Regulation of Respiration

 

Regulation of respiration is normally involuntary

It is voluntary during singing speaking etc

There are three types,

1.    Neural control of respiration

2.    Chemical control of respiration

3.    Non chemical control

 

1.    Neural control of respiration

It involves,

·       Respiratory centers

·       Afferent nerves

·       Efferent nerves

Two separate mechanisms

1.    Voluntary system

·       Located in cerebral cortex

 

2.    Autonomic system

·       Located in pons and medulla

Respiratory centers

·       A collection of functionally similar neurons

·       Collects information about level of Oxygen and Carbon dioxide in blood

·       Send signals to respiratory muscles

-        Medulla – basic respiratory center – produce and control respiratory rhythm

-        Pons - basic respiratory center – produce and control respiratory rhythm

-        Higher respiratory center – cerebral cortex, hypothalamus, limbic system

-        Spinal cord: respiratory motor neuron

Two types of respiratory centers

-        Medullary centers

1.    Inspiratory center

2.    Expiratory center

-        Pontine centers

1.    Apneustic center

2.    Pneumotaxic center

           

Inspiratory center (dorsal group of respiratory neurons)

·       Located in upper part of medulla oblangata

·       Function – involves in inspiration

Expiratory center (ventral group of respiratory neurons)

·       Located in medulla oblangata and anterior and lateral to inspiratory center

·       Function – inactive during quite breathing. Only inspiratory center is active. This is active in forced breathing and when inspiratory center is inactive.

Pneumotaxic center

·       Located in upper pons

·       Function – duration of inspiration is controlled

Apneustic center

·       Located in lower pons

·       Function – increases the depth of inspiration

Dorsal groups of neurons

·       Involves inspiration

·       Supplies diaphragm (via phrenic nerve) and external intercostal muscles (via intercostal nerves)

·       Produce ramp signals

·       Vagal and Glossopharyngeal nerves, transmit sensory signals into the respiratory center from,

-        Peripheral chemoreceptors

-        Baroreceptors

-        Several types of receptors in lungs

Dorsal respiratory group neurons fire in burst

                                🠇 

Firing leads to contraction of inspiratory muscles - inspiration

                                🠇

When firing stops, passive expiration

The rhythm generated in the medulla can be modified by the neurons in the pons

The Apneustic center 

Ventral group of neurons

•      Silent in quiet breathing
•      Active in forced breathing
•      Increased activity of expiratory system, inhibit inspiratory system and stimulate expiratory muscles

Active expiration during Hyperventilation

The dorsal and ventral groups are,

    bilaterally paired

    cross communication between them

    as a consequence they behave in synchrony and the respiratory movements are symmetrical

2.Chemical control of respiration

 

The goal of control of respiration is to maintain proper concentration of Oxygen, Carbon dioxide and H ions in the tissues

Receptors that respond to the change of the partial pressure of Carbon dioxide and Oxygen are called as Chemoreceptors

There are two types of chemoreceptors,

-        Central – 85% control

-        Peripheral – 15% control

Central chemoreceptors

            Site – on ventral surface of the medulla

            Stimulus – H ions concentration in CSF and surrounding interstitial fluid

Mechanism – Carbon dioxide cross the blood brain barrier and forms H ions, that   stimulates central chemoreceptors

Oxygen does not have a direct effect on respiratory center and acts on peripheral chemoreceptors located in carotid and aortic bodies. These in turn transmit signals to the respiratory center.

Chemo sensitive area

·       Located in medulla

·       Is highly sensitive to changes in either blood PCO2 or H ions in turn excites the other portions of the respiratory center

Receptor sensory activity is increased very strongly by changes in blood Carbondioxide

A change in blood Carbon dioxide has a potent acute affect on controlling respiratory drive and a weak chronic effect. So after a few days adaptation takes place

 

Peripheral Chemoreceptors

 

Sites

            Carotid Artery ( carotid body) – most

            Aortic aorta ( aortic body) – few

 

Stimulus – sensitive to reduction in partial pressure of Oxygen

 

·       When the oxygen concentration in the arterial blood is decreased, the chemoreceptors become highly stimulated

·       An increase in either Carbon dioxide or H ions also excites the chemoreceptors and indirectly increases respiratory activity (the central effect is more potent)

·       Stimulation od peripheral chemoreceptors occurs more rapidly than central stimulation, so that the peripheral chemoreceptors important in increasing the rapidity of response to Carbon dioxide at the onset of exercises