Autochthonous back muscles

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The autochthonous back muscles ("local back muscles") form the most important part of the active musculoskeletal system of the back in vertebrates and lie directly on the axial skeleton as the original deep muscle layer.

In contrast to the overlying allochthonous ("immigrated") trunk and shoulder girdle muscles (e.g. latissimus dorsi muscles , trapezius muscles ), the autochthonous muscles of the back develop in an individual where they are located. It extends on both sides along the spine from the pelvis over the chest to the head and is often called the erector spinae muscle because of its function as an erector and stabilizer of the spine . In addition to the developmental criterion, the autochthonous back muscles are defined by two anatomical features:

  • It is innervated from the dorsal branches ( rami dorsales ) of the spinal nerves , while the remaining skeletal muscles are innervated by the abdominal branches ( rami ventrales ) of the spinal nerves,
  • and it lies wrapped in the thoracolumbar fascia .

With this definition, the autochthonous back muscles do not include any muscles of the trunk of anterior origin (such as the intercostal muscles , the abdominal muscles or the serrati anterior , posterior superior and posterior inferior muscles ). The levatores costarum muscles lie partly outside the thoracolumbar fascia and experience a double innervation of rami dorsales and rami ventrales of the spinal nerves, which is why they are not dealt with in some textbooks together with the remaining autochthonous back muscles.

The autochthonous musculature of the back includes several rows of muscle systems extending to different extents in two tracts

According to its innervation via lateral or medial branches from the Rr. Dorsales , the autochthonous back muscles can be divided into two tracts on each side, a lateral and a medial tract, the muscles of which are each divided into different systems.

Lateral tract ( tractus lateralis )

The lateral or superficial tract is innervated by the lateral rami of the dorsal (or posterior) rami.

Intertransversales System ( Systema intertransversale )

The intertransversal system consists of muscles that pull from a transverse process ( processus transversus ) to a transverse process of a vertebra located further towards the head. These intertransversarii muscles can be divided into:

  • The intertransversarii mediales lumborum muscles connect the accessorii processes of neighboring lumbar vertebrae .
The intertransversarii laterales lumborum muscles connect the transverse processes of adjacent lumbar vertebrae and, strictly speaking, are not part of the autochthonous back muscles, as they are innervated by the ventral branch. They can be seen as analogues of the intercostal muscles.
  • The intertransversarii thoracis muscles connect the transverse processes of adjacent thoracic vertebrae .
  • The intertransversarii posteriores cervicis muscles connect the tubercula posteriora of adjacent cervical vertebrae .
The intertransversarii anteriores cervicis muscles connect the anterior tuberosity of adjacent cervical vertebrae and, strictly speaking, are not part of the autochthonous back muscles. They too can be seen as analogues of the intercostal muscles.

When activated on one side, these muscles cause the spine to incline; when both sides contract, the spine is stretched.

Spinotransversales System ( Systema spinotransversale )

The muscles contract by the spinous processes ( spinous processes ) to transverse processes of the vertebrae further cephalad. Only two muscles belong to this system:

With unilateral activation, these muscles cause the cervical spine and head to rotate to the activation side. With bilateral contraction, they cause the cervical spine and head to stretch.

Sacrospinal system ( Systema sacrospinale )

There are two muscles involved in this system. They arise in the pelvis and insert on the transverse processes and the ribs .

  • Musculus longissimus (thoracis, cervicis et capitis): Unilateral activation causes the spine and head to tilt and the head to turn to the same side. Activation on both sides stretches the spine and head.
  • Musculus iliocostalis (lumborum, thoracis et cervicis): The one-sided activation causes a tilt, the bilateral a stretching of the spine.

Rib lifting muscles ( Musculi levatores costarum )

The levatores costarum muscles run obliquely downwards (caudally and laterally) from the transverse processes to the next lower rib ( levatores costarum breves ) or to the next lower rib ( levatores costarum longi ). Contrary to what they are called, these muscles do not lift the ribs , but rather pull the vertebral body downwards, thus causing sideways flexion when contracting on one side and dorsal extension when contracting on both sides (straightening the spine ).

Medial tract ( Tractus medialis )

The tractus medialis or profundus is innervated from the rami mediales to the rami dorsales (or posteriores).

Interspinous system ( Systema interspinale )

The muscles of the interspinous system move from one spinous process to a spinous process further towards the head. If they skip a segment, they are called the interspinous muscles , if they skip more than one segment, they are called the spinal muscles :

Transversospinal system ( Systema transversospinale )

The muscles of this system pull vertebrae lying further cephalad from the transverse processes to the spinous processes. They are named differently depending on their length. If a muscle skips a segment, it is called the rotator brevis muscle , with two segments rotator longus , between three and five segments it is called multifidus and from six segments it is called semispinalis :

Suboccipital muscles ( Musculi suboccipitales of the Trigonum suboccipitale )

The four short neck muscles on each side also belong to the autochthonous back muscles; they form the rear group of the suboccipital muscles ( Musculi suboccipitales ) in humans

The deep or short neck muscles belong to the suboccipital muscles ( Musculi suboccipitales ) and are supplied from an (unofficial) network of rami dorsal (or posterior ) cervical spinal nerves . They are of particular importance for the finely tuned rotation, inclination and dorsiflexion of the head, with which moving objects in view can be followed, or for fine adjustments to the head posture. They stretch under the occiput in the shape of a triangle ( Trigonum suboccipitale ), as

While the first three neck muscles are innervated via the medial branch, the superior obliquus capitis is innervated by the lateral branch of the dorsal branch of the 1st cervical spinal nerve (C1) and is therefore not assigned to the medial but to the lateral tract.

The functionally similar musculus rectus capitis lateralis as well as the musculus rectus capitis anterior - a prevertebral neck muscle, tilting the head and bending slightly forward, do not belong to the autochthonous muscles of the back ; these are of ventral origin, as shown by their supply by the ventral rami of the superior spinal nerves. However, the two are combined as the front group with the previously mentioned four neck muscles of the rear group as the suboccipital muscles .

literature

H. Frick, H. Leonhardt, D. Starck: Special anatomy. Volume 1, Issue 4, chapter arrangement and innervation of the autochthonous back muscles. Georg Thieme Verlag 1992, ISBN 9783133569040 .

Individual evidence

  1. ↑ H. Frick, H. Leonhardt, D. Starck: Spezial Anatomie. Volume 1, Thieme 1992, ISBN 9783133569040 , p. 490f.