Muscles and the Sliding Filament Theory
Topics: Muscle contraction, Myosin, Muscular system, Skeletal muscle, Actin, Muscle / Pages: 4 (469 words) / Published: Feb 1st, 2015

Muscles and the
Sliding Filament

(ALL) Give 2 examples of voluntary and involuntary muscle movements
 (MOST) Explain the purpose of the sliding filament theory
 (FEW) explain the key stages of the sliding filament theory
 (MOST) Give 4 examples of voluntary and involuntary muscle movements

Recap of Muscles
Remember skeletal muscle is under voluntary control
 It is also called striated muscle because of its striped appearance.
 Skeletal muscle fibres are large. They may reach from one end of a muscle to the other. They are a fusion of many individual cells which make up a long, cylindrical muscle fibre which has many nuclei.

Each muscle fibre is made up of smaller fibres called myofibrils. These contain even smaller structures called actin and myosin filaments. These filaments slide in and out between each other to form a muscle contractions, hence the sliding filament theory! 

The diagram above shows part of a myofibril called a sarcomere. This is the smallest unit of skeletal muscle that can contract. Sarcomeres repeat themselves over and over along the length of the myofibril. The structures involved:
Myofibril: A cylindrical organelle running the length of the muscle fibre, containing Actin and Myosin filaments.
Sarcomere: The functional unit of the
Myofibril, divided into I, A and H bands.
Actin: A thin, contractile protein filament, containing 'active' or 'binding' sites.
Myosin: A thick, contractile protein filament, with protusions known as Myosin Heads.
Tropomyosin: An actin-binding protein which regulates muscle contraction.
Troponin: A complex of three proteins, attached to Tropomyosin.

Stage 1

Nervous impulse arrives at neuro-muscular junction – acetylcholine is released. This causes calcium to be released from the sarcoplasmic reticulum.

The calcium binds to troponin, changing its shape and so moving tropomyosin. This exposes the active binding site of the
 The Myosin filaments can now attach

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