a)Describe the structure of the contractile elements of skeletal muscle
b)Sketch a graph of the relationship between developed tension and muscle length and explain the shape of the curve in terms of the interaction between thick and thin myofilaments
C) sketch a graph of the relationship between total tension and muscle length and explain the shape of the curve in terms of the developed and passive tension
a) The contractile elements of skeletal muscle are composed of repeating units called sarcomeres. Sarcomeres are the basic functional units of muscle contraction and are responsible for generating force and enabling muscle movement.
Within the sarcomeres, there are two types of myofilaments: thick filaments and thin filaments. The thick filaments are made up of a protein called myosin, while the thin filaments consist of actin, tropomyosin, and troponin proteins.
b) A graph of the relationship between developed tension (force) and muscle length would typically display a bell-shaped curve. This curve is known as the length-tension relationship.
At shorter muscle lengths, the overlap between thick and thin filaments is minimal, resulting in fewer myosin binding sites on actin being available. Thus, fewer cross-bridges can form between the filaments, leading to lower tension development.
As the muscle is stretched to an optimal length, maximal tension is achieved. At this point, there is optimal overlap between the thick and thin filaments, allowing for maximum cross-bridge formation and force generation.
However, as the muscle is stretched beyond its optimal length, the overlap between filaments decreases, and the tension starts to decrease. At extreme lengths, the myosin and actin filaments no longer optimally interact, resulting in reduced force production.
c) The relationship between total tension and muscle length would also resemble a bell-shaped curve. This curve represents the combined effect of both developed tension (active tension) and passive tension.
Developed tension is the active force generated by the contractile elements in response to neural stimulation. Passive tension refers to the tension generated by the muscle's elastic components when it is stretched.
At shorter muscle lengths, both developed and passive tension are relatively low. As the muscle is stretched to its optimal length, both tensions increase, reaching a peak. The developed tension is directly influenced by the interaction between the thick and thin filaments, while the passive tension is primarily due to the stretching of structural proteins in the muscle.
However, when the muscle is stretched beyond its optimal length, the developed tension begins to decline, as explained earlier. Simultaneously, the passive tension continues to increase due to the elongation of the elastic components. These opposing forces result in a gradual drop in total tension.