page_title: Asynchronous muscles
section_title: Molecular
hierarchical_section_title: Asynchronous muscles / Structure / Molecular
caption_attribution_description: English: Molecular components of myofibrils. Used from Servier Medical Art under the Creative Commons Attribution 3.0 Unported License.
context_page_description: Asynchronous muscles are muscles in which there is no one-to-one relationship between electrical stimulation and mechanical contraction. These muscles are found in 75% of flying insects and have convergently evolved 7-10 times. Unlike their synchronous counterparts that contract once per neural signal, mechanical oscillations trigger force production in asynchronous muscles. Typically, the rate of mechanical contraction is an order of magnitude greater than electrical signals. Although they achieve greater force output and higher efficiency at high frequencies, they have limited applications because of their dependence on mechanical stretch.
context_section_description: The exact molecular mechanisms used by asynchronous muscles are unknown, but it is believed that asynchronous muscles have no unique molecular structures as compared to their synchronous counterparts. A study investigating the asynchronous power muscles in bumblebees with X-ray diffraction videos showed that actin and myosin alone are sufficient for generating asynchronous behavior. This finding helps explain how asynchronous muscles independently evolved across insect taxa. More recent work using similar X-ray diffraction techniques in Lethocerus discovered that troponin bridges may play a critical role in stretch activation. As the muscle is stretched, these bridges move tropomyosin to reveal myosin-actin binding sites. The muscle can only produce force when these sites are activated.
caption: Molecular components of myofibrils. Muscle can only contract when actin binding sites are revealed for myosin heads to attach. Created by Servier Medical Art and used under a Creative Commons Attribution 3.0 Unported License.
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