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OBJECTIVES

OBJECTIVES

After studying this chapter, you should be able to:

  • Locate the pre-Bötzinger complex and describe its role in producing spontaneous respiration.

  • Identify the location and probable functions of the dorsal and ventral groups of respiratory neurons, the pneumotaxic center, and the apneustic center in the brainstem.

  • List the specific respiratory functions of the vagus nerves and the respiratory receptors in the carotid body, the aortic body, and the ventral surface of the medulla oblongata.

  • Describe and explain the ventilatory responses to increased CO2 concentrations in the inspired air.

  • Describe and explain the ventilatory responses to decreased O2 concentrations in the inspired air.

  • Describe the effects of each of the main nonchemical factors that influence respiration.

  • Describe the effects of exercise on ventilation and O2 exchange in the tissues.

  • Define periodic breathing and explain its occurrence in various disease states.

INTRODUCTION

Spontaneous respiration is produced by rhythmic discharge of motor neurons that innervate the respiratory muscles. This discharge is totally dependent on nerve impulses from the brain; breathing stops if the spinal cord is transected above the origin of the phrenic nerves. The rhythmic discharges from the brain that produce spontaneous respiration are regulated by alterations in arterial PO2, PCO2, and H+ concentration, and this chemical control of breathing is supplemented by a number of nonchemical influences. The overall respiration control system thus consists of a network of neurons in cortex and medulla/pons that exert voluntary control and automatic control, respectively. The system adjusts the rate of ventilation as environmental conditions change (eg, from normoxic to hypoxic condition) and arterial PO2, PCO2, and H+ concentration ([H+]) alter. The mechano- and chemoreceptors in the system sense the changes in force/displacement and arterial levels of gases and metabolites, and adjust the rate of ventilation to ensure optimal gas exchange in the lungs (Figure 36–1). The physiological bases for these phenomena are discussed in this chapter.

FIGURE 36–1

Diagram of the overall respiratory control system. The volunteer control center is in cerebral cortex and the automatic control centers are in medulla and pons. The nerve impulses or electrical signals from the respiratory neurons in these centers regulate the activity of respiratory muscles (including diaphragm) and thus the rate and depth of breathing (ventilation). The mechanoreceptors and chemoreceptors (central and peripheral) then sense the physical changes in the lungs and chest wall and the chemical changes in the blood (eg, arterial PCO2, arterial PO2 and [H+]) to further adjust the control of breathing. (Modified from Berne RM, Levy MN (eds): Physiology, 2nd ed. Mosby, 1988.)

NEURAL CONTROL OF BREATHING

CONTROL SYSTEMS

Two separate neural ...

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