Talk:Chemical synapse

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Contents 1 Older edits 2 Synapses and circuits 3 Synaptic Strength 4 Lack of references 5 Dimension of a synapse ? 6 New diagrams 7 Include Number of Synapses in Human Brain 8 Featured article removal candidate 9 Chemical vs. electrical 10 Merge Synaptic Bouton 11 Removal of the 2nd & 3rd sentence from the Anatomy and physiology

[edit] Older edits

That's as maybe, but I want also to add that there are different kinds of synapse. Most are chemical in nature, such as are already described. However, there is evidence for some very fast acting synapses which are electrical. These are reported to have been discovered in fish. Assuming that this has not been discredited, it would be worth having a section on electrical synapses. David Martland 00:06, 16 Jan 2004 (UTC)

Electrical synapses between GABA-releasing interneurons. Nat Rev Neurosci. 2001 Jun; 2(6): 425-33. Galarreta M, Hestrin S.

• Although gap junctions were first demonstrated in the mammalian brain about 30 years ago, the distribution and role of electrical synapses have remained elusive. A series of recent reports has demonstrated that inhibitory interneurons in the cerebral cortex, thalamus, striatum and cerebellum are extensively interconnected by electrical synapses. Investigators have used paired recordings to reveal directly the presence of electrical synapses among identified cell types. These studies indicate that electrical coupling is a fundamental feature of local inhibitory circuits and suggest that electrical synapses define functionally diverse networks of GABA-releasing interneurons. Here, we discuss these results, their possible functional significance and the insights into neuronal circuit organization that have emerged from them.

Yes, I think electrical synapses deserve a section, if not some systemic changes to admit to the recently broadened concept of synapse. Gap junctions didn't used to be considered synapses, but evidently now they are. 168... 16:31, 16 Jan 2004 (UTC)

[edit] Synapses and circuits

"Synapses define the circuits in which the neurons of the central nervous system interconnect."

was changed to "Synapses are circuits...."

Synapses are functional contacts for communication between nearby cells. Most synapses are between adjacent neurons, but some synapses are from neurons onto other cell types such as muscle cells. Synapses are of two types: electrical synapses and chemical synapses. Electrical synapses provide cytoplasmic connections between adjacent cells where ions can carry charges from one neuron to another. Chemical synapses provide cell-to-cell communication that is mediated by neurotransmitters. A neurotransmitter is a chemical that is released from one neuron, moves to a nearby neuron, and acts to modulate the physiology of the target cell. Neurotransmitters often work by binding to receptor proteins on the surface of cells. However, some neurotransmitters pass through cell membranes and directly influence target proteins inside their target neurons. Structurally, synapses are usually regions of close contact between adjacent neurons. Most neurotransmitters are packaged into vesicles at the presynaptic side of synapses. Most neurotransmitter receptors are concentrated in post-synaptic densities on the post-synaptic side of synapses. When activated by neurotransmitters, neurotransmitter receptors typically change ion flow across the surface membrane of postsynaptic neurons. Neurotransmitter receptors can have other effects such as regulation of gene transcription and the regulation of synaptic plasticity (changes in the functional and structural properties of the synapses themselves). The interconnected networks of neuronal cell bodies, axons, synapses and dendrites can be thought of as circuits that carry signals using a mixture of chemical synapses, electrical synapses, action potential propagation, and signals in the form of graded potential changes at cell surface membranes. JWSchmidt 23:41, 29 Mar 2004 (UTC)

This may be syntax curmudgeonery, but I think the original was more acurate. As you said, "The interconnected networks of neuronal cell bodies, axons, synapses and dendrites can be thought of as circuits" but that doesn't make synapses circuits themselves, as the sentence implies, only components of them. This stuck out to me immediately upon reading the article. I'm changing it to "synapses form the circuits" because that seems to say everything that's needed. 24.0.213.140 20:28, 29 Aug 2004 (UTC)

[edit] Synaptic Strength

• "Synaptic strength is the amount of current, or more strictly the change in transmembrane potential of the synapse."
• "One regulatory trigger of synaptic strength involves the simple coincidence sensory stimuli and action potentials in the synaptically linked cells."

1) I'm not sure why these two "sentences" seem to have a charmed life on the synapse page. They both should be fixed.

2) If you look in a neuroscience textbook (example) you will find discussion of synaptic strength mostly in the context of synaptic plasticity. I tried adding some basic information about synaptic plasticity. It was removed, leaving these two (above) problem sentences.

In summary, the "Synaptic Strength" section needs help but I'm not sure I should make any more effort to help it. JWSchmidt 00:47, 30 Mar 2004 (UTC)

[edit] Lack of references

Hi this article no longer meets the criteria for a featured article because it does not cite its sources. Please help fix this so that all featured articles can meet the same standards. Best would be the most trusted resources in the field being added, some print resources especially, but also online references are better than none. Those sources would likely help with good material to further improve the article anyway. - Taxman 23:00, Oct 26, 2004 (UTC)

I added two of the most common neuroscience textbooks (Kandel and Bear) as references. If anyone who contributed to this article had more specific references in mind, please add them. Sayeth 17:43, Nov 1, 2004 (UTC)

Would you say you are very confident that the material in those books agrees with what is here? Otherwise that is potentially dishonest to list them as references. - Taxman 19:11, Nov 1, 2004 (UTC)

Yes, both books state what is now the established dogma of synaptic transmission and action potential propagation, which is repeated in the wikipedia articles. In all likelihood, at least some of the authors of these articles used the Kandel or Brown textbooks as their source, since these are the primary textbooks for graduate and undergraduate courses in neuroscience. If the articles delved into more the esoteric mechanics of these neural functions, then there might be some conflict with the books, but as it stands now, they agree. Sayeth 17:03, Nov 2, 2004 (UTC)

Ok, sounds good to me. Thanks for helping and being willing to explain. - Taxman 18:35, Nov 2, 2004 (UTC)

I used Kandel & Schwartz in graduate school and think it's a perfect reference.

[edit] Dimension of a synapse ?

Which is the average size of a synapse ? It is probably smaller than a micron since the neurons size is between 5 and 150 microns, but I would like to know their real size.

It's hard to tell exactly what dimensions you're speaking of, but I'd bet you're asking about the distance between pre- and postsynaptic neurons. The gap is called the synaptic cleft and it is typically 20-30 nm across. Here's a nice visual. --David Iberri | Talk 22:09, Apr 13, 2005 (UTC)

What is the typical cross section area of a synaptic cleft? The volume?

--Erland Lewin 10:25, 3 August 2006 (UTC)

[edit] New diagrams

Hello, just wanted to tell you that I have drawn a few diagrams related to synapse. Please check the french version of the article fr:Synapse. The pictures are on Commons. Dake 13:13, 2 September 2005 (UTC)

• I have a few comments about these diagrams: 1) The picture of a synapse is nice, but I think the one on the English article already is more complete and maybe more accurate and it is already annnotated directly, so I wouldn't suggest changing it. 2) The images of a neuromuscular junction are nice and I would suggest you put them in the NMJ article. However I did notice that the second image has no repetors on the postsynaptic surface! 3) The synapse article does not have a picture of an electrical synapse, and your looks nice, one thing I'm not sure about though is whether presynaptic Ca++ channels are important for electrical transmission and if not why are they in the diagram. 4) Finally, there are separate articles for action potentials and EPSPs. Also, why is the EPSP waveform so strange looking. I think the images are of very good quality, but perhaps not as complete or accurate as they may be. I'd normally be happy to comment on the French version of synapse to look for completeness/accuracy, but alas I don't speak French well enough to do so. It looks very thorough however. Cheers, Nrets 14:00, 2 September 2005 (UTC)

[edit] Include Number of Synapses in Human Brain

A common question is how many synapses are in the human brain. I suggest mentioning current estimates. It's 1000 trillion for a one year old baby, declining to about 500 trillion for an adolescent. Recent data indicates this number stays constant into adulthood, unlike earlier estimates stating it declined to 100 trillion. (Shore, Rima, Rethinking the Brain: New Insights into Early Development, Families and Work Institute, 1997) Joema 17:18, 21 December 2005 (UTC)

• I think that's a great idea, maybe it might fit better (or also) in the brain article. However, I'm a bit dubious about the source of these estimates. Would you be able to identify the primary sources mentioned in the book you quote, or perhaps a more established secondary source would do (such as a major textbook in the field). Nrets 21:48, 21 December 2005 (UTC)

Well, this is harder than I thought. I've done many internet and library database searches, and there's apparently no uniform consensus. Evidently there's general agreement a three-year-old child has 1,000 trillion synapses. However estimates vary on number of adult synapses from 100 trillion to 500 trillion. Below are a few more authoritative references. The statement about 7,000 synapses per neuron, one trillion synapses per cc seems authoritative. However at an average of 1241 cc for the male brain, that equates to 124 trillion synapses.

Because of this I'd recommend saying something like: "The human brain has a gigantic number of synapses. Each of 100 billion neurons has on average 7,000 synaptic connections to other neurons. Most authorities estimate total number of synapses at 1,000 trillion for a three-year-old child. This number declines and with age, stabilizing by adulthood. Estimates vary for an adult from 100 to 500 trillion synapses. [[1]]

That way you provide useful information without stating more than references indicate. Because of the wide Wikipedia readership, just stating this might engender more authoritative expert commentary. Joema 18:37, 22 December 2005 (UTC)

References:

Biophysics of Computation. Information Processing in Single Neurons, C. Koch, New York: Oxford Univ. Press, 1999, page 87).

Above says total synapses in the cerebral cortex are 240 trillion

COGNITIVE NEUROSCIENCE AND CLASS ROOM DESIGN, John P. Eberhard, Ilya Monosov (PDF): [2]

Above states 1000 trillion synapses at age 3, and 500 trillion from age 15 onward

FUNDAMENTALS OF EEG MEASUREMENT M. Teplan Institute of Measurement Science, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia

"Adults have about 500 trillion (5.10E14) synapses"

Do we have brain to spare? David A. Drachman, MD From the Department of Neurology, University of Massachusetts Medical School, Worcester, MA.

[3]

"Neurons have 7,000 synaptic connections each. The cerebral cortex has about 0.15 quadrillion synapses—or about a trillion synapses per cubic centimeter of cortex."

• Your sentence sounds good, I copied into the Neuron entry, but I couldn't figure out where to put it in the Synapse article. Nrets 19:34, 22 December 2005 (UTC)

• • Personally I think it's such an obvious question, it wouldn't be out of place in the first section. You could abbreviate it something like "Young children can have 1,000 trillion synapses. This number declines and with age, stabilizing by adulthood. Estimates for an adult vary from 100 to 500 trillion synapses." Joema 20:25, 22 December 2005 (UTC)

• Sounds reasonable. I have no complaints if you add that there. Nrets 20:30, 22 December 2005 (UTC)

• • OK I made my best guess at location and wording. Make any changes you see fit. Joema 00:08, 23 December 2005 (UTC)

Disagree, I have removed it. Why is it included in the WP:LEAD? It makes no sense whatsoever. I have removed the numbers, per WP:BOLD. --Parker007 06:28, 7 March 2007 (UTC)

[edit] Featured article removal candidate

As I claim on WP:FARC, this article no longer fulfils the criteria for being a Featured Article. Specifically, it does not cover the subject in adequate depth and breadth by today's standards, and lacks in references; specifically, it needs inline references. I believe these are serious shortcomings and that the article will be better served by being demoted rather than half-hearted attempts at fixing it just so it can barely scrape acceptance as an FA. It would be nice to be convinced that the article can be swiftly and impressively fixed, but will defend my proposal to demote in the absence of any such activity.

Regards,

Samsara (talk • contribs) 19:58, 21 May 2006 (UTC)

• Keep, most, if not all of the factual information is found in the references cited and represent years of neurophysiology research, adding inline refs for every fact in the article would make it hugely unweildy. Recently I expanded, corrected and reorganized the entire article, adding new diagrams and such and I think it definitely still meets the FA quality. Since this is such a big topic I think that it is appropriate to keep many of the sub areas as separate articles (ie. postsynaptic potential, neuromuscular junction, etc.) thus it explains why this article is not so long. I've been continuously checking the article to make sure everything is up-to-date. Nrets 00:48, 22 May 2006 (UTC)

[edit] Chemical vs. electrical

Chemical synapse redirects here. Electrical synapse does not. Any thoughts? - Samsara (talk • contribs) 18:01, 24 May 2006 (UTC)

This article basically describes a chemical synapse which is the "prototypical" synapse, electrical synapse has its own article. We could merge these? Nrets 18:57, 24 May 2006 (UTC)

It would be cumbersome to the reader to have chemical, electrical, and immunological synapses all on the same page. Instead, each topic should have its own article. As "synapse" most often refers to the chemical sort, a redirect from Synapse to Chemical synapse would be in order. --David Iberri (talk) 03:48, 4 June 2006 (UTC)

I've moved the page from synapse to chemical synapse per above. Now chemical, electrical, and immunological synapses have their own articles. --David Iberri (talk) 17:01, 21 June 2006 (UTC)

[edit] Merge Synaptic Bouton

Synaptic Bouton is more or less orphaned, a stub, and really a part of a chemical synapse. I say we add what little content it has to this article and redirect synaptic bouton here. --Selket 07:54, 1 February 2007 (UTC)

Sound like a good plan. Nrets 17:56, 2 February 2007 (UTC)

[edit] Removal of the 2nd & 3rd sentence from the Anatomy and physiology

Second Sentence

• The biological membrane of the two cells side each other across a slender gap, the narrowness of which enables signalling neurotransmitters to pass rapidly from one cell to the other by diffusion. This gap, which is about 20 nm wide, is known as the synaptic cleft.

• Which 2 cells? --Parker007 06:20, 7 March 2007 (UTC)

Third sentence

• Such synapses are asymmetric both in structure and in how they operate.

• Which such syapses? --Parker007 06:23, 7 March 2007 (UTC)