Neural Mechanism Of Breathing Regulation

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.