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[1] This phenomenon is known as an excitatory postsynaptic potential (EPSP). It may occur via direct contact between cells (i.e., via gap junctions ), as in an electrical synapse , but most commonly occurs via the vesicular release of neurotransmitters from the presynaptic axon terminal into the synaptic cleft , as in a chemical synapse .
Acetylcholine is a choline molecule that has been acetylated at the oxygen atom. Because of the charged ammonium group, acetylcholine does not penetrate lipid membranes. . Because of this, when the molecule is introduced externally, it remains in the extracellular space and at present it is considered that the molecule does not pass through the blood–brain
[72] [note 1] Nicotine, a compound found in tobacco, is a direct agonist of most nicotinic acetylcholine receptors, mainly located in cholinergic neurons. [67] Opiates, such as morphine, heroin, hydrocodone, oxycodone, codeine, and methadone, are μ-opioid receptor agonists; this action mediates their euphoriant and pain relieving properties. [67]
Similarly, acetylcholine released from parasympathetic neurons may interact with M 2 and M 4 receptors to inhibit further release of acetylcholine. An atypical example is given by the β-adrenergic autoreceptor in the sympathetic peripheral nervous system, which acts to increase transmitter release. [1]
[1] [3] [4] According to their site of actions, cholinergic blocking drugs can be classified into two general types — antimuscarinic and antinicotinic agents. [1] Antimuscarinic agents (also known as muscarinic antagonists), including atropine and hyoscine, block acetylcholine at the muscarinic acetylcholine receptors.
[1] [4] Chemicals in this family can act either directly by stimulating the nicotinic or muscarinic receptors (thus mimicking acetylcholine), or indirectly by inhibiting cholinesterase, promoting acetylcholine release, or other mechanisms. [5] Common uses of parasympathomimetics include glaucoma, Sjögren syndrome and underactive bladder. [6]
A muscarinic acetylcholine receptor agonist, also simply known as a muscarinic agonist or as a muscarinic agent, is an agent that activates the activity of the muscarinic acetylcholine receptor. [1] The muscarinic receptor has different subtypes, labelled M1-M5, allowing for further differentiation.
Two molecular mechanisms for synaptic plasticity involve the NMDA and AMPA glutamate receptors. Opening of NMDA channels (which relates to the level of cellular depolarization) leads to a rise in post-synaptic Ca 2+ concentration and this has been linked to long-term potentiation, LTP (as well as to protein kinase activation); strong depolarization of the post-synaptic cell completely ...