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Anticonvulsants and anxiolytics: Barbiturates
Anticonvulsants and anxiolytics: Benzodiazepines
Medications for neurodegenerative diseases
Opioid agonists, mixed agonist-antagonists and partial agonists
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Nondepolarizing Neuromuscular Blocking Drugs
Inhaled anesthetics, dantrolene
Neuromuscular blockers are a class of medications that prevent acetylcholine from acting at the neuromuscular junction, which prevents the triggering of skeletal muscle contractions.
Okay, first things first. In order for a skeletal muscle to contract, your brain sends a signal, in the form of an action potential in an upper motor neuron.
The upper motor neuron then activates a lower motor neuron in the spinal cord.
From here, the action potential is sent through an axon down to its ending branches, called axon terminals, to muscle fibers which they innervate.
The place where an axon terminal meets the muscle fiber is the neuromuscular junction.
The neuromuscular junction has three main parts: a presynaptic membrane, which is the membrane of an axon terminal; a postsynaptic membrane, which is the membrane of a skeletal muscle fiber and is also called a motor end-plate; and a synaptic cleft, which is the gap between the presynaptic and postsynaptic membranes.
When an action potential reaches the axon terminal, synaptic vesicles that contain neurotransmitters, called acetylcholine, fuse with the cell membrane of the axon terminal, releasing the acetylcholine into the synaptic cleft.
The acetylcholine then diffuses over to the motor end plate on the muscle fiber and binds to ligand-gated ion channels, also called nicotinic receptors.
When that happens, these ligand-gated ion channels open up, letting lots of sodium ions rush into the skeletal muscle fiber, and a few potassium ions leak out of the cell as well. But overall there’s an increase in positive charge on the inside of the muscle fiber causing it to depolarize.
Neuromuscular blockers are medications used to relax the muscles during surgical procedures and mechanical ventilation. They work by inhibiting the actions of acetylcholine on nicotinic receptors at the neuromuscular junction. Inhibition of these receptors disrupts the transmission of nerve impulses to the muscles, thus causing them to become relaxed and unable to move.
Neuromuscular blockers are divided into non-depolarizing blockers, like atracurium, vecuronium, and rocuronium; and depolarizing agents like succinylcholine. Non-depolarizing blockers work by competing with acetylcholine for receptors. They are used in mechanical ventilation and to aid in surgery. On the other hand, depolarizing agents cause prolonged stimulation and subsequent desensitization of the receptors. They can facilitate tracheal intubation or short surgical procedures.
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