Our example wants us to arrange the following from superficial to deep by placing the correct letter in each blank. We have myofilaments, epimysium, perimysium, endomysium, and sarcolemma. When I think of a muscle and the structure of a muscle, what's most superficial, what surrounds the entire muscle, is going to be a layer of connective tissue. We call that layer of connective tissue that surrounds the entire muscle the epimysium. So I'm going to put 'b' first. Remember, 'epi' means on the surface or on the outside of something. The epimysium is the connective tissue layer that surrounds the entire muscle.
Within the epimysium, we're going to have these bundles of fascicles. Looking down at the fascicles, well, it's two arrows down. There's a space between it. What surrounds the fascicle? We have another connective tissue layer, and that's going to be the perimysium. So 'c' perimysium, the connective tissue layer that surrounds the fascicle, is going to come next.
Well, the fascicle is a bundle. It’s a bundle of muscle fibers, but I don't see 'muscle fibers' on my list here. So when I look I think what's associated with the muscle fiber, what I see next is the sarcolemma. The sarcolemma is going to be the cell membrane of the muscle fiber. However, there's another connective tissue layer that comes first. The connective tissue layer that surrounds each muscle fiber and, therefore, surrounds the sarcolemma is going to be the endomysium. Remember, the prefix 'endo' means within. It's deep within the fascicle. So, the endomysium surrounds the sarcolemma. The sarcolemma is the cell membrane of the muscle fiber, so 'e' comes next.
And now we've made it to the myofibrils. Myofibrils, remember, are those long rod-like organelles that make up the majority of the inside of a muscle fiber. Well, what are these myofibrils made of? They're made of the contractile proteins. We're going to call these the myofilaments. We only had one option left, but it was the right answer.
Alright. So the myofilaments, the proteins that are actually going to do the contracting, deep, deep within the muscle. To recap, superficially, we have the epimysium that surrounds the entire muscle. The perimysium is within the epimysium, and it surrounds the fascicle. The fascicle is going to be a bundle of muscle fibers, but each muscle fiber is surrounded by the endomysium. The endomysium surrounds the cell membrane of the muscle fiber, which is the sarcolemma. Within the sarcolemma, we have the rod-like organelles called myofibrils, and the proteins that make those up are going to be the myofilaments. That's our answer. More problems to follow. I'll see you there.