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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)
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)
"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)
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)
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 used Kandel & Schwartz in graduate school and think it's a perfect reference.
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.
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)
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 1 quadrillion is about right - no one has counted them all. For the cerebral cortex the density is around 1 billion per cubic millimeter. Frankly the best one can hope is right order of magnitude, and 1 quadrillion is easy to remember (though difficult to visualize: I tell my students think 1 cent in the entire US economy). —Preceding unsigned comment added by Paulhummerman (talk • contribs) 03:12, 15 May 2010 (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.
"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."
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)
Can you help with this one?
I am researching 'A Theory Of Mind' which has, as one of its props, a speculation that a 'bit' of memory resides in the synapse. I am led to this belief because the count of total number of sensory inputs which the brain could receive in a normal life-span is roughly equal to the estimated number of synapses which exist. If so, it is logical to assume that a synapse might be armed with a 'bit' of memory at the time of the original experience. It is also possible that the number of vesicles provided (pre-synapse) might correlate with the degree of emotional pain/pleasure felt at that precise moment. If this assumption is correct then the number of vesicles present in the axon should vary in concord with the strength of the original emotion. The effect would be to mirror that same emotion at recall.
Is there any clinical evidence to support/refute these assumptions?
Regards, Don Nicol 9 Jun 2007
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)
Chemical synapse redirects here. Electrical synapse does not. Any thoughts? - Samsara (talk • contribs) 18:01, 24 May 2006 (UTC)
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)
Second Sentence
Third sentence
Synapses are not all biochemically identical. The way they increase their effiency upon activation, and the rate of they regression upon inactivation undoubtedly is different from one synpse to another. At any moment each synapse will be in a certain state of efficiency. The mental state of the organism is then given by the momentary state of efficiency of each of the synapses.
Being alive then means that the organism is in continual change in witch at any moment a certain part of the neurons and the synapses transmit impulses, which are distributed into the network of neurons according to the current state of efficiency of the synapses, each synaptic eficiency in its turn being changed by the transmission intensity it is subjected to, typically increasing when the intensity is high, decreasing when it is low. —Preceding unsigned comment added by Mightunit (talk • contribs) 12:11, August 24, 2007 (UTC)
Would it not be better just to have this at synapse instead of having a more specific name? The former just redirects here, so why not move it to the simpler name as has been done with other articles, e.g. biological reproduction. Richard001 01:53, 25 August 2007 (UTC)
"At an archetypal chemical synapse, such as those found at dendritic spines, a mushroom-shaped bud projects from each of two cells and the caps of these buds press flat against one another. At this interface, the membranes of the two cells flank each other across a slender gap, the narrowness of which enables signaling molecules known as 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."
So do the caps really press flat against one another, or is there actually a gap between them? If there is a gap, how is it that the two really press flat against one another? If there is actually a gap, would it be accurate to say, then, that there is only the appearance of the direct physical contact via the membranes that's also suggested? I don't quite understand. Is it that the membranes are pressed against one another, but contain a gap (or the synaptic cleft) within, or inside that zone of contact? The idea that one gets from the synapse illustration (for example, http://en.wikipedia.org/wiki/Image:SynapseIllustration2.svg and http://en.wikipedia.org/wiki/Image:Complete_neuron_cell_diagram.svg) is that there is no actual membrane contact, only a very close proximity that, nonetheless, precisely falls short of the two cells pressing against one another due to the synaptic cleft. I admit that I am missing something, but perhaps this is because of the ambiguity inherent in the description supplied. Could someone please clarify this point, on the article page or even here?
-72.68.221.206 (talk) 20:39, 18 November 2007 (UTC)
I didn´t spot it in the article so my question is: Why does the presynaptic cell align with the postsynaptic cell in such an exact way?
Kinda hard to find the correct words for it, so lets say we have a regenerating neuron that´s currently in the progress of remaking the connection with another cell after injury: How do they connect to each other in the first place? What makes the presynaptic terminal "connect"? Fernando Hulio (talk) 14:08, 8 July 2008 (UTC)
I find computer scientists, when creating neural network simulators, create synapses with three attributes: a strength, a synaptic delay, and a synaptic duration. The strength value is self explanatory (albeit over simplified). The synaptic delay represents the axonal delay+delay from end of axon to axon buttons. The synaptic duration is the one that strikes me as a bit odd. I know that exocytosis is extremely rapid (<200 microseconds), and I know that the strength of a presynaptic synapse is characterized by the probability of vesicle release (p) and the number of release sites (N), but is there also a temporal component to synaptic strength? Do stronger synapses release their neurotransmitters for a longer period of time? I highly doubt this. Paskari (talk) 18:01, 23 July 2008 (UTC)
Yes I realize that, and I don't support having a single neuron equation for an artificial neuron. But that single equation models the axon hillock, and the entire somatic and dendritic membrane is ignored. But with synaptic duration, it seems as if it never existed, and computer programmers devised it. Paskari (talk) 15:16, 31 July 2008 (UTC)
I suppose that does answer my question, so once an axon terminal button releases its neurotransmitters, the spines open up their channels for some synaptic duration. So if you were running a simulation at a one millisecond precision, once the channels are opened, you would provide an input to the neuron model for a duration which could be longer than a single cycle (1 ms). Thanks Paskari (talk) 18:14, 2 August 2008 (UTC)
There was a contradiction with the article Neuron in the numbers for the estimates of the number of synapses in the adult human brain. In the talk section above, #Include Number of Synapses in Human Brain and in the first edit concerning this way back in 23 December 2005 [4], this was given as 100-500 trillion. Then on 16 November 2006, someone added it in scientific notation, but got the number wrong, putting 15 instead of 14 [5] and the next day, the numbers were changed from 100 to 500 trillion to 1,000 to 5,000 trillion. I've changed the numbers back to the way they were, making them the same as those given in Neuron. --121.45.173.99 (talk) 10:23, 3 August 2008 (UTC)
I have never heard of the term homotropic modulation or heterotropic modulation applied to synapses. It is more common to refer to homosynaptic or heterosynaptic plasticity. There were errors in the content of that section as well. I'm not aware of any example where the size of vesicles is affected by the neuron's own activity or other neurons' activity.--Pkatz (talk) 15:08, 30 August 2008 (UTC)
I have boldy removed the refimprove tag from the article. Synapses are the central topic in neuroscience, and are discussed thoroughly in every basic neuroscience textbook, so there is no problem in verifying most of the assertions in this article. If there are specific assertions that you think require verification, please feel free to mark them with a "fact" tag. Looie496 (talk) 17:15, 15 September 2008 (UTC)
Can we please settle this on the talk page rather than edit warring? It is definitely true that volume transmission is an important concept that ought to be mentioned in this article -- in fact, Wikipedia ought to have an article about it; currently Volume transmission redirects to a section of Brain. What isn't true is that it is a new concept -- people have been studying this for decades, and there is a massive literature on it. (And I'm not talking about electrical synapses, I'm talking about chemical transmitters acting extra-synaptically.) Let's see, please, if we can find a good review of this topic and add a mention at an appropriate place in the article. Looie496 (talk) 18:06, 24 November 2009 (UTC)
My initial edit referred to signaling in the absence of synapses - how this sounded like it was about electrical synapses is beyond me. I take your point about referencing, and included the Nature ref in my second edit. I retained the blog reference, as I assumed this would be more penetrable to the layperson.
If you agree that volume transmission should be covered in this wiki, please take the time to edit the text or contribute an alternative rather than edit warring, as Looie496 has correctly pointed out. Tryptofish, I have pasted the text of my most recently deleted edit below - perhaps you or someone else can take a stab at rewriting, rewording, or copyediting. As I said before, it is extremely frustrating to have legitimate attempts at improving an entry deleted without any effort to consider the content.
New section heading title: Signaling without synapses
Section text: Until recently, synaptic transmission had been considered the exclusive mechanism by which neurons communicate. However, this is no longer thought to be the case[16]. Oláh et al. (2009)[17] found that a type of neurons called neurogliaforms can communicate using a mechanism called volume transmission, where neurochemicals diffuse in a cloud through the extracellular fluid. This occurs even when no synapses are present. The group found that approximately 78% of neurogliaforms do not form classical synapses. This is the first example of neurons communicating where synapses are not present.
References: Ref 16: "Your Teacher was Wrong!". Dolan DNA Learning Center. http://blogs.dnalc.org/g2conline/2009/11/12/your-teacher-was-wrong/. Retrieved 2009-11-12. Ref 17: Oláh S, Füle M, Komlósi G, Varga C, Báldi R, Barzó P, Tamás G. (2009). "Regulation of cortical microcircuits by unitary GABA-mediated volume transmission.". Nature 461 (7628): 1278-1281. PMID 19865171. http://www.ncbi.nlm.nih.gov/sites/entrez/19865171. —Preceding unsigned comment added by Joconnol (talk • contribs) 14:43, 25 November 2009 (UTC)
I've added a quick paragraph about symmetry of synapses in the structure section. I've not sourced it yet, there's some stuff here http://thebrain.mcgill.ca/flash/capsules/pdf_articles/synapses.pdf plus some more content if the section gets expanded, including the history of the teriminology. There's already a reference to the chemical synapse being "asymmetric in structure and function" because the signalling is one way (although you might argue that autoreceptors mean that the process isn't exclusively one directional). However, as far as I can tell, this isn't the same as the structural symmetry of the synaptic membranes.Keepstherainoff (talk) 14:06, 20 July 2010 (UTC)
In cooperation with user Looie I have created a 60 seconds video clip on the basic processes of the chemical synapse. This is a 13MB file. Smaller resolutions (equals smaller size) is possible but video quality drops to rubbish.
I welcome any advice / critique on improving the clip (I am not a neuroscientist, so please keep it simple).
Please leave a message on my user page if you think that another article could use a video clip to help WP users understanding the subject matter better.
--Cookatoo.ergo.ZooM (talk) 15:03, 9 October 2010 (UTC)
I have reduced the size of the video clip to 1.5MB. Loading and playing with the old size of 13MB was a pain in the, erm I seem to have fogotten the medical term:) Greetings. --Cookatoo.ergo.ZooM (talk) 19:36, 14 November 2010 (UTC)
Astrocytes can help remove neurotransmitters, apart from the already enlisted 129.180.166.53 (talk) 15:04, 10 June 2012 (UTC)
What is the relationship between the two terms? Are they simply different names for the exact same structure, or is one (I would guess "presynaptic terminal") a more specific term for part of the other? This might or might not be relevant to a "History" section here. I know there are such things as "extra-synaptic" receptors (progesterone on ∂-subunit GABA-A neurons.[1]..), so I guess maybe a "presynaptic terminal" might also have a specific meaning other than "just" another name for the synapse. Jimw338 (talk) 19:23, 30 December 2014 (UTC)
The comment(s) below were originally left at Talk:Chemical synapse/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
Rated "top" importance because neurotransmission redirects here and is highschool/SAT biology content. - tameeria 20:09, 28 April 2007 (UTC) Rating changed to "high" since neurotransmission has been split into its own article. - tameeria 15:57, 8 May 2007 (UTC) |
Last edited at 15:57, 8 May 2007 (UTC). Substituted at 11:25, 29 April 2016 (UTC)
What structure (force?) holds 2 neurons close together, but still separated in very small distance so that there will be functional synaptic cleft? Nimelik 7. january 2018, 13:31 — Preceding unsigned comment added by Nimelik (talk • contribs) 11:34, 7 January 2018 (UTC)