Question

A skeletal muscle is a composition of several components bundled one into the other. At which structural level in the muscle does contraction occur to bring about contraction in the whole muscle?
myofibril

Answer 1

Skeletal muscle is one of three major muscle types, the others being cardiac muscle and smooth muscle. It is a form of striated muscle tissue which is under the voluntary control of the somatic nervous system.[1] Most skeletal muscles are attached to bones by bundles of collagen fibers known as tendons.

Skeletal striated muscle/ Striated voluntary muscle

A top-down view of skeletal muscle

DetailsIdentifiersLatinmuscularis striatus skeletalisTHH2.00.05.2.00002Anatomical terminology

[edit on Wikidata]

A skeletal muscle refers to multiple bundles (fascicles) of cells called muscle fibers. The fibres and muscles are surrounded by connective tissue layers called fasciae. Muscle fibres, or muscle cells, are formed from the fusion of developmental myoblastsin a process known as myogenesis. Muscle fibres are cylindrical, and have more than one nucleus. They also have multiple mitochondria to meet energy needs.

Muscle fibers are in turn composed of myofibrils. The myofibrils are composed of actin and myosin filaments, repeated in units called sarcomeres, which are the basic functional units of the muscle fiber. The sarcomere is responsible for the striated appearance of skeletal muscle, and forms the basic machinery necessary for muscle contraction.

Answer 2

The event of muscle contraction starts at fiber’s sarcomeres. Contraction of sarcomere results in muscle contraction.

During muscle contraction, thick and thin filaments which are myosin and actin respectively contract and get denser.  

Moreover, sarcomeres join together to form a myofibril thus, myofibril and muscle contracts as the sarcomere contracts.