the contraction part starts with the binding
of my SN heads on the actin calcium allows us to happen
because 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