Anatomy & Physiology

Anatomy & Physiology Study Guide gas molecules diffusing out of the liquid as quickly as they enter it. If the partial pressure goes up, more gas molecules will go into solution; if the partial pressure goes down, gas molecules will come out of solution. Charles’ Law Jacques Charles explored the relationship between the volume of a gas and how it relates to temperature. By filling balloons with various gases (Oxygen, Nitrogen, Carbon Dioxide, etc.) and raising the atmospheric temperature, he noticed that the balloons all inflated to the same volume level. Causing Charles to develop Charles' Law: if the pressure is held constant, the volume of a fixed gas will increase proportionately with the temperature in Kelvins of the gas (i.e., the gas expands as the temperature increases). 22.7 The Respiratory Centers of the Brain Respiratory control has both involuntary and voluntary components. Your brain's involuntary centers regulate the activities of the respiratory muscles and control the respiratory minute volume by adjusting the frequency and depth of pulmonary ventilation. They do so in response to sensory information arriving from your lungs and other portions of the respiratory tract, as well as from a variety of other sites. The voluntary control of respiration reflects activity in the cerebral cortex that affects either the output of the respiratory centers in the medulla oblongata and pons or of motor neurons in the spinal cord that control respiratorymuscles. The respiratory centers are three pairs of nuclei in the reticular formation of the medulla oblongata and pons. In general, the respiratory reflexes control the motor neurons in the spinal cord, but they can also be controlled voluntarily through commands delivered by the corticospinal pathway. Respiratory Centers in the Medulla Oblongata The pace of respiration is controlled by the respiratory centers in the medulla oblongata. The center can be subdivided into a dorsal respiratory group (DRG) and a ventral respiratory group (VRG). The DRG's inspiratory center contains neurons that control lower motor neurons. The DRG functions in every respiratory cycle, whether quiet or forced. The VRG functions only during forced breathing. It includes neurons that innervate lower motor neurons controlling accessory respiratory muscles involved in active exhalation (an expiratory center) and maximal inhalation (an inspiratory center). Reciprocal inhibition occurs between the neurons involved with inhalation and exhalation. Inspiratory and expiratory neurons cannot be active simultaneously. Only one can occur at a time. The way neurons interact between the two groups is dependent on if the person is experiencing quiet or forced breathing. The basic pattern of respiration thus reflects a cyclic interaction between the DRG and the VRG.

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