Visible Muscles in Anatomical Context
The visible muscles in anatomical context include the diaphragm, intercostal muscles, scalene muscles, sternocleidomastoid, pectoralis major, abdominal muscles, and upper airway muscles including the genioglossus and intrinsic laryngeal muscles. 1
Respiratory Muscles
Primary Respiratory Muscles
- Diaphragm: The principal muscle of respiration, separating the thoracic and abdominal cavities
- External intercostal muscles: Located between ribs, elevate the ribs during inspiration
- Internal intercostal muscles: Located between ribs, depress the ribs during forced expiration
- Scalene muscles: Elevate the first two ribs during inspiration
Accessory Respiratory Muscles
- Sternocleidomastoid: Assists with forced inspiration by elevating the sternum
- Pectoralis major: Can assist with forced inspiration when arms are fixed
- Abdominal muscles: Including rectus abdominis, external and internal obliques, and transversus abdominis - assist with forced expiration
Upper Airway Muscles
- Genioglossus: Important tongue muscle that prevents airway collapse
- Intrinsic laryngeal muscles: Control vocal cord movement
- Alae nasi: Dilate the nostrils during breathing
Functional Considerations
Respiratory Muscle Assessment
- Surface electromyography (EMG) can be used to assess diaphragm, intercostal, scalene, and abdominal muscle activity 1
- Esophageal electrodes can measure crural diaphragm EMG with less cross-talk from adjacent muscles 1
- Intramuscular electrodes provide more precise recordings but are invasive 1
Muscle Coordination Patterns
- Normal adults and children demonstrate synchronous breathing between rib cage and abdominal compartments 1
- Asynchronous chest wall motion may indicate:
- Neuromuscular weakness
- Respiratory muscle fatigue
- Abnormal lung mechanics
- Upper airway obstruction
Upper Airway Muscle Function
- Upper airway muscle activity is crucial for maintaining airway patency
- Visualization methods include fiberoptic endoscopy, fluoroscopy, and magnetic resonance imaging 1
- Upper airway collapsibility can be assessed by monitoring pharyngeal pressure during airway occlusion 1
Clinical Implications
Respiratory Muscle Weakness
- When respiratory muscles are chronically weak, accessory muscles become more visibly active
- Palpable contraction of scalenes, sternocleidomastoids, pectoral muscles, or abdominal muscles during quiet breathing suggests increased respiratory motor output 1
- Respiratory muscle weakness may lead to elevated arterial PCO2 when muscles cannot generate sufficient alveolar ventilation 1
Facial Muscles
- The face consists of 30 different muscles arranged in three planes: superficial, middle, and deep 1
- These muscles play a crucial role in facial expression and aging
- With age, facial muscles become hypertrophic, causing permanent visible wrinkles 1
Important Considerations
- Electrode selection and placement significantly impact the quality of respiratory muscle assessment 1
- Surface electrodes provide noninvasive assessment but are subject to cross-talk from adjacent muscles 1
- Esophageal electrodes provide better recordings of diaphragmatic activity but are more invasive 1
- Interpretation of respiratory muscle activity must consider the clinical context, as abnormal patterns may have multiple causes 1
Understanding the visible muscles and their functional relationships is essential for accurate clinical assessment of respiratory function and diagnosis of neuromuscular disorders affecting respiration.