1 00:00:01,059 --> 00:00:02,430 This here is a model of a sarcomere. 2 00:00:03,359 --> 00:00:03,670 A Sarcomere 3 00:00:03,960 --> 00:00:06,840 is a contractile unit for skeletal muscle fibers. 4 00:00:07,369 --> 00:00:08,359 This covering 5 00:00:08,609 --> 00:00:11,310 which is acting as a dust cover, but it actually represents 6 00:00:11,649 --> 00:00:16,559 the sarcoplasmic reticulum, which is a modified ER which is storing calcium, 7 00:00:16,569 --> 00:00:18,510 which is crucial for muscle contraction. 8 00:00:18,700 --> 00:00:23,069 The parts of this you should know. This is the transverse tubule or T tubule. 9 00:00:23,229 --> 00:00:24,799 These are the terminal cisternae. 10 00:00:24,930 --> 00:00:28,159 Off to the sides of that, and they make this triad structure. 11 00:00:28,709 --> 00:00:31,209 OK. So, then you can look at this. This is the actual sarcomere. 12 00:00:31,540 --> 00:00:31,989 The sarcomere’s 13 00:00:32,200 --> 00:00:33,009 boundaries 14 00:00:33,290 --> 00:00:34,169 are shown at 15 00:00:34,500 --> 00:00:37,380 the left and right. This is the Z discs 16 00:00:37,560 --> 00:00:39,970 and they're actually shaped like the letter Z. 17 00:00:40,799 --> 00:00:42,189 OK. So, what a sarcomere is 18 00:00:42,419 --> 00:00:45,479 creating the striations that you see under a microscope. 19 00:00:45,490 --> 00:00:47,619 Now, the striations, these light and dark 20 00:00:47,799 --> 00:00:50,240 bands that the muscle has 21 00:00:50,349 --> 00:00:53,990 as a result of these thin and thick myofilaments. 22 00:00:54,509 --> 00:00:57,549 So, this is a thin myofilament containing mostly actine, 23 00:00:58,139 --> 00:01:00,639 and this is the thick myofilament containing myosine. 24 00:01:01,709 --> 00:01:05,279 So, what happens is the acting is attached to the Z discs, right? 25 00:01:05,290 --> 00:01:08,699 You can see that on both sides, the thin myofilament is attached here. 26 00:01:09,389 --> 00:01:13,580 The thick myofilament is connected here in the middle, this is called the M line. 27 00:01:14,029 --> 00:01:17,300 And during the muscle contraction, the thick filaments, 28 00:01:17,309 --> 00:01:20,540 the myosin, walk the actine towards the middle, 29 00:01:21,110 --> 00:01:23,089 and it happens on both sides simultaneously. 30 00:01:23,099 --> 00:01:27,220 So, the whole thing shortens the Z discs actually get closer together. 31 00:01:27,760 --> 00:01:31,699 So, what's creating the striated appearance when you look at it under a microscope? 32 00:01:32,529 --> 00:01:34,260 And when you look at this area here, 33 00:01:34,699 --> 00:01:38,209 just this region here will appear light under a microscope. 34 00:01:38,330 --> 00:01:40,889 That's called an eye band or light band. 35 00:01:41,419 --> 00:01:44,660 It appears light because it only has thin myofilaments, 36 00:01:45,739 --> 00:01:48,559 this area from here to here, 37 00:01:49,459 --> 00:01:53,449 that will appear dark under a microscope. And that's called the A band or dark band. 38 00:01:53,459 --> 00:01:55,360 The reason why it appears dark is because 39 00:01:55,370 --> 00:01:57,830 it contains thick myofilaments and they're thicker, 40 00:01:57,839 --> 00:01:58,440 of course. 41 00:01:59,010 --> 00:02:01,540 There is a special area right here, 42 00:02:01,769 --> 00:02:04,440 where there is no overlap with thick and thin. 43 00:02:04,449 --> 00:02:08,320 You can see just this middle region where it's just thick myofilaments 44 00:02:08,740 --> 00:02:10,070 That's called the H band. 45 00:02:10,080 --> 00:02:13,350 And if you actually look at it from up top, it looks like the letter H. 46 00:02:14,110 --> 00:02:14,610 All right. 47 00:02:15,589 --> 00:02:19,630 Additionally, there's some accessory proteins here with the thin myofilament. 48 00:02:19,639 --> 00:02:21,869 You will learn about this in lecture troponin, 49 00:02:22,240 --> 00:02:24,970 tropomyosin. That's not something we really go over 50 00:02:25,360 --> 00:02:26,050 in lab. 51 00:02:26,500 --> 00:02:27,979 But those are the parts of a sarcomere.