Deep Back Muscles

Question 1

The muscles of the deep back can be divided into three layers. What are the muscles of each of the three layers?

Answer 1

Superficial

1) Splenius capitis
2) Splenius cervicis

Intermediate

1) Iliocostalis
2) Longissimus
3) Spinalis

Deep

1) Semispinalis
2) Multifidus
3) Rotatores
4) Interspinales
5) Intertranversalis
6) Levatores costarum

Question 2

Splenius capitis?

Answer 2

The superficial muscles are also known as the spinotransversales. There are two muscles in this group - splenius capitis and splenius cervicis. There are both associated with movements of the head and neck.

They are located of the posterolateral aspect of the neck, covering the deeper neck muscles.

Origin - lower aspect of the ligamentum nuchae, and the spinous process of C7-T3/T4 vertebrae.

Insertion - fibres ascend, attaching to the mastoid process and the occipital bone of the skull.

Innervation - posterior rami of the spinal nerves C3 and C4.

Actions - rotate head to the same side.

Question 3

Splenius cervicis?

Answer 3

Origin - spinous processes of T3-T6 vertebrae.

Insertion - fibres ascend, attaching to the transverse processes of C1 - C3/4.

Innervation - posterior rami of the lower cervical spinal nerves.

Actions - rotate head to the same side.

Note: the two splenius muscles can also act together to extend the head and neck.

Question 4

Iliocostalis?

Answer 4

The muscles of the intermediate deep back form a column, known as the erector spinae.

The erector spinae is situated posterolaterally to spinal column, between the vertebral spinous processes and costal angle of the ribs.

All three muscles can be subdivided by their superior attachments (into lumborum, thoracic, cervicis and capitis). They also all have a common tendinous origin, which arises from:

• Lumbar and lower thoracic vertebrae
• Sacrum
• Posterior aspect of iliac crest
• Sacroiliac and supraspinous ligaments

The iliocostalis muscle is located laterally within the erector spinae. It is associated with the ribs and can be divided into three parts - lumborum, thoracis, and cervicis.

Origin - arises from the common tendinous origin.

Insertion - costal angle of the ribs and the cervical transverse processes.

Innervation - posterior rami of the spinal nerves.

Actions - acts unilaterally to laterally flex the vertebral column. Acts bilaterally to extend the vertebral column and head.

Question 5

Longissimus?

Answer 5

The longissimus muscle is situated between the iliocostalis and spinalis. It is the largest of the three columns. It can be divided into three parts - thoracic, cervicis and capitis.

Origin - arise from the common tendinous origin

Insertion - lower ribs, the transverse processes of C2-T12, and the mastoid process of the skull.

Innervation - posterior rami of the spinal nerves.

Actions - acts unilaterally to laterally flex the vertebral column. Acts bilaterally to the extend the vertebral column and the head.

Question 6

Spinalis?

Answer 6

The spinalis muscle is located medially within the erector spinae. It is the smallest of the three muscle columns. It can be divided into the thoracic, cervicis and capitis (although the cervicis part is absent in some individuals).

Origin - arises from the common tendinous origin.

Insertion - spinous processes of C2. T1-T8, and the occipital bone of the skull.

Innervation - posterior rami of the spinal nerves.

Actions - acts unilaterally to laterally flex the vertebral column. Acts bilaterally to extends the vertebral column and head.

Question 7

Semispinalis?

Answer 7

These deep portion of the deep back muscles are located beneath the erector spinae muscles, and are collectively known as the transversospinales. They are a group of short muscles, associated with the transverse and spinous processes of the vertebral column.

The semispinalis is the most superficial of the deep intrinsic muscles. Much like the intermediate muscles, it can be divided by its superior attachments into thoracic, cervicis and capitis.

Origin - transverse processes of C4-T10

Insertion - fibres ascend 4-6 vertebral segments, attaching to the spinous processes of C2-T4, and to the occipital bone of the skill.

Innervation - posterior rami of the spinal nerves.

Actions - Extends and and contralaterally rotates the head and the vertebral column.

Question 8

Multifidus?

Answer 8

The multifidus is located underneath the semispinalis muscle. It is best developed in the lumbar area.

Origin - has a broad origin - arises from the sacrum, posterior iliac spine, common tendinous origin of the erector spinae, mamillary processes of the lumbar vertebrae, transverse processes of T1-T3 and articular processes of C4-C7.

Insertion - fibres ascend 2-4 vertebral segments, attaching the spinous processes of the vertebrae.

Innervation - posterior rami of the spinal nerves.

Actions - stabilises the vertebral column.

Question 9

Rotatores?

Answer 9

The rotatores are most prominent in the thoracic region.

Origin - vertebral transverse processes.

Insertion - fibres ascend and attach to the lamina and spinous processes of the immediately superior vertebrae.

Innervation - porsterior rami of the spinal nerves.

Actions - stabilises the vertebral column, and has a proprioceptive function.

Question 10

Other minor deep intrinsic muscle?

Answer 10

1) Interspinales - spans between adjacent spinous processes. Acts to stablise the the vertebral column.
2) Intertransversari - spans between adjacent transverse processes. Acts to stablise the vertebral column.
3) Levatores costarum - originates from the transverse processes of C7-T11, and attaches to the rib immediately below. Acts to elevate the ribs.