Interspinales

The interspinales (Latin: musculi interspinales) are short, paired deep muscles of the back that lie in the deepest layer of the group. They extend between the spinous processes of two adjacent vertebrae. The interspinales extend throughout the entire length of the spine. However, they are most developed in the cervical and lumbar regions. In the thoracic region, they are underdeveloped or often completely absent. The primary function of the interspinales muscles is to stabilize the spine during movements and maintain a body posture. They also aid other deep back muscles in extending the spine.

Interspinales cervicis

The interspinales cervicis (Latin: musculi interspinales cervicis) are paired muscles lying deep within the back of the neck, extending between the spinous processes of two adjacent cervical vertebrae.

Origin

The interspinales cervicis muscles originate from the superior aspects of the spinous processes of the third cervical to first thoracic vertebrae (C3 - T1).

Insertion

The interspinales cervicis are located on either side of the interspinous ligaments. These muscles insert one level above the origin sites on the inferior aspects of the spinous processes of the second to seventh cervical vertebrae (C2 - C7), respectively.

Action

The interspinales cervicis muscles provide the extension of the cervical spine. Most importantly, these muscles stabilize the cervical spine and maintain a body posture.

Innervation

The interspinales cervicis are innervated by the dorsal rami of the cervical spinal nerves.

Blood supply

The arterial blood supply to the interspinales cervicis muscles is provided by the branches of the vertebral, deep cervical, occipital and transverse cervical arteries. The vertebral artery arises from the subclavian artery, while the occipital artery is a branch of the external carotid artery. The deep cervical artery branches off the costocervical trunk, and the transverse cervical artery originates from the thyrocervical trunk.

Interspinales thoracis

The interspinales thoracis (Latin: musculi interspinales thoracis) are deep muscles of the thoracic region of the back, extending between the spinous processes of two adjacent thoracic vertebrae. These muscles are usually underdeveloped or absent, with only some areas having distinct muscle fascicles. Typically three pairs of the interspinales thoracis muscles are only present.

Origin

The three pairs of the interspinales thoracis muscles arise from the superior aspects of the spinous processes of the second (T2), eleventh (T11) and twelfth thoracic vertebrae (T12). However, the origin sites of the interspinales thoracis can vary.

Insertion

Each interspinales thoracis muscle attaches to the inferior aspects of the spinous processes of the vertebra one level above the origin site. They insert on the first (T1), tenth (T10) and eleventh thoracic vertebrae (T11) accordingly to the origin sites.

Action

The interspinales thoracis are usually underdeveloped muscles, but they may aid in extending the thoracic spine.

Innervation

The interspinales thoracis are innervated by the dorsal rami of the thoracic spinal nerves.

Blood supply

These interspinales thoracis muscles are supplied by the branches of the superior and posterior intercostal arteries and subcostal artery. The superior intercostal artery arises from the costocervical trunk, while the posterior intercostal artery originates from the superior intercostal artery and thoracic aorta. And finally, the subcostal artery is also a branch of the thoracic aorta.

Interspinales lumborum

The interspinales lumborum (Latin: musculi 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

The fibers of the interspinales lumborum muscles originate from the superior aspects of the spinous processes of the second to fifth lumbar vertebrae (L2 - L5).

Insertion

The interspinales lumborum muscles insert on the inferior aspects of the spinous processes of the adjacent vertebrae one level above the origin site - on the first to fourth lumbar vertebrae (L1 - L4), accordingly.

Action

The interspinales lumborum muscles stabilize the lumbar spine and provide a body posture, and they also aid in the extension of the lumbar spine.

Innervation

The interspinales lumborum are innervated by the dorsal rami of the lumbar spinal nerves.

Blood supply

The arterial blood supply to the interspinales lumborum muscles is provided mainly by the lumbar arteries that arise from the abdominal aorta.