Explain how the cellular and subcellular structures of skeletal muscle cause muscle contraction. Solution Myofilaments are arranged parallel in the sarcoplasm; they run along the entire length of the muscle fibre. A huge portion of the sarcoplasm is occupied by these filaments. The myofilaments are composed of two types of proteins called actin and myosin (structural components of sarcomere), which are responsible for the contractility of myofibrils. Influx of sodium ions depolarizes the membrane (activation) and the membrane becomes positively charged inside. This membrane activation triggers the release of Ca2+ from the sarcoplasmic reticulum. These calcium ions bind to the troponin C to convert this to tropomyosin in the muscle filament, which causes the exposure of myosin binding sites. Actin-myosin cross bridges are formed, actin filaments contract over the stationary myosin filaments. After the action potential ends, the Ca2+ detaches and removed by active transport into sarcoplasmic reticulum, and the muscle fiber relaxes. Subcellular structures in muscle contraction: The myofilaments are composed of two types of proteins called actin and myosin (structural components of sarcomere), which are responsible for the contractility of myofibrils. The myosins are made of ATP dependent motor proteins. The actin filaments are made of 300 to 400 globular subunits (G-actin) that are arranged in two rows and one twists another. The groves of G-actin monomers contain another protein known as tropomyosin. Troponin is another protein that is attached to the tropomyosin. The three protein complex units of troponin are, During the muscle contraction, the calcium tends to bind with troponin C and move the tropomyosin. Now the myosin binds to stationary actin filaments causing muscle contraction..

1. Explain how the cellular and subcellular structures of skeletal muscle cause muscle contraction.
Solution
Myofilaments are arranged parallel in the sarcoplasm; they run along the entire length of the
muscle fibre. A huge portion of the sarcoplasm is occupied by these filaments. The myofilaments
are composed of two types of proteins called actin and myosin (structural components of
sarcomere), which are responsible for the contractility of myofibrils.
Influx of sodium ions depolarizes the membrane (activation) and the membrane becomes
positively charged inside. This membrane activation triggers the release of Ca2+ from the
sarcoplasmic reticulum. These calcium ions bind to the troponin C to convert this to tropomyosin
in the muscle filament, which causes the exposure of myosin binding sites.
Actin-myosin cross bridges are formed, actin filaments contract over the stationary myosin
filaments. After the action potential ends, the Ca2+ detaches and removed by active transport
into sarcoplasmic reticulum, and the muscle fiber relaxes.
Subcellular structures in muscle contraction:
The myofilaments are composed of two types of proteins called actin and myosin (structural
components of sarcomere), which are responsible for the contractility of myofibrils.
The myosins are made of ATP dependent motor proteins. The actin filaments are made of 300 to
400 globular subunits (G-actin) that are arranged in two rows and one twists another.
The groves of G-actin monomers contain another protein known as tropomyosin. Troponin is
another protein that is attached to the tropomyosin. The three protein complex units of troponin
are,
During the muscle contraction, the calcium tends to bind with troponin C and move the
tropomyosin. Now the myosin binds to stationary actin filaments causing muscle contraction.