Transversus Thoracis

Thorax · Trunk

The Transversus Thoracis is found among the Thorax muscles of the Trunk. It arises from Posterior surface of the lower body of the sternum and xiphoid process and attaches to Internal surfaces of the costal cartilages of ribs 2–6. Its chief action is that it depresses the costal cartilages, weakly aiding expiration. Innervation is provided by the Intercostal nerves (T2–T6).

Origin, Insertion, Action & Nerve

Origin

Posterior surface of the lower body of the sternum and xiphoid process

Insertion

Internal surfaces of the costal cartilages of ribs 2–6

Action

Depresses the costal cartilages, weakly aiding expiration

Nerve

Intercostal nerves (T2–T6)

Attachments explained

The Transversus Thoracis 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

Posterior surface of the lower body of the sternum and xiphoid process

Insertion

Internal surfaces of the costal cartilages of ribs 2–6

Action & function

When the Transversus Thoracis contracts, it produces the following movement: Depresses the costal cartilages, weakly aiding expiration.

As part of the Thorax 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 Transversus Thoracis receives its nerve supply from the Intercostal nerves (T2–T6). This nerve carries fibres from spinal segment(s) T2, T6.

Because a muscle can only contract when its nerve is intact, injury to the Intercostal nerves or to its spinal roots (T2, T6) can weaken or paralyse the Transversus Thoracis, impairing the movements it normally produces (depresses the costal cartilages, weakly aiding expiration). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Transversus Thoracis (the OIANS method)

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