NEURAL MECHANISM OF BREATHING REGULATION

• “Voluntary” control.

• “Automatic” control.

VOLUNTARY CONTROL:

• Voluntary system –Eg: During singing, whistling, blowing etc.

– Located in cerebral cortex.

– Sends impulses to respiratory motor neurons via corticospinal tracts.

– Tracts bypass pontomedullary centers.

– Also directly descend to lower motor neurons supplying respiratory muscles.

2. AUTOMATIC CONTROL:

• Exerted by “Pontomedullary” respiratory centers.

• Enables smooth & unconscious execution of respiratory activities without any voluntary effort.

2a. MEDULLARY RESPIRATORY GROUP:

• Principal areas in medulla oblongata concerned with respiratory regulation.

Includes,

• Dorsal respiratory group (DRG).

• Ventral respiratory group (VRG).

• Pre-Botzinger complex.

• Peripheral inputs.

DORSAL RESPIRATORY GROUP (DRG):

• DRG neurons – 

– Mainly concerned with inspiration.

– Descend & terminate on spinal motor neurons innervating primary inspiratory muscles.

– I.e., Diaphragm & External intercostal muscles.

VENTRAL RESPIRATORY GROUP (VRG):

• VRG neurons – 

– Mainly concerned with forceful expiration.

– Minimal activities w.r.t inspiration.

– Contributes to both expiration & inspiration.

SUBDIVISIONS:

• 2 subtypes – Rostral & Ventral VRG.

1. Rostral VRG neurons:

• Involves inspiratory activity

• Terminate on spinal motor neurons supplying accessory inspiratory muscles.

– I.e., Sternocleidomastoid, Scalenes & Anterior serrati.

• Also referred “Inspiratory (I) neurons”.

2. Ventral VRG neurons:

• Mostly “Expiratory (E) neurons”.

• E neurons are silent mostly.

– Because expiration is passive process.

• Shows activity during forceful expiration.

– Eg: During exercise.

• Neurons terminate in spinal motor neurons.

• Supplies expiratory muscles.

– I.e., Internal intercostal & abdominal muscles.

PRE-BOTZINGER COMPLEX:

• Located in ventrolateral medulla.

• Neurons responsible for “Respiratory Rhythm Generation”.

• Contains “Pacemaker cells” – 

– Respiration regulatory cells.

PERIPHERAL INPUTS:

Inputs include,

1. Afferent impulses from carotid & aortic bodies,

• Chemoreceptors carried by glossopharyngeal & vagus nerves.

• Hypoxia, hypercapnia & acidosis stimulate respiration via this process.

2. Afferent impulses from pulmonary stretch receptors –

• Carried by vagus nerve.