MUSCLES OF THE BACK

I. MUSCLES OF THE BACK ‑ divisible into three groups: superficial muscles are associated with the upper extremity; intermediate muscles are associated with respiration; deep muscles are associated with movements of the trunk and back.

A. Superficial group (Atlas Fig. 4.28)

1. Trapezius

2. Latissimus dorsi

3. Levator scapulae

4. Rhomboideus minor

5. Rhomboideus major

Note: Thoracolumbar (Lumbar) Fascia ‑ covers deep muscles of back; attached medially to spines of vertebrae; inferiorly to ilium; provides for muscle attachments.

Note: Triangle of Auscultation (Atlas Fig. 4.28)‑ located medial to scapula; bounded inferiorly by Latissimus dorsi, superiorly by Trapezius, laterally by Rhomboideus major; floor of triangle has no large muscles; good place for listening to internal organs with a stethoscope (overlies 6th intercostal space).

B. Intermediate group (Atlas Figs. 4.29, 4.34)

1. Levatores costarum

2. Serratus posterior superior

3. Serratus posterior inferior

C. Deep group ‑ divisible into three sub‑groups: splenius, erector spinae and transversospinalis; individual muscles within a group are named for area in which they are found: (Atlas Figs. 4.30-4.34)

Capitis ‑ insert to head (see Atlas Fig. 4.35, Fig. page 314)

Cervicis ‑ insert to neck

Thoracis ‑ insert to thoracic vertebrae and ribs

Lumborum ‑ insert to lumbar vertebrae

(ex. Iliocostalis Lumborum is part of Iliocostalis found in lumbar region)

Note: All deep muscles extend trunk when they act bilaterally; all are located dorsal to the vertebral column; all are innervated by dorsal (posterior) rami of spinal nerves.

1. Splenius muscles - located deep to trapezius; both splenius muscles have same origins, differ in insertions; often fused. (Atlas Figs. 4.29, 4.30)

a. Splenius Cervicis

b. Splenius Capitis

Note: Both splenius muscles extend the head and neck in bilateral action, rotate head and neck in unilateral action.

2. Erector Spinae ‑ three columns of muscle lying in parallel. (Atlas Figs. 4.30, 4.31, Fig. page 314)

a. Iliocostalis ‑ Origins: Ilium and ribs; Insertions ‑ Ribs and/or transverse processes above (superior to) origin.

b. Longissimus ‑ Origins: Transverse processes; Insertions: transverse processes above origin (Note: capitis inserts to mastoid process of temporal bone).

c. Spinalis ‑ Origins: spinous processes; Insertions: spinous processes above origin

3. Transversospinalis (Atlas. Figs. 4.32, 4.33, Fig. page 314) ‑ All extend from transverse processes of vertebrae and to spines of vertebrae above (except capitis muscles); each part differs in how many vertebrae it extends across; all muscles extend trunk in bilateral action and rotate spinal column in unilateral action.

a. Semispinalis ‑ extend across 5 or 6 vertebrae

b. Multifidus ‑ extend across 3 or 4 vertebrae.

c. Rotatores ‑ extend across 1 or 2 vertebrae.

MUSCLE	ORIGIN	INSERTION	ACTION	NERVE
Trapezius	Skull - External occipital protuberance Fascia - ligamentum nuchae Vertebrae - spines of C7, T1-12	Clavicle - lateral 1/3 Scapula - acromion and spine	Both elevates (upper fibers) and depresses (lower fibers) shoulder; retracts scapula; also extends head	Accessory n. (Cranial nerve XI)
Latissimus dorsi	Vertebrae - spines of T6-T12 Fascia - thoracolumbar fascia Pelvic bone - iliac crest	Humerus - Intertubercular (bicipital) groove	Adducts, extends, and medially rotates arm	Thoracodorsal n.
Levator scapulae	Vertebrae - transverse processes of C1-C4	Scapula - superior angle and medial border	Elevates and adducts scapula	Dorsal scapular n.
Rhomboid minor	Vertebrae - spines of C7, T1	Scapula - Medial border	Elevates and adducts scapula	Dorsal scapular n.
Rhomboid major	Vertebrae - spines of T2-T5	Scapula - Medial border to inferior angle	Elevates and adducts scapula	Dorsal scapular n.

INTERMEDIATE MUSCLES OF THE BACK - Atlas Figs. 4.29, 4.34

MUSCLE	ORIGIN	INSERTION	ACTION	NERVE
Levatores costarum	Vertebrae - Transverse processes of C7, T1-11	Ribs - inferior to origin	Raise ribs in inspiration	Dorsal rami of thoracic spinal nerves
Serratus posterior superior	Vertebrae - Spines of cervical and upper thoracic vertebrae	Ribs	Raise ribs in inspiration	Intercostal nerves
Serratus posterior inferior	Vertebrae - Spines of upper lumbar and lower thoracic vertebrae	Ribs	Lower ribs in expiration	Intercostal nerves

DEEP MUSCLES OF THE BACK - Atlas Figs. 4.30 - 4.34

MUSCLE	ORIGIN	INSERTION	ACTION	NERVE
Splenius	Vertebrae - Spines of T1-T4	Splenius Capitis to Skull - Occipital and temporal bones Splenius Cervicis to Vertebrae - Transverse processes of C2-C3	Extend neck and head (rotate in unilateral action)	Dorsal rami of spinal nerves
Erector Spinae 1) Iliocostalis 2) Longissimus 3) Spinalis	1) Iliocostalis from Ilium and ribs 2) Longissimus from transverse processes of vertebrae 3) Spinalis from spinous processes	1) Iliocostalis to ribs and transverse processes 2) Longissimus to transverse processes of vertebrae 3) Spinalis to spinous processes	Extend trunk and vertebral column	Dorsal rami of spinal nerves
Transverso- spinalis 1) Semispinalis 2) Multifidus 3) Rotatores	All take origin from transverse processes of vertebrae	All insert upon spines of vertebrae superior to origin: Differ in how many vertebrae they extend across 1) Semispinalis extend across 5 or 6 vertebrae 2) Multifidus extend across 3 or 4 vertebrae 3) Rotatores extend across 1 or 2 vertebrae	All extend trunk in bilateral action and rotate vertebral column in unilateral action	Dorsal rami of spinal nerves