Often asked: When two or more graded potentials arrive at the trigger zone, which of the following could happen?

What causes a graded potential to degrade?

Graded potentials are initiated by a stimulus, like a drug or neurotransmitter, that activates a ligand-gated channel – for example, a ligand gated Na+ channel. In this example, that would lead to local depolarization that would diffuse through the dendrite, eventually degrading.

Where do most graded potentials come from?

Graded potentials are brought about by external stimuli (in sensory neurons) or by neurotransmitters released in synapses, where they cause graded potentials in the post-synaptic cell. Action potentials are triggered by membrane depolarization to threshold.

When a second EPSP arrives at a single synapse before the effects of the first have disappeared What occurs?

If one nerve impulse arrives at a synapse before the effects of a previous postsynaptic potential have disappeared, the two postsynaptic potentials summate in time, producing a larger change in the membrane potential of the receiving cell.

When two EPSPs arrive at a single postsynaptic neuron at the same time what occurs?

If the sum of the two EPSPs (E1 + E2) depolarizes the postsynaptic neuron sufficiently to reach the threshold potential, a postsynaptic action potential results. Summation thus allows subthreshold EPSPs to influence action potential production.

What are the two types of graded potentials?

Graded potentials can be of two sorts, either they are depolarizing or hyperpolarizing (Figure 1).

How does a graded potential occur?

A graded potential is produced when a ligand opens a ligand-gated channel in the dendrites, allowing ions to enter (or exit) the cell. The graded potential will degrade with distance, so it would decrement before reaching the end of the axon if an action potential were not generated.

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Are EPSPs graded potentials?

EPSPs. Graded potentials that make the membrane potential less negative or more positive, thus making the postsynaptic cell more likely to have an action potential, are called excitatory postsynaptic potentials ( EPSPs ). This shows the temporary and reversible nature of graded potentials.

Are graded potentials self propagating?

An action potential is generated due to membrane potential reaching threshold due to a graded potential. At this point action potentials become self propagating. This means that one action potential automatically triggers the neghboring membrane areas into producing an action potential.

Why do graded potentials decrease with distance?

Graded potentials die out over a short distance. The reason for this is because the membrane will always default to the resting membrane potential because ions are free to diffuse across the membrane. The way nerves get around this is by insulating themselves in myelin.

Which type of synapse is most prevalent in the nervous system?

Axodendritic synapses are the commonest type of synapse in the CNS and are described fully in Chapter 6, p. 110. Axosomatic synapse: here the axon synapses directly with the soma – these may be excitatory or inhibitory.

When the neuron is at rest Which statement is true?

When a neuron is at rest the internal charge inside the cell is lower than that of the surrounding charge outside. The internal cellular charge is considered as negative as the charge inside the cell is lower than that of the outside.

Which neural term is a synonym for action potential?

Whats the synonym to action potential? AP, spike, nerve impulse, conduction signal.

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Are EPSPs stronger than IPSPs?

Although the particulars of postsynaptic action can be complex, a simple rule distinguishes postsynaptic excitation from inhibition: An EPSP has a reversal potential more positive than the action potential threshold, whereas an IPSP has a reversal potential more negative than threshold (Figure 7.6D).

What happens when two or more synapses on a single postsynaptic neuron are activated at the same time?

However, when the synapses fire at nearly the same time, the EPSPs add up to produce an above -threshold depolarization, triggering an action potential. This process is shown on a graph of voltage in millivolts vs. time in milliseconds. The graph monitors the membrane potential—voltage—at the axon hillock.

What causes EPSPs and IPSPs?

EPSPs can also result from a decrease in outgoing positive charges, while IPSPs are sometimes caused by an increase in positive charge outflow. The flow of ions that causes an EPSP is an excitatory postsynaptic current (EPSC). EPSPs, like IPSPs, are graded (i.e. they have an additive effect).

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