All cells in the human body come from
special cells called stem cells, which are
unique in that they have the ability to:
1) become any specialized cell, such as a
muscle cell, in the body and
2) to make stem cells just like it.
You can think of human development like a ball
rolling down a hill, where the stem cell sits at
the top, with the ability to roll in any
direction. As time goes on, the ball becomes more
committed to one path and is less able to, say,
roll around to the other side of the hill. Cells
are the same way, where the more specialized
they get the less ability they have to become
other types of cells. For example, a
muscle cell can't just decide one day it's going
to be a skin cell.
Instead, we rely on stem cells dividing to make
new muscle cells, and other stem cells dividing to
give us new skin cells. In fact, we can see the
differences between skin and muscle stem cells as
early as when an embryo looks like a big, hollow
water balloon full of cells, called a blastula!
Muscle cell development is especially cool because
of one of the most important things you need as a
muscle cell: energy. So muscle cells are
actually formed by fusing multiple cells
together, resulting in multiple nuclei and
lots of mitochondria in the muscle cell and
helping it provide all the energy needed to move!
Hope that helps,
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