phrenicus

Phrenicus is a Latin adjective meaning related to the diaphragm and is used in anatomy to describe structures associated with the diaphragm, most notably the phrenic nerves. The term is the basis for the English word phrenic, as in nervus phrenicus (phrenic nerve). In historical physiology the diaphragm was sometimes linked with the mind, but in modern usage phrenic denotes diaphragmatic innervation and function.

There are two phrenic nerves, right and left, arising chiefly from spinal nerves C3 to C5. They descend through the neck, typically passing anterior to the scalene muscles, and enter the thorax. Within the mediastinum they travel on the surface of the pericardium and diaphragmatic pleura to reach the diaphragm. Each nerve provides motor branches to the diaphragmatic muscle and carries sensory fibers from the central portion of the diaphragmatic pleura and pericardium, enabling both movement and certain reflex sensations.

Functionally, the phrenic nerves supply the diaphragm, the primary muscle of respiration. Contraction of the diaphragm increases thoracic volume, facilitating inhalation. They also convey sensory information from the diaphragmatic pleura and pericardium, contributing to reflexes related to respiratory and mediastinal irritation. Variations in their course exist, and in some individuals there may be accessory phrenic nerves.

Clinical relevance includes phrenic nerve injury or irritation, which can cause diaphragmatic paralysis or weakness. Causes include surgical trauma, neck or chest injury, tumors, or inflammatory processes. Unilateral phrenic palsy may be compatible with life at rest but can worsen dyspnea on exertion; bilateral involvement can lead to significant respiratory compromise and may require monitoring, supportive care, or diaphragmatic pacing in select cases.