Question

When your biceps brachii (upper arm) muscle contracts, ultimately and most directly, what is producing the movement?

Answer 1

It is the proteins present underneath the cells of the biceps brachii, which slide past each other lengthwise, thus shortening the muscle.  

The biceps crosses both the elbow and shoulder joints, its prime role is at the elbow where it flexes the forearm and supinates the forearm. The biceps brachii refers to a bi-articular muscle, that is, it assists in monitoring the movement of two different joints, the elbow, and the shoulder.  

Answer 2

Protein molecules that slide past each other produce movements of the upper arm when a muscle contracts.

Further Explanation:

Muscle is comprised of muscle cell which is known as muscle fiber. The muscle fibers consist of the sarcolemma, sarcoplasmic reticulum and sarcomere. Sarcomere acts as the unit of contraction. It is made up of proteins such as actin and the myosin molecule.

Actin molecules are thin polymeric molecules while the myosin molecules are the thick molecule.

Sliding filament theory is the theory that was developed to explain the mechanism of muscle contracts. In accordance with this theory, the myosin molecule slide passes the actin molecule to generate the movement. During this movement, there is no change in the length of these two protein molecules.

During the contraction of muscle, the length of the sarcomere present in the myofibril decreases. The calcium molecule is the main molecule that plays an important role in providing this movement.

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Answer Details:

Grade: Middle school

Chapter: Body movement

Subject: Biology

Keywords:

Protein, muscle, muscle fiber, cell, sarcolemma, sarcoplasmic reticulum, sarcomere, actin, myosin, sliding filament theory, movement, myofibril, calcium.