Muscles that help in respiration are called respiratory muscles. Respiratory muscles are- diaphragm, intercostal muscles, sternocleidomastoid, scalene, pectoralis, trapezius, latissimus dorsi, erector spinae, iliocostalis, quadratus lumborum, serratus, transverse thoracis, subclavius etc.
1. Diaphragm: The fleshy membrane located transversely between the thoracic cavity and the abdominal cavity is called diaphragm. It is made up of voluntary muscles. During inhalation the diaphragm contracts, descends and flattens. As a result, the volume of the lungs increases and air enters the lungs. During exhalation it expands, rises upwards and bends like a bow. As a result, the volume of the lungs decreases and air escapes from the lungs.
2. Intercostal muscles: The muscles located between the two ribs of the thorax are called intercostal muscles. During inhalation the intercostal muscles contract and the ribs rise upwards. As a result, the volume of the lungs increases and air enters the lungs. During exhalation it relaxes or expands and the parshukas descend. As a result, the volume of the lungs decreases and air escapes from the lungs.