Hi,
I don’t know if definitive number of muscles (skeletal, cardiac and smooth muscles) in the human body has ever been definitively calculated/enumerated or if it is even possible. Has the number been fixed or is it a matter of debate? I look forward to your feedback.
There should be no debate on this, (other than it being posted on the SDMB).
Off to General Questions.
Afaik, smooth muscles aren’t really given names. They just considered part of the organ they serve.
Some skeletal muscles don’t appear in all people. Palmaris longus for example.
Some muscles are sometimes thought of in single units or as a functional group. Like the quadriceps or iliopsoas.
In the end I don’t think there’s a debate. The anatomy is solidly known and any different counts would be based on what your purpose for counting them was.
So when I see posts discussing hair follicle muscles, can we safely dismiss that?
Dismiss what? They do exist, if that is what you are asking.
My interest Tamerlane is to determine how many muscles there are in the body. What number do you put on it? Can we add hair follicle muscles to that figure or is that no acceptable? And if not, why not?
Generally only skeletal muscles are counted and even then the number varies by up to a third depending on who is counting and who is counted - 650-840 is often cited. The number of smooth muscles like arrector pili muscles is literally uncounted and to some extent uncountable. Because there is often no way to separate out each bit of smooth muscle surrounding each capillary and whatnot - they all blend together and come apart differently. Not to mention that individual variation is almost certainly pretty substantial - there are smooth muscle sheets all over the place.
So you can ask how many skeletal muscles are there and get a very rough approximation, as above. However, frustrating though it may be, you cannot and will not get an answer to how many muscles are there in a human, period. Because they cannot be counted in a standardized way and there is not enough consistency in humans as individuals to make a count mean anything. We each have our own muscle count that will not be the same as the person in the next cubicle over.
ETA: comprehensively ninja’d by Tamarlane’s latest.
Start by defining what constitutes a distinct “muscle” to you. Defend that decision. Then we can dig into the databases.
e.g. cats can certainly make the fur on their back stand up. But how many distinct muscles do they use to do that?
One per fur follicle? Or one per cat with a bunch of regional sections each enervated separately? Or maybe several separate regional muscles each singly enervated? Are these same muscle cells used for other purposes or should we count them separately for each of their uses? Is separate enervation a meaningful distinction? If not, what features are?
Here’s how you might get a fair count. Inside the spine, there is a big bundle of nerves. Each nerve has separate fibrils, where each fibril is a single cell that is several meters long. Your limit on how many distinct actions you can take at any single instant in time is the number of distinct channels of control you have, or that fibril count.
Problem is, it’s going to be very labor intensive and a pain to get a count. You would have to dissect a cadaver spine, then somehow splay out the bundle after you cut it, and then count every fibril. And then do that over and over.
And yeah, it probably varies person to person. Maybe not by 1/3 but the exact count is going to be slightly different.
Oh, and I think the nerves controlling your eyes and face take different paths than the spine, so you need to include those as well in your count.
Cranial nerves - Wikipedia covers that last item you mention: the category of non-spinal nerves. There are 12 or 13 in humans depending on how one counts.
Thank you all. Very helpful.