Ventilation Inspiration: inhaling Expiration: exhaling Respiratory cycle: one complete inspiration and expiration

Muscle of Ventilation External intercostals: the contractions of these muscles cause a lifting of the rib cage. This increases volume in the chest cavity letting the lungs expand lowering pressure in the lung Pressure outside the lung is higher then in the lung causing air to flow in and fill lung

Muscle of Ventilation Internal intercostals: contractions of these muscles pull down the rib cage The ribcage pushes on the lungs decreasing volume and increasing pressure Pressure in the lung is higher then outside the lung causing air to flow out of lung

Muscle of Ventilation Diaphragm: is a band of muscle that rests above the liver and separates the thoracic cavity into upper and lower The diaphragm is the primary mover of air with the intercostals as synergist Diaphragm contracts and descends during inspiration and relaxes and ascends during expiration Why?

Neural Control of Ventilation The brainstem has several respiratory centers that control certain parts of the breathing process Regulation is based on CO2 levels in the blood by chemoreceptors As CO2 and waste products of metabolism increase the pH of blood becomes more acidic causing AP’s in chemoreceptors and increase in respiration

Measurements of ventilation Voluntary control: respiration can be changed by the use of the motor cortex to a “breaking point” where the autonomic system takes over Know the respiratory volumes and capacities in table 22.2 Pg 874