Final answer:
The non-contractile elements in the sarcoplasm are the nuclei and mitochondria, which are necessary for muscle fiber function but don't participate in muscle contraction.
Step-by-step explanation:
The non-contractile elements in the sarcoplasm include structures such as the nuclei and mitochondria. These components are critical for the maintenance and energy supply of the muscle fiber but do not directly participate in the contraction mechanism. Myosin and actin are the contractile proteins that form the thick and thin filaments, respectively, and are involved in muscle contraction. Sarcomeres are composed of myosin and actin and are the contractile units of the muscle, while Z-discs are structural proteins that anchor the actin filaments. Troponin and tropomyosin are regulatory proteins involved in muscle contraction, hence they are also not considered non-contractile elements. Thus, the correct answer to the question regarding non-contractile elements in the sarcoplasm is b. nuclei and mitochondria.