Anatomy of the Back Muscles

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

10 Questions