Exam 3 - Ch 43

What type of ion channel is responsible for the depolarization phase of an action potential? See Section 43.2 (Page 905) .

Voltage-gated Na+ channels

True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane.

false

A stimulus has opened the voltage-gated sodium channels in an area of a neuron's plasma membrane. As a result, _____ rushes into the neuron and diffuses to adjacent areas; this in turn results in the _____ in the adjacent areas.

sodium ... opening of voltage-gated sodium channels

A neuron has a resting potential of about _____ millivolts.

-70 This is the resting potential, the charge difference found across the plasma membrane of a "resting" neuron.

Rank the axons from slowest to fastest conduction speed. If two axons have the same conduction speed, place one on top of the other.

20 um, 30 um, 40um, 30 um with bubbles

Which neurotransmitter is responsible for the voluntary movement of muscles in your arm? See Section 43.3 (Page 909) .

Acetylcholine

Which term describes an electrical signal generated by neurons?

Action potential.

Which statement correctly describes what causes the second voltage-gated Na+ channel to open?

After the first channel opens, the movement of many types of ions (both inside and outside the cell) alters the distribution of charges near the second channel, causing it to open.

Where in the neuron do action potentials begin?

Axon hillock. -The axon hillock is the region where voltage-gated channels begin in a neuron, near the cell body.

What would be a best control for this experiment? See Section 43.3 (Page 909) .

Collect solution around the nerve end from heart #1 without stimulating the vagus nerve and apply to heart #2.

Sort the phrases into the appropriate bins depending on which type of postsynaptic potential they describe. If a phrase describes both types of potentials, drag it to the "both" bin.

EPSP: depolarizes the postsynaptic membrane results from the movement of \rm Na^+ ions into the postsynaptic cell brings the postsynaptic membrane potential closer to threshold IPSP: hyperpolarizes the postsynaptic membrane results from the movement of \rm K^+ ions out of the postsynaptic cell moves the postsynaptic membrane potential farther away from threshold both: is a graded potential

Which of the following terms describes how a neuronal membrane's potential is altered in the presence of inhibitory signals?

Hyperpolarization. -Inhibitory signals hyperpolarize the membrane and make the membrane potential even more negative than normal.

Drag the labels onto the graph to indicate which presynaptic neuron produced each change in the axon hillock's membrane potential. Assume that the same number of ligand-gated ion channels opens at each synapse. (To review the effect of distance between the synapse and the axon hillock, see Hint 2.) Labels can be used once, more than once, or not at all.

I2,E2,E1,I1,E2,E1

Which term describes the difference in electrical charge across a membrane?

Membrane potential.

Identify two possible mechanisms by which axons conduct action potentials more rapidly. See Section 43.2 (Page 905) .

Increase axon diameter and axon myelination

Which of the following would hyperpolarize a cell's resting potential? See Section 43.2 (Page 905) .

Increasing the permeability of the cell membrane to potassium

What would be the effect on the EPSP if the concentration of the enzyme responsible for degrading the excitatory neurotransmitter increased dramatically in the synapse? See Section 43.3 (Page 909) .

It would decrease the magnitude of the EPSP.

Resting neurons are most permeable to which of the following ions?

K+

Which structure is not part of a neuron?

Myelin sheath. -myelin sheath is the layer of Schwann cells wrapped around a neuron.

In the experiment by Otto Loewi, what type of compound was responsible for the slowing of the heart rate in the second heart? See Section 43.3 (Page 909) .

Neurotransmitter

Which channel is mainly responsible for the resting potential of a neuron?

Potassium leak channel.

What would occur if sodium channels remained open once membrane depolarization was complete?

Repolarization would occur, but much more slowly.

How is an action potential propagated down an axon after voltage-gated sodium channels open in a region of the neuron's membrane?

Sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon. -The entry of sodium ions into the neuron and their diffusion to adjacent areas of the membrane causes those portions of the membrane to become depolarized and results in the opening of voltage-gated sodium channels farther down the axon, which release potassium ions to the outside, returning the charge to its previous state.

Which event triggers the creation of an action potential?

The membrane depolarizes above a certain threshold potential. -Influx of Na+ ions into the neuron can lead to membrane depolarization above the threshold potential; this event triggers the creation of an action potential.

What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?

The sodium channel opens, and Na+ ions flow in.

Which channel maintains the concentration gradients of ions across a neuronal membrane?

The sodium-potassium pump moving Na+ ions out and K+ ions in.

Which of the following statements about action potentials in a given neuron is false?

They are propagated down the length of the dendrite. -propagated down the length of axon

Drag the labels onto the flowchart to indicate the sequence of events that occurs in the presynaptic cell (orange background) and the postsynaptic cell (blue background) after an action potential reaches a chemical synapse.

a. Ca2+ channels in presynaptic membrane open briefly b. Ca2+ ions enter the presynaptic cell c. neurotransmitter-containing vesicles fuse with presynaptic membrane d. neurotransmitter released into presynaptic cleft e. neurotransmitter binds to ligand-gated ion channels in postsynaptic membrane; channels open f. neurotransmitter degraded or removed from cleft; ligand-gated ion channels close

Drag the appropriate labels onto the graph to indicate the status (open or closed) of the voltage-gated Na+ and K+ channels during each phase of an action potential. Labels may be used once, more than once, or not at all.

a. closed, closed b. open, closed c. closed, open d. closed, open e. closed, closed

Drag the labels onto the table to indicate which type(s) of gated ion channels are found in each membrane associated with a chemical synapse. (The letters in the table refer to the lettered structures in the image above.) Labels can be used once, more than once, or not at all.

a. voltage-gated Na+, voltage-gated K+ b. voltage-gated Na+, voltage-gated K+, voltage-gated Ca2+ c. ligand-gated d. none e. voltage-gated Na+, voltage-gated K+

Which of these causes the release of neurotransmitter molecules?

an action potential reaching the end of the axon -When an action potential reaches the end of an axon, vesicles fuse with the plasma membrane and release neurotransmitter into the synaptic cleft.

An action potential moves along a(n) _____.

axon An axon is the only portion of a neuron capable of generating an action potential.

Enter the sequence in which the action potential would pass through the points. Enter the letters in the correct order separated by commas. For example if the order is point (c), then (b), then (a), enter c, b, a. If the action potential would not pass though a point, do not include that point in your answer.

b,a,c Under the artificial conditions, the axon membrane is initially at resting potential everywhere except at the location indicated by the red arrow (where the membrane is artificially brought to threshold). Voltage-gated Na+ channels at that location open and Na+ ions rush into the cell. The depolarization caused by this influx of Na+ ions is "felt" both to the right and left of the open channels. Voltage-gated Na+ channels on both sides open, resulting in an action potential that moves in both directions. It reaches nearby locations (on both sides) first, then locations farther away.

Neurotransmitters are released from neurons in response to the increase in intracellular concentration of what ion?

calcium

The simultaneous arrival of graded depolarization and a graded hyperpolarization of equal but opposite magnitude at a particular location on the dendritic membrane is likely to _____.

cancel each other out, making it appear as if there was no change in membrane potential --Grade potentials are summable, so a depolarization and a hyperpolarization can offset each other to make it appear that there were no changes in membrane potential at that location.

True or false? Action potentials travel in only one direction down an axon because potassium channels in the neuron are refractory and cannot be activated for a short time after they open and close.

false -Action potentials travel in only one direction down an axon because sodium channels in the neuron are refractory.

Which of the following characteristics determines when the refractory period ends?

how long it takes for the voltage-gated Na+ channels to reactivate at the end of an action potential

Which of the following is most likely to result in an action potential at a postsynaptic neuron?

many EPSPs and few IPSPs

The transmission first triggers the _____.

opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron --As a result of the inward flux of sodium ions, that region of the neuron depolarizes.

Drag the labels onto the flowchart to show the sequence of events that occurs once the membrane potential reaches threshold. You may use a label once or not at all.

membrane potential reaches threshold many voltage-gated Na+ channels open Na+ ions rush into the cell membrane potential rises

In a neuron, during the depolarization phase that may trigger an action potential _____.

some voltage-gated sodium channels are open -When a stimulus depolarizes the membrane, some gated sodium channels open, causing further depolarization. If the threshold is reached, most gated sodium channels open, triggering an action potential.

The space between an axon of one neuron and the dendrite of another neuron is called a(n) _____.

synaptic cleft

Neurons store neurotransmitter molecules in vesicles located within _____.

synaptic terminals -Vesicles within synaptic terminals contain neurotransmitter that may be released into the synaptic cleft.

At rest, which of these plays a role in establishing the charge differential across a neuron's plasma membrane?

the sodium-potassium pump moving sodium ions out of the neuron and potassium ions into the neuron -The sodium-potassium pump moves more sodium ions out of the cell than potassium ions into the cell; this net loss of positive ions establishes a charge differential across the plasma membrane.

Part complete Select the choice that describes neurons with the fastest conduction velocity for action potentials.

thick, myelinated neurons -Increased diameter and myelination yields very high conduction velocities for action potentials.