A sarcomere is best described as . Multiple Choice a group of fascicles a group of myofibrils a contractile unit within a myofibril a part of the sarcoplasmic reticulum

Arrangement of the actin and Myosin filament

Explanation:

SACROMERE :An elastic membrane which serves for the *arrangement of the actin and myosin filament *

The fasciculi consist of still smaller bundles of elongated, cylindrical muscle cells, the fibre. Each fibre is a syncytium, i. e, has many nuclei. With the aid of an electron microscope, it can be seen that the muscle fibre is made up of smaller units, the myofibrils. Each myofibrils consists of small protein filaments known as *ACTIN and MYOSIN* filaments. The myosin filaments are slightly thicker and make up the darkband(or A-band). The actin filaments make up the light bands(I-band) which are situated on either side of the dark band. The actin filaments are attached to the Z-line.

During the contractions of skeletal muscle, the actin filaments slide inwards between the myosin filaments. Mitochondria provides the energy for this to take place. This action causes the shortening of the sacromeres(Z-lines move closer together, which in turn causes the whole muscle fibre to contract.This can bring shortening of the entire muscle such as biceps, depending on the number of muscle fibres that were stipulated. The contraction of the skeletal muscle is very quick and forceful.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

carbon atoms, hydrogen, oxygen, and nitrogen.