Breathing and spirometry

How do we control rhythmic breathing?

• The basic breathing system is a reflex action under the control of the nervous system, controlled by the medulla oblongata.

• This contains a breathing centre consisting of 2 groups of nerve cells- expiratory and inspiratory centres.

• Nerves arising from these centres innervate (make contact with) the intercostal muscles and diaphragm, supplying them with nerves.

Whats the difference between thoracic nerves and phrenic nerves?

Thoracic nerves innervate the intercostal muscles. The phrenic nerves innervate the diaphragm.

How does inspiration happen?

A pattern of nerve impulses travels along the vagus nerve to the respiratory centres, leading to inhibition of the inspiratory centre and stimulation of the expiratory centre.

What happens to alveoli in inspiration?

At the height of inspiration, they are inflated and stretched, stimulating stretch receptors in their walls.

What happens to the diaphragm and intercostal muscles in inspiration?

Impulses travelling along the thoracic and phrenic nerves from the inspiratory centre lead to contraction of the diaphragm and intercostal muscles.

How does expiration happen?

A pattern of nerve impulses travels along the vagus nerve to the respiratory centres, leading to stimulation of the inspiratory centre and inhibition of the expiratory centre.

What happens to alveoli in expiration?

The alveoli deflate and stretch so the receptors are no longer stimulated.

What happens to the diaphragm and intercostal muscles in expiration?

Impulses travelling along the thoracic and phrenic nerves from the expiratory centre lead to relaxation of the diaphragm and intercostal muscles.

How is the volume of air inspired / expired in different circumstances measured?

The volume of air inspired / expired in different circumstances, can be measured using a spirometer. Volume changes are recorded with a pen from the lid onto a rotating drum (shown in a kymograph).