CONTROL OF RESPIRATION

Control Of Respiration Respiratory process is involuntary process, but under voluntary control as we can stop breathing. Respiratory center is in the brain stem. It causes rhythmic breathing pattern of inspiration and expiration. Inspiratory and Expiratory muscles are skeletal muscles and contract only when stimulated by their nerve supply.

Neural Control Of Respiration 1. Center that generate inspiration and expiration. 2. Factors that regulate rate and depth of respiration . 3. Factors modifying the respiratory activity (voluntary eg.Speech or involuntary eg. Cough or sneeze)

Respiratory Centers In Medulla - Inspiratory center(Dorsal respiratory group) - Expiratory center (Ventral respiratory group) These are neuronal cells that provide output to respiratory muscles for inspiration and expiration. In Pons - Pneumotaxic center – upper pons - Apneustic center – lower pons Pontine Center influence the output from medullary centers.

Respiratory Centers Inspiratory and Expiratory neurons in the medullary center. We are breathing rhythmically in and out during quiet breathing because of alternate contraction and relaxation of inspiratory muscles [diaphragm and External-intercostal muscles] supplied by phrenic nerve [C345], and intercostal nerves .

Respiratory Centers Order comes from medullary center to spinal cord motor neuron cell bodies [anterior horn cells]. When these motor neurons are activated, they stimulate the inspiratory muscles leading to inspiration. When these neurons are not firing, the inspiratory muscles relax and expiration takes place.

Respiratory Centers ‘Summary’ Inspiratory center [DRG] – Inspiration (Pre-Botzinger complex, generates respiratory rhythm) Expiratory center [VRG] – used during active/ forced Expiration Pneumotaxic center – acts on inspiratory center to limit duration of inspiration,therefore regulates inspiration and letting expiration to occur normally. Apneustic center – causes Apneusis [deep inspiration]. Apneusis occurs in certain severe type of brain damage.

Hering-Breur reflex Over inflation of lungs is prevented by this reflex Pul. stretch receptors in airways are stimulated by stretching of lungs by large tidal volume. Action potential from these receptors go to medullary center and inhibit insp. Neurons. Insp. is cut down & lung is prevented from over inflation.

Chemical Control Of Breathing Chemical factors which affect the ventilation are -PO2 -PCO2 -H+ ion Their effect is mediated via respiratory chemoreceptor. We will study chemoreceptors first .

Peripheral Chemoreceptors There are two types of Chemoreceptors 1. Peripheral Chemoreceptors 2. Central Chemoreceptors Peripheral Chemoreceptors Peripheral Chemoreceptors are Carotid bodies & Aortic bodies. Carotid Bodies Carotid body is present near the carotid artery bifurcation on each side. They contain cells which can sense the level of PO2, PCO2 , H+ ion.

Peripheral Chemoreceptors Carotid bodies [cont] Carotid body sends impulse to respiratory center in medulla via IX cranial nerve [glassophyrangeal]. Aortic bodies These receptors are situated in the aortic arch . They also sense the O2, CO2, and H+ ion changes in the blood. Aortic body sends impulse to respiratory center in medulla via X cranial nerve [vagus].

Central Chemoreceptors They are located in the medulla near the respiratory center . These central chemoreceptors monitor the effect of PO2, PCO2 , and H+ ion. When CO2 increases, we get: CO2 + H2O  H+ + HCO3- Increased H+ directly stimulates the central chemoreceptors.

‘Summary’ Decreased PO2, increased PCO2, increased H+ ion concentration in arterial blood stimulates Peripheral Chemoreceptors. Most important stimulating factor is decreased PO2 on peripheral chemoreceptors. Increased PCO2 in the arterial blood and increased H+ ion in the brain ECF strongly stimulates the central chemoreceptors and dominant control of ventilation. -Decreased PO2 in the arterial blood – depresses the central chemoreceptors.

What You Should Know From This Lecture Neural Control of Respiration Name of Respiratory centers in the Brain stem Chemical Control of Breathing Peripheral Chemoreceptors Central Chemoreceptors Effect of decreased PO2, increased PCO2 and H+ on Peripheral and Central Chemoreceptors