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Human Anatomy & Physiology 8/3/2017 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 1 of 2 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 2 of 2
