are wrapped in myelin
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Tetrodotoxin blocks voltage-gated sodium channels and ouabain blocks sodium-potassium pumps. If you added both tetrodotoxin and ouabain to a solution containing neural tissue, what responses would you expect?
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Immediate loss of action potential with gradual loss of resting potential
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Which of the following will increase the speed of an action potential moving down an axon?
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-Action potentials move faster in larger diameter axons
-Action potentials move faster in axons lacking potassium ion channels
-Action potentials move faster in myelinated axons
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In multiple sclerosis the myelin sheaths around the axons of the brain and the spinal cord are damaged and demyelination results. How does this disease manifest at the level of the action potential?
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Action potentials move more slowly along the axon
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Neurotransmitters are released from axon terminals via ______________
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Exocytosis
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Acetylcholine release into the junction between a motor neuron and a skeletal muscle binds to a sodium channel and opens it. This is an example of ___________
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A ligand-gated sodium channel
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An inhibitory postsynaptic potential (IPSP) occurs in a membrane made more permeable to ____________
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Potassium ions
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Sequence of events for various stages in transmission at a chemical synapse
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1. An action potential depolarizes the membrane of the presynaptic axon terminal
2. Calcium ions rush into neuron's cytoplasm
3. The synaptic vesicles release neurotransmitter into the synaptic cleft
4. Neurotransmitter binds with receptors associated with the postsynaptic membrane
5. The ligand-gated ion channels open
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The activity of acetylcholine in a synapse is terminated by its ____________
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Degradation on the postsynaptic membrane
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Ionotropic receptors found at synapses are operated via __________
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Ligand-gated ion channels
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An example of a ligand-gated ion channel is ________
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Acetyltlcholine receptors at the neuromuscular junction
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Neurotransmitters categorized as inhibitory are expected to ________
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Hyperpolarize the membrane
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Excitatory postsynaptic potentials (EPSPs) produced nearly simultaneously by different synapses on the same postsynaptic neuron can also add together, creating __________
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A spatial summation
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When two excitatory postsynaptic potentials (EPSPs) occur at a single synapse so rapidly in succession that the postsynaptic neuron's membrane potential has no returned to the resting potential before the second EPSP arrives, the EPSPs add together producing ________
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Temporal summation
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Receptors for neurotransmitters are of primary functional importance in assuring one-way synaptic transmission because they are mostly found on the ________________
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postsynaptic membrane
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Neurotransmitters affect postsynaptic cells by ________
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-initiating signal transduction pathways in the cells
-causing molecular changes in the cells
-affecting ion-channel proteins
-altering the permeability of the cells
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The amino acids that operates as most inhibitory synapses in the brain is __________
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GABA- gamma-aminobutyric acid
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The bolulinum toxin, which causes botulism, reduces the synaptic release of _________
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Acetylcholine
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The heart rate decreases in response to the arrival of __________
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Acetylcholine
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A chemical that affects neuronal function but is not stored in presynaptic vesicles is __________
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Nitric oxide
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Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal?
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Voltage-gated calcium channels in the membrane open
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How could you increase the magnitude of inhibitory postsynaptic potentials (IPSPs) generated at a synapse?
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Increase the K+ permability
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What happens if twice as many inhibitory postsynaptic potentials (IPSPs) as excitatory postsynaptic potentials (EPSPs) arrive at postsynaptic neuron in close proximity?
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No action potential results
