Control of respiration

Control of respiration

1. CONTROL OF RESPIRATION Ms.Anu Sebastian: B.Pharm ; M.Pharm Assistant Professor, Dept. Of Pharmacology Nirmala College Of Pharmacy Muvattupuzha,Ernakulam,Kerala

2. The basic rhythm of respiration is controlled by respiratory centres located in the medulla and pons of the brain stem. Medullary rhythmicity area : In medulla oblongata Pneumotaxic area : In the upper pons Apneustic area : In the lower pons MEDULLARY RHYTHMICITY AREA Its function is to control the basic rhythm of respiration. It contains Inspiratory area & Expiratory area.

3. INSPIRATORY AREA The inspiratory center sends nerve impulses along the phrenic nerve to the diaphragm and along the intercostal nerves to the external intercostals muscles. The nerve impulses to the diaphragm and the external intercostal muscles continue for a period of about 2 seconds. This stimulates the inspiratory muscles to contract, initiating inspiration. The neurons stop firing or about 3 seconds, which allows the muscles to relax. The elastic recoil of the lungs and chest wall leads to expiration. This automatic, rhythmic firing produces the normal resting breathing rate ranging between 12-15 breaths per minute.

4. EXPIRATORY AREA The expiratory area appears to function mainly during forced expiration, stimulating the internal intercostals and abdominal muscles to contract. In addition, other respiratory centers within the pons modify inspiration and allow for smooth transitions between inspiration and expiration.

5. PNEUMOTAXIC AREA In the upper pons Transmit inhibitory impulses to the inspiratory area, turn of the inspiratory area before the lungs become too full of air. Shortens the duration of inhalation When the pneumotaxic area is more active, breathing rate is more rapid. APNEUSTIC AREA In the lower pons Sends stimulatory impulses to the inspiratory area that activate it & prolong inhalation. The result is a long deep inhalation When the pneumotaxic area is active, it overrides signals from the apneustic area.

6. REGULATION OF RESPIRATORY CENTRE The basic rhythm set by inspiratory area is modified by other brain centers, receptors in PNS and other factors. 1. Cortical influences on respiration Cerebral cortex has neuronal connections with respiratory center, so we can voluntarily alter the breathing pattern. This voluntary control is protective as it prevent the entry of irritating gases or water entering the lungs.

7. Increase in PCO2 & H+ ↓ Stimulate inspiratory area ↓ Activate phrenic and intercostals muscles ↓ Contraction of diaphragm & external intercostals muscles ↓ Breathing Emotional stimuli ↓ Activate hypothalamus & limbic ↓ Stimulate respiratory center ↓ Alter breathing

8. 2. Chemoreceptor regulation The sensory neurons that respond to changes in chemicals are called chemo receptors. These are located centrally and peripherally to monitor the levels of O2 & CO2 The central chemoreceptors are located near to medulla oblongata in CNS. They respond to changes in H+/PCO2 or both in CSF. Peripheral chemoreeptors are located in : Aortic bodies : Located in the wall of arch of aorta Carotid bodies : Located in the all of right and left common carotid artery, where they divide into external and internal carotid arteries .

9. 3. Proprioceptor regulation Proprioceptor monitor movements of joints and muscles. During exercise ↓ Changes in movements of Joints & muscles motor neuron ↓ Activation of proprioceptors ↓ Sending input to inspiratory area in medulla ↓ Alter breathing

10. 4. Inflation reflex / Hering Breuer reflex Over inflation of lungs Activation of baro / stretch receptors on the walls of bronchioles Activation of vagus nerve Send impulses to inspiratory area & apneustic area Inhibition of apneustic area & inspiratory area Exhalation As air leaves the lungs, it deflates Inactivation of stretch receptors Activation of Inspiratory area & apneustic area Inhalation begins

11. 5. Other influences on respiration Limbic system : Emotions/anxiety etc stimulate limbic system, activate inspiratory are & increase rate & depth of Respiration. T emperature : Increase in body temperature, increase rate of respiration & vice versa. Pain : Prolonged somatic pain, increase rate of respiration & visceral pain decreases rate of respiration. Stretching of anal sphincture muscle : Increases respiratory rate. Irritation of airways : Irritation in the airways causes immediate cessation of breathing followed by coughing & sneezing. Blood pressure : sudden rise in B.P, decrease rate of respiration and fall in BP increases respiratory rate.

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