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I think it is the na+ ions because they bring the AP closer to threshold
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∙ 12y ago
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What a neurotransmitter is?
A neurotransmitter is a chemical or peptide in synapses, usually between neurons, a neuron and muscle or a neuron and other organ. The neurotransmitter transmits information to and from and within the brain. When a neurotransmitter is released from the presynaptic cell in response to depolarization of the cell by an action potential, it diffuses across the synaptic cleft and binds a receptor or ligand-gated ion channel on the postsynaptic cell. Binding on the postsynaptic cell alters the resting potential of the postsynaptic cell in either an inhibitory or excitatory manner, making the cell less susceptible or more susceptible (respectively) to an action potential. Examples include, but are not limited to, acetylcholine, GABA, noradrenaline, serotonin and dopamine.
How does a neuron decide whether or not to produce action potentials?
A neuron decides whether or not to produce an action potential by a summation of excitatory and inhibitory signals at the trigger point of the neuron, the axon hillock (or, the initial segment of the axon immediately following the axon hillock), plus a sufficient density of voltage-gated sodium ion pores at the trigger point.Neurons can receive both excitatory and inhibitory inputs at the same time, and if a confluence of those multiple signals at the axon hillock/initial axon segment (or alternatively, an occasion of sufficiently quickly repeated excitatory signals) sums to yield a membrane potential there of about -55 mv, this will cause the large number of voltage-gated sodium ion pores present there to open, allowing a sufficient influx of sodium ions to raise the membrane potential momentarily higher, which depolarizes adjacent regions of the axon, allowing more voltage-gated ion pores to open, allowing more sodium ions in; these actions repeat and continue along the axon, achieving the action potential.It's important to understand that although the level of the summation of signal voltages is the trigger for the action potential, the initial firing of the action potential could not occur if there wasn't a sufficient density of voltage-gated sodium ion pores at the trigger point to allow sufficient sodium ions in to cause the membrane potential in adjacent regions to be high enough to open theirv-gated Na ion pores, so that the action potential could continue to propagate along the axon.
If the axolemma becomes more permeable to potassium ion?
a stronger stimulus will be required to cause an action potential
What happens when presynaptic cell's produce action potentials?
When presynaptic cells produce action potentials, it triggers the opening of voltage-gated calcium channels in the presynaptic membrane. This influx of calcium ions into the presynaptic cell triggers the release of neurotransmitter molecules from small, membrane-bound vesicles. The released neurotransmitters then diffuse across the synapse and bind to receptors on the postsynaptic cell, generating a response in the postsynaptic cell.
How does calcium channels help a synapse create a action potential?
They let calcium ions in, which cause neurotransmitters to be released into a synapse, which cause a neural impulse to flow down a dendrite toward the axon hillock, where the action potential is generated. In more detail: The first steps occur in an axon terminal, which is where the calcium channels are located. When calcium channels are caused to open by the arrival of an action potential at an axon terminal, calcium ions enter the axon terminal, where the calcium ions bind to vesicles containing neurotransmitters, which causes the vesicles to fuse to the cell membrane, forming an opening through which the neurotransmitters are released into the synaptic cleft. The neurotransmitters diffuse quickly across the synaptic cleft (the gap between two neurons), where they fit into receptors on the surface of the postsynaptic neuron, usually on a dendrite or a dendritic spine, and cause ligand-gated sodium ion pores to open, allowing sodium ions into the postsynaptic neuron, which causes an electrotonic impulse to travel down a dendrite, across the soma, to the axon hillock, where the impulses are summed up, and if a sufficient voltage potential is realized, an action potential is initiated in the initial segment of the axon.
How does the end plate potential differ from a EPSP on a post synaptic cell?
End plate potential is the change in potential from neurotransmitters. It can be excitatory or inhibitory. If the action potential wants to continue, it will be excitatory and vice versa. It can be additive, if more action potentials are fired it will increase the end plate potential. An action potential is an all or none response. It will either proceed or it will not proceed depending on the terms of the threshold. It cannot be additive, because there is an absolute refractory period where no additional action potentials can be fired.
What a neurotransmitter is?
A neurotransmitter is a chemical or peptide in synapses, usually between neurons, a neuron and muscle or a neuron and other organ. The neurotransmitter transmits information to and from and within the brain. When a neurotransmitter is released from the presynaptic cell in response to depolarization of the cell by an action potential, it diffuses across the synaptic cleft and binds a receptor or ligand-gated ion channel on the postsynaptic cell. Binding on the postsynaptic cell alters the resting potential of the postsynaptic cell in either an inhibitory or excitatory manner, making the cell less susceptible or more susceptible (respectively) to an action potential. Examples include, but are not limited to, acetylcholine, GABA, noradrenaline, serotonin and dopamine.
What is the difference between the way excitatory and inhibitory transmitters work?
As a rule more than one presynaptic action potential is needed to fire the postsynaptic neuron or muscle so that the trigger to initiate an action potential are either many subthreshold local potentials from different sources or from the same neuron received within a short period of time. The first case is called spatial summation and the second case is called temporal summation. Whether a postsynaptic potential (another term for a local potential) is excitatory or inhibitory depends on what ion channels are affected by the transmitter released from the presynaptic vesicles.
How does a neuron decide whether or not to produce action potentials?
A neuron decides whether or not to produce an action potential by a summation of excitatory and inhibitory signals at the trigger point of the neuron, the axon hillock (or, the initial segment of the axon immediately following the axon hillock), plus a sufficient density of voltage-gated sodium ion pores at the trigger point.Neurons can receive both excitatory and inhibitory inputs at the same time, and if a confluence of those multiple signals at the axon hillock/initial axon segment (or alternatively, an occasion of sufficiently quickly repeated excitatory signals) sums to yield a membrane potential there of about -55 mv, this will cause the large number of voltage-gated sodium ion pores present there to open, allowing a sufficient influx of sodium ions to raise the membrane potential momentarily higher, which depolarizes adjacent regions of the axon, allowing more voltage-gated ion pores to open, allowing more sodium ions in; these actions repeat and continue along the axon, achieving the action potential.It's important to understand that although the level of the summation of signal voltages is the trigger for the action potential, the initial firing of the action potential could not occur if there wasn't a sufficient density of voltage-gated sodium ion pores at the trigger point to allow sufficient sodium ions in to cause the membrane potential in adjacent regions to be high enough to open theirv-gated Na ion pores, so that the action potential could continue to propagate along the axon.
How does neurotransmitters initiate depolarization?
Let's picture a presynaptic neuron, a synaptic cleft, and a postsynaptic neuron. An action potential reaches the terminal of a presynaptic neurone and triggers an opening of Ca ions enters into the depolarized terminal. This influx of Ca ions causes the presynaptic vesicles to fuse with the presynaptic membrane. This releases the neurotransmitters into the synaptic cleft. The neurotransmitters diffuse through the synaptic cleft and bind to specific postsynaptic membrane receptors. This binding changes the receptors into a ion channel that allows cations like Na to enter into the postsynaptic neuron. As Na enters the postsynaptic membrane, it begins to depolarize and an action potential is generated.
If the axolemma becomes more permeable to potassium ion?
a stronger stimulus will be required to cause an action potential
What is nernst potential-?
The Nernst potential refers to the reversal potential of the membrane potential at which there is no net flow of a particular number of ion from one side of the membrane to another.
Electric potential energy of an ion?
The electrical potential energyof an ion is Es= -e^2zc/4pi r.
Which ion enters an axon to start a nerve impulse?
Sodium is the first ion to enter the axon, initiating the action potential.
What happens when presynaptic cell's produce action potentials?
When presynaptic cells produce action potentials, it triggers the opening of voltage-gated calcium channels in the presynaptic membrane. This influx of calcium ions into the presynaptic cell triggers the release of neurotransmitter molecules from small, membrane-bound vesicles. The released neurotransmitters then diffuse across the synapse and bind to receptors on the postsynaptic cell, generating a response in the postsynaptic cell.
What would happen if a chemically gated sodium channel in the postsynaptic membrane were completely blocked?
The nervous system would not work if ion channels were blocked. It would be like parking your car on a hose and trying to get water out of the hose.
What cause the membrane potential of a neuron?
Opening or closing of ion channels at one point in the membrane produces a local change in the membrane potential, which causes electric current to flow rapidly to other points in the membrane.
