Diaphragm

The diaphragm is a large, dome-shaped muscle positioned at the base of the lungs, serving as the primary muscle engaged in the process of respiration, or breathing^[1]. Acting as a barrier, it also segregates the thoracic cavity, which contains the heart and lungs, from the abdominal cavity^[2].

When the diaphragm contracts, it descends, thereby expanding the volume of the thoracic cavity and reducing intra-thoracic pressure, facilitating the inflow of air into the lungs^[4]. Conversely, when the diaphragm relaxes, it results in a reduction in the volume of the thoracic cavity, leading to an increase in intra-thoracic pressure and the expulsion of air from the lungs^[5].

The diaphragm receives innervation from the phrenic nerves, emanating from the cervical spinal roots C3 to C5^[6]. Each phrenic nerve provides motor and sensory innervation to one half of the diaphragm. Consequently, damage to one phrenic nerve may not entirely incapacitate the diaphragm^[7].

The central nervous system regulates the contraction and relaxation of the diaphragm, assimilating sensory data concerning blood gases and pH to modulate the frequency and depth of breathing^[8]. Involuntary control of the diaphragm is maintained by the medulla oblongata and the pons in the brainstem, which uphold automatic respiratory rhythms^[9]. Voluntary control of the diaphragm, such as when one holds their breath, is overseen by cortical centers in the brain^[10].