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baggier t1_j4kdmz1 wrote

Muscle action depends on ions moving. If a fibre was too large it would take too long for the ions to diffuse or be pumped in and out. So muscle is faster by having lots of little fibres bundled than one big lump

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DoomGoober t1_j4jyi02 wrote

My understanding was that each fascicle (muscle fiber bundle) has its own nerves and blood vessels.

Thus, the fascicle structure facilitates shared nerve control and energy/waste management of grouped muscle fiber cells.

Since the muscle fibers in each fascicle are trying to generate the same motion and generally all have the same function, it makes sense to bundle them together and link them all to the same nerves. And the same vessels (which facilitate the metabolic behavior of the muscle fibers.)

Edit: Sorry, I clearly wrote this badly. My writing implies that all the fibers fire at the same time with one set of nerves firing them all at once (I wish I could do that, as I could generate a lot more force when lifting weights! But then again, I might injure myself more easily.) Rather, while the muscle fibers share the same nerves bundles, I did not meant that they all fire at the same time or that the nerves don't branch off and act somewhat independently of each other even within the fascicle. Thanks for all of the corrections!

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Grumblepanda t1_j4k1yk6 wrote

There is a redundency factor in our bodies. If you had one main nerve firing one entire muscle that then gets damaged, you would lose entire control over that muscle and its function. If nerve pathways weren't shared, it would individualize group function (motor units). Think of it like roads in a city. The fascicles allow for micro stabilization within the muscles plane of movement, creating strength/integrity through changing force/velocity. (More data required) Developmentally we stress our bodies with different demand and stimuli, creating a reaction in how our muscles create shape. As we all have a similar bone and joint structure (compared to other animals) we have similar patterns to the base demands that our body develops in response to, so similar fascial presentations develop.

Please strike me down for any inaccuracies or incorrect generalizations. It sounds like you have some solid education behind you already.

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goosebattle t1_j4kwyqh wrote

This also helps us regulate muscle force output more like a dimmer switch rather than an on off switch.

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Grumblepanda t1_j4luxop wrote

Contrary to the instructor who once said there is only "On or Off" for muscle engagement. I really hope I misunderstood their intention with that.

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goosebattle t1_j4m0zj0 wrote

Motor units (and single muscle cells) are almost operating as on/off. There is some minor modulation possible with changes in firing frequency. Each muscle has many (typically >>100) motor units varying in size, each with an on/off switch. The net result of having so many motor units is the muscle behaves as if it is operating with a dimmer switch.

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goosebattle t1_j4kvw57 wrote

This is incorrect. Our muscles fire in a mosaic pattern, not as fascicles. Fibre type grouping occurs in disease and aging when muscle fibres lose innervation and become reinnervated by near neighbours resulting in the regional firing patterns you describe.

Edit: an advantage of mosiac firing pattern is that it spreads the stresses across the muscle rather than generating regions of high local stresses. Fascicles (i.e., the perimysium) help transmit the stresses from fibres to tendons.

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