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Control of Respiration Week 4. Dr. Walid Daoud A. Professor. Respiratory Center (RC). Respiratory center is composed of a collection of neurons located bilaterally in pons and medulla. These neurons are either:

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control of respiration week 4

Control of RespirationWeek 4

Dr. Walid Daoud

A. Professor

respiratory center rc
Respiratory Center (RC)

Respiratory center is composed of a collection of neurons located bilaterally in pons and medulla.

These neurons are either:

- Inspiratory (discharge during inspiration) or - Expiratory (discharge during expiration).

Inspiratory neurons are inhibited during expiratio and expiratory neurons are inhibited during inspiration.

medullary respiratory centers
Medullary Respiratory Centers

1- Dorsal Respiratory Group (DRG)

. In dorsomedial position in medulla.

. Located bilaterally in nucleus tractus

solitarius which is sensory termination of vagus and glossopharyngeal nerve and receive sensory information from

mechanoreceptors, baroreceptors and

chemoreceptors in the body

medullary respiratory centers1
Medullary Respiratory Centers

1- Dorsal Respiratory Group (DRG)

- Inspiratory neurons having inherent

rhythmicity with spontaneous depolarization.

- Responsible for inspiratory activity.

- DRG sends afferent impulses to:

Inspiratory muscles and VRG.

- DRG receives:

Excitatory impulses from apneustic center.

Inhibitory impulses from lung stretch receptors

medullary respiratory centers2
Medullary Respiratory Centers

2- Ventral Respiratory Group (DRG)

. Lies ventrolateral to DRG.

. Composed of both inspiratory and expiratory

neurons as they contribute to both forced

inspiration & expiration during hyperventilation

. Remains inactive during quiet breathing i.e,

no rhythm.

pontine respiratory centers
Pontine Respiratory Centers

They modify and regulate the function of the medullary centers.

1- Apneustic Center (APC):

. In lower pons.

. Responsible for SWITCH ON point of


. It stimulates pneumotaxic center.

pontine respiratory centers1
Pontine Respiratory Centers

1- Apneustic Center (APC):

. It receives inhibitory impulses from:

- Lung stretch receptors.

- Pneumotaxic center (PNC).

. When APC is inhibited , inspiration will stop

which will turn off the excitation of inspiratory

muscles and allow el;astic recoil of the lung to cause expiration.

pontine respiratory centers2
Pontine Respiratory Centers

2 - Pneumotaxic Center (PNC):

. PNC lies in upper pons.

. It controls SWITCH OFF point of inspiration

by sending inhibitory impulse to APC.

. PNC by switching off inspiration will limit the

duration of inspiration.

role of vagus nerve
Role of Vagus Nerve

Hering-Breuer reflex:

Stretch of the lungs stimulate stretch receptors in the lungs which will send impulses through vagi to APC and DRG.

This will adjust the rate and depth of respiration at tidal volume 500 ml.

The reflex is active in animals and newborn children. In adult human only during exercise.

genesis of rhythmic respiration
Genesis of Rhythmic Respiration

-APC sends continuous regular discharge of

signals exciting inspiratory neurons of DRG .

-DRG sends impulses down the spinal cord to

diasphragm and external intercostal muscles

causing inspiration and stimulation of stretch

receptors in the lungs which will inhibit APC and

DRG via vagus. At the same time , PNC inhibits

APC to switch off inspiration.

-This stops inspiration and brings expiration

regulation of respiration
Regulation of Respiration

Regulation of respiratory center activity:

I- Chemical regulation:

Effects of variation of blood O2, CO2 , H ions

on ventilation via chemoreceptors.

It is basic mechanism for regulation of resp.

II-Non-chemical (nervous) regulation:

It is superimposed on the basic chemical

regulation of respiration in particular


chemical regulation of respiration
Chemical Regulation of Respiration

It is the basic mechanism for regulation of breathing.

-Increase arterial PCO2

-Increase arterial H ion

-Decrease arterial PO2

Stimulate respiratory chemoreceptors

Increase activity of respiratory center and

Increase pulmonary ventilation.

central chemoreceptors
Central Chemoreceptors


Located bilaterally just beneath central surface of medulla.


1- Response to H ion ( primary stimulus).

2- Response to PCO2.

3- Response to Po2.

chemoreceptors peripheral


Aortic bodies: over aortic arch

Carotid bodies: at bifurcation of each common carotid artery.


Carotid bodies: glossopharyngeal nerve

Aortic bodies: vagus nerve

mechanism of stimulation of peripheral chemoreceptors
Mechanism of stimulation of peripheral chemoreceptors

1- Oxygen tension.

2- H ion concentration.

3- CO2 tension