Overview
This lecture outlines the key steps and anatomical structures involved in the dissection of the posterior triangle of the neck, with emphasis on its boundaries, contents, and clinical importance.
Introduction to the Posterior Triangle
- The posterior triangle is a key anatomical area on the lateral aspect of the neck.
- Dissection of this region helps reveal important nerves, vessels, and muscles.
Boundaries of the Posterior Triangle
- Anterior border: posterior edge of the sternocleidomastoid muscle.
- Posterior border: anterior edge of the trapezius muscle.
- Inferior border: middle third of the clavicle.
- Apex: where sternocleidomastoid and trapezius meet on the superior nuchal line.
Major Contents of the Posterior Triangle
- Muscles: splenius, levator scapulae, and the scalene group (anterior, middle, posterior).
- Nerves: spinal accessory nerve (CN XI), roots of the brachial plexus, cervical plexus, and phrenic nerve.
- Vessels: external jugular vein, subclavian artery, transverse cervical artery, suprascapular artery.
- The omohyoid muscle crosses the triangle and divides it into occipital and supraclavicular (subclavian) triangles.
Dissection Steps & Tips
- Identify and reflect (move aside) the sternocleidomastoid and trapezius muscles.
- Trace the external jugular vein as it traverses the triangle superficially.
- Locate the spinal accessory nerve crossing the triangle.
- Expose branches of the cervical and brachial plexuses deep to the muscles.
- Observe the floor of the triangle, which includes the scalene muscles.
Clinical Relevance
- Knowledge of structures in the posterior triangle is critical for nerve blocks and vascular access.
- Injury to the spinal accessory nerve during procedures can cause trapezius muscle weakness.
Key Terms & Definitions
- Posterior triangle — an anatomical region of the neck bounded by the sternocleidomastoid, trapezius, and clavicle.
- Sternocleidomastoid — a major neck muscle forming the anterior border of the triangle.
- Trapezius — a large back muscle forming the posterior border.
- Brachial plexus — a network of nerves supplying the upper limb, passing through the triangle.
- Spinal accessory nerve (CN XI) — innervates the trapezius and sternocleidomastoid muscles.
- Omohyoid muscle — muscle dividing the posterior triangle into two smaller triangles.
- Cervical plexus — a network of nerves supplying the neck and diaphragm.
Action Items / Next Steps
- Review the dissection steps PDF linked in the course resources.
- Study the diagrams of the posterior triangle and its contents.
- Prepare for hands-on identification of nerves and vessels during laboratory dissection.