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Inside the brain the electrical signals are transmitted from one neuron to another by using special chemicals, called "neurotransmitters" from the axon terminals.

Can anyone could help me out to calculate approximate value of the delay time of transmitting the information from one neuron to another. I am thinking that it will less than pico-seconds!

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  • $\begingroup$ I've done a nice experiment once where you stimulate the nerve around your elbow making your hand twitch. You need time the interval between stimulation and twitch. Following, you stimulate the nerve near your wrist and time it again. Between these two positions there are no axon-terminals, but shortly after the wrist there are. You'll see that the timing will not vary much between elbow and wrist (between which is a pretty long axon). The most time-consuming part will thus follow after the wrist, that is, after an axon terminal. $\endgroup$ – Robin Kramer Mar 23 '17 at 7:27
  • $\begingroup$ @Robert Kramer Is there any approximate numerical value for the transfer of information between a set of neurons? $\endgroup$ – Suraj Sharma Mar 23 '17 at 7:31
  • $\begingroup$ I'm not sure. I did the test once in my first year of study (about 6 years ago). I am inclined to guess about 250 ms. A quick google search gave me this paper: ncbi.nlm.nih.gov/pmc/articles/PMC3314961 but I wasn't able to find an answer at first glance. If you do, feel free to answer your own question and I'll upvote :) $\endgroup$ – Robin Kramer Mar 23 '17 at 7:35
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You mentioned the neurotransmitters released at the synaptic cleft, but seem to be interested in the complete picture. An action potential is actually very slow to propagate down an axon with a conduction velocity from 0.5 to 150 m/s, depending on how myelinated the axon is (https://www.ncbi.nlm.nih.gov/books/NBK10921/). A toddler can run faster than the slowest signals! The length of axons in the brain varies greatly as well, from a few micrometers to a few centimeters, but only a fraction of a percent actually grow longer than one centimeter.

We will make a very rough calculation. Pretending the average axon length is half a centimeter (5 millimeters), and the average conduction velocity is 25 meters/second (or 25,000 millimeters/second), then the delay incurred from the action potential down the axon will be 0.005 seconds (or 5 milliseconds).

This doesn't include the time it takes the presynaptic cell to release neurotransmitters, the postsynaptic cell to absorb the neurotransmitters and transduce them into electrical impulse again, and propagate the electrical impulse to the soma for integration. For that, the delay is somewhere around 0.5 to 4 milliseconds (https://www.ncbi.nlm.nih.gov/pubmed/14980200).

Obviously there are lots of variations in all these numbers. So how long does it take for a signal to be transmitted from the soma to the neuron's axon terminal to another? A few milliseconds. How long does it take for release and absorption of neurotransmitters? Perhaps another few milliseconds. If you're the type who wants a simple, idealized, singular number that ignores the complexity of the facts, then I would estimate something like 7 milliseconds for the total process.

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    $\begingroup$ good discussion. one important thing to note is that "gap junction" refers to direct electrical communication between cells. What you are really discussion is chemical transmission at synapses. $\endgroup$ – honi Mar 24 '17 at 3:07
  • $\begingroup$ Oops, you're right. Got curious on what the delay is at electrical synapses and my reading got confused with my writing. I changed it to synaptic cleft. Thanks. $\endgroup$ – aiwyn Mar 24 '17 at 6:13

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