PHSI 208 Lecture Notes - Lecture 2: External Intercostal Muscles, Alveolar Pressure, Scalene Muscles
Document Summary
During ventilation, air flows because of pressure gradients. (barometric = atmosphere) Inspiration occurs when alveolar pressure decreases: how we change alveolar pressure: according to boyle"s law, an increase in volume will cause a decrease in pressure. Inspiration: external intercostal muscles slope obliquely between ribs, forward and downward. Because the attachment to the lower rib is farther forward from the axis of rotation, contraction raises the lower rib more than it depresses the upper rib. During forced inspiration, additional accessory or secondary muscles become activated. These include sternocleidomastoids, neck and back muscles and upper respiratory tract muscles: sternocleidomastoids lift the sternum outward, contributing to the water pump handle effect. More recently, they have been thought to play a role in quiet inspiration as well: neck and back muscles elevate the pectoral girdle and extend back, increasing the thoracic volume, upper respiratory tract muscles decrease airway resistance.
