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Lecture 19

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University of Toronto St. George
Michelle French

Lecture 19  Case Study: Boy with Ondine’s curse (Congenital Central Hypoventilation Syndrome)  Liam is an 11-year-old boy. During the day breathes on own, but anytime he falls asleep he must be attached to a ventilator (has a trachea tube).  What factors can affect breathing?  Rhythmic breathing (medulla and pons) can be influenced by:  Voluntary control (speech) from the motor cortex  Chemoreceptors, the chemical control of breathing  Reflexes like sneezing and coughing  Posture affects the intercostal and abdominal muscles  Startling effects  Emotions like fear, anxiety and sorrow  Exercise immediately increases breathing  Sensory information sent from muscles  Pain increases breathing  All of these involve the central nervous system  What is the common pathway for all systems attempting to control the respiratory muscles  Respiratory Motoneurons (Spinal Chord)  Coughing, Sneezing  Medulla  Voluntary Control  Motor Cortex  Posture  Cerebellum  Rhythm Generator  Medulla  Reticular Formation  Respiratory Motoneurons  Sensory Stimuli (Pain, Startle)  Emotions  Forebrain  Limbic System  What is the final common pathway for control of the respiratory system?  Spinal Chord  Phrenic motoneurons whose axons make up the phrenic nerve, which drives the diaphragm, are found in cervical spinal chord segment, C3, C4, and C5  The motoneurons for the intercostal nerve, which drive the intercostal muscles are found in the thoracic spinal segments T1 and T2  Relationships between Tidal volume and Phrenic Nerve Activity  Phrenic nerve is active during inspiration and not active relatively during expiration  Rhythmic activity of respiratory motor neurons mainly controlled by pre-motor neurons in the medulla  Brainstem  spinal phrenic neurons  phrenic nerve  diaphragm  How is respiratory rhythm generated  Clusters of neurons located in the Pons and the Medulla form regions of the Pontine Respiratory Group (located in the Pons), Dorsal Respiratory Group, Ventral Respiratory Group (located in the medulla)  Within the DRG lies a region, Nucleus Tractus Solitarius  In the general sense, output from the dorsal respiratory group goes to inspiratory muscles and output from the ventral respiratory group goes to some expiratory and some inspiratory  Sensory information, specially mechanical (chemoreceptor) is coming into the dorsal respiratory group  The region, Pre-Botzinger Complex, located within the ventral respiratory group is extremely important for generating the respiratory rhythm  Summary Notes  Rhythm generating neurons (in the pre-Botzinger complex) produce respiratory rhythm (pacemaker activity).  Pattern generating neurons (mostly in the VRG) control the pattern of activation of the pre-motor neurons  Regulate motor neurons  Afferent relay neurons (mostly in the DRG) integrate afferent inputs and distribute the information to rhythm and pattern generating neurons.  Input from peripheral receptors such as chemo receptors  Cranial motoneurons (in the nucleus ambiguus, a part of the VRG) activate the muscles of the airway like the larynx and pharynx, as well as the bronchiolar smooth muscle.  e.g. bronchiorestriction  Pre-motor neurons (in the VRG and DRG) activate the respiratory motoneurons (e
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