Breathing goes on twenty-four hours a day. We can regulate it mindfully from the cerebral cortex if we want, in the same way that we can regulatc-our movement and posture, but most of the time our minds are occupied elsewhere and we rely on other motor centers to manage respiration. These respiratory control centers are located in the two lowest segments of tht brain stem (the continuation of the spinal cord into the brain). A crudi rhythm for respiration is generated in the lowest of these segments—thf medulla—and this is fine-tuned by the next higher segment—the pons (fig 2.12). Input from these centers to the motor neurons of respiration if unconscious. Willed respiration, of course, is directed from the cerebral corter and can override the rhythms generated by the lower segments of the brain. But even if higher centers have been destroyed by a stroke or traumati head injury (fig. 2.12, site a), the controlling centers for respiration in th< pons or even just the medulla may still survive, allowing someone who 1 otherwise brain-dead to continue breathing indefinitely
We depend on the respiratory centers to manage somatic aspects 1 breathing automatically, but sometimes the mechanisms do not wor perfectly. In a rare form of sleep apnea—the central hypoventilation syndrome—the automatic control of ventilation is lost but the ability t breathe voluntarily is preserved. This is roughly similar to a circumstanc immortalized in Jean Giraudoux's play Ondine. Ondine, a water nymp and an immortal, married Hans, a mortal, even though she knew that sucl a union was forbidden and that Hans was doomed to die if he was unfaithft to her. When the prophecy was fulfilled, Hans was deprived of his automata functions. "A single moment of inattention," he tells Ondine, "and I forgt to breathe. He died, they will say, because it was a nuisance to breathe." Ant so it came to be. This form of sleep apnea is now known as Ondine's curse Although the respiratory pathways in the brain stem support the most primitive form of rhythmic breathing, higher centers can either smooth this out or disrupt it. We all know that when we are in intense emotional
2 BREATHING Hy states our breathing becomes jerky and irregular. Watch a baby struggle to breathe while it is preparing to cry, or think of how uncontrollable laughing affects a teenager's breathing. By contrast, when we are calm, the somatic motor circuits for respiration will be delicately balanced and our breathing will be smooth and even. Maintaining such even-tempered states is one of the aims of yoga.
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A complete guide on Eastern practices of breathing, mental, psychic and spiritual development. The book teaches that Yoga is divided into several branches, ranging from that which teaches the control of the body, to that which teaches the attainment of the highest spiritual development.