<P> From the respiratory center, the muscles of respiration, in particular the diaphragm, are activated to cause air to move in and out of the lungs . </P> <P> Breathing is normally an unconscious, involuntary, automatic process . The pattern of motor stimuli during breathing can be divided into an inhalation stage and an exhalation stage . Inhalation shows a sudden, ramped increase in motor discharge to the respiratory muscles (and the pharyngeal constrictor muscles). Before the end of inhalation, there is a decline in, and end of motor discharge . Exhalation is usually silent, except at high respiratory rates . </P> <P> The respiratory centre in the medulla and pons of the brainstem controls the rate and depth of respiration through various inputs . These include signals from the peripheral chemoreceptors and central chemoreceptors; from the vagus nerve and glossopharyngeal nerve carrying input from the pulmonary stretch receptors, and other mechanoreceptors in the lungs . as well as signals from the cerebral cortex and hypothalamus . </P> <Ul> <Li> Medulla <Ul> <Li> ventral respiratory group (includes the nucleus ambiguus, and the pre-Bötzinger complex). The ventral respiratory group controls voluntary forced exhalation and acts to increase the force of inhalation . Regulates rhythm of inhalation and exhalation . </Li> <Li> dorsal respiratory group (solitary nucleus). The dorsal respiratory group controls mostly movements of inhalation and their timing . </Li> </Ul> </Li> <Li> Pons <Ul> <Li> pneumotaxic center . <Ul> <Li> Coordinates speed of inhalation and exhalation </Li> <Li> Sends inhibitory impulses to the inspiratory area </Li> <Li> Involved in fine tuning of respiration rate . </Li> </Ul> </Li> <Li> apneustic center <Ul> <Li> Coordinates speed of inhalation and exhalation . </Li> <Li> Sends stimulatory impulses to the inspiratory area--activates and prolongs inhalations </Li> <Li> Overridden by pneumotaxic control from the apneustic area to end inhalation </Li> </Ul> </Li> </Ul> </Li> </Ul>

Nerve impulses from the medulla and pons cause of the respiratory muscles