Anatomy of the Back Muscles

Study Notes

Divided into extrinsic and intrinsic back muscles
Intrinsic muscles are located deep to the extrinsic muscles, separated by the thoracolumbar fascia

Superficial extrinsic muscles:
- Trapezius
- Latissimus dorsi
- Rhomboid major
- Rhomboid minor
- Levator scapulae
Intermediate extrinsic muscles:
- Serratus posterior superior
- Serratus posterior inferior
Serratus posterior muscles:
- Span from vertebrae to ribs
- Serratus posterior superior:
  - Origin: nuchal ligament and spines C7-T3
  - Insertion: ribs 2-5
  - Nerve supply: intercostal nerves
  - Action: assists breathing by elevating ribs during inspiration
- Serratus posterior inferior:
  - Origin: spines of vertebrae T11-L2
  - Insertion: ribs 9-12
  - Nerve supply: intercostal nerves
  - Action: assists breathing by depressing ribs during expiration

Classified into:
- Superficial intrinsic muscles
- Intermediate intrinsic muscles
- Deep intrinsic muscles

Iliocostalis, longissimus, and spinalis (I Like Standing)
Form a column known as the erector spinae
Situated between the vertebral spinous processes and the costal angle of the ribs
Common tendinous origin:
- Lumbar and lower thoracic vertebrae
- Sacrum
- Posterior aspect of iliac crest
- Sacroiliac and supraspinous ligaments
Nerve supply: posterior rami of the spinal nerves
Actions:
- Bilaterally: extends the vertebral column and head
- Unilaterally: laterally flexes the vertebral column
Iliocostalis:
- Located laterally within the erector spinae
- Associated with the ribs
- Divided into three parts: lumborum, thoracis, and cervicis
- Origin: common tendinous origin
- Insertion: attaches to the costal angle of the ribs and the cervical transverse processes (C3-7)
Longissimus:
- Situated between the iliocostalis and spinalis
- Largest of the three columns
- Divided into three parts: thoracic, cervicis, and capitis
- Origin: common tendinous origin
- Insertion: lower ribs, the transverse processes of C2-T12, and the mastoid process of the skull
Spinalis:
- Located medially within the erector spinae
- Smallest of the three muscle columns
- Divided into three parts: thoracis, cervicis, and capitis (although the cervicis part is absent in some individuals)
- Origin: common tendinous origin
- Insertion: spines of C2-T8 and the occipital bone of the skull

Located underneath the erector spinae
Known collectively as the transversospinales
A group of short muscles, associated with the transverse and spinous processes of the vertebral column
Three major muscles in this group:
- Semispinalis
- Multifidus
- Rotators
Semispinalis:
- Most superficial of the deep intrinsic muscles
- Divided by its superior attachments into thoracic, cervicis, and capitis
- Origin: transverse processes of C4-T10
- Insertion: spines of 5-6 above its origin, and to the occipital bone of the skull
- Nerve supply: posterior rami of the spinal nerves
- Actions:
  - Extends and rotates the head and vertebral column
Multifidus:
- Located underneath the semispinalis muscle
- Best developed in the lumbar area
- Origin:
  - Transverse processes of vertebrae
  - Posterior aspect of sacrum
  - Posterior superior iliac spine (PSIS) of ilium
  - Posterior sacroiliac ligament
- Insertion: spines of the vertebrae 3-4 levels above origin
- Nerve supply: posterior rami of the spinal nerves
- Actions:
  - Stabilizes the vertebral column
  - Bilateral contraction: extension of spine
  - Unilateral contraction: lateral flexion and rotation of vertebral column
Rotators:
- Most prominent in the thoracic region
- Origin: from the vertebral transverse processes
- Insertion: to the spine of the immediately superior vertebrae
- Nerve supply: posterior rami of the spinal nerves
- Action: stabilizes the vertebral column, extension and rotation of vertebral column

Interspinalis: spans between adjacent spinous processes, acts to stabilize the vertebral column
Intertransversari: spans between adjacent transverse processes, acts to stabilize the vertebral column
Levators costarum: originates from the transverse processes of vertebrae and attaches to the rib immediately below, acts to elevate the ribs