What happens when the action potential reaches the synaptic knob?

Answer 1

release of acetylcholine

Answer 2

Synaptic Knob

Answer 3

Synaptic Bulb

Answer 4

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RE:
What happens when the action potential reaches the synaptic knob?

Answer 5

most generally the stimulus will travel in one direction either afferent or efferent the stimulus is chemical (neurotransmitters) between neurons and electrical inside of each neuron that's why it's called an electro-chemical stimulus the chemical leaves one neuron and crosses the synapse to the next neuron it opens ligand gated channels that let ions into the next neuron the ions build charge (depolarizing) the cell body in other words, the cell body integrates the accumulated charge into electrical called an action potential the action potential electric stimulus travels down the axon if the axon is myelinated it travels faster when the electric stimulus reaches the end of the axon it releases chemical that chemical (neurotransmitter) crosses the synapse to the next neuron

Answer 6

When the action potential of a neuron propagates all the way down the axon, it arrives at the presynaptic terminal (or synaptic bouton). This terminal is a specialized structure, essentially a swelling of the axon end, that is in very close apposition to the postsynaptic dendrite. It is completely filled with vesicles containing the neurotransmitter released by the cell.

When the action potential arrives, it depolarizes the membrane (as it does everywhere else in the cell as the action potential moves forward). This collapse of potential across the membrane triggers voltage-activated calcium channels to open (similar to the way voltage-gated sodium channels activate at threshold and start the action potential), causing a rapid influx of calcium ions into the cell at specialized areas of presynaptic membrane, called "active zones". Calcium is a very special ion in the cell because, in addition to being used for current like other ions, it's also used as a signaling molecule. The calcium triggers a complicated set of molecular events which cause the vesicles containing neurotransmitters to concertedly fuse with the plasma membrane at the active zones, dumping their cargo into the synaptic cleft.

Here the neurotransmitter diffuses across the synapse where it binds to its receptors on the post-synaptic cell, and brings that cell closer or further from threshold (depending on the neurotransmitter you're talking about).

Answer 7

What all this following stuff (from wikipedia) means is:

action potential reaches terminus of axon (where neurotransmitter is waiting in vesicles ready for release)

membrane calcium receptors open and let influx of Ca++

increased intracellular Ca++ causes vesicles to fuse with axon membrane and dump neurotransmitters into synaptic cleft

Neurotransmitters diffuse and are
1) taken back up by the presynaptic axon
2) bind to postsynaptic receptors
or
3) are metabolised



---{cut and paste from wikipedia}---
The release of neurotransmitter is triggered by the arrival of a nerve impulse (or action potential) and occurs through an unusually rapid process of cellular secretion, also known as exocytosis: Within the pre-synaptic nerve terminal, vesicles containing neurotransmitter sit "docked" and ready at the synaptic membrane. The arriving action potential produces an influx of calcium ions through voltage-dependent, calcium-selective ion channels. Calcium ions then trigger a biochemical cascade which results in vesicles fusing with the presynaptic-membrane and release their contents to the synaptic cleft. Vesicle fusion is driven by the action of a set of proteins in the presynaptic terminal known as SNAREs. Receptors on the opposite side of the synaptic gap bind neurotransmitter molecules and respond by opening nearby ion channels in the post-synaptic cell membrane, causing ions to rush in or out and changing the local transmembrane potential of the cell. The resulting change in voltage is called a postsynaptic potential. In general, the result is excitatory, in the case of depolarizing currents, or inhibitory in the case of hyperpolarizing currents. Whether a synapse is excitatory or inhibitory depends on what type(s) of ion channel conduct the post-synaptic current display(s), which in turn is a function of the type of receptors and neurotransmitter employed at the synapse.

Answer 8

You get excited.