How Muscle Contractions Work - The Exploring Nature ...€¦ · How Muscle Contractions Work During...
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How Muscle Contractions Work During a muscle contraction, every sarcomere will shorten (1) bringing the Z-lines closer together (2). e myofibrils shorten (3) too, as does the whole muscle cell. Yet the myofilaments (the thin and thick filaments) do not get shorter (4). ey slide by each other, overlapping as the Z-lines pull closer together, the I-Bands shorten (5), the H-Zones disappear (6) and the A-Bands move closer together (7). ©Sheri Amsel www.exploringnature.org thin filament (Actin) thick filament (Myocin) Z-Line M-Line I-Band (Light Band) A-Band (Dark Band) sarcomere Myofilaments: H-Zone myofibril 2) Z-lines move closer together. 3) myofibrils shorten muscle contraction 4) Myofilaments (thin and thick filaments) do not get shorter. sarcomere sarcomere 1) Sarcomeres shorten. Z-Line 5) I-Bands shorten 7) A-Bands move closer together. 6) H-Zones disappear
Transcript of How Muscle Contractions Work - The Exploring Nature ...€¦ · How Muscle Contractions Work During...
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How Muscle Contractions WorkDuring a muscle contraction, every sarcomere will shorten (1) bringing the Z-lines closer together (2). The myofibrils shorten (3) too, as does the whole muscle cell. Yet the myofilaments (the thin and thick filaments) do not get shorter (4). They slide by each other, overlapping as the Z-lines pull closer together, the I-Bands shorten (5), the H-Zones disappear (6) and the A-Bands move closer together (7).
©Sheri Amsel www.exploringnature.org
thin filament(Actin)
thick filament(Myocin) Z-Line
M-LineI-Band
(Light Band)A-Band (Dark Band)
sarcomere
Myofilaments:
H-Zone
myofibril
2) Z-lines move closer together.
3) myofibrils
shorten
mus
cle
cont
ract
ion
4) Myofilaments (thin and thick filaments) do not get shorter.
sarcomere
sarcomere
1) Sarcomeres shorten.
Z-Line5) I-Bands
shorten
7) A-Bands move closer together.
6) H-Zonesdisappear
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How Muscle Contraction WorksDuring a muscle contraction, every sarcomere will shorten (1) bringing the Z-lines closer together (2). The myofibrils shorten (3) too, as does the whole muscle cell. Yet the myofilaments – the thin and thick filaments – do not get shorter (4). They slide by each other, overlapping as the Z-lines pull closer together, the I-Bands shorten (5), the H-Zones disappear (6) and the A-Bands move closer together (7).
©Sheri Amsel www.exploringnature.org
thin filament(Actin)
thick filament(Myocin) Z-Line
M-LineI-Band
(Light Band)A-Band (Dark Band)
sarcomere
Myofilaments:
H-Zone
myofibril
2) Z-lines move closer together.
3) myofibrils
shorten
mus
cle
cont
ract
ion
4) Myofilaments (thin and thick filaments) do not get shorter.
sarcomere
sarcomere
1) Sarcomeres shorten.
Z-Line5) I-Bands
shorten
7) A-Bands move closer together.
6) H-Zonesdisappear
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How Muscle Contraction Works - Close UpTo understand how this happens, we will have to look closer to the myosin and actin contractile proteins. When the nerve stimuli comes into the muscle cell to start a muscle contraction, the thick filaments’ myosin cross bridges (globular heads) grab onto an active site (1) on the thin filament (F-actin strands) adjacent to them and pull back (2) and release several times (think of a cranking ratchet: attach-pull-detach-reset). This pulls the thin filament in toward the center of the sarcomere (3), shortening it over all. This reaction is happening at the same instant throughout the entire muscle (which received the stimuli), so the muscle contracts. Muscle contractions (myosin cross bridge attachment) need calcium, which is released into the cell by the SR when the stimulus to contract occurs.
©Sheri Amsel www.exploringnature.org
Globular Heads (myosin Cross Bridges of the thick filaments)
F-Actin (fibrous actin strands - or thin filaments)
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2
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Pulls the thin filament in toward the center of the sarcomere.
