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21.10A: Neural Mechanisms (Respiratory Center)

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    8001
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    The medulla and the pons are involved in the regulation of the ventilatory pattern of respiration.

     

    LEARNING OBJECTIVES

     

    Describe the neural mechanism of the respiratory center in respiration control

     

    KEY TAKEAWAYS

    Key Points

     

    • The ventral respiratory group controls voluntary forced exhalation and acts to increase the force of inspiration.
    • The dorsal respiratory group (nucleus tractus solitarius) controls mostly inspiratory movements and their timing.
    • Ventilatory rate (minute volume) is tightly controlled and determined primarily by blood levels of carbon dioxide as determined by metabolic rate.
    • Chemoreceptors can detect changes in blood pH that require changes in involuntary respiration to correct.The apneustic (stimulating) and pnuemotaxic (limiting) centers of the pons work together to control rate of breathing.
    • The medulla sends signals to the muscles that initiate inspiration and expiration and controls nonrespiratory air movement reflexes, like coughing and sneezing.

     

    Key Terms

     

    • respiratory control centers: The medulla which sends signals to the muscles involved in breathing, and the pons which controls the rate of breathing.
    • chemorecepters: These are receptors in the medulla and in the aortic and carotid bodies of the blood vessels that detect changes in blood pH and signal the medulla to correct those changes.

    Involuntary respiration is any form of respiratory control that is not under direct, conscious control. Breathing is required to sustain life, so involuntary respiration allows it to happen when voluntary respiration is not possible, such as during sleep. Involuntary respiration also has metabolic functions that work even when a person is conscious.

     

    The Respiratory Centers

    This is a cutaway view of the brainstem. It shows the cerebrum at the top, the cerebellum under it, and the pons and medulla next to and under the cerebellum.

     

     

    Anatomy of the brainstem: The brainstem, which includes the pons and medulla.

    Involuntary respiration is controlled by the respiratory centers of the upper brainstem (sometimes termed the lower brain, along with the cerebellum). This region of the brain controls many involuntary and metabolic functions besides the respiratory system, including certain aspects of cardiovascular function and involuntary muscle movements (in the cerebellum).

    The respiratory centers contain chemoreceptors that detect pH levels in the blood and send signals to the respiratory centers of the brain to adjust the ventilation rate to change acidity by increasing or decreasing the removal of carbon dioxide (since carbon dioxide is linked to higher levels of hydrogen ions in blood).

    There are also peripheral chemoreceptors in other blood vessels that perform this function as well, which include the aortic and carotid bodies.

     

    The Medulla

     

    The medulla oblongata is the primary respiratory control center. Its main function is to send signals to the muscles that control respiration to cause breathing to occur. There are two regions in the medulla that control respiration:

    • The ventral respiratory group stimulates expiratory movements.
    • The dorsal respiratory group stimulates inspiratory movements.

    The medulla also controls the reflexes for nonrespiratory air movements, such as coughing and sneezing reflexes, as well as other reflexes, like swallowing and vomiting.

     

    The Pons

     

    The pons is the other respiratory center and is located underneath the medulla. Its main function is to control the rate or speed of involuntary respiration. It has two main functional regions that perform this role:

    • The apneustic center sends signals for inspiration for long and deep breaths. It controls the intensity of breathing and is inhibited by the stretch receptors of the pulmonary muscles at maximum depth of inspiration, or by signals from the pnuemotaxic center. It increases tidal volume.
    • The pnuemotaxic center sends signals to inhibit inspiration that allows it to finely control the respiratory rate. Its signals limit the activity of the phrenic nerve and inhibits the signals of the apneustic center. It decreases tidal volume.

    The apneustic and pnuemotaxic centers work against each other together to control the respiratory rate.