The interspinales are short, paired deep muscles of the back that lie in the deepest layer. They stretch between the spinous processes of two adjacent vertebrae. These muscles extend throughout the entire spine. However, they are most developed in the cervical and lumbar regions.

All interspinales receive innervation via the dorsal rami of the spinal nerves. The primary function of the interspinales muscles is to stabilize the spine during movements and maintain an anatomical body posture. They also aid other deep back muscles in extending the spine.

The interspinales muscles can be subdivided into three portions - interspinales cervicis, interspinales thoracis and interspinales lumborum.

Interspinales cervicis

The interspinales cervicis are paired muscles lying deep within the back of the neck and extending between the spinous processes of two adjacent cervical vertebrae. They are located one on either side of the interspinous ligament.

Origin: superior aspects of the spinous processes of the third cervical to first thoracic vertebrae (C3 - T1).

Insertion: inferior aspects of the spinous processes of the second to seventh cervical vertebrae (C2 - C7).

Action: extension of the cervical spine; they participate in stabilizing the cervical spine and maintaining an anatomical posture of the body.

Innervation: dorsal rami of the cervical spinal nerves.

Blood supply: vertebral, deep cervical, occipital and transverse cervical arteries.

Interspinales thoracis

The interspinales thoracis muscles are located within the thoracic spine and extend between the spinous processes of two adjacent thoracic vertebrae. They are usually underdeveloped or even absent, with only some portions having distinct muscle fascicles. Typically, three pairs of the interspinales thoracis muscles are only present.

Origin: superior aspects of the spinous processes of the second (T2), eleventh (T11) and twelfth thoracic (T12) vertebrae.

Insertion: inferior aspects of the spinous processes of the vertebrae one level above (T1, T10 and T11).

Action: these muscles are usually underdeveloped, but they may aid in extension of the thoracic spine.

Innervation: dorsal rami of the thoracic spinal nerves.

Blood supply: superior intercostal, posterior intercostal and subcostal arteries.

Interspinales lumborum

The interspinales lumborum is a group of paired muscles located deep within the lumbar region of the back, extending between the spinous processes of two adjacent lumbar vertebrae.

Origin: superior aspects of the spinous processes of the second to fifth lumbar vertebrae (L2 - L5)

Insertion: inferior aspects of the spinous processes of the first to fourth lumbar vertebrae (L1 - L4).

Action: extension of the lumbar spine; they also participate in stabilizing the lumbar spine and providing an anatomical body posture.

Innervation: dorsal rami of the lumbar spinal nerves.

Blood supply: lumbar arteries.

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Interspinales muscles