Postural and ventilatory functions of intercostal muscles

Area of Science:

• Respiratory Physiology
• Neuroscience
• Musculoskeletal System

Background:

• Interchondral muscles exhibit diaphragm-like activity during spontaneous breathing.
• External and internal intercostal muscles show electrical activity independent of the ventilatory rhythm.

Purpose of the Study:

• To investigate the distinct roles of intercostal, interchondral, and diaphragmatic muscles in respiration and posture.
• To correlate muscle activity patterns with histological findings regarding muscle spindle density.

Main Methods:

• Electrophysiological recordings of muscle activity during spontaneous and stimulated breathing.
• Experimental manipulation of muscle length and spinal dorsal root sections.
• Histological analysis of muscle spindle density in different respiratory muscles.
• Electrical stimulation of the bulbar pyramids in decerebrate cats.

Main Results:

• External and internal intercostals are reflexly activated by length variations, unlike the diaphragm and interchondrals.
• Spinal dorsal root sections abolish intercostal activity but spare diaphragm and interchondral respiratory function.
• Electrical stimulation of the bulbar pyramids activates intercostals and leg muscles without affecting diaphragmatic or interchondral rhythmic activity.
• Intercostal muscles are predominantly involved in postural control.

Conclusions:

• Intercostal muscles play a primary role in posture, mediated by reflexes sensitive to muscle length and spinal input.
• Diaphragm and interchondral muscles are primarily involved in rhythmic respiration, with distinct neural control mechanisms.
• Higher muscle spindle density in external intercostals correlates with their postural function and reflex responsiveness.