Interspinales thoracis muscles

At a glance

English

Interspinales thoracis muscles

Latin (TA2)

Musculi interspinales thoracis

System

Muscle

Region

Back

Side

Paired, left and right

About the interspinales thoracis muscles

The interspinales are short muscles of the deepest layer of the back, each bridging the gap between the spines of two neighbouring vertebrae. They are well formed in the neck and the lumbar region, where the spines are broad and the spine bends freely. In the thoracic region the spines are long and overlapping, movement between them is limited, and the muscles are poorly developed.

Thoracic interspinales are therefore present only at the ends of the region. A pair is usually found between T1 and T2, continuing the cervical series, and sometimes also between T2 and T3. At the lower end, a pair may be present between T11 and T12, where the spine begins to take on lumbar form. Elsewhere they are usually missing or replaced by fibrous tissue.

Where present, each muscle runs straight up from one spine to the next and lies beside the interspinous ligament. Its pull can help to extend the spine and keep the segment steady, but the force is tiny. Its likely main role, as with other small segmental muscles, is to provide information on the position and movement of the vertebrae.

They are supplied by medial branches of the dorsal rami of the thoracic spinal nerves and receive blood from the dorsal branches of the posterior intercostal arteries. Their scarcity in the thoracic region reflects the stiffness given to that part of the spine by the ribs.

Attachments, action and supply

Origin

Spinous process of a thoracic vertebra, at the top or bottom of the thoracic region.

Insertion

Spinous process of the vertebra immediately above.

Action

Help to extend and steady the spine segment by segment; signal vertebral position.

Nerve supply

Medial branches of the dorsal rami of the thoracic spinal nerves.

Blood supply

Dorsal branches of the posterior intercostal arteries.