#sarcomere

[num8ers]

[francois-chung]

First high-resolution image of thick filaments of muscle cells

Scientists gain insight into the organization of the mammalian heart muscle

« Our aim is to paint a complete picture of the sarcomere one day. The image of the thick filament in this study is ‘only’ a snapshot in the relaxed state of the muscle. To fully understand how the sarcomere functions and how it is regulated, we want to analyze it in different states e. g. during contraction. »

[bpod-bpod]

Muscling In

Cut through a bungee cord and you’ll see many elastic strands bundled together, flexing to give strength to the overall rope. Muscle is often described in a similar way – a bundle of parallel tube-like myofibrils stretching independently but at the same time, to contract or relax the muscle. Yet these simulations tell a slightly different story, based on scans of mouse muscles with an advanced scanning electron microscope. Instead of being entirely separate, stretchy regions called sarcomeres (measured between the vertical black bands) often form branches between neighbouring myofibrils – connected regions are highlighted in different colours. While this occurs to different degrees in cardiac muscle (top) compared to skeletal muscle (bottom), it suggests that mice muscles, and ours, may behave more like muscular meshes than bungee cords, raising new questions for how these structures are affected by age and disease.

Written by John Ankers

Image adapted from work by T. Bradley Willingham and colleagues

National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA

Image originally published under a Creative Commons Licence (BY 4.0)

Published in Nature Communications, July 2020

You can also follow BPoD on Instagram, Twitter and Facebook

[bpod-bpod]

Want Big Muscles?

From a body-builder’s bulging bicep to the tiny flight muscles that keep a fruit fly’s wings beating, muscles are all made from bundles of long fibres divided into short, repeated segments called sarcomeres. When an animal makes a move, interlocking molecules within the sarcomere move past each other and cause the muscle to contract. These images show flight muscle fibres from six fruit flies, each with a different genetic change affecting a structure called the Z-disc (yellow), which marks the end of each sarcomere. Changes in a gene called Zasp affect the size of the Z-disc, in turn affecting the diameter of the fibre and altering the overall size and function of the muscle. Zasp is also involved in setting sarcomere size in the muscles of other animals, including humans. Some of these genetic changes mimic the effects seen in some types of muscle disease (myopathies), pointing towards future treatments.

Written by Kat Arney

Image from work by Nicanor González-Morales and colleagues

Department of Biology, McGill University, Montreal, Canada

Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)

Published in eLife, November 2019

You can also follow BPoD on Instagram, Twitter and Facebook

[dr-frenchtoaststick]

[svtturlan]

Animation sur le muscle  Pour les spé SVT on verra ça dans quelques mois... Going to the gym? Take this with you. Source : An animated guide to the human body : The muscle edition

[msagostino]

How do muscles contract?

To explore the sliding filament theory, students built a working model of a sarcomere. The straws represented the actin and the foam sheet represented the myosin filaments. The pipecleaner wrapped around the actin was the tropomyosin. Velcro adhesive allowed the myosin heads to attach to the actin and paper fasteners allowed the myosin to cause a “power stroke” and pull the actin toward the midline. 

[thegaitguys]

Why is that muscle so tight?

We often think of neurological reasons (increased facilitation of the agonist, decreased reciprocal inhibition of the antagonist, increase gamma drive, etc), but how about the series elastic element (ie the connective tissue)? Or perhaps the sarcomere (individual contractile unit of the muscle)? How can we fix that? It is easier than you thought!

An oldie but a goodie. A great FREE FULL TEXT paper on sarcomere loss and how to prevent it. Yep, would you have guessed static stretching? Yes, this study was on mice and it seems plausible that it would be applicable to humans as well.

"When muscle is immobilised in a shortened position there is both a reduction in muscle fibre length due to a loss of serial sarcomeres and a remodelling of the intramuscular connective tissue, leading to increased muscle stiffness. Such changes are likely to produce many of the muscle contractures seen by clinicians, who find that such muscles cannot be passively extended to the full length, which normal joint motion should allow, without the production of muscle pain or injury.

...These experiments show that in addition to preventing the remodelling of the intramuscular connective tissue component daily periods of stretch of 1/2 h or more also prevent the loss ofserial sarcomeres which occurs in mouse soleus muscles immobilised in the shortened position."

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1004076/pdf/annrheumd00439-0044.pdf

 link to full text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1004076/pdf/annrheumd00439-0044.pdf