the contraction part starts with the binding
0:07of my SN heads on the actin calcium allows us to happen
0:13because again it reveals the binding sites on the act in which
0:16rest are covered by the troponin what are the things necessary for muscle
0:22contraction
0:22energy and we store energy in molecules of ATP
0:26attention try phosphate so the first thing that has to happen
0:30is that the myosin must be in a position
0:34to reach out and grab the actin at the binding sites
0:38so even if the calcium reveals
0:42the binding site on the actin if there's no energy for the myosin had to be
0:47energized
0:47and become oriented in a position to grab the actin
0:51nothing can happen so ATP is necessary
0:55so what's going to happen in the contraction part
0:59is that the myosin heads are gonna break down
1:03ATP into 8dp
1:06and phosphate tennis and try phosphate into a Denison
1:10die phosphate and fasting that is going to
1:14reorient the position up to my ass in a position to grab the actin
1:18and energized then the myosin heads
1:23crap the Acton that bind to the binding sites on the Act informing what's called
1:28a cross bridge
1:29a bridge between the pic Philip
1:32and the thin filament ADP
1:36still down here myosin heads using that energy now
1:40going to rotate towards
1:45the midline of the sarcomere that rotation of the myosin
1:50head is going to Paul the thin filament
1:55towards the center of the sarcomere and this is happening on both sides up the
2:01AM lineup the sarcomere
2:03so that to thin filament are being polled
2:06toward the midline at the same time the mice and had then binds to some ATP
2:12and the binding site is released so the cross bridges between the fic
2:18content film and detach because of the presence of ATP's
2:22energy is necessary for this process to and not just to be getting
2:27and the presence of that ATP allows
2:30for the myosin heads to reenergize and start this process again the myosin
2:35heads
2:36can powerstroke which is the polling a potential in toward the midline
2:40up the sarcomere about five times a second
2:44it takes multiple power Strokes to create
2:47for muscle contraction the fin filaments will not be drawn toward the midline
2:51completely by one powerstroke
2:53its many partial click or scholarship
2:57so what this is creating
3:02when this happens is
3:05a sliding up the thick and thin filaments
3:08in a typical sarcomere you have a degree of overlap of
3:14pic confidential on it that is maybe about 50 percent
3:17overlap so let's say that the sea lines up the sarcomere
3:21are one centimeter apart and this is
3:25this is a very large estimation using this number just for simplicity purposes
3:29when there's fifty-percent overlap between the second film
3:34after the power strokes after the mice and had to reach out and grab the actin
3:38and pole the thin filaments toward the midline this way
3:44we end up with a lot more
3:48overlap which creation overall shortening
3:52of this distance maybe to half a centimeter
3:57so the sarcomere which is the contractile unit of the muscle cell
4:01shortens overall by the increase
4:04in overlap up the two filaments that they cannot fit that is called a sliding
4:09filament theory of muscle contraction the filaments slide over one another
4:14increasing their overlap if you do this to a few million circle mir's at one
4:20time
4:21you can result in an overall shortening up the whole muscle
4:25that overall shortening up the whole muscle forces it to
4:29poll on its attachments ike's on the Skelton
4:32so whatever joint that muscle crosses will have to decrease its angle
4:39pics flexor muscle like this
4:42or increase its angle if it's an extension muscle
4:46like this because muscle that crosses that
4:50joint is shortening that's how skeletal muscles move our skilled
4:56it starts with the excitation have the muscle by using the nervous system
5:02and result in the contraction of the muscle using a sliding filament theory a
5:05muscle contraction
5:09the overall concept is that thick and thin filaments
5:13slide over one another increasing the degree of overlap
5:17and shortening and overall unit up the muscle cell called the sarcomere
อัปโหลดเมื่อ 20 ม.ค. 2012