Chapter 8 : Mastering Homework

Drag and drop the following steps associated with the action potential in the correct sequential order.

1. Graded potential that depolarizes membrane to threshold reaches the trigger zone 2. Voltage-gated Na+ channels open 3. Na+ permeability increases 4. Rising phase causes the membrane potential to reach +30 mV 5. Voltage-gated K+ channels open 6. K+ permeability increases 7. Falling phase causes the cells membrane potential to become negative 8. Cell becomes more negative than resting membrane potential due to slow closure of voltage-gated K+ channels 9. Resting membrane potential is re-established

1. _________ ions are more concentrated on the _________of the cell, this would result in diffusion of the ion into the cell. 2. __________ ions are more concentrated on the __________ of the cell, this would result in diffusion of the ion out of the cell.

1. Sodium, outside 2. potassium, inside

What is the magnitude (amplitude) of an action potential?

100 mV - the membrane goes from -70 mV to +30 mV. Thus, during the action potential, the inside of the cell becomes more positive than the outside of the cell.

Which of the following is a similarity between slow synaptic potentials and fast synaptic potentials? a. Both are stimulated by neurotransmitters binding to receptor-channels. b. Both stimulate the opening or closing of ion channels. c. Both stimulate G-protein coupled receptors, which results in opening or closing of ion channels. d. Both start and end quickly.

B

Which is a similarity between spatial summation and temporal summation? a. Both allow subthreshold graded potentials to trigger an action potential. b. Both involve inhibitory postsynaptic potentials (IPSPs) triggering action potentials. c. Both occur when graded potentials overlap in time. d. Both occur when more than one neuron stimulates graded potentials.

A

Which of the following neurons or groups of neurons is NOT considered to be a part of the efferent pathway? a. Sensory b. Somatic motor c. Parasympathetic d. Sympathetic

A

Which two properties determine how fast neurons conduct action potentials? a. Axon diameter and the leak resistance of the membrane b. The leak resistance of the membrane and myelination c. The voltage-gated K+ ion channel concentration and axon diameter d. Myelination and voltage-gated Na+ channel concentration

A

Which of the following would have the fastest action potentials?

A myelinated axon with a large diameter

Most neurons have at least two processes extending from the soma, or cell body. Which type of neuron only has one process extending from the cell body?

A pseudounipolar neuron

What is the definition of an ionotropic receptor?

A receptor that alters ion flow when it binds with its ligand

Which is a difference between the synaptic cleft and the synapse?

A synaptic cleft is the space between a presynaptic axon terminal and a postsynaptic dendrite, and a synapse includes all three of these structures.

How is an action potential propagated along an axon?

An influx of sodium ions from the current action potential depolarizes the adjacent area. Submit

Which is a similarity between graded potentials and action potentials? a. Both need a threshold stimulus to initiate. b. Both can involve voltage-gated sodium channels. c. Both occur in the dendrites. d. Both can involve chemically gated potassium channels.

B

Which of the following statements best describes the resting membrane potential? Choose the best answer. a. an osmotic pressure difference that exists between the intracellular and extracellular fluids b. an electrical gradient that exists between the intracellular and extracellular fluids c. the differences that exist between excitable cells and non-excitable cells d. a concentration gradient that exists between the intracellular and extracellular fluids

B

You were hired to work on a research project to design a drug. Which of these drug mechanisms would decrease the amount of neurotransmitter in the synaptic cleft? a. Inhibiting enzymes that break down neurotransmitters b. Stimulatinguptake c. Blocking receptors with an antagonist d. Decreasing diffusion

B

The two cells below are hypothetical cells with a concentration of 100 mOsm of K+ inside the cells and containing only leak channels for K+ within the membrane. Each cell is placed into a different solution containing different concentrations of K+ in the extracellular fluid. Which of the two cells below has a higher permeability to K+ and why? Choose the best answer.

B, because it has more ion leak channels for K+ than A.

Which characteristic of channels is determined by the gating state of the channel?

Conductance

What type of conduction takes place in unmyelinated axons?

Continuous conduction

Which of the following statements best describes the concept of permeability? Choose the best answer. a. the surface area of a cell and its relationship to the diffusion of water b. the rate at which a molecule crosses the membrane c. whether or not a molecule moves across the cell via passive or active mechanisms d. the ability of a molecule to cross the cell membrane

D

Based upon the changes in permeability seen in the trace below and your knowledge of ion distributions across a cell, predict how ion movements would change during an action potential. Drag and drop each phrase into the appropriate box on the action potential trace.

Image

Below is the action potential of the cardiac contractile cell. Apply the concepts you have gained from neuronal action potential production to the action potential of cardiac contractile cells. Drag and drop the boxes to their appropriate places on the action potential trace.

Image

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open.

Where do most action potentials originate?

Initial segment

During an action potential, activation of voltage-gated sodium and potassium channels occurs at different rates. What is the effect of this difference on ion flow across an axon membrane?

Initially, Na+ flows into the cell and then K+ flows out of the cell.

Drag the labels to identify the sequence of events that occurs at a synapse.

LABELED

Identify whether each of the following would result in the membrane potential becoming more positive or more negative. Drag and drop each statement into the appropriate change.

More Positive: -Increasing the concentration of K+ in the extracellular fluid -Increasing the concentration of Na+ in the extracellular fluidMore Negative: -Decreasing the concentration of K+ in the extracellular fluid -Decreasing the number of leak channels for Na+ along the cellular membrane -Inserting more K+ leak channels into the cellular membrane

In which type of axon will velocity of action potential conduction be the fastest?

Myelinated axons with the largest diameter - The large diameter facilitates the flow of depolarizing current through the cytoplasm. The myelin sheath insulates the axons and prevents current from leaking across the plasma membrane.

Which neural term is a synonym for action potential?

Nerve impulse

Which type of receptor would bind acetylcholine and be found in skeletal muscle?

Nicotinic cholinergic

Which glial cells form myelin in the central nervous system?

Oligodendrocytes

What characterizes repolarization, the second phase of the action potential?

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

Drag and drop each of the following events into the correct columns depicting each of the phases of an action potential.

Rising Phase: -The opening of voltage -gated Na+ (sodium) channels. -Na+ ions move into the axon.-Membrane potential becomes positive. Falling Phase:-Voltage -gated K+ (potassium) channels open. -K+ ions move out of the axon. -Voltage-gated Na+ channels close.After-Hyperpolarization: -Some voltage-gated channels still open .-K+ continues to move out of the axon.

Why does the action potential only move away from the cell body?

The areas that have had the action potential are refractory to a new action potential.

The sympathetic and parasympathetic nervous systems are divisions of which system?

The autonomic nervous system

Why does regeneration of the action potential occur in one direction, rather than in two directions?

The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential.

Why is an action potential conducted in only one direction, from an axon hillock to an axon terminal?

The membrane channels are refractory and cannot open.

What characterizes depolarization, the first phase of the action potential?

The membrane potential changes from a negative value to a positive value.

What event triggers the generation of an action potential?

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

What is the function of the myelin sheath?

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

What triggers exocytosis of synaptic vesicle contents from an axon terminal?

The opening of voltage-gated Ca2+ channels

What would the sudden increase in axonal permeability to sodium cause?

The rising phase of an action potential

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels

What is the first change to occur in response to a threshold stimulus?

Voltage-gated Na+ channels change shape, and their activation gates open.

A neuron has a resting potential of -70 mV and a threshold voltage of -50 mV. There are currently three active synapses on the neuron's dendrites, each located the same distance from the axon. The potential changes are + 40 mV at synapse 1, + 20 mV at synapse 2, and -10 mV at synapse 3. These synaptic potentials decrease by 50% by the time they reach the trigger zone. Will this neuron produce an action potential at this time? Explain. (Hint: Draw a graph of the voltage changes.)

Yes. At the trigger zone, all potentials have halved and will sum as follows: +20 mV (originated at synapse 1), + 10 mV (originated at synapse 2), -5 mV (originated at synapse 3) sum to produce a total potential change of +25 mV. The neuron required a minimum change of +20 mV (-70 mV + 20 mV = -50 mV), so it will fire an action potential.

Whether a neuron fires an action potential depends on __________.

a graded potential above threshold voltage reaching the trigger zone

The velocity of the action potential is fastest in which of the following axons?

a small myelinated axon

A ligand binds to a receptor-channel that stimulates a channel to open. This is a chloride channel. This will stimulate __________.

an inhibitory postsynaptic potential (IPSP)

Where in the neuron is an action potential initially generated?

axon hillock : this region (first part of the axon) receives local signals (graded potentials) from the soma and dendrites and has a high concentration of voltage-gated Na+ channels.

An action potential is self-regenerating because __________.

depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment

Hyperpolarization results from __________.

slow closing of voltage-gated K+channels

Neurotransmitters are usually released into synapses by __________.

exocytosis

The neurons of the central nervous system are also known as __________.

interneurons

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron.....

ion channels in the plasma membrane of the receiving neuron open.

In most cells, the concentration of ions contributing to the membrane potential is __________ in the intracellular fluid compared with the extracellular fluid, with the exception of __________ ions.

lower; potassium

A molecule that carries information across a synaptic cleft is a?

neurotransmitter.

A stronger stimulus to a neuron results in __________.

stronger graded potentials

The small space between the sending neuron and the receiving neuron is the?

synaptic cleft.

The repolarization phase of an action potential results from __________.

the opening of voltage-gated K+channels - as the voltage-gated K+ channels open, K+ rushes out of the cell, causing the membrane potential to become more negative on the inside, thus repolarizing the cell.

If a signal from a sending neuron makes the receiving neuron more negative inside.....

the receiving neuron is less likely to generate an action potential.

When calcium ions enter the synaptic terminal,.....

they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.

The depolarization phase of an action potential results from the opening of which channels?

voltage-gated Na+ channels - when the voltage-gated Na+ channels open, Na+ rushes into the cell causing depolarization.