Neural Control of Breathing PDF

Neural control of breathing Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE  Describe the neural mechanisms in controlling respiration. Describe the role...

Neural control of breathing Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE  Describe the neural mechanisms in controlling respiration. Describe the role of medullary centers in control of respiration Explain the function of pontine centers. Describe the role of higher centers in the control of respiration. Discuss Hering Breuer reflex and other reflexes and its importance in controlling our respiration  Control of breathing Neural control: Spontaneous respiration is produced by rhythmic discharge of motor neurons that innervate the respiratory muscles. This discharge is totally dependent on nerve impulses from the brain. Chemical control: The rhythmic discharges from the brain that produce spontaneous respiration are regulated by alterations in arterial PO2, PCO2, and H+ concentration  Respiratory center Site: Pons and Medulla oblongata Medulla Pons oblongata Dorsal Pneumotaxic respiratory group(DRG) center Ventral Apneustic respiratory center group(VRG)  Medullary center Are bilaterally located and bilaterally connected. They are Dorsal respiratory group (DRG) (Inspiratory center) Lies in the dorsal part of the medulla Function: 1. Generation of basic rhythm of respiration, rhythmic respiration is initiated by a small group of pacemaker cells in the pre-Bötzinger complex (pre-BÖTC). 2. Stimulation of DRE emit signals to → contraction of the diaphragm and external intercostal → inspiration. 3. Inhibition of DRE → relaxation of the diaphragm and external intercostal → Expiration.  Medullary center Ventral respiratory group (VRG) (Expiratory center) Lie in the ventral part of the medulla. Are inactive during normal quiet breathing. Active during deep expiration Function: 1. Stimulation of VRG → contraction of abdominal and internal intercostal muscles → deep expiration  Pontine center Apneustic center It is present in the lower part of the pons. Function: It stimulates DRG inspiratory neurons → prevents these neurons from being switched off and prolongs the duration of inspiration.  Pontine center Pneumotaxic center It is present in the upper pons. Function: play a role in switching between inspiration and expiration It inhibits the DRG inspiratory neurons → (shortens) the duration of inspiration and increases the rate of breathing. Strong pneumotaxic signals → decrease the duration of inspiration and increase respiratory rate (30-40/min). Week Pneumotaxic signals (damage of Pneumotaxic center) → breathing becomes prolonged slower and deeper (greater tidal volume).  Hering –Breuer's reflex Afferent from vagus nerve has the same effect of Pneumotaxic center. Stimulus: when the lungs are overstretched → stimulation of stretch receptors in the wall of the bronchi and bronchioles → inhibition of inspiratory center → decrease the duration of inspiration and increase the rate.  Neural control of respiration The function of respiratory center is regulated by afferent impulses from. 1. Higher centers 2. Lung 3. The air passages 4. Circulatory system 5. Skeletal muscles and joints 6. Visceral reflex  Neural control of respiration 1- Higher centers 1- Cerebral cortex The normal automatic pattern of breathing can be modified by impulses from the cerebral cortex direct to the motor neurons in the spinal cord that supply respiratory muscles. This voluntary control of respiration occurs for example during speech, singing, voluntary hyperventilation or voluntary apnea (breath holding). 2. Limbic system and hypothalamus Strong emotions and pain activating sympathetic center in the hypothalamus modulate the respiration in rate and depth. Also, when temperature regulating center in the hypothalamus is stimulated in hot weather, the respiratory center becomes stimulated.  Neural control of respiration 2- Lung 1- Pulmonary stretch receptors (Hering Breuer’s reflex). Stimulus: overstretch of the lung Receptors: Stretch receptors in bronchi and bronchioles Afferent: Vagus nerve. Response: inhibition of inspiration 2- Lung irritant receptors Stimulus: inhalation of irritant. Receptors: wall of bronchi and bronchioles Afferent: Vagus nerve. Response: Shallow rapid breathing and bronchoconstriction 3- J receptors (Juxta medullary capillary receptors) Stimulus: pulmonary congestion, pulmonary edema and pulmonary emboli. Receptors: pulmonary capillaries close to alveoli Afferent: Vagus nerve. Response: Shallow rapid breathing and feeling of dyspnea.  Neural control of respiration 3- Air passages These reflexes protect alveoli from irritants. Reflex Sneezing Coughing Swallowing Stimulus Irritation of nasal mucosa Irritation of respiratory Stimulation of pharyngeal mucosa mucosa Afferent Trigeminal Nerve Vagus Nerve Glossopharyngeal Nerve Response Deep inspiration followed by Deep inspiration followed Swallowing apnea forced expiration against open by forced expiration “stoppage of respiration epiglottis. against closed epiglottis and closure of epiglottis” which opens suddenly Aim To get rid of the irritant. To get rid of the irritant. To prevent food aspiration  Neural control of respiration 4- Circulatory system 1- from arterial side (Baroreceptor depressor impulse). When ABP is altered → respiratory movement are affected. Increase ABP → reflex decrease rate and depth of breathing and decrease tone of abdominal muscle → decrease venous return → decrease C.O → decrease ABP toward normal. N.B : Intravenous injection of large dose of adrenaline → generalized vasoconstriction → marked increase ABP → stoppage of respiration (adrenaline apnea). 2- from venous side (stretch receptors in right atrium) Increase venous return → stimulates stretch receptors in right atrium →stimulate respiratory system to increase ventilation of this venous return.  Neural control of respiration 5- Muscle and joints During exercise: impulse from proprioceptors from muscles, joints ligaments & tendons → stimulate the respiratory centre, thus help in increasing ventilation during muscular exercise. 6- Viscera During swallowing and vomiting → inhibition of respiration and closure of glottis occur to prevent aspiration of food or vomitus into the respiratory passages.  Review Questions Which of the following structures acts to inhibit inspiration to regulate inspiratory volume and respiratory rate? A. Apneustic center B. Dorsal respiratory group C. Medulla D. Pneumotaxic center E. Ventral respiratory group https://exchange.scholarrx.com/brick/control-of-breathing  Summary Describe the neural mechanisms in controlling respiration. Describe the role of medullary centers in control of respiration Explain the function of pontine centers. Describe the role of higher centers in the control of respiration. Discuss Hering Breuer reflex and other reflexes and its importance in controlling our respiration  Learning Resources  Hall JE, Hall ME. Guyton and Hall textbook of medical physiology e-Book. 14ed, Elsevier Health Sciences; 2020. Chapter 42 , 531 – 540. https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3-s2.0-B9780323597128000424 https://exchange.scholarrx.com/brick/control-of-breathing  Power-point presentation in the Moodle. www.gmu.ac.ae COLLEGE OF MEDICINE