HUB105 Lecture 23 Control Of Respiration 2024 PDF

Lecture 23 Control of Respiration BChD I HUB 105 2024 Dept. Medical Biosciences University of the Western Cape Introduction Basic rhythm of breathing is set and controlled by portions of the nervous system found in the brain’s respiratory centres; located in the medulla oblongata a...

Lecture 23 Control of Respiration BChD I HUB 105 2024 Dept. Medical Biosciences University of the Western Cape Introduction Basic rhythm of breathing is set and controlled by portions of the nervous system found in the brain’s respiratory centres; located in the medulla oblongata and brainstem. This centre sends impulses via nerves to the effector muscles of inspiration and expiration: diaphragm and intercostal muscles. Normal breathing rate at rest is about 12 -18 breaths per minute The normal rhythm of respiration can be modified in response to metabolic demands of the body or external environmental factors (pollution, pain) Theses regulatory mechanisms are controlled by respiratory reflexes, but can also be controlled voluntarily through commands from the cerebral cortex. Respiratory centres of the brain  several groups of neurons located bilaterally in the medulla oblongata and pons of the brainstem are involved in the involuntary control of respiration 1. Medullary respiratory centers These centers consist of 2 groups of neurons: a) the dorsal respiratory group (DRG) = function as inspiratory centre b) the ventral respiratory group (VRG) =function only during forced breathing ⇒these groups generate the basic respiratory rhythm From: Indu Khurana and Arushi (2009). Textbook of 2. Pontine respiratory centers Anatomy and Physiology for Nurses and Applied These centers consist of 2 groups of Health Scinces, 1st Ed. neurons: a) the apneustic centre (APN) b) the pneumotaxic centre (PNC) ⇒ these groups modify the activity of the medullary centers Respiratory centres of the brain Respiratory rhythmicity centre Quiet Breathing pattern: The basic rhythm of respiration is det. by nerve impulses generated in the inspiratory centre of the DRG. DRG neurons innervate the contraction of the external intercostal muscles and diaphragm. DRG neurons send action potentials along the phrenic and intercostal nerves to stimulate the diaphragm and external intercostal muscles. Inspiratory muscles contract for 2 seconds and is followed by a period of inactivity of the inspiratory centre. During this inactivity, passive expiration occurs for a period of 3 seconds. After the 3 sec expiration, DRG suddenly and automatically becomes active, the pattern repeats to produce the basic respiratory rhythm Respiratory centres of the brain Respiratory rhythmicity centre  Figure 23-25a Basic Regulatory Patterns of Respiration Quiet Breathing INHALATION (2 seconds) Diaphragm and external intercostal muscles contract and inhalation occurs. Dorsal Dorsal respiratory respiratory group active group inhibited Diaphragm and external intercostal muscles relax and passive exhalation occurs. EXHALATION (3 seconds) Respiratory centres of the brain Respiratory rhythmicity centre Forced Breathing pattern: Expiratory neurons remain inactive during normal, quiet respiration. normal breathing produces active contraction of inspiratory muscles, and expiration is a passive elastic recoil of the lungs and thoracic wall. Forceful breathing stimulates impulses from both the DRG and VRG neurons to activate the accessory muscles of inhalation. After inhalation, active exhalation occurs as VRG neurons stimulate the expiratory accessory muscles. VRG primarily stimulates the accessory muscles involved in inhalation and exhalation.  Figure 23-25b Basic Regulatory Patterns of Respiration Forced Breathing INHALATION Muscles of inhalation contract, and opposing muscles relax Inhalation occurs, DRG and DRG and inspiratory inspiratory center of VRG center of VRG are active. are inhibited. Expiratory center Expiratory of VRG is center of VRG inhibited. is active. Muscles of inhalation relax and muscles of exhalation contract. Exhalation occurs. EXHALATION Respiratory centres of the brain Pontine respiratory centre Apneustic (APN) and Pneumotaxic centres (PNC) are paired nuclei (mass of neurons) located in the pons. Coordinated activities betw the 2 centres assist to adjust the functioning of the respiratory rhythmicity centres. Play a role in respiratory rate and depth of respiration in response to external sensory stimuli or from parts of the brain. Apneustic centre Sends continuous stimulatory impulses to the DRG during quiet breathing that assist with inhalation over the 2sec. This centre when stimulated by sensory stimuli, during forced breathing, helps with the inflation of lungs and increases duration of inhalation APN is inhibited by the impulses sent from the PNC to prevent over inflation of lungs. Respiratory centres of the brain Pontine respiratory centre Pneumotaxic Centre Send action potentials that inhibit the APN results in - shortened inspiration - shallow and rapid respiratory rhythm Under passive or active breathing, PNC action potentials limit the duration of inspiration by inhibiting the apneustic centre and facilitate expiration. Rate and depth of breathing is modify by both the APN and PNC Important action of both pons respiratory areas is to fine-tune the respiratory rhythm and prevent over inflation of the lungs. Respiratory centres of the brain Regulation of Respiratory centre activity Although the respiratory centers in the medulla and pons establish and fine-tune the rate and depth of breathing, their activities can be influenced by input from other parts of the brain and by input from respiratory reflexes Cerebral cortex Chemical regulation reflexes Inflation reflexes/ Hering-Breuer reflex Cerebral cortex (CC) Voluntary control of the respiration by cerebral cortex has various effects on the respiratory centres: eg  Conscious thoughts relating to strong emotions (fear, anger) alters breathing rate.  Emotional states affects the Sympathetic and Parasympathetic division, this increases or decreases respiration rate, respectively. Higher centres in the brain are important in the respiratory control mechanism at an involuntary level eg speaking, singing, swimming. Inhibitory effect is important, as higher centres can override the apneustic, DRG and VRG. (eg holding your breath) Regulation of Respiratory centre activity Chemical regulation reflexes Certain chemical stimuli determine how fast and deep breaths are taken. Chemoreceptors are stimulated to increase depth and rate of breathing. Central chemoreceptors located in the medulla = sensitive to change in PCO2 and pH of the Cerebrospinal fluid (CSF) Peripheral chemoreceptors found in carotid and aortic bodies = sensitive to decrease in PO2 in blood Carotid bodies send impulses via Glossopharyngeal nerve (IX) to medulla Aortic bodies send impulses via Vagus nerve (X) to respiratory centre in medulla. Stimulate DRG to increase rate and depth of inspiration, could lead to hyperventilation) Regulation of Respiratory centre activity Effects of CO2 on respiration CO2 levels mainly responsible for regulating respiratory activity. Slight increase to PCO2 contributes to pH changes, like during hypoventilation. Slow and shallow breathing can lead to hypoventilation. CSF is highly sensitive to theses changes and peripheral chemoreceptors in carotid and aortic bodies detect changes. Leads to the respiratory centres being highly activated, and the rate and depth of breathing increases. Rapid and deep breathing , allows exhalation of more CO2 until PCO2 and pH normal. Chemoreceptors are not stimulated and don’t stimulate respiratory centres by low levels of PCO2, but sets a pace to accumulate CO2. Regulation of Respiratory centre activity Inflation reflexes/ Hering-Breuer reflex this reflex limits the degree to which inspiration can occur & it prevents overinflation of the lungs during forced breathing, as during exercise this reflex is initiated by stretch receptors in the visceral pleura and in the smooth muscle of the bronchi and bronchioles these receptors are stimulated when the lungs become inflated action potentials are sent via the vagus nerve to the medulla oblongata where the DRG is gradually inhibited and the VRG is stimulated inhalation therefore stops as the lungs near maximum volume, and active exhalation begins Respiratory regulators acting on respiratory centers. Higher brain centers (cerebral cortex—voluntary control over breathing) Other receptors (e.g., pain) + and emotional stimuli acting – through the hypothalamus + – Respiratory centers (medulla and pons) Peripheral + chemoreceptors O2 , CO2 , H+ + – Stretch receptors in lungs Central Chemoreceptors – CO2 , H+ + Irritant receptors Receptors in muscles and joints Revision Questions: 1. Define following: respiratory rhythmicity centre, DRG, VRG, pneumotaxic, apneustic, chemoreceptors 2. Indicate the areas in the brain where all the respiratory centres are found. 3. Explain the pattern of breathing during normal and forced breathing. 4. Explain how overinflation of the lungs are controlled by the respiratory centre of the pons. 5. How’s does the VRG assist with forced breathing? 6. List the regulatory mechanisms that assist breathing. 7. Design a flow diagram explaining forced breathing. 8. Explain the Hering-Breuer reflex. 9. What happens to the chemoreceptors when PCO2 increases?