external intercostal muscles

When the external intercostal muscles contract and lift the ribs, the upper ribs are able also to push the sternum up and out.

During inhalation, the diaphragm contracts, thus enlarging the thoracic cavity (the external intercostal muscles also participate in this enlargement).

Anteriorly, the external intercostal muscles do not directly attach to the sternum, but are replaced by the anterior intercostal membrane.

Deep to these muscles are the osseous portions of the 6th and 7th ribs and the internal and external intercostal muscles.

During eupnea, neural output to respiratory muscles is highly regular, with rhythmic bursts of activity during inspiration only to the diaphragm and external intercostal muscles.

The external intercostal muscles are used only to enlarge the chest cavity, whilst the counterplay between the diaphragm and abdominal muscles is trained to control airflow.

When neurons in the DRG fire, impulses travel down the phrenic and intercostal nerves to stimulate the diaphragm and external intercostal muscles.

Diaphragm (innervated by phrenic nerve) and external intercostal muscles (innervated by segmental intercostal nerves) contract, creating a negative pressure around the lung.

This process can be made forceful through the contraction of the external intercostal muscles, forcing the rib cage to expand and aiding to the negative pressure within the intrapleural space, which causes the lungs to fill with air.

The response is that the respiratory centre (in the medulla), sends nervous impulses to the external intercostal muscles and the diaphragm, via the intercostal nerve and the phrenic nerve, respectively, to increase breathing rate and the volume of the lungs during inhalation.

Both the external intercostal muscles and the intercondral elevate the ribs, thus increasing the width of the thoracic cavity, while the diaphragm contracts to increase the vertical dimensions of the thoracic cavity, and also aids in the elevation of the lower ribs.