From the Guidelines
The correct statement regarding innervation of respiratory muscles is that skeletomotor fibers innervating the thoracic diaphragm originate from the ventral horn of C3, C4, and C5. This is accurate because the phrenic nerve, which is the primary nerve supplying the diaphragm, arises from these cervical segments. The other options contain inaccuracies:
- the scalenes are actually innervated by branches of the cervical plexus (C3-C8), not the spinal accessory nerve;
- respiratory muscles are skeletal (not smooth) muscles that can function both automatically and voluntarily;
- and the intercostal muscles are innervated by intercostal nerves (branches of thoracic spinal nerves T1-T11), not the phrenic nerve. Understanding the correct innervation patterns of respiratory muscles is essential for diagnosing and treating conditions affecting breathing, as damage to specific nerve pathways can lead to predictable patterns of respiratory compromise, as discussed in 1.
Some key points to consider:
- The phrenic nerve is responsible for innervating the diaphragm, and its dysfunction can lead to significant respiratory compromise, as noted in 1.
- The intercostal muscles play a crucial role in respiratory function, and their innervation by intercostal nerves is essential for proper breathing, as discussed in 1.
- The scalene muscles, while important for accessory respiratory function, are not innervated by the spinal accessory nerve, but rather by branches of the cervical plexus, as mentioned in 1.
- Respiratory muscles are skeletal muscles that can function both automatically and voluntarily, and their proper innervation is critical for maintaining adequate ventilation, as discussed in 1.
Overall, understanding the correct innervation patterns of respiratory muscles is crucial for diagnosing and treating respiratory disorders, and can help clinicians provide more effective care for patients with breathing difficulties, as emphasized in 1.
From the Research
Innervation of Respiratory Muscles
- The statement that skeletomotor fibres innervating the thoracic diaphragm originate from the ventral horn of C3, C4, and C5 is correct, as the phrenic nerve, which innervates the diaphragm, originates from these spinal segments 2.
- The scalenes are innervated by the spinal accessory nerve (CN XI) and the ventral rami of C3 and C4, but they also receive input from the dorsal scapular nerve, and their primary function is to elevate the ribs and assist in inspiration 3.
- Breathing is not entirely automatic, and respiratory muscles are comprised of skeletal muscle, which is innervated by the somatic nervous system, rather than smooth muscle and the autonomic nervous system 2.
- The intercostal muscles are innervated by the intercostal nerves, which arise from the thoracic spinal segments, rather than the phrenic nerve 3.
Respiratory Muscle Function
- The diaphragm is the primary muscle responsible for inspiration, and its function can be affected by phrenic nerve damage or dysfunction 4, 5.
- The nondiaphragmatic respiratory muscles, including the intercostal muscles and the scalenes, play an important role in compensating for diaphragmatic paralysis or dysfunction 5.
- Phrenic nerve stimulation may be a useful approach to maintaining diaphragm activity and achieving lung and diaphragm protective ventilatory targets in patients with acute respiratory failure 4, 6.