Question

In human beings, the rib cage and sternum move upwardly and outwardly during.
A. Exercise
B. Sudden back injury
C. Expiration
D. Inspiration

Answer 1

Hint: Sternum is a flat bone present on the ventral midline of the thorax. It provides a surface where muscles attach and help in the respiratory mechanism. Rib is a thin flat bone which is dorsally connected to the vertebral column and ventrally to the sternum. Rib is a thin flat bone which is dorsally connected to the vertebral column and ventrally to the sternum.

Complete answer:
The movement of air into and out of the lungs is carried out by creating a pressure gradient between lungs and the atmosphere. This process is called respiration. Pressure gradient is the pressure difference which creates the flow of gases from their higher-pressure region to their lower pressure region. For example, pressure of $\mathop O\nolimits_2 $in atmospheric air is higher than alveoli, so $\mathop O\nolimits_2 $, diffuses from atmospheric air to alveoli.
Now let us gather information about given options :-
Exercise :- during the time when we perform exercise the expiratory muscles play an active role in breathing. During each single breath the action of them is highly coordinated with that of the inspiratory rib cage muscles. During inspiration, while the rib cage muscles contract, the abdominal muscles gradually relax, and vice versa during expiration.
Sudden back injury :- sudden back injury may be due to the fact in tears of organs . The ribs may get damage and sternum also but it is not necessary that they move upward and outwards.
Expiration :- it is moving air out of lungs. Relaxation of the diaphragm and the external intercostal muscles that are muscles of ribs returns the diaphragm and sternum to their normal thoracic volume and thereby pulmonary volume.
Inspiration :- during inspiration , external intercostal muscles play an important role . These muscles are present between ribs. The contraction of these muscles lift ribs and sternum up and outward causing an increase in the volume of the thoracic cavity in the dorso-ventral axis, i.e., backward-forward direction.

Note: Breathing includes inspiration and expiration. Inspiration means to inhale or to breathe in and Expiration means to exhale or to breathe out. Whenever air enters into the chest it raises up and when air exhales out it goes down. Respiration or breathing is a complex process that usually occurs in a number of steps.