How Is Respiration Controlled?

The control centers for respiration, located in the brain regions known as the medulla and pons, work together with the nervous system, cardiovascular system, lungs, diaphragm and other parts of the brain and body to regulate respiratory function in the body.

Localized Control

Oxygen delivery rate in each tissue and pickup at the lungs are largely regulated at the local level. If a peripheral tissue, such as an arm or foot, becomes more active, the level of oxygen between cells decreases and carbon dioxide increases. This results in more oxygen being delivered to and more carbon dioxide being removed from the affected tissues. A secondary effect is the relaxation of smooth muscle in arteriole walls and capillaries in the area, which increases the blood flow.

Involuntary Control

In response to sensory information sent from the lungs or other parts of the respiratory tract, the brain's involuntary centers control respiratory muscle activities and volume by adjusting the depth and frequency of the physical movement of air in and out of the respiratory tract, known as pulmonary ventilation.

Voluntary Control

The voluntary control of respiration is based on activities in the cerebral cortex affecting either the output of respiratory centers in the medulla and pons section of the brain or motor neurons in the spinal cord.

Medulla Centers

Respiration pace is set by the respiratory rhythmicity centers of the medulla, each of which has a dorsal respiratory group (DRG) and ventral respiratory group (VRG). The DRG, which controls the diaphragm and intercostal muscles that move the ribs, functions in every respiratory cycle. The VRG functions only during forced respiration. The basic pattern of respiration reflects a cyclic interaction between the DRG and VRG, which is thought to be established by pacemaker cells that spontaneously undergo rhythmic patterns of activity.

External Factors

Respiratory rate can be increased by central nervous system stimulants, such as amphetamines or caffeine, or decreased by depressants, such as barbiturates or opiates.

Pons Centers

The apneustic and pneumotaxic centers of the pons are pairs of nuclei that adjust the output of respiratory rhythmic centers in response to sensory stimuli or input from other centers. During quiet respiration, stimulation from apneustic centers helps increase the intensity of inspiration over the following two seconds after which (under normal circumstances) the signals from the pneumotaxic centers inhibit this activity. During forced respiration, the apneustic centers also respond to sensory input from the vagus nerves regarding lung inflation. Centers in the hypothalamus and cerebrum of the brain can change respiratory rate and depth by way of the pneumotaxic centers.

Respiratory Reflexes

Respiratory center activities are modified by sensory information from special neurons, known as chemoreceptors, which are sensitive to carbon dioxide, oxygen and pH (acid/alkaline) levels; changes in blood pressure in the aorta or carotid sinuses; lung volume changes; physical or chemical irritants in the nasal cavity, larynx or bronchial tree or other sensations such as pain or changes in body temperature.

References

• "Fundamentals of Human Anatomy and Physiology"; Frederic H. Martini, Ph.D.; 1998