Regulation of respiration Lecture by Dr Sandeep :30-9:30am

Nervous system normally adjusts the rate of alveolar ventilation almost exactly to the demands of the body The respiratory center is composed of several groups of neurons located bilaterally in the medulla oblongata and pons of the brainstem It is divided into 3 major collection of neurons 1) dorsal respiratory group, located in the dorsal portion of medulla 2) ventral respiratory group, located in the ventrolateral part of medulla, and 3) the pneumotaxic center, located in the superior portion of the pons

The basic rhythm of respiration is generated mainly in the dorsal respiratory group of neurons and is conveyed to inspiratory muscle, diaphragm Inspiratory “ramp” signals begins weakly and increases steadily in a ramp manner for about 2 sec, then it ceases abruptly for 3 sec The advantage of ramp is that it causes a steady increase in the volume of the lungs during inspiration

A pneumotaxic center, located dorsally in the nucleus parabrachialis of the upper pons, transmits signals to the inspiratory area The primary effect of this center is to control the “switch- off” point of the inspiratory ramp, thus controling the filling phase of the lung cycle The function of the pneumotaxic center is primarily to limit inspiration

Ventral respiratory group of neurons Located in each side of the medulla, about 5 mm anterior and lateral to dorsal respiratory group of neurons These neurons remain totally inactive during normal respiration During increased pulmonary ventilation, these neurons contributes to extra respiratory drive These neurons contributes in both inspiration and in expiration, signals to abdominal muscles during expiration

In addition to the central nervous system, sensory nervous system from lungs also help control respiration Most imp are located in the walls of bronchi and bronchioles as stretch receptors When lungs are over stretched, stretch receptors are stimulated send inhibitory signals and inspiratory ramps are switched off This is called the Hering-Breuer inflation reflex. Function is to prevent overstretching of lungs

Chemical control of respiration The ultimate goal is to maintain proper concentration of O 2 and CO 2 in the body Excess of CO 2 or excess of hydrogen ions in the blood mainly act directly on the respiratory center itself, causing increasing in the strength of both inspiratory and expiratory signals O 2 does not have significant direct effect on respiratory center

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Peripheral chemoreceptor system This is special nervous chemical receptors, called chemoreceptors mainly located outside brain They are important in detecting change in O 2 in the blood rather than CO 2 They are called “carotid bodies” located in the bifurcation of the common carotid arteries and in arch of aorta

Basic mechanism of stimulation The exact mechanism is still unknown. However, these bodies have multiple highly characteristic glandular-like cells called glomus cells That synapses directly or indirectly on the nerve endings When there is low O 2 level in the blood these cells are stimulated and stimulates afferent nerve fibers there by stimulating inspiratory center

Regulation of respiration during exercise In strenuous exercise, O 2 consumption and carbon dioxide formation can increase as much as 20 fold What causes intense ventilation during exercise? When a person begins to exercise, a large share of the total increase in ventilation begins immediately on initiation of the exercise, even before blood chemical change Most of this increase is from neurogenic signals

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