Interspinales Thoracis 1–3
Back · Trunk
The interspinales thoracis are short, paired muscles that bridge the gap between adjacent spinous processes in the upper thoracic region, where they are only inconsistently developed. Each fascicle runs from the superior surface of one thoracic spinous process to the inferior surface of the spinous process of the vertebra immediately above, lying on either side of the interspinous ligament. Because their fibres are oriented almost vertically and sit close to the axis of the spine, they are poorly placed to generate powerful movement and instead act as short extensors that pull neighbouring spinous processes together. They contribute to extension of the thoracic vertebral column and, more importantly, to fine segmental stabilisation between vertebrae. They are supplied by the posterior (dorsal) rami of the thoracic spinal nerves.
Origin, Insertion, Action & Nerve
Origin
Superior surface of a thoracic spinous process
Insertion
Inferior surface of the spinous process of the vertebra above
Action
Extends the thoracic vertebral column and stabilizes adjacent vertebrae
Nerve
Posterior (dorsal) rami of thoracic spinal nerves
Attachments explained
The Interspinales Thoracis 1–3 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
Superior surface of a thoracic spinous process
Insertion
Inferior surface of the spinous process of the vertebra above
Action & function
When the Interspinales Thoracis 1–3 contracts, it produces the following movement: Extends the thoracic vertebral column and stabilizes adjacent vertebrae.
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 Interspinales Thoracis 1–3 receives its nerve supply from the Posterior (dorsal) rami of thoracic spinal nerves.
Because a muscle can only contract when its nerve is intact, injury to the Posterior can weaken or paralyse the Interspinales Thoracis 1–3, impairing the movements it normally produces (extends the thoracic vertebral column and stabilizes adjacent vertebrae). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Interspinales Thoracis 1–3 (the OIANS method)
Study these as one member of a family of tiny, spine-to-spine and transverse-process-to-transverse-process muscles. The name tells you everything you need: inter means between, spinales means spinous processes, and thoracis places them in the thorax. If you fix that its origin is the spinous process below and its insertion is the spinous process above, the vertical pull that produces extension follows without memorising a separate action.
Anchor the nerve supply by the rule that the deep intrinsic back muscles are all served by posterior (dorsal) rami. Group the interspinales thoracis mentally with their cervical and lumbar counterparts, since they differ only in the region they occupy and the number of segments involved. Remembering that they are best developed in the more mobile cervical and lumbar regions helps explain why the thoracic set spans only the first few levels.
Frequently asked questions
Where is the Interspinales Thoracis 1–3 located?
The Interspinales Thoracis 1–3 is a muscle of the Back group, located in the Trunk.
What is the origin of the Interspinales Thoracis 1–3?
Superior surface of a thoracic spinous process
What is the insertion of the Interspinales Thoracis 1–3?
Inferior surface of the spinous process of the vertebra above
What movements does the Interspinales Thoracis 1–3 produce?
Extends the thoracic vertebral column and stabilizes adjacent vertebrae
What nerve supplies the Interspinales Thoracis 1–3?
Posterior (dorsal) rami of thoracic spinal nerves
Is the Interspinales Thoracis 1–3 free to study in OIANS?
The Interspinales Thoracis 1–3 is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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