FRC Day 2: Series: Sliding and Sticking

Here are some highlights from Day 2, though the coup de grace on the old anatomy was delivered by Jaap van der Wal, but more on him later.

The theme of the day was the sideways connections of the fascia within the muscle. Jst how does the muscle convey its force to the fascia and vice versa?

Carla Stecco of the famous Stecco family started the day by tracing the ‘trellis’ (I would say onion bag) arrangement of the fascia at rest, with additional ‘crimping’ in the tissue. Dense irregular tissue is not ‘irregular’ at all, but has a variety of directions at very precise angles for dealing with the forces. What slides, and what is fixed?

How much is the thoracolumbar fascia a sense organ and how much a force transmitter? asks Jonas Tesarz.

Jean_Paul Delage, working with Guimberteau, shows the cells in the paratendon (what we used to think of as the sheath).

Peter Purslow showed great pictures of the honeycomb of the endomysium, showing the same angle of fibers Stecco described, which go longitudinal when the muscle is stretched, and go circumferential when the muscle is contracted. Interestingly, while the endomysium is well-equiped to transmit force, the perimysium – which is continuous with the epimysium – is poorly constructed to transmit force – so what it is for?

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One Response to “FRC Day 2: Series: Sliding and Sticking”

  1. sarasotajoe Says:

    Thanks for these FRC posts Tom. And the trip to the coffeehouse was fun too 🙂

    Hmmm. This is really interesting.

    Perhaps defining the functional unit of a muscle as motor unit is only half the story. It is a model that comes from a time when the nervous system was king and fascia was the dirt that needed to be excavated to find the archeological treasures of the body.

    If endomysium conveys force throughout a fascicle, but that force is largely contained by perimysium within the fascicle, then the fascicle is at some level the functional unit of myofascia, defining direction of force. Engaging more or fewer motor units within a fascicle simply changes the amount of force generated by that fascicle. Both the motor unit and the fascicle would both be functional units of sorts.

    In Boston we learned that 30% of a muscle’s force is transmitted through the epimysium to neighboring muscles. It would seem that in order for the force of any musle fiber contraction to be conveyed through the epimysium, it would have to be first conveyed through perimysium, but apparently this is not so. Perhaps there is something about the gross change in shape of the entire muscle that is transmitted through epimysium.

    In any case, the fascicle is the only level at which we have anything approaching a contained mechanical unit, neither the individual muscle fiber nor the named muscle are so contained, though it is usually the muscle that is taught that way. (I also realize the fascicle is not exactly contained either, but it comes closest).

    If it weren’t for the overwhelming complexity that would result, it would perhaps be a better model to name all the fascicles, instead of the muscles. That would be absurdly elaborate though, and I should be careful about replacing what I’ve called the tyranny of the epimysium with a similar despotism of perimysium.

    I’ve not been able to find any information about how many motor units there are in a typical fascicle – or if its one to one. All the texts reference these as separate discussions.

    I’m curious what Purslow and Stecco thought the implications of their findings were, and if I’m onto anything. And what I’m missing (aside from an amazing experience in Amsterdam!)

    Joe

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