<unk>  (also known as inspiration) is the movement of air from the external environment, through the airways, into the alveoli during breathing.<unk>  begins with the onset of contraction of the diaphragm, which results in expansion of the intrapleural space and an increase in negative pressure according to Boyle's law.  This negative pressure generates airflow because of the pressure difference between the atmosphere and alveolus.  Air enters, inflating the lung through either the nose or the mouth into the pharynx (throat) and trachea before entering the alveoli.
Other muscles that can be involved in<unk>  include:
External intercostal muscles
Scalene muscles
Sternocleidomastoid muscle
Trapezius muscle
Inhalation
Injection 
Inoculation
Adsorption
Intramuscular injection
Oxygenation
Position 
Geothermal