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Regarding your question about losing synapses; yes, synapses are regularly lost in a process called Synaptic Pruning. From the Wikipedia article: A decrease in synapses is seen after adolescence reflecting synaptic pruning, and approximately 50% of neurons during development do not survive until adulthood. Pruning is influenced by environmental factors ...


13

A synapse from a neuron unto itself is called an Autapse. Not a whole lot is known about them. Tamas et al. (1) give a summary: Van der Loos and Glaser (1972)proposed the word “autapse” to describe a transmitter release site made by the axon of a neuron and its own somatodendritic domain. In addition to their original Golgi study in rabbit neocortex ...


12

Spine formation (spinogenesis) is almost certainly due to chemical, rather than electrical, signalling between neurons. Although there are exceptions (gap junctions, for one), most forms of inter-cellular communication are mediated by chemicals released by one cell and detected by another. You are right that the cues for synaptogenesis are probably localized ...


12

Dendritic spines are thought to grow and recede under LTP and LTD, respectively. See (Bosch and Hayoshi 2011) for a review. From there, much of the synaptogenesis occurs due to surface molecules present both on the dendrite and the presynaptic axon in the growth cone. Localization and guidance are achieved through gradients of growth factors in the ...


12

An inhibitory synapse works just like an excitatory one! When a presynaptic neuron fires it will release a neurotransmitter at its terminal(s). This neurotransmitter can be excitatory or inhibitory, the main excitatory one in the central nervous system being glutamate and the main inhibitory one GABA.* GABA and Glu are far from being the only ...


8

Q: We know neurons can organize into very complex networks, but how? The answer is your first guess: Neurons find other target neurons with specific chemical signals. Q: What are the names of said mechanisms? This process is called axon guidance, by which the growth cones of developing axons are directed to reach their targets. This process depends upon a ...


7

There are membrane proteins that act as structural components of the gap (i.e. the synapses aren't just floating there, they are anchored to each other via membrane proteins). https://en.wikipedia.org/wiki/Neuroligin https://en.wikipedia.org/wiki/Neurexin The most common examples are neurexin (expressed on the pre-synaptic terminal) and neuroligin (...


6

If firing rate is from 1 Hz to 200 Hz, 100 trillion to 20 quadrillion synaptic firings. Neuronal (say, measured from soma) firings will add up to 86 billion to 17.2 trillion action potentials per second. It important to remember, that synaptic firings "sum up" in soma or interfere between each other, so the are more of those. Read more: http://neuroblog....


6

From your comment to nico's good answer, it seems that your question is really about how synaptic potentials propagate through dendrites. Canonically, synaptic potentials travel passively along membranes and is described by cable theory. The cable equation describes how the voltage will change over time and space along a cable. The theory was originally ...


6

You can tell that the structures labelled At are axons, or rather axon terminals, due to the presence of the synaptic vesicles. I think this is a fine photo that's a bit more a clear representation: Source PSDs are really just protein aggregates that are thought to facilitate neurotransmitter trafficking. So the structures here make sense. At least, they ...


6

Synapses are held together by adhesion molecules, like cadherins and neuroligins/neurexins, so they aren't just loose adjacent membrane, they are securely anchored in place. The adhesion molecules serve both a structural and regulatory role, being important for synapse formation and plasticity. Missler, M., Südhof, T. C., & Biederer, T. (2012). ...


5

Two classes of factors contributing to spinogenesis have been described in the literature, based on whether they can be considered extrinsic or intrinsic to the dendrite (my classification). Here is a short list of evidence in favor of either: A. Extrinsic: the presence of extracellular glutamate facilitates spine formation in tissue from very young mice (...


5

You are correct that cocaine "fills the tunnel" (the pharmacology terminology is that it "blocks the transporter"). But it is not an autoreceptor, so the reuptake transporter does not send a stop signal, it just removed neurotransmitter from the cleft. But once you've blocked it with cocaine, neurotransmitter is not being removed from the cleft so it has a ...


5

There isn't enough research out there to explain the role of autapses however having read a selection of the latest research I can perhaps explain some of the proposed theory. Autapses may self inhibit or self excite. In the latter, one of their roles is thought to be to make a rhythmic action potential. This allows the brain to have an action potential ...


5

Short answer A rough indication of the delay in monosynaptically connected cortical neurons is 6 - 14 ms. Background As @Jonathan correctly states, there are many variables involved in neuronal delays. However, because you ask for an estimate of the order of magnitude of the neuronal delay between two coupled neurons in the neocortex, I will suffice by ...


4

The conduction velocity can vary by orders of magnitude based on many factors, so more information would be needed for a useful answer. Unmyelinated axon conduction velocities range from about 0.5 to 10 m/s, whereas myelinated axon conduction velocities can reach up to 150 m/s1. I'm also not sure what you mean by "dense network". The brain is not a dense ...


4

Frequency of tremor typically remains constant for the person. Levadopa (sinemet) does not change the frequency. Typically the tremor frequency will be in the range from 3Hz to 7Hz. There is a common phrase when dealing with PWP (Person With Parkinson's Disease). If you have seen one PWP, you have seen one PWP. Currently I am part of a study by the ...


4

Neurons are all about specialized structures having specialized roles. You've given a good justification for dendrites---an efficient way to fit lots of connections in a small space. A pyramidal neuron in cortex, for instance, will have tens of thousands of synapses. If you only had axosomatic connections, the soma would have to be enormous to fit all of ...


4

Having just read this article (http://www.ncbi.nlm.nih.gov/books/NBK11164/) there are several advantages/functional reasons that seem apparent and important in having electrical synapses with gap junctions compared to just a very long neuron. a) signals in electrical synapse can be bidirectional. b) electrical synapse synchronize electrical activity among ...


4

You are looking for a review on vesicle cargoing along the cytoskeleton. This open access article is the most recent I found on the subject. From the abstract: How synaptic cargos achieve specificity, directionality and timing of transport is a developing area of investigation. Recent studies demonstrate that the docking of motors to their cargos is a ...


4

Three reasons: Most of the storage capacity of the brain is used to store implicit knowledge. For example how to move your body, how to automatically recognise objects or how to hear and parse your language. These things may seem easy to you, but they require a lot of learning. Just look at how clumsy five year olds still are, they have been training how to ...


4

The answer by bpedit is a good explanation of temporal/spatial summation, which can be partly a postsynaptic phenomenon (due to membrane time constants or second messenger sytems, for example). Your specific question is about whether extracellular neurotransmitter levels sum over time. This definitely occurs regularly with "neuromodulatory" ...


4

Excellent question. Different neurotransmitters operate at different temporal scales (and even the same transmitter can operate at different temporal scales). Examples of the fastest-acting neurotransmitters are glutamate, GABA, and acetylcholine (with the caveat that they can also act more slowly). These neurotransmitters (usually) open ion channels in the ...


3

As far as I can see this paper is being a little misleading, by saying "VPA mimics Nogo-66 receptor deletion". The action of VPA doesn't seem to be related to this receptor. It seems that blocking this receptor and applying VPA both increase plasticity, but it is like taking a car or taking a train -- entirely different modes of transport that achieve the ...


3

This is a very good question. There are specific chemical signals, for instance: 1.) LRR proteins, which help signal neurons to each other. These are transmembrane proteins which are characterised by their leucine-rich repeat. They serve as some kind of protein labels for other neurons. These proteins are also known in pathogen recognition in our immune ...


3

Effective integration time of a typical neuron is in the order of 10-100 ms. You might want to look into this classic paper (read it with a critical mindset): Shadlen, M. N. and Newsome, W. T. (1994). Noise, neural codes and cortical organization. Curr. Opin. Neurobiol., 4:569-579. Or some biophysics book like: Biophysics of Computation by Christof Koch


3

There are two types of synapses namely Electrical synapse and Chemical synapse. In electrical synapse there is physical contact between two cells through gap junctions. In chemical synapse there is a small gap between two cells which is termed as synaptic cleft. The presynaptic and postsynaptic membranes at chemical synapses are separated by a synaptic ...


2

Short answer is yes, of course. Maintaining a healthy synapse is very energy-consuming process. Let me first note that forgetting as we know it is more complicated than just pruning of synapses. It might involve rearrangement of proteins in pre/post-synaptic membrane and near it, local de-regulation of local protein synthesis, decrease in synaptic mRNA ...


2

"Synaptic clearance" is referring to the clearing of a neurotransmitter from a synaptic cleft. A synapse is a place where one neuron can stimulate another neuron. The tiny gap between the neurons is called the synaptic cleft. The presynaptic (stimulating) neuron releases a neurotransmitter (such as dopamine) into the cleft and some of the neurotransmitter ...


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