Human Anatomy & Physiology
3/7/2016
05C.1 Muscle Contraction: Parts of the Sarcomere
Muscle cells are long and have bundles of myofibrils. Each
myofibril is made up of repetitive units called Sarcomeres.
These sarcomeres are where contraction happens.
Sarcomeres are known as the ‘functional unit’ of the muscle
cell/fiber.
1. Z-lines (thin actin filaments are anchored here)
2. A Band (thick myosin filaments)
3. I Band (thin actin filaments)
4. H Zone (space between the actin filaments)
Z- line to Z- line is one Sarcomere.
Relaxed Sarcomere
05C.1 Muscle Contraction: Parts of the Sarcomere
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Contracted Sarcomere
Notice how the sarcomere shortens. This comes about
because the thick filaments (myosin) pull the thin filaments
(actin) towards the H zone. When the pull occurs, the Z Lines
are pulled in and causes the sarcomere to shorten. When
several hundred of these sarcomeres shorten, the muscle fiber
shortens.
Activity to show muscle shortening
Reduce, Recite, Reflect, & Review!
05C.1 Muscle Contraction: Parts of the Sarcomere
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