Coracobrachialis

Arm · Upper Limb

Coracobrachialis belongs to the Arm group of the Upper Limb. Originating at Coracoid process of scapula, it inserts at Middle third of medial surface of humerus. Its chief action is that it flexion and adduction of arm at the shoulder. Its nerve supply is the Musculocutaneous nerve (C5, C6, C7).

Origin, Insertion, Action & Nerve

Origin

Coracoid process of scapula

Insertion

Middle third of medial surface of humerus

Action

Flexion and adduction of arm at the shoulder

Nerve

Musculocutaneous nerve (C5, C6, C7)

Attachments explained

The Coracobrachialis is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.

Origin

Coracoid process of scapula

Insertion

Middle third of medial surface of humerus

Action & function

When the Coracobrachialis contracts, it produces the following movement: Flexion and adduction of arm at the shoulder.

As part of the Arm group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.

Nerve supply & clinical relevance

The Coracobrachialis receives its nerve supply from the Musculocutaneous nerve (C5, C6, C7). This nerve carries fibres from spinal segment(s) C5, C6, C7.

Because a muscle can only contract when its nerve is intact, injury to the Musculocutaneous nerve or to its spinal roots (C5, C6, C7) can weaken or paralyse the Coracobrachialis, impairing the movements it normally produces (flexion and adduction of arm at the shoulder). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Coracobrachialis (the OIANS method)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Coracobrachialis, work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.

Most students remember the Coracobrachialis fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.