Question

One myosin filament in the myofibril of skeletal muscle fibre is surrounded by how many actin filaments?
A. Two
B. Four
C. Six
D. Three

Answer 1

The muscle system in an organism forms an active part of the movement and locomotion of the body. In higher invertebrates, the muscle system is an important system of connective tissues, muscle fibres and bones. The muscles fibres perform many functions as they have the ability to contract.
A myofibril which is also known as a muscle fibril, is the unit of a muscle cell. It is a rod-like structure. Muscles are made up of tubular cells called myocytes.

Complete answer:
Skeletal muscle or voluntary muscles are associated with the skeletal movements and are required for movement and changing postures. The skeletal muscle fibres are important for various physiological and morphological properties. Skeletal muscle is composed of various integrated tissues including muscle fibres, blood vessels, nerve fibres, and connective tissue.
Each skeletal muscle has three layers of connective tissue that surround it and provide a definite structure to the muscle. The muscle fibres are divided into several compartments within the muscle. As skeletal muscle cells are long and cylindrical and are referred to as muscle fibres. This muscle fibre is also known as myofibers. The length of the skeletal muscle fibres can be quite large in comparison to other cells.
The plasma membrane of muscle fibres is called the sarcolemma and the cytoplasm present in muscle fibre called sarcoplasm. Within a muscle fibre, proteins are organized into structures called myofibrils that spread through the length of the cell and contain sarcomeres connected in series. Myofibrils are very small in diameter, hundreds to thousands of myofibrils can be present inside one muscle fibre.
Myofibrils are formed during embryonic development through a process which is known as myogenesis. They are consisting of long chains of proteins like actin, myosin and some other proteins that hold them together. These proteins are constructed of some thick and thin filaments which are known as myofilaments. These myofilaments are arranged repeatedly along the length of the myofibril in sections called sarcomeres.
The contractile proteins myosin and actin which present sarcomeres, that proteins are bound with each other during the compression muscle. The myosin filament is surrounded by six actin filaments and each actin filament is in turn surrounded by three myosin filaments. This arrangement of the actin and myosin filaments produce a striated appearance to the muscle.

Therefore, the correct option is option C.

Note: Myofibril is a rod-like structure which is considered as the unit of the muscle cell. This is a combination of several proteins including actin, myosin with other some types of proteins. In myofilaments, myosin and actin are arranged in a specific way where six actin surrounded one myosin, and each actin surrounded by three myosin filaments.