Lab #6

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

100 mV

axon potential

Also called a nerve impulse transmitted by axons.

How is an action potential propagated along an axon?

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

What is the role of calcium in synaptic activity?

Calcium influx into the synaptic terminal causes vesicle fusion with the presynaptic membrane.

What is TRUE about the relative refractory period? A. It is possible to generate an action potential if the stimulation strength is large enough. B. The relative refractory period comes after the absolute refractory period. C. Some of the voltage-gated Na+ channels have "reset" and are no longer inactivated. D. All of the above are true.

D. all of the above

relative refractory response

During this time an exceptionally strong stimulus can trigger a response.

During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)?

at the end of the depolarization phase, as the membrane potential approaches its peak value

Where are action potentials regenerated as they propagate along a myelinated axon?

at the nodes of Ranvier

What has a role in the postsynaptic cell during synaptic activity?

chemically gated channels

During the action potential, when does sodium permeability initially decrease?

during the peak of depolarization

Neurotransmitter is released from presynaptic neurons through what mechanism?

exocytosis

Where in the neuron is an action potential initially generated?

initial segment or axon hillock

How does the membrane potential change during depolarization?

it becomes less negative

What happens during the absolute refractory period?

it is impossible to generate an action potential in that section of membrane, regardless of the stimulus strength.

voltage-gated channels

open and close in response to changes in the membrane potential

mechanically gated channels

open in response to physical deformation of the receptor (as in sensory receptors for touch and pressure)

chemically gated channels (ligand gated channels)

open when the appropriate chemical (in this case a neurotransmitter) binds

In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?

reuptake and degradation

The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.

saltatory conduction

An axon terminal forms a synapse on a dendrite and fires several action potentials in quick succession, resulting in multiple EPSPs in the postsynaptic cell that can be added together to create a greater depolarization of the postsynaptic membrane. This is known as________.

temporal summation

An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism?

the generation of local currents

During an action potential, the rapid decrease in sodium permeability and simultaneous increase in potassium permeability is responsible for __________.

the repolarization phase

What type of channel has an "inactivation" phase?

voltage-gated Na+ channels

Action potentials are due to which type of ion channels?

voltage-gated channels

How do action potential propagation speeds compare in myelinated and unmyelinated axons?

Propagation is faster in myelinated axons.

What is meant by Na+ channel inactivation?

The Na+ channel no longer allows Na+ ions to pass through it.

What is the significance of the refractory period in an axon?

The action potential can only travel one-way down the axon because of the refractory period.

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.

depolarization

The interior of the cell becomes less negative due to an influx of sodium ions

What must happen before an action potential is generated?

The membrane potential at the axon hillock must reach a trigger point called threshold potential.

depolarize

The membrane potential is becoming more positive than the resting membrane potential.

hyperpolarize

The membrane potential is more negative than the resting membrane potential.

repolarize

The membrane potential is moving from a more positive value toward resting membrane potential.

absolute refractory period

The neuron can't respond to a second stimulus, no matter how strong

In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon?

The nodes are more permeable to ions.

During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?

The previous axonal segment is in the refractory period.

Why does resting membrane potential occur?

It is due to K+ and Na+ leakage channels.

During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?

K+ channels close. Na+ channels go from an inactivated state to a closed state.

During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.

K+ ions diffusing through voltage-gated channels

The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________.

K+ ions leaving the cell through voltage-gated channels

What is meant by spatial summation?

Multiple synapses generate EPSPs and IPSPs on the postsynaptic cell that are added together as they travel toward the axon hillock.

The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?

Na+ (sodium)

What is happening to voltage-gated channels at the peak of action potential?

Na+ channels are inactivating, and K+ channels are opening.

During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?

Na+ is entering the cell.

What is the role of neurotransmitter at a chemical synapse?

Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane.

repolarization

The specific period during which potassium ions diffuse out of the neuron due to a change in membrane permeability.

The myelin on myelinated neurons can be degraded or destroyed in diseases such as multiple sclerosis-a process called demyelination. If a myelinated neuron was affected by demyelination, how would this affect action potentials in that neuron?

The speed of action potential propagation would be slower.

EPSPs (Excitatory PostSynaptic Potentials)

They are excitatory. They depolarize the postsynaptic cell and make it more likely to fire an action potential.

Do Na+ channels or K+ channels open more slowly in generating action potential?

Voltage-gated K+ channels open more slowly than voltage-gated Na+ channels, even though they are activated at the same time.

What type of channel on the postsynaptic membrane binds neurotransmitter?

a chemically gated channel

A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?

a neuron

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

a small myelinated axon