Thoracic Muscles and Anatomy

Overview

This lecture covers the muscles of the thorax, including their anatomy, imaging, and clinical significance, with a focus on the diaphragm.

The thoracic wall is composed of skeletal structures, fascia, muscles, and neurovascular components forming a protective cage.
Key muscle groups: external, internal, and innermost intercostal muscles; subcostalis; transversus thoracis.
Other important thoracic muscles: levatores costarum, serratus posterior superior and inferior, pectoralis major and minor, subclavius, and serratus anterior.

Superior thoracic aperture (thoracic inlet) boundaries: T1 vertebra (posterior), manubrium (anterior), first rib (lateral).
Structures passing through the superior aperture: subclavian and carotid arteries, veins, phrenic and vagus nerves, trachea, esophagus, thoracic duct.
Inferior thoracic aperture (thoracic outlet) boundaries: T12 vertebra (posterior), xiphoid process (anterior), ribs 11/12, costal margin (lateral), diaphragm (inferior).
Major structures passing through the diaphragm: aorta, esophagus, inferior vena cava, vagus nerves.

Intercostal muscles occupy 11 spaces, divided into external (superficial), internal (middle), and innermost (deep).
External intercostals aid forced inspiration; internal and innermost intercostals assist forced expiration.
Subcostal muscles bridge 2-3 intercostal spaces and pull ribs down during exhalation.
Transversus thoracis attaches the sternum to ribs 2-6, stabilizing the thoracic wall.

Levatores costarum: 12 small muscles connecting thoracic vertebrae to ribs, aiding forced respiration.
Serratus posterior superior elevates ribs; serratus posterior inferior depresses ribs during respiration.
Pectoralis major adducts and internally rotates the arm; pectoralis minor assists scapular movement and respiration.
Subclavius stabilizes clavicle and shields neurovascular structures in clavicle injuries.
Serratus anterior attaches ribs 1-8/9 to the scapula, allowing scapular movement.

The diaphragm is a dome-shaped skeletal muscle separating thoracic and abdominal cavities; primary muscle of inspiration.
Attaches to the xiphoid process, costal margin, 11th/12th ribs, and lumbar vertebrae via arcuate ligaments.
Contraction increases thoracic cavity volume, lowers intrathoracic pressure, and enables lung expansion.

Thoracic Aperture — Openings at the top (superior) and bottom (inferior) of the thoracic cavity.
Intercostal Muscles — Muscles located between ribs, aiding breathing.
Transversus Thoracis — Intrinsic chest wall muscle stabilizing anterior thoracic wall.
Levatores Costarum — Small muscles from thoracic vertebrae to ribs, assisting breathing.
Diaphragm — Main muscle for inspiration, separating thoracic and abdominal cavities.