Under normal circumstances, a nerve comes into contact with a muscle at a neuromuscular junction. In a normal nerve ending, there exist multiple preformed vesicles containing the neurotransmitter acetylcholine. When a nerve is stimulated, an action potential travels along the entire distance of the nerve until it reaches the nerve ending. This action potential causes the vesicles to dock to the terminal membrane of the neuromuscular junction. Acetylcholine from the vesicles is released into the synaptic cleft after fusing of the membranes. This acetylcholine becomes bound to the post-synaptic muscle which allows a muscular contraction to be initiated.  Acetylcholine is released into the synaptic cleft following stimulation of a nerve The "synaptic fusion complex" is what allows the vesicles containing preformed acetylcholine to dock and fuse to the membrane. This complex is made of a group of proteins known as the SNARE proteins (soluble N-ethylmaleimide-sensitive factor attachment protein receptors). These SNARE proteins are the site of action of botulinum toxins. When the SNARE proteins are damaged, the synaptic fusion complex is impaired, and muscle contraction is inhibited.  This is the reason that Botox® is helpful for "dynamic" wrinkles, or wrinkles that result from the contraction of muscles. With time and with repeated injections of Botox®, the muscles that produce unwanted wrinkles will become smaller, and this may result in treatments that last longer or in treatments that require few units of the toxin. To read more about what areas can be treated with Botox®, click here. |
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