Part C – What Determines How Soon One Action Potential Can Follow Another??

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Part C – What Determines How Soon One Action Potential Can Follow Another??

The Na+ channels must reactivate before Na+ ions can move into the cell again, and the rising phase of the second action potential can begin. In this way, the refractory period determines how closely one action potential can follow another.

What determines action potential propagation?

An action potential is generated in the body of the neuron and propagated through its axon. … Because of this, an action potential always propagates from the neuronal body, through the axon to the target tissue. The speed of propagation largely depends on the thickness of the axon and whether it’s myelinated or not.

What determines action potential duration?

Typical MUAP duration is between 5 and 15 ms. Duration is defined as the time from the initial deflection from baseline to the final return of the MUAP to baseline. It depends primarily on the number of muscle fibers within the motor unit and the dispersion of their depolarizations over time.

Why does one action potential trigger another?

A triggering event occurs that depolarizes the cell body. This signal comes from other cells connecting to the neuron, and it causes positively charged ions to flow into the cell body.

Refractory Periods.
Graded Potentials Action Potentials
Triggered by input from the outside Triggered by membrane depolarization

What factors determine the action potential threshold?

Changes in the ion conductances of sodium or potassium can lead to either a raised or lowered value of threshold. Additionally, the diameter of the axon, density of voltage activated sodium channels, and properties of sodium channels within the axon all affect the threshold value.

What does action potential depend on?

Action potentials are driven by channel proteins whose configuration switches between closed and open states as a function of the voltage difference between the interior and exterior of the cell. These voltage-sensitive proteins are known as voltage-gated ion channels.

What are the steps of an action potential?

The action potential has three main stages: depolarization, repolarization, and hyperpolarization.

What does it mean to prolong action potential?

Action potential prolongation is a common finding in human heart failure and in animal models of cardiac hypertrophy. The mechanism of action potential prolongation involves altered expression of a variety of depolarising and hyperpolarising currents in the myocardium.

What causes the long action potential and the plateau?

During phase 1, there is partial repolarization, because of a decrease in sodium permeability. Phase 2 is the plateau phase of the cardiac action potential. Membrane permeability to calcium increases during this phase, maintaining depolarization and prolonging the action potential.

Can action potentials vary in duration?

Action potentials do not vary in amplitude or intensity. They are ”all or nothing” events. If the intensity of a stimulus falls below the neuron’s excitation threshold, nothing happens. … Either way, an action potential will be triggered, and its amplitude and frequency will always be the same for any given cell.

What characterizes repolarization the second phase of the action potential?

What characterizes repolarization, the second phase of action potential? Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70mV.

What causes relative refractory period?

The relative refractory period is the interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before. Refractory periods are caused by the inactivation gate of the Na+ channel.

What causes the rapid change in the resting membrane potential that initiates an action potential?

The electrical signals are rapidly conducted from one node to the next, where is causes depolarisation of the membrane. If the depolarisation exceeds the threshold, it initiates another action potential which is conducted to the next node. In this manner, an action potential is rapidly conducted down a neurone.

Where are action potentials the fastest?

Smaller fibers without myelin, like the ones carrying pain information, carry signals at about 0.5-2.0 m/s (1.1-4.5 miles per hour). The fastest signals in our bodies are sent by larger, myelinated axons found in neurons that transmit the sense of touch or proprioception – 80-120 m/s (179-268 miles per hour).

How is action potential measured?

The potential across the plasma membrane of large cells can be measured with a microelectrode inserted inside the cell and a reference electrode placed in the extracellular fluid. The two are connected to a voltmeter capable of measuring small potential differences (Figure 21-7).

What are the 5 steps of an action potential?

The action potential can be divided into five phases: the resting potential, threshold, the rising phase, the falling phase, and the recovery phase.

What determines membrane resistance?

The membrane resistance is a function of the number of open ion channels, and the axial resistance is generally a function of the diameter of the axon. The greater the number of open channels, the lower the rm. The greater the diameter of the axon, the lower the ri.

How does an action potential spread along the cell membrane?

How does an action potential spread along the cell membrane? a) Potassium leak channels quickly reverse the action potential to move the membrane depolarization away from the original site.

How is resting membrane potential generated and maintained?

The negative resting membrane potential is created and maintained by increasing the concentration of cations outside the cell (in the extracellular fluid) relative to inside the cell (in the cytoplasm). … The actions of the sodium potassium pump help to maintain the resting potential, once established.

What are the 7 steps of an action potential?

7 Cards in this Set
STEP 1 Threshold stimulus to -55mv Stimulus
STEP 4 At +30mv, Na channels close and K ions channels open K ions
STEP 5 K floods out of the cell Out of cell
STEP 6 Hyperpolarization to -90mv Hyper
STEP 7 K channels close and tge resting potential is re-established at -70 Re-established

What triggers an action potential quizlet?

An action potential occurs when a neuron sends information down an axon, away from the cell body. … When the depolarization reaches about -55 mV a neuron will fire an action potential. This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire.

Which one of the following is the correct sequence of events that follows a threshold potential?

What is the correct sequence of these events that follow a threshold potential? (1) The membrane becomes depolarized. (2) Sodium channels open and sodium ions diffuse inward. (3) The membrane becomes repolarized.

What is primarily responsible for the brief hyperpolarization near the end of the action potential?

What is primarily responsible for the brief hyperpolarization near the end of the action potential? Although both types of voltage-gated channels open and close in response to changes in membrane voltage, the voltage-gated potassium channels open and close much more slowly than the voltage-gated sodium channels.

Does hyperpolarization cause action potential?

Hyperpolarization is a change in a cell’s membrane potential that makes it more negative. It is the opposite of a depolarization. It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold.

What happens when action potential is shortened?

If the APD is reduced owing to changes in the K+ channel, the conduction wavelength of the heart is shortened, and the reentry can be easily induced. Conversely, prolonged APD can induce torsades de pointes tachycardia, leading to cardiac death [5, 6].

What causes the rapid depolarization phase of a contractile cell action potential?

In nerve and muscle cells, the depolarization phase of the action potential is caused by an opening of fast sodium channels. This also occurs in non-pacemaker cardiac cells; however, in cardiac pacemaker cells, calcium ions are involved in the initial depolarization phase of the action potential.

How do action potentials move through the heart?

In a normal functioning heart the SA node generates the action potential that will ultimately lead to cardiac contraction. The action potential travels to the AV node, through the bundle of His, into the right and left bundle branches, and lastly through the Purkinje fibers.

What causes the elongated plateau phase of an action potential in cardiac muscle cells Group of answer choices?

Cardiac muscle has a prolonged period of slow repolarization called the plateau phase. … Early repolarization of cardiac muscle cells occurs when voltage-gated Na+ ion channels close and voltage-gated K+ ion channels open.

Why can action potentials travel long distances?

The regenerative properties of Na+ channel opening allow action potentials to propagate in an all-or-none fashion by acting as a booster at each point along the axon, thus ensuring the long-distance transmission of electrical signals.

Do action potentials degrade over distance?

The action potential, as a method of long-distance communication, fits a particular biological need seen most readily when considering the transmission of information along a nerve axon. … Due to the resistance and capacitance of a wire, signals tend to degrade as they travel along that wire over a distance.

What allows the action potential to travel quickly quizlet?

Nodes of Ranvier are gaps in the myelin along the axons; they contain sodium and potassium ion channels, allowing the action potential to travel quickly down the axon by jumping from one node to the next.

What characterizes depolarization the first phase of an action potential?

What characterizes depolarization, the first phase of the action potential? The membrane potential changes from a negative value to a positive value. … Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

Which of the following causes depolarization phase of an action potential?

Depolarization is caused by a rapid rise in membrane potential opening of sodium channels in the cellular membrane, resulting in a large influx of sodium ions. Membrane Repolarization results from rapid sodium channel inactivation as well as a large efflux of potassium ions resulting from activated potassium channels.

What produces the brief hyperpolarization during the action potential?

What produces the brief hyperpolarization during the action potential? Potassium ions continue to leave the cell until all the potassium channels have closed. … The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential.

Can an action potential be generated during the relative refractory period?

During the absolute refractory period, the neuron cannot be excited to generate a second action potential (no matter how intense the stimulus). … During the relative refractory period, the neuron can be excited with stimuli stronger than that needed to bring a resting neuron to threshold.

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