Question

On stimulation of the skeletal muscle, calcium is immediately made available for binding to troponin from
(a) Blood
(b) Lymph
(c) Bone
(d) Sarcoplasmic reticulum

Answer 1

They are a membrane-bound structure found in muscle cells that is close to the endoplasmic reticulumThey are a form of the smooth muscle endoplasmic reticulum. They are located in the skeletal muscles and store calcium ions.

Complete answer:
On stimulation of the skeletal muscle, calcium is promptly made accessible for binding to troponin from sarcoplasmic reticulum. Sarcoplasmic reticulum stores calcium ions and liberates them into the sarcoplasm on the generation of action potential throughout muscle contraction. Binding of calcium ions to troponin produces the masking of active sites of myosin found on actin filaments. Sarcoplasmic reticulum is functional as a regulator of calcium storage and in the releasing homeostasis during the process of muscle contraction and after that. Therefore, the primary function of sarcoplasmic reticulum is to regulate excitation-contraction-coupling and in the intracellular calcium concentrations in the relaxation and contraction process.

Additional Information:
The thin filaments slip over the thick filaments during muscle contraction. The intersection between the engine neuron and the sarcolemma is the neuromuscular interface. When a neural signal enters the junction, acetylcholine is released and the action potential of sarcolemma is produced.
As the muscle fiber expands, it releases the calcium ion in the sarcoplasm. Calcium then connects actin filaments to troponin and reveals active myosin sites. Myosin binds with the energy from the hydrolysis of ATP on the exposed active site of actin. The actin is guided to the core. The Z lines are also pulled, and contraction takes place. Myosin is in a state of relaxation.
Therefore, the hydrolysis of ATP begins on the head of the myosin, leading to further slipping. This is repeated until calcium ions have been pumped back to the sarcolemma and the actin sites are covered. In its original positions, the Z lines reverse. This gives rise to relaxation.

So, the answer is ‘Sarcoplasmic reticulum’.

Note:
- Muscular contraction is initiated by a signal transmitted by the central nervous system via the motor neuron.
- Muscle tiredness occurs due to repetitive muscle activation that leads to lactic acid accumulation.
- The muscle skeleton is composed of muscle fibers that are called myofibrils in smaller units. Each myofibril consists of three kinds of proteins; contractile, regulatory, and structural.