Chemical Synapses Synaptic Transmission


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Chemical Synapses Synaptic Transmission

Arkansas Tech University, US has reference to this Academic Journal, Synaptic Transmission Chapter 4 Pages 95-122 Chemical Synapses Most synapses in the brain are chemical. Electronically coupled gap junction synapses occur in special circumstances (embryos, cardiac muscle) where close coordination needed. Chemical synapses release a chemical into the synaptic cleft which transfers information (a neural signal) from one neuron so that another.

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How a Synapse Works The presynaptic neuron experiences an action potential. Presence of the action potential at the terminal button permits calcium (Ca++) so that enter the neuron via voltage-gated calcium channels. Calcium triggers the release of neurotransmitter from synaptic vesicles. Neurotransmitter crosses the synaptic cleft in addition to opens ion channels in the post-synaptic neuron. Ion Channels Found in all cells throughout the body. Open in addition to close in response so that signals. Selectively permeable so that specific ions High rate of flow (conductance) Resting channels ? usually open Gated channels ? open in addition to close Refractory period ? temporarily cannot be opened Control of Gating Binding of neurotransmitters, hormones, or second messengers from within the cell. Voltage-gated ? responds so that a change in the membrane potential. Stretch or pressure gated ? mechanical forces. Phosphorylation ? energy comes from a phosphate that binds alongside the channel. Dephosphorylation ? removal of the phosphate.

Kinds of Receptors All neurotransmitters bind in addition to act at more than one kind of receptor. Two main kinds of receptors: Ion channel receptors G-protein-coupled receptors Effects of Drugs Exogenous ligands ? drugs that come from outside the body. Endogenous ligands ? naturally occurring Agonist ? binds alongside in addition to opens a channel. Endogenous or exogenous (e.g., drug) Receptors are often named in consideration of their agonists Antagonist ? binds alongside in addition to closes a channel. Reversible (curare) or irreversible (snake venom) Three Kinds of Neurotransmitters Amino acids ? released from synaptic vesicles Monoamines ? released from synaptic vesicles Peptides ? larger molecules released from secretory granules. There may be more substances that act as neurotransmitters

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Amino Acids Glutamate (Glu) ? excitatory, widespread. GABA ? inhibitory, widespread. Glycine (Gly) ? inhibitory at some locations. The poison Strychnine blocks GABA receptors interfering alongside inhibition so excitations overwhelm the brain. Monoamines Cholinergic ? Acetylcholine (ACh), used by muscles Catecholaminergic ? regulate thinking, mood, synethesized from tyrosine: Dopamine (DA) Norepinephrine (Noradrenaline) (NE) Epinephrine (Adrenaline) ? widespread Serotonin (5-HT) ? broken down by MAO LSD binds at 5-HT receptors. Peptides Formed by chains of amino acids. Oxytocin ? released during childbirth so that regulate maternal behavior. Vasopressin ? regulates proper blood volume in addition to salt concentration in body. Opioids (endorphins) ? naturally occurring painkillers Morphine binds alongside opioid receptors.

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