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In Vivo Imaging of Human Sarcomere Twitch Dynamics in Individual Motor Units

PainSci » bibliography » Sanchez et al 2015
Tags: neat, biology

PainSci notes on Sanchez 2015:

Biology and medicine are still in their scientific adolescence, and one of the clearest demonstrations of this is the surprisingly primitive state of our understanding of how muscle cells work. You wouldn’t think so looking at a textbook full of complicated diagrams of sarcomeres and the arcane biological details of energy metabolism, but there are still profound gaps in our knowledge. The business of muscle cell contraction is all conducted on a nearly invisible (molecular) scale. But to truly understand pathology, you have to really understand how something works in the first place, and one of the best ways to do that is to see it. Which is why this new muscle §microscope is a big deal:

A team of Stanford researchers has developed a microscope that can visualize and measure the force-generating contractions of these patients’ individual motor units. This action has been studied for nearly 100 years, but this is the first time it has ever been observed in the muscles of a living human.

Good job, Stanford!

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

Motor units comprise a pre-synaptic motor neuron and multiple post-synaptic muscle fibers. Many movement disorders disrupt motor unit contractile dynamics and the structure of sarcomeres, skeletal muscle's contractile units. Despite the motor unit's centrality to neuromuscular physiology, no extant technology can image sarcomere twitch dynamics in live humans. We created a wearable microscope equipped with a microendoscope for minimally invasive observation of sarcomere lengths and contractile dynamics in any major skeletal muscle. By electrically stimulating twitches via the microendoscope and visualizing the sarcomere displacements, we monitored single motor unit contractions in soleus and vastus lateralis muscles of healthy individuals. Control experiments verified that these evoked twitches involved neuromuscular transmission and faithfully reported muscle force generation. In post-stroke patients with spasticity of the biceps brachii, we found involuntary microscopic contractions and sarcomere length abnormalities. The wearable microscope facilitates exploration of many basic and disease-related neuromuscular phenomena never visualized before in live humans.

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