BIOL 3402 Lecture Notes - Lecture 2: Rib Cage, Thoracic Cavity, Accessory Muscle
Document Summary
Pressure relative to atmosphere: pressure and volume inversely related, pressure goes up = volume goes down, pressure drops = volume raises. Add about 1/3 of air that ventilates the lungs. Used for forced respiration: accessory muscles used too. Normal quiet expiration: energy-saving passive process achieved by the elasticity of lungs and thoracic cage, as muscles relax, structures recoil to original shape and original (smaller) size of thoracic cavity, results in airflow out of lungs. Forced expiration: rectus abdominis, internal intercostals , greatly increased abdominal pressure pushed viscera up against diaphragm, increasing thoracic pressure, forcing air out, important for abdominal breathing, energy-expensive. Valsalva maneuver: abdominal pressure to push, childbirth, urination, defecation, vomiting. Exact mechanism for respiratory rhythm unknown: medulla. Depends on repetitive stimulation of skeletal muscles from brain and will cease if spinal cord is severed high in neck: skeletal muscles require nervous stimulation, interaction of multiple respiratory muscles require coordination. Respiratory nuclei in medulla and pons: ventral respiratory group (vrg)
