ANAP Lab 6

Action 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.

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

During the peak of depolarization

Describes EPSPs and IPSPs?

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

What is meant when we say the action potential is an "all-or-none"event?

For a given neuron, once the action potential is generated, it maintains the same amplitude and duration as it travels down the axon.

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)

Absolute Refractory Period

Na+ channels begin to recover from inactivation and if strong enough stimuli are given to the neuron, it may respond again by generating action potentials.

What is meant by Na+ channel inactivation?

Na+ channels no longer allow Na+ ions to pass through it

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 TRUE about the resting membrane potential (RMP)?

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 must happen before an action potential is generated?

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

Hyperpolarize

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

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

The repolarization phase

Relative Refractory Period

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

Depolarize

-The membrane potential is becoming more positive than the resting membrane potential. -The interior of the cell becomes less negative due to an influx of sodium ions.

Repolarize

-The membrane potential is moving from a more positive value toward resting membrane potential. -The specific period during which potassium ions diffuse out of the neuron due to a change in membrane permeability.

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

100 mV

List in order of events that occur during synaptic activity 1. Voltage-gated calcium channels open 2. Neurotransmitter binds to receptors 3. Action potential arrives at axon terminal 4. Neurotransmitter is removed from the synaptic cleft 5. Neurotransmitter released into synaptic cleft 6. Graded potential generated in postsynaptic cell

3, 1, 5, 2, 6, 4

A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell? A.) a neuron B.) a secretory cell C.) a muscle cell D.) a Schwann cell

A.) a neuron -This is the only type of presynaptic cell

During the absolute refractory period A.) it is impossible to generate an action potential in that section of membrane, regardless of the stimulus strength. B.) you can stimulate an action potential if the stimulus strength is great enough. C.) the voltage-gated Na+ channels are closed, and are ready to open when the membrane gets depolarized. D.) the voltage-gated K+ channels are closed and cannot open.

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

Where in the neuron is an action potential initially generated?

Axon hillock

Neurotransmitter is released from presynaptic neurons through what mechanism? A.) phagocytosis B.) endocytosis C.) pinocytosis D.) exocytosis

D.) exocytosis

How do action potential propagation speeds compare in myelinated and unmyelinated axons? A.) Propagation is faster in unmyelinated axons. B.) Propagation is faster in myelinated axons. C.) Propagation in unmyelinated axons is faster over short distances, but propagation is faster in myelinated axons over long distances. D.) Propagation speeds are similar in both axon types.

B.) Propagation is faster in myelinated axons

The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________. A.) continuous conduction B.) saltatory conduction C.) local conduction D.) myelinated conduction

B.) Salatory Conduction

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? A.) Action potentials would propagate in both directions along the axon. B.) The speed of action potential propagation would be slower. C.) Initial generation of action potentials would be more difficult. D.) The speed of action potential propagation would be faster.

B.) The speed of action potential propagation would be slower

All of the following are characteristics of graded (synaptic) potentials EXCEPT: A.) They can be excitatory or inhibitory. B.) They are considered to be "all-or-none". C.) Their amplitude decays over distance. D.) They can vary in amplitude.

B.) They are considered to be "all-or-none".

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 A.) spatial summation B.) temporal summation C.) synaptic transmission D.) action potential propagation

B.) temporal summation

Where are action potentials regenerated as they propagate along a myelinated axon? A.) at the axon hillock B.) at the myelinated segments C.) at the nodes of Ranvier D.) at every segment of the axon

C.) At the nodes of Ranvier

In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon? A.) The nodes are longer segments of the axon. B.) The nodes are wrapped in myelin. C.) The nodes are more permeable to ions. D.) The nodes are less numerous.

C.) More permeable to ions

What is the significance of the refractory period in an axon? A.) The refractory period leads to saltatory conduction in the axon. B.) The velocity of the action potential propagation is slower during the refractory period. C.) The action potential can only travel one-way down the axon because of the refractory period. D.) Less neurotransmitter is released during the refractory period.

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

During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction? A.) New action potential generation near the soma repels previously generated action potentials, causing them to always propagate away from the soma. B.) Positive charges only move in one direction after they enter the cell. C.) The previous axonal segment is in the refractory period. D.) The extracellular sodium concentration is too low around the previous axonal segment for an action potential to be (re)generated.

C.) The previous axonal segment is in the refractory period

What type of channel on the postsynaptic membrane binds neurotransmitter? A.) a leakage channel B.) a voltage-gated channel C.) a chemically gated channel D.) a mechanically gated channel

C.) a chemically gated channel

In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity? A.) exocytosis and degradation B.) excitation and degradation C.) reuptake and degradation D.) reuptake and inhibition

C.) reuptake and degradation

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 are true.

What is the role of calcium in synaptic activity? A.) Calcium diffuses across the synaptic cleft and binds to receptors on the postsynaptic neuron. B.) Calcium degrades neurotransmitter in the synaptic cleft. C.) Calcium influx into the axon causes an action potential to propagate into the synaptic terminal. D.) Calcium influx into the synaptic terminal causes vesicle fusion with the presynaptic membrane.

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

Which one of the following statements about membrane potential changes is TRUE? A.) During hyperpolarization, the membrane potential becomes more positive. B.) During depolarization the membrane potential becomes more negative. C.) During repolarization, the membrane potential moves from 0 mV to +30 mV. D.) During depolarization, the membrane potential becomes less negative. E.) All the statements are true.

D.) During depolarization, the membrane potential becomes less negative.

What is the role of neurotransmitter at a chemical synapse? A.) Neurotransmitter causes calcium to flood into the presynaptic cell. B.) Neurotransmitter causes an action potential in the postsynaptic cell. C.) Neurotransmitter causes vesicles to fuse with the presynaptic membrane. D.) Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane.

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

Which of the following has a role in the postsynaptic cell during synaptic activity? A.) calcium channels B.) axon terminal C.) vesicles filled with neurotransmitter D.) chemically gated channels

D.) chemically gated channels -Neurotransmitter binds to the receptor on the postsynaptic cell -These chemically gated channels open, allowing the transfer of the "signal" from a presynaptic neuron to the postsynaptic cell.

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.

Action potentials are due to which type of ion channels?

Voltage-gated Channels

What is TRUE about the opening of voltage-gated Na+ and K+ channels?

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

Which type of channel has an "inactivation" phase?

Voltage-gated Na+ channels

Refractory Period

a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.

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

a small myelinated axon

Chemically Gated Channels

also known as ligand-gated channels, open when the appropriate chemical or ligand (in this case a neurotransmitter) binds.

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

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).

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