Latissimus Dorsi

Back · Trunk

Located in the Back of the Trunk, the Latissimus Dorsi is a key muscle for anatomy study. Its origin is Spinous processes of T7–T12, thoracolumbar fascia, iliac crest, and lower 3–4 ribs, and it inserts onto Floor of intertubercular (bicipital) groove of humerus. Its chief action is that it extension, adduction, and medial rotation of arm. Its nerve supply is the Thoracodorsal nerve (C6, C7, C8).

Origin, Insertion, Action & Nerve

Origin

Spinous processes of T7–T12, thoracolumbar fascia, iliac crest, and lower 3–4 ribs

Insertion

Floor of intertubercular (bicipital) groove of humerus

Action

Extension, adduction, and medial rotation of arm

Nerve

Thoracodorsal nerve (C6, C7, C8)

Attachments explained

The Latissimus Dorsi 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

Spinous processes of T7–T12, thoracolumbar fascia, iliac crest, and lower 3–4 ribs

Insertion

Floor of intertubercular (bicipital) groove of humerus

Action & function

When the Latissimus Dorsi contracts, it produces the following movement: Extension, adduction, and medial rotation of arm.

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

Nerve supply & clinical relevance

The Latissimus Dorsi receives its nerve supply from the Thoracodorsal nerve (C6, C7, C8). This nerve carries fibres from spinal segment(s) C6, C7, C8.

Because a muscle can only contract when its nerve is intact, injury to the Thoracodorsal nerve or to its spinal roots (C6, C7, C8) can weaken or paralyse the Latissimus Dorsi, impairing the movements it normally produces (extension, adduction, and medial rotation of arm). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Latissimus Dorsi (the OIANS method)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Latissimus Dorsi, 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 Latissimus Dorsi 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.