QS Study

Nervous Regulation of Respiration

The group of neurons in the brain which regulates the respiration rhythmically is collectively known as a respiratory centre. Respiratory system has the responsibility of meeting needs of the body by altering the rate and depth of respiration in order to keep the PO2 and PCO2 at normal levels. The medulla and the pons are involved in the regulation of the ventilatory pattern of respiration.

Nervous regulation: Two separate neural mechanisms regulate respiration –

  1. Voluntary control of respiration
  2. Automatic control of respiration.

Voluntary control of respiration: The voluntary system is located in the cerebral cortex and sends impulses to the respiratory motor neurons via the corticospinal tracts.

Automatic control of respiration (control of rhythmic breathing): Respiration is automatically controlled by the respiratory center located in the pons and medulla.

Mechanism

Fig: mechanism of control of rhythmic breathing by respiratory centre

Here;

Pn = Pneumotaxic centre, Ap = Apneustic centre, In = Inspiratory centre, Ex = Expiratory centre, X – vagus afferent from lung parenchyma.

(a) Under the influence of the stimulatory effect of the arterial PCO2 and the tonic activity of the apneustic center, the inspiratory centre becomes stimulated.

(b) The inspiratory centre discharges over pathways in the spinal cord to the cervical (C- 3, 4, 5) and thoracic spinal anterior horn cells.

(c) Through these nerves nervous signal is transmitted to the primary inspiratory muscles in a ramp manner, i.e., the signal begins weakly and increases steadily, for 2 seconds.

(d) This causes contraction of inspiratory muscles and inspiratory occurs.

Meanwhile, the inspiratory centre discharges also to the pneumotoxic centre which in turn discharges inhibitory impulses to the apneustic centre.

As the same time, inhibitory discharge relayed by the vagus from pulmonary stretch receptors cease to activate the inspiratory centre.

As a result, this centre stops discharging and expiration takes place passively.

Next, the inspiratory signal begins again for another cycle; this cycle repeats again and again, with expiration occurring in between.

Thus rhythmic breathing is controlled.