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.
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.
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)
depolarization
Depolarization
Depolarization of the cell membrane. When the sodium channels open there is a rush of sodium ions down their concentration gradient into the cell. As they carry positive charge they reduce the potential difference (inside negative) across the membrane of the neuron.
action potential has a threshold stimulus and depolarization is just change in membrae potential where inside becomes for positive relative to outside. The AP has the ability to actually transmit info over long distance in axons once threshhold stimulus/depolarization is reached
The sodium potassium pump does not function during depolarization, but rather after repolarization. During repolarization, potassium ions flow out of the cell into the extracellular space to reestablish membrane polarity. What the sodium potassium exchange pump does is reestablish the initial ionic concentrations. It does this by exchanging three sodium ions inside the cell for every two potassium ions outside the cell.
Potassium and Sodium
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.
depolarization
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.
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.
depolarization.
opening of sodium channels
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.
depolarization
Depolarization
Yes. Positive ions (sodium) move across the membrane.
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.