Question

Describe the basics of nervous control of ventilation relative to the brain and 3 main kinds of lung receptors.

Answer 1

Nervous control of the respiration -

1)autonomic control

2)voluntary control

Autonomic control - certain groups of neurons in medulla and pons constitute the medullary and pontine respiratory Centres respectively.

Medullary Centre consists of dorsal and ventral group of neurons.

Dorsal group of neurons are located In the nucleus of tractus solitarius. They provide rhythmic drive to the diaphragm via phrenic motor neurons.

Ventral group of neurons present in nucleus ambiguis and retroambiguis. It innervates the accessory muscles of respiration and intercostal muscles.

Pontine respiratory Centre - consists of pneumotaxic centre and apneustic centre. Pneumotaxic centre neurons are active in respiration and inhibits the neurons of apneustic centre to prevent apnea.

Voluntary control - Respiration can be modified both in rate and depth at will for a specific period only, for example, voluntary hyperventilation breath holding, forceful inspiratory and expiratory efforts. The pathway for such a control via corticospinal tract which originates from cerebral cortex to end on spinal motor neurons innervating the respiratory group of muscles.

3 main types of receptors -

1)pulmonary stretch receptors

2)Juxta pulmonary capillary receptors

(J- receptors )

3)Irritant receptors

Pulmonary stretch receptors - These are located in the smooth muscles of airways. They relay in the medulla via myelinated afferent in the vagus nerve.Steady inflation of the lungs stimulate these receptors,impulses travel via vagus nerve to inhihiy the apneustic centre thus inhibiting inspiration producing prolonged expiration, called as Hering Bruer Inflation reflex.

J-receptors - Marked inflation of the lungs stimulates these receptors located in the alvelor wall. Impulses travel via vagus nerve reinforcing the action of the pneumotaxic centre in producing intermittency of inspiratory neuronal discharge, thus producing reflex apnea followed by tachypnoea (shallow rapid breathing), hypotension and bradycardia.

Irritant receptors - Throughout the airways from trachea to respiratory bronchioles there are endings of myelinated vagal afferents that function as irritant receptors. Stimulation of these receptors occurs by dust, pollen in the conducting zone of respiratory passage producing coughing and sneezing while in the respiratory zone it produces tachypnoea and brochoconstriction.