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For depolarisation to occur as part of an action potential, +40 mV inside the neuron fibre compared to outside the membrane.

For summation after a synapse to determine whether the post-synaptic neuron will fire an action potential, the threshold is +20mV inside the neuron compared to the outside.

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13y ago
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15y ago

In muscle cells an influx of sodium ions into the depolarize the cell. This is because the resting potential of the cell is about -70 mV while the reversal or Nernst potential for sodium is approaching +40mV.

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15y ago

The threshold is the point at which sodium ions start to move into the cell (instead of out of the cell) to bring about the membrane depoloarization. (From Physiology Book)

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Q: At the threshold stimulus sodium ions start to move into the cell or out of cell to bring about the membrane depolarization?
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Related questions

When a nerve is activated by a threshold stimulus the membrane becomes more permeable to?

Potassium and Sodium


Why don't the terms depolarization and action potential mean the same thing?

Depolarization occurs when a stimulus opens sodium channels which allow more sodium to go into the membrane making it less negative and more positive (toward reaching threshold). An action potential can only occur once the membrane reaches threshold which means it has reached the level needed through depolarization. An action potential is a brief reversal in polarity of the membrane making the inside more positive and the outside more negative, the reverse occurs again once the membrane reaches resting potential.


The greater influx of sodium ions results in what of the membrane?

depolarization


What ion is rapidly moving into the cell during the depolarization period of an action potential?

Sodium.A positive ion (cation) that enters the cell (influx) rapidly when the membrane threshold is reached and the voltage gated sodium channels open.This occurs during the rising phase of an action potential, i.e. membrane depolarization beyond the threshold for activation.


What effect of the action potential if sodium channels are kept closed?

The action potential will not generate if the sodium channels are kept closed.This is because the sodium channels are responsible for the dramatic rising phase of membrane depolarization that occurs when the threshold of activation is reached. As a membrane potential gradually depolarizes (which can occur for a variety of reasons such as neurotransmitter stimulation, mechanical deformation of the membrane, etc), that membrane potential gradually comes closer to that threshold of activation. Once that threshold is reached, the voltage gated sodium channels open and allow for a dramatic influx of sodium ions into the cell. This results in a rapid depolarization which is seen as the rising phase of that upward spike noted in an action potential. Without the ability to open these sodium channels we may reach the threshold of activation, but the actual action potential will not occur.


Opening of sodium channels in the membrane of a neuron results in?

depolarization.


Depolarization of the nerve membrane begins with?

opening of sodium channels


When the ions are moving across the membrane during the depolarization and repolarization phases of an action potential they are moving by?

Depends on what stage you are talking about. Stimulus of sodium ions from dendrites of other neurons must reach a threshold. Once that threshold is reached, sodium ions quickly diffuse into the neuron via facilitative diffusion, depolarizing the neuron. Upon this occurring, sodium channels close and potassium ions are pumped out of the neuron via active transport, leading to repolarization of the neuron.


Binding of the neurotransmitters with muscle membrane receptors causes the membrane to become permeable to sodium resulting in the influx of sodium ions an what of the membrane?

depolarization


The combining of the neurotransmitter with the muscle membrane receptors causes the membrane to become permeable to sodium ions and blank of the membrane?

Depolarization


During depolarization does the neurons membrane become negative?

Yes. Positive ions (sodium) move across the membrane.


What is sub threshold Depolarization of nerves?

Subthreshold depolarization refers to a small increase in the membrane potential of a nerve cell that does not reach the threshold for generating an action potential. It is a graded response that occurs when the membrane potential of the nerve cell approaches but does not exceed the threshold for firing an action potential. Subthreshold depolarizations can summate or integrate within the cell to reach the threshold and trigger an action potential.