hello anatomy friends this is dr alsup and we are going to start exploring the wonderful
world of the skeletal muscle tissue at a more microscopic level with a focus on skeletal muscle
fibers which are really just another name for the muscle cell muscle cells are called muscle fibers
because of their relatively long shape so you will hear me say both muscle cell or muscle fiber
very interchangeably and both are fair game for assessment before we talk about the composition
of the muscle fibers so the organelles and what's inside them in this video we're going to discuss
how these cells actually form and importantly how they grow how they get bigger and we will finish
our conversation talking about satellite cells which are closely associated with muscle cells
all right during embryonic development hundreds of myoblasts which are these small mesodermal cells
are going to um start their their mesodermal cells which remember the mesoderm is one of
the germ layers so they will start to kind of collect together and they will begin to fuse
and they will continue to fuse until you have a mature muscle cell which you're
looking at right here and that mature muscle cell will have hundreds of nuclei
and that's all because of how it formed with these you know multiple cells fusing together
which still you would have those nuclei so that is why you see all these these nuclei throughout
once a muscle cell is fully fused and considered mature cell division is not possible all right so
in order for a muscle cell to get larger which we know muscles are capable of think of a bodybuilder
but even just regular muscle growth through the juvenile period so for it to get larger
the muscle cell has to hypertrophy all right which hypertrophy is going to be the enlargement
of existing muscle fibers and this hypertrophy is possible by the increased production of structures
within the cell so most notably the myofib fibre fibrils which we'll talk about what that is in
a bit more detail in subsequent videos but you could also have other portions of the cell that
will enlarge or increase and that would be the sarcoplasm the sarcoplasmic reticulum mitochondria
and other organelles so that you'd have an increased production of these organelles
so it is hypertrophy not hyperplasia which would be an increase in the number of cells
so you're not getting more cells the cells that exist are getting larger
during childhood certain hormones like human growth hormones or sex hormones can lead to
the hypertrophy of the existing cells but after the juvenile period usually it's
more muscle hypertrophy occurring due to repeated forceful muscular activity
like weight training and that can certainly lead to an increase in muscles and juveniles as well
some myoblasts can persist and be closely associated with skeletal muscle cells
and some research shows that these cells retain some capacity to fuse with one another or with
damaged muscle fibers but i do want to also note there's quite a bit of ongoing research regarding
satellite cells and some have some conflicting findings we're going to kind of go with what a lot
of the textbooks say so the number of satellite cells are typically not enough to compensate
for significant skeletal muscle damage which if you have that significant damage that would lead
to something called fibrosis which is the replacement of damaged muscle fibers with fibrous
scar tissue and just think if you had that fiber scar tissue that would really limit
the functions and capabilities of the muscles so satellite cells can play a role in terms of
helping damaged muscle cells but not to a significant extent if you have significant damage
okay our question for this video is very big picture something i definitely want you to take
away from this video so true or false muscle grows via hyperplasic or plastic activity sometimes
you'll hear plagic activity so is this true or false and when ready what do you say do you say
true or false and if you said false why well the answer is false alright so false is correct
muscles grow through hypertrophy not hyperplastic or hyperplasic activity so it would be trophy here
mark that out there muscle cell fibers arise before birth through the fusion
of those myoblasts and most cells will last a lifetime if it were hyperplasia that would be
an increase in the number of muscle cells which we know we have a pretty set amount
after birth excellent great work and if you miss this no problem you just now know that you
need to review this area a bit more which isn't uncommon when learning something new as always
please feel free to reach out to me with any questions thank you for your time and attention