ANATOMY

Detailed explanation-1: -The myofibrils are made up of thick and thin myofilaments, which help give the muscle its striped appearance. The thick filaments are composed of myosin, and the thin filaments are predominantly actin, along with two other muscle proteins, tropomyosin and troponin.

Detailed explanation-2: -Myofilaments (see also Chapter 3) The myofilament contractile proteins consist of thick filament myosin and thin filament actin proteins. Bound to actin are a complex of regulatory proteins, which include tropomyosin and troponin-T, C, and I.

Detailed explanation-3: -The main proteins involved are myosin, actin, and titin. Myosin and actin are the contractile proteins and titin is an elastic protein. The myofilaments act together in muscle contraction, and in order of size are a thick one of mostly myosin, a thin one of mostly actin, and a very thin one of mostly titin.

Detailed explanation-4: -Thin filaments are composed primarily of the contractile protein actin. As illustrated in Figures 2-8, A and B, actin is composed of small globular subunits (G actin) that form long strands called fibrous actin (F actin).

Detailed explanation-5: -The I bands contain only thin (actin) filaments, whereas the A bands contain thick (myosin) filaments. The myosin and actin filaments overlap in peripheral regions of the A band, whereas a middle region (called the H zone) contains only myosin.