Understanding Chapter 8

Whether a neuron fires an action potential depends on

A graded potential above threshold voltage reaching the trigger zone

Putting together each phase of the action potential with the correct events

Rising phase- Opening of voltage gated Na* channels Sodium ions move in to the axon Membrane potential becomes positive Falling phase- Voltage gated Na* channels close Potassium ions move out of the axon Voltage gated K* channels open After hyperpolarization- Potassium continues to move out of the axon Some voltage gated K+ channels still open

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 type of conduction takes place in unmyelinated axons?

continuous conduction

Which of the following statements best describes the resting membrane potential? Choose the best answer

an electrical gradient that exists between the intracellular and extracellular fluids

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

A molecule that carries information across a synaptic cleft is a

neurotransmitter

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

When calcium ions enter the synaptic terminal,

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

What opens first in response to a threshold stimulus?

voltage-gated Na+ channels

Which of the following statements best describes the concept of permeability? Choose the best answer

The ability of a molecule to cross the cell membrane

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

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

Synaptic response to an action potential

1. An action potential arrives at the synaptic terminal. 2. Calcium channels open, and calcium ions enter the synaptic terminal. 3. Vesicles containing neurotransmitter fuse with the plasma membrane of the sending neuron. 4. Neurotransmitter molecules diffuse across the synaptic cleft. 5. The neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron causing ion channels there to open.

Putting the events of the action potentials into the correct sequential order

1. Graded potential that depolarizer 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

Arrange the following events in the correct order from left to right with respect to the function of channels, ion permeability, and changed in the membrane potential

1. Opening of voltage gated Na+ channels 2. Na+ ion flow into the neuron increases 3. Depolarization of the membrane to +30 mV 4. K+ ion flow out of the neuron increases 5. Repolarization of the membrane

Ion movement during an action potential

1. Sodium ions move into the cell 2. Sodium ions stop moving in 3. Potassium ions move out of the axon 4. Less potassium ions move out of the axon

Applying the concept of and ion channels and permeability to a different action potential

1. Voltage gated Na+ channels open 2. Voltage gated Ca2+ channels open 4. Voltage gated K+ channels open

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? A= 300mosmol w/ 3 channels B= 50 mosmol w/ 5 channels

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

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.

What would happen to a patients cellular EK+ if a nurse accidentally administered a potassium solution that caused the patients extracellular potassium ion concentration to rise to 6.01 mM? Assume the body temperature of 37 C

It would become less negative, -85 mV

What would happen to the membrane potential if a resting cell suddenly became more permeable to Ca++?

It would depolarize

Repolarization

Potassium ions are moving out and the membrane potential is becoming more negative as it moves back toward the resting membrane potential

Hyperpolarization

Potassium ions are moving out and the membrane potential is becoming more negative than the resting membrane potential

___ ions are more concentrated on the ___ of the cell, this would result in diffusion if the ion out of the cell

Potassium, inside

Identify whether each of the following would result in the membrane potential becoming more positive or more negative.

More positive- Increasing the concentration of Na+ in the ECF Increasing the concentration of K+ in the ECF More negative- Inserting more K+ leak channels into the cellular membrane Decreasing the number of leak channels for Na+ along the cellular membrane Decreasing the concentration of K* in the ECF

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

Myelinated axons with the largest diameter

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.

Depolarization

Sodium ions are moving in and the membrane potential is becoming less negative than the resting membrane potential

___ ions are more concentrated on the ___ of the cell, this would result in diffusion if the ion into the cell

Sodium, outside

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 time an axon terminal?

The membrane channels are refractory and cannot open

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

The opening of voltage gated Ca2+ channels

During an action potential, where does sodium ion permeability begin to significantly decline?

The peak of depolarization

During an action potential, the rapid decrease in sodium ions permeability and the stimultaneous and rapid increase in potassium ions permeability is responsible for

The repolarization phase

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

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

Neurotransmitters are usually released into the synapses by

exocytosis

Where do most action potentials originate?

initial segment

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.

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

synaptic cleft

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.