Overview
This lecture covers the major muscles of the trunk, including both anterior (front) and posterior (back) muscles, their locations, layers, attachment points, and functions.
Anterior Trunk Muscles (Superficial Layer)
- Platysma is a thin muscle that covers the neck and tenses the skin.
- Pectoralis Major attaches to the sternum and humerus (intertubercular groove) and adducts and internally rotates the arm.
- Rectus Abdominis flexes the abdomen anteriorly and increases intra-abdominal pressure; it’s divided by tendinous intersections and covered by the rectus sheath.
- Linea Alba is a white midline tendinous line connecting rectus sheath from xiphoid process to pubic bone.
Anterior Trunk Muscles (Deep Layers)
- Serratus Anterior attaches to true ribs and the medial border of the scapula; moves the scapula and assists in raising arms above the head and forced breathing.
- External Oblique has V-shaped fibers, contributes to the rectus sheath.
- Internal Oblique has triangle-shaped fibers, located deep to the external oblique, also contributes to the rectus sheath.
- Transversus Abdominis has horizontal fibers and is the deepest abdominal muscle.
- Inguinal Ligament runs from the anterior superior iliac spine (ASIS) to the pubis.
Deep Anterior Trunk Muscles
- Pectoralis Minor attaches to coracoid process of scapula and ribs 3–5; moves scapula and acts as accessory muscle for inspiration when shoulders are fixed.
- Intercostal Muscles include three layers: external (V-shaped fibers), internal (perpendicular fibers), and innermost (not visible here); involved in breathing.
Posterior Trunk Muscles (Superficial Layer)
- Trapezius attaches from occipital condyle and spinous processes to the scapula; elevates, retracts, and depresses scapula depending on fiber direction.
- Deltoid attaches to spine of scapula and deltoid tuberosity of humerus; principal abductor of the arm.
- Latissimus Dorsi attaches to spinous processes of T7–L5 and humerus; extends, adducts, and helps internally rotate the arm.
Posterior Trunk Muscles (Deep Layer)
- Levator Scapulae attaches to superior medial border of scapula and transverse processes of cervical vertebrae; elevates scapula.
- Rhomboid Major and Minor retract and slightly elevate scapula; attach to medial border of scapula.
- Serratus Posterior Inferior (not detailed) is mentioned.
- Erector Spinae group maintains posture and balance by extending the spine.
Key Terms & Definitions
- Trunk — The central part of the body excluding limbs and head.
- Rectus Sheath — Tendinous sheath covering the rectus abdominis.
- Linea Alba — Midline white tendinous line in the abdomen.
- Inguinal Ligament — Ligament running from the ASIS to the pubis.
- Intertubercular Groove — Groove on the humerus for muscle attachment.
- Spinous Process — Bony projection off the posterior (back) of each vertebra.
- Transverse Process — Bony projection on the side of each vertebra.
Action Items / Next Steps
- Review the muscle layers and their attachments for both anterior and posterior trunk in your textbook.
- Prepare for lab by identifying these muscles on anatomical models or diagrams.
- Watch the next video on the pectoral girdle, rotator cuff, and upper limb muscles.