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Topic: Chemical synapses

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	Chemical synapse - Wikipedia, the free encyclopedia
		Chemical synapses are specialized junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands.
		A chemical synapse between a motor neuron and a muscle cell is called a neuromuscular junction.
		Chemical synapses are not the only type of biological synapse: electrical and immunological synapses exist as well.
	en.wikipedia.org /wiki/Synapse (1414 words)

	Synapse - Biocrawler (Site not responding. Last check: 2007-10-23)
		Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical signals into chemical ones.
		Synapses are specialized junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands.
		Whether a synapse is excitatory or inhibitory depends on what type(s) of ion channel conduct the post-synaptic current, which in turn is a function of the type of receptors and neurotransmitter employed at the synapse.
	www.biocrawler.com /encyclopedia/Synapse (1043 words)

	Electrical synapse - Wikipedia, the free encyclopedia
		Without the need for receptors to recognize chemical messengers, signaling at electrical synapses is more rapid than that which occurs across chemical synapses, the predominant kind of junctions between neurons.
		Electrical synapses are abundant in the retina and cerebral cortex of vertebrates.
		Modern understanding of the coexistence of chemical and electrical synapses, however, suggests that both models are physiologically significant; it could be said that the Nobel committee acted with great foresight in awarding the Prize jointly.
	en.wikipedia.org /wiki/Electrical_synapse (751 words)

	Synapses
		A synapse is composed of three constituents: the presynaptic element, the synaptic cleft and the postsynaptic component (Fig.
		In the type Ii synapse, in contrast, the postsynaptic density is less readily identifiable and the narrower cleft does not contain a dense plaque; the overall configuration is symmetrical.
		Accordingly, in chemical synapses the vesicles contain quanta of the neurotransmitter which is discharged into the synaptic cleft after the vesicle has fused with the presynaptic membrane.
	sabryabdelfattah.tripod.com /docs/Synapses.htm (2228 words)

	Ch.5: Synaptic Activity
		At a chemical synapse, the arrival of a nerve impulse at the endfoot of an axon triggers the release of a chemical agent, a neurotransmitter or neuromodulator substance, which falls upon the membrane of the postsynaptic cell.
		The chemical synapse is composed of the endfoot (or terminal button) of the sending neuron, the membrane of the receiving neuron, the space between them, and some associated intracellular structures on both sides.
		Synapses may also be classified according to the distribution of dense material on the presynaptic and postsynaptic membranes, as seen by electron microscopy with conventional staining methods.
	albany.edu /faculty/cafrye/apsy601/Ch.04feb10,psychopharmacology.html (8354 words)

	Structure of Chemical Synapses (Site not responding. Last check: 2007-10-23)
		In aldehyde-fixed tissue, asymmetric synapses include axons that contain predominantly round or spherical vesicles and form synapses that are distinguished by a thickened, postsynaptic density.
		In contrast, symmetric synapses involve axons that contain clusters of vesicles that are predominantly flattened or elongate in their appearance.
		The sterotypical and most abundant synapse in the central nervous system is the asymmetric synapse occurring between an axon and a dendritic spine.
	synapses.mcg.edu /anatomy/chemical/synapse.stm (476 words)

	Chapter 13 - Synapses
		For example, the interval between the arrival of the presynaptic spike at the synapse and the change in membrane potential, the synaptic delay, is shorter at the neuromuscular junction, where acetylcholine is the transmitter substance, than at sympathetic postganglionic synapses, where norepinephrine is the transmitter substance.
		Because the postsynaptic potentials at chemical synapses result from changes in permeability of the postsynaptic membrane to sodium, potassium, chloride, or other ions, their amplitude and polarity are greatly affected by the polarity and magnitude of the membrane potential.
		Chemical synapses are capable of amplification, they have a finite synaptic delay, and they are influenced by changes in postsynaptic membrane potential.
	www.unmc.edu /Physiology/Mann/mann13.html (10836 words)

	Synapses (Site not responding. Last check: 2007-10-23)
		This type of synapse involves an axon which makes contact with the pre-synaptic neuron just beyond a cleft of the dendrite.
		This type of synapse involves an axon which makes contact with the pre-synaptic neuron within a cleft of the dendrite.
		This type of synapse involves a physical break in both the membrane of the axon and the membrane of the dendrite.
	retina.anatomy.upenn.edu /~lance/retina/synapse.html (239 words)

	Richard Durbin's Thesis - chapter 7
		Part of the difference in chemical synaptic connectivity between the two animals is that there are more chemical synapse connections in the U series than the H series (916 as opposed to 819), and the extra connections are certain to be unmatched.
		Although chemical synapse formation is correlated with adjacency when all pairs of neurons are considered, between any particular pair both the probability of forming a connection, and the number of synapses made, are essentially independent of adjacency.
		The probability of a chemical synaptic connection being formed, which may depend on environmental as well as genetic factors, and the number of synapses formed, appear to be regulated so as not to depend on the amount of contact between a pair of cells.
	www.wormatlas.org /durbinv1.2/chapter7.html (6129 words)

	[No title] (Site not responding. Last check: 2007-10-23)
		The synaptic delay seen in chemical synapses is due to the differences between neurotransmitter and receptors within the synapse.
		A wider variety of postsynaptic effects are seen with chemical synapses due to the complexity of chemical synapses.
		Axodendritic synapses are considered excitatory because the synaptic contact occurs on regions along the dendrites (spine and shaft).
	www.muhealth.org /~md2004/draft3/1-17neurotransmission.doc (814 words)

	An Animated Discovery of Neuroscience
		The purpose of the astrocyte is to regulate the chemical content of the remaining space or extracellular space.
		At almost all chemical synapses, electrical impulses going down the axon is converted to a chemical signal that crosses the synaptic cleft.
		This chemical signal is converted to an electrical signal when it reaches the postsynaptic membrane.
	www.cise.ufl.edu /~psze/glias.html (1094 words)

	Introduction to Synapses (Site not responding. Last check: 2007-10-23)
		However, the synapses, as well as dendritic and somatic surfaces, are blanketed by neural connective tissue cells (glia) as well as a continuous basement membrane (none of this is shown in the "Synapse" figure at right).
		Such synapses are usually excitatory, but their effect is to increase sensitivity of the target synaptic bed rather than to activate that bed.
		The early evidence, however, favored a chemical transmission method, and new neurotransmitters were identified at a rapid rate in the latter half of that century.
	sky.bsd.uchicago.edu /lcy_ref/synap/synapse.html (5469 words)

	Hardwiring goes soft: long-term modulation of electrical synapses in the mammalian brain
		This raises the enticing possibility that electrical synapses might also contribute to neural plasticity and challenges the notion that in the mammalian CNS they are a simple mechanism for ‘hardwiring’ discrete neuronal populations.
		Electrical synapses are formed by the direct connection of neurons via gap junctions (GJs) which are specialized cell-to-cell contacts consisting of a collection of intercellular channels [reviewed in 7-11].
		Although electrical synapses have been widely investigated in invertebrates, their precise distribution and key physiological significance in the mammalian CNS are only now starting to be fully appreciated [7-11].
	www.cellscience.com /reviews7/Gap_junctional_modulation_thalamus.html (3496 words)

	Citebase - On the role of chemical synapses in coupled neurons with noise
		On the role of chemical synapses in coupled neurons with noise
		In particular, our numerical simulations show that chemical synapses are more efficient than gap junctions in enhancing coherence at an optimal noise (what is known as array-enhanced coherence resonance): in the case of (nonlinear) chemical coupling, we observe a substantial increase in the stochastic coherence of the system, in comparison with (linear) electrical coupling.
		We interpret this qualitative difference between both types of coupling as arising from the fact that chemical synapses only act while the presynaptic neuron is spiking, whereas gap junctions connect the voltage of the two neurons at all times.
	citebase.eprints.org /cgi-bin/citations?id=oai:arXiv.org:q-bio/0502025 (256 words)

	Lecture 20: Nervous system II
		A neuron that terminates at a synapse is called presynaptic and the neuron that begins in the synapse is post synaptic.
		These are diffusable transmitter chemicals released from thousand of synaptic vesicles in the nerve terminal.
		Synapses are also the site of action of many mind altering drugs.
	research.umbc.edu /~farabaug/nerve2.html (565 words)

	[No title]
		The synapse is often bidirectional (this is well described in gap junction in cardiac and smooth muscle), and occasionally conducts more easily in one direction than the other to produce rectification.
		The neuromuscular junction (NMJ) is a synapse between a peripheral myelinated efferent nerve (motor nerve) and the cells of skeletal muscle.
		The patch of chemically excitable membrane under the nerve terminal maintains a sustained depolarization in the short term (Many minutes) as long as the receptor is occupied.
	www.med.mun.ca /tedhoekman/synapse/nmj.htm (2957 words)

	Sequential Development of Electrical and Chemical Synaptic Connections Generates a Specific Behavioral Circuit in the ...
		Electrical synapses in embryos commonly exhibited "negative rectification" for both directions of current flow (double rectification), shown by the larger responses during the negative portion of the stimulus ramp.
		Inhibitory chemical synapses first appeared at 55% ED and reached their maximum embryonic amplitude between 60 and 65% ED, which is close to the stage when LB appears.
		Bonnot AS, Whelan PJ, Mentis GZ, O'Donovan MJ (2002) Spatiotemporal pattern of motoneuron activation in the rostral lumbar and the sacral segments during locomotor-like activity in the neonatal mouse spinal cord.
	www.jneurosci.org /cgi/content/full/25/10/2478 (8397 words)

	APStracts 2:0090N, 1995. (Site not responding. Last check: 2007-10-23)
		Under our control conditions (isolated pairs of neurons, removal of modulatory input), most of the graded chemical synapses were weak and some synapses were nonfunctional.
		The output synapses of the Ventricular Dilator (VD) neuron were significantly stronger than the other synapses.
		This amine strengthened the weak chemical output synapses of the anterior burster (AB), lateral pyloric (LP) and pyloric constrictor (PY) neurons and weakened (and in some cases abolished) the strong chemical output synapses of the VD neuron.
	www.uth.tmc.edu /apstracts/1995/jn/April/90n.html (504 words)

	Transient Electrical Coupling Delays the Onset of Chemical Neurotransmission at Developing Synapses -- Szabo et al. 24 ...
		Chemical and electrical synaptic connectivity at 19-110 neuronal contacts were inversely correlated.
		In contrast, chemical synaptic connections from neuron 19 onto neuron 110 were virtually absent in these pairs.
		) at the onset of chemical synaptogenesis (Kandler and Katz,
	www.jneurosci.org /cgi/content/full/24/1/112 (6737 words)

	CHEMICAL SYNAPTIC TRANSMISSION
		This observation naturally led to the suggestion that Ach might be the chemical messenger released by nervous tissue.
		The peripheral synapse between vertebrate motor neurons and skeletal muscle cells served for many years as the prototype for understanding fast, excitatory chemical synaptic transmission between neurons.
		-However, a single chemical messenger, such as Ach, may act as either a neurotransmitter or a neuromodulator depending on which class of Ach receptors are present in the postsynaptic cells.
	www.bios.niu.edu /lotshaw/bios493/synapse.html (2584 words)

	Neuroscience for Kids - The Synapse
		In the figure on the right, the postsynaptic ending is a dendrite (axodendritic synapse), but synapses can occur on axons (axoaxonic synapse) and cell bodies (axosomatic synapse).
		When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential.
		The word synapse was first used in a book called A Textbook of Physiology, part three: The Central Nervous System, by Michael Foster and assisted by Charles S. Sherrington, in 1897.
	faculty.washington.edu /chudler/synapse.html (401 words)

	Lecture 5 Notes
		A chemical molecule, a neurotransmitter, is released from the presynaptic neuron, it diffuses across the synaptic cleft (20-50 nm) and binds with a receptor on the postsynaptic membrane.
		Synaptic release at a neuromodulatory synapse - G-protein-coupled receptors
		The measure of how effective a given synapse is in contributing to spatial summation is the length constant (or space constant), l (Fig.
	www.isr.syr.edu /course/neu211/lecture_notes/lec05.html (1298 words)

	Citebase - Cluster synchronization in an ensemble of neurons interacting through chemical synapses
		In networks of periodically firing spiking neurons that are interconnected with chemical synapses, we analyze cluster state, where an ensemble of neurons are subdivided into a few clusters, in each of which neurons exhibit perfect synchronization.
		To clarify stability of cluster state, we decompose linear stability of the solution into two types of stabilities: stability of mean state and stabilities of clusters.
		IF neurons with fast decaying synapses show the low entrainment capability, which is explained by a pitchfork bifurcation appearing in two-cluster state with change of synapse decay time constant.
	citebase.eprints.org /cgi-bin/citations?id=oai:arXiv.org:nlin/0504057 (278 words)

	6. Intrinsic Chemical Synapses and their Role in Network Oscillations
		The hyperpolarization in synaptically coupled dendrites was thought to initiate spindle oscillation and to spread it to adjacent elements.
		There is indeed evidence for both dendrodendritic (10, 11) and axoaxonic synapses (42), which mediate inhibitory interactions in the RE nucleus (25, 39).
		In sum, the present demonstration of prolonged hyperpolarizations leading to spindles and generated locally in the RE nucleus is in keeping with the proposal that spindles are initiated in the pacemaking RE nucleus (2, 7, 43).
	www.theses.ulaval.ca /2004/22126/ch07.html (4394 words)

	Both Electrical and Chemical Synapses Mediate Fast Network Oscillations in the Olfactory Bulb -- Friedman and ...
		There is anatomical evidence for the presence of electrical synapses onto interneurons in the olfactory bulb.
		depolarized with mGluR agonists in the absence of chemical synaptic
		Landis DM, Reese TS, and Raviola E. Differences in membrane structure between excitatory and inhibitory components of the reciprocal synapse in the olfactory bulb.
	jn.physiology.org /cgi/content/full/89/5/2601 (5338 words)

	Amacrine II
		Chemical synapses in sublamina a of the inner plexiform layer
		electrical synapses onto cone bipolar axons in sublamina b of the inner plexiform layer
		Contacts made via electrical synapses onto cone bipolar axons in sublamina b
	retina.anatomy.upenn.edu /~lance/retina/amacrine_aii.html (266 words)

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