[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.06,0:00:02.43,Default,,0000,0000,0000,,This here is a model of a sarcomere.
Dialogue: 0,0:00:03.36,0:00:03.67,Default,,0000,0000,0000,,A Sarcomere 
Dialogue: 0,0:00:03.96,0:00:06.84,Default,,0000,0000,0000,,is a contractile unit for skeletal muscle fibers.
Dialogue: 0,0:00:07.37,0:00:08.36,Default,,0000,0000,0000,,This covering
Dialogue: 0,0:00:08.61,0:00:11.31,Default,,0000,0000,0000,,which is acting as a dust cover, but it actually represents
Dialogue: 0,0:00:11.65,0:00:16.56,Default,,0000,0000,0000,,the sarcoplasmic reticulum, which is a modified ER which is storing calcium,
Dialogue: 0,0:00:16.57,0:00:18.51,Default,,0000,0000,0000,,which is crucial for muscle contraction.
Dialogue: 0,0:00:18.70,0:00:23.07,Default,,0000,0000,0000,,The parts of this you should know. This is the transverse tubule or T tubule.
Dialogue: 0,0:00:23.23,0:00:24.80,Default,,0000,0000,0000,,These are the terminal cisternae. 
Dialogue: 0,0:00:24.93,0:00:28.16,Default,,0000,0000,0000,,Off to the sides of that, and they make this triad structure.
Dialogue: 0,0:00:28.71,0:00:31.21,Default,,0000,0000,0000,,OK. So, then you can look at this. This is the actual sarcomere.
Dialogue: 0,0:00:31.54,0:00:31.99,Default,,0000,0000,0000,,The sarcomere’s
Dialogue: 0,0:00:32.20,0:00:33.01,Default,,0000,0000,0000,,boundaries
Dialogue: 0,0:00:33.29,0:00:34.17,Default,,0000,0000,0000,,are shown at
Dialogue: 0,0:00:34.50,0:00:37.38,Default,,0000,0000,0000,,the left and right. This is the Z discs
Dialogue: 0,0:00:37.56,0:00:39.97,Default,,0000,0000,0000,,and they're actually shaped like the letter Z.
Dialogue: 0,0:00:40.80,0:00:42.19,Default,,0000,0000,0000,,OK. So, what a sarcomere is
Dialogue: 0,0:00:42.42,0:00:45.48,Default,,0000,0000,0000,,creating the striations that you see under a microscope.
Dialogue: 0,0:00:45.49,0:00:47.62,Default,,0000,0000,0000,,Now, the striations, these light and dark
Dialogue: 0,0:00:47.80,0:00:50.24,Default,,0000,0000,0000,,bands that the muscle has
Dialogue: 0,0:00:50.35,0:00:53.99,Default,,0000,0000,0000,,as a result of these thin and thick myofilaments.
Dialogue: 0,0:00:54.51,0:00:57.55,Default,,0000,0000,0000,,So, this is a thin myofilament containing mostly actine,
Dialogue: 0,0:00:58.14,0:01:00.64,Default,,0000,0000,0000,,and this is the thick myofilament containing myosine.
Dialogue: 0,0:01:01.71,0:01:05.28,Default,,0000,0000,0000,,So, what happens is the acting is attached to the Z discs, right?
Dialogue: 0,0:01:05.29,0:01:08.70,Default,,0000,0000,0000,,You can see that on both sides, the thin myofilament is attached here.
Dialogue: 0,0:01:09.39,0:01:13.58,Default,,0000,0000,0000,,The thick myofilament is connected here in the middle, this is called the M line.
Dialogue: 0,0:01:14.03,0:01:17.30,Default,,0000,0000,0000,,And during the muscle contraction, the thick filaments,
Dialogue: 0,0:01:17.31,0:01:20.54,Default,,0000,0000,0000,,the myosin, walk the actine towards the middle,
Dialogue: 0,0:01:21.11,0:01:23.09,Default,,0000,0000,0000,,and it happens on both sides simultaneously.
Dialogue: 0,0:01:23.10,0:01:27.22,Default,,0000,0000,0000,,So, the whole thing shortens the Z discs actually get closer together.
Dialogue: 0,0:01:27.76,0:01:31.70,Default,,0000,0000,0000,,So, what's creating the striated appearance when you look at it under a microscope?
Dialogue: 0,0:01:32.53,0:01:34.26,Default,,0000,0000,0000,,And when you look at this area here,
Dialogue: 0,0:01:34.70,0:01:38.21,Default,,0000,0000,0000,,just this region here will appear light under a microscope.
Dialogue: 0,0:01:38.33,0:01:40.89,Default,,0000,0000,0000,,That's called an eye band or light band.
Dialogue: 0,0:01:41.42,0:01:44.66,Default,,0000,0000,0000,,It appears light because it only has thin myofilaments,
Dialogue: 0,0:01:45.74,0:01:48.56,Default,,0000,0000,0000,,this area from here to here,
Dialogue: 0,0:01:49.46,0:01:53.45,Default,,0000,0000,0000,,that will appear dark under a microscope. And that's called the A band or dark band.
Dialogue: 0,0:01:53.46,0:01:55.36,Default,,0000,0000,0000,,The reason why it appears dark is because
Dialogue: 0,0:01:55.37,0:01:57.83,Default,,0000,0000,0000,,it contains thick myofilaments and they're thicker,
Dialogue: 0,0:01:57.84,0:01:58.44,Default,,0000,0000,0000,,of course. 
Dialogue: 0,0:01:59.01,0:02:01.54,Default,,0000,0000,0000,,There is a special area right here,
Dialogue: 0,0:02:01.77,0:02:04.44,Default,,0000,0000,0000,,where there is no overlap with thick and thin.
Dialogue: 0,0:02:04.45,0:02:08.32,Default,,0000,0000,0000,,You can see just this middle region where it's just thick myofilaments
Dialogue: 0,0:02:08.74,0:02:10.07,Default,,0000,0000,0000,,That's called the H band.
Dialogue: 0,0:02:10.08,0:02:13.35,Default,,0000,0000,0000,,And if you actually look at it from up top, it looks like the letter H.
Dialogue: 0,0:02:14.11,0:02:14.61,Default,,0000,0000,0000,,All right.
Dialogue: 0,0:02:15.59,0:02:19.63,Default,,0000,0000,0000,,Additionally, there's some accessory proteins here with the thin myofilament.
Dialogue: 0,0:02:19.64,0:02:21.87,Default,,0000,0000,0000,,You will learn about this in lecture troponin,
Dialogue: 0,0:02:22.24,0:02:24.97,Default,,0000,0000,0000,,tropomyosin. That's not something we really go over 
Dialogue: 0,0:02:25.36,0:02:26.05,Default,,0000,0000,0000,,in lab.
Dialogue: 0,0:02:26.50,0:02:27.98,Default,,0000,0000,0000,,But those are the parts of a sarcomere.