Radha was running on a treadmill at a great speed for 15 minutes continuously. She stopped the treadmill and abruptly came out. For the next few minutes, she was breathing heavily/fast. Answer the following questions.
(a) What happened to her muscles when she did strenuously exercised?
(b) How did her breathing rate change?
(a) Due, to continuous exercise her muscles got fatigues because of the accumulation of lactic acid within skeletal muscles. Pain is also oftenly experienced in the fatigued muscles.
(b) Her breathing rate changes from normal to high as during exercise, her body muscle require more oxygen for the ATP production, than the normal value, hence her breathing enhances, to lake most oxygen from the atmosphere.
ATP (Adenosin Triphosphate) is the source of energy for muscle contraction. The head of each myosin molecule contains an enzyme called myosin ATPase.
In the presence of this enzyme along with $\mathrm{Ca}^{2+}$ then, and $\mathrm{Mg}^{2+}$ ions the ATP molecule breaks down into ADP and inorganic phosphate, thus releasing energy in the head of myosin.
$$\text { ATP } \longrightarrow \text { ADP }+P_i+\text { Energy }$$
Energy from ATP causes energised myosin to cross bridges and to bind with actin and in this way initiates muscle contraction.
Pectoral girdle Each half of the pectoral girdle consist of a clavicle and a scapula. The dorsal flat, triangular body of scapula has a slightly elevated ridge called the spine that, projects a flat expanded process called the acromion and the clavicle articulating with it.
Below the acromion their is a depression called the glenoid cavity which articulates with the head of the humerous to form the shoulder joint. Pelvic girdle consist of two coxal bones. each formed by the fusion of three bones, ilium, ischium and pubis. It articulates with femur through a cavity called acetabulum forming thigh joint.
For the muscle fibre to contract, the binding site on thin filaments must be uncovered. This occurs when $\mathrm{Ca}^{2+}$ bind to another set of regulatory proteins, called troponin complex which control the position of tropomyosin on the thin filament.
The calcium binding rearranges the tropomyosin, troponin complex, exposing the myosin-binding sites on the thin filament. When $\mathrm{Ca}^{2+}$ is present in the cytosol, the thin and thick filament slide part each other resulting in muscle contraction.
Similarly, when the $\mathrm{Ca}^{2+}$ concentration falls, the binding sites get covered and contraction stops. In case of tetany there occur low calcium levels in body fluid due to diminished function of parathyroid gland. This gland is mainly involved in the secretion of parathyroid hormone which is associated in regulating calcium levels in blood. Tetany results in periodic painful muscular spasm (wild contraction) and tremors.