Anatomy for MRCEM primary exam

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Upper limb Anatomy

Pectoralis Minor muscle

Surface markings, actions and nerve supply of Pectoralis minor

Origin3,4,5th ribs
InsertionCoracoid process of Scapula
Nerve supplyMedial Pectoral nerve
ActionsDraws the scapula down and forwards and elevates the ribs
Pectoralis minor Origin and Insertions

Pectoralis minor Origin and Insertions – Image modified from BodyParts3D, © The Database Center for Life Science licensed under CC Attribution-Share Alike 2.1 Japan

The Pectoralis Minor muscle lies underneath the Pectoralis major in the chest – frontal aspect. It originates from 3rd to 5th ribs and inserts on to the coracoid process of Clavicle as shown in the image.

Regarding actions, if the muscle contracts there 2 possibilities, if ribcage is kept stationary, it will draw scapula down and forward. Similarly, if Scapula is stabilized, rib cage will be pulled up to elevate (helps in deep inspiration).

Thoracic outlet syndrome

Compression and irritation of the neurovascular structures of upper limb. (brachial plexus and the blood vessels – subclavian and axillary arteries and veins) will lead to pain, swelling in the upper limb.

Possibility of compression at 3 regions: (numbered on the image below)

  1. between the anterior and middle scalene muscles, and the 1st rib; (more on this in Thorax module)
  2. between the clavicle and first rib
  3. in the subcoracoid space between the pectoralis minor tendon and it’s attachment on coracoid process.
Thoracic outlet syndrome possible locations of compression.
Thoracic outlet syndrome possible locations of compression.

Check previous lesson for Pectoralis Major and Next lesson for Trapezius muscle.