Muscles of the Back

Question 1

i. Trapezius

Answer 1

1. Origin – external occipital protuberance, ligamentum nuchae, spinous processes of C7 to T12
2. Insertion – posterior border of lateral third of the clavicle, acromion process, and spine of the scapula
3. Innervation – spinal root of the accessory n. CN XI
4. Action – elevation from the upper fibers, retraction from the middle fibers and depression from the lower fibers

Question 2

ii. Latissimus Dorsi

Answer 2

1. O – spinous processes of the vertebrae T7-L5, thoracolumbar fascia, iliac crest, inferior 3 to 4 ribs and inferior angle of the scapula
2. I – medial lip of intertubercular groove of the humerus (anterior to teres major)
3. N – thoracodorsal n.
4. A – extends, adducts and medially rotates the humerus, elevates the body when climbing

Question 3

iii. Levator Scapulae

Answer 3

1. O – posterior tubercles of transverse processes of C1 to C4 vertebrae
2. I – superior part of the medial border of the scapula
3. N – dorsal scapular nerve (C4-5)
4. A – elevates scapula, rotates head to the same side

Question 4

iv. Rhomboid major

Answer 4

1. O – spinous process of T2 to T5 vertebrae
2. I – medial border of the scapula from the level of the spine to the inferior angle
3. N – dorsal scapular n. (C4-5)
4. A – retracts and downwardly rotates the scapula

Question 5

v. Rhomboid minor

Answer 5

1. O – spinous processes of C7 and T 1 and the ligamentum nuchae
2. I – medial border of the scapula from the level of the spine to the inferior angle
3. N – dorsal scapular n. (C4-5)
4. A – retracts and downwardly rotates the scapula

Question 6

i. Serratus Posterior Superior

Answer 6

1. 0 – ligamentum nuchae, spinous process of C7 thru T3
2. I – 2nd to 5th ribs
3. N – ventral primary rami of first 3 to 4 thoracic nerves
4. A – elevates the superior 4 ribs to increase the size of the thorax

Question 7

ii. Serratus Posterior Inferior

Answer 7

1. 0 – spinous processes of T11 thru L2
2. I – the inferior three or four ribs
3. N – ventral primary rami of last 4 thoracic nerves
4. A – depress the inferior 3 to 4 ribs to prevent superior pull by the diaphragm

Question 8

a. Splenius capitis

Answer 8

i. 0 – ligamentum nuchae and spinous processes of C7 to T3
ii. I – mastoid process, occipital bone
iii. N – dorsal primary rami
iv. A – rotate the head and neck to the same side; neck and head extension

Question 9

b. Splenius Cervicis

Answer 9

i. O – Spinous processes of T3 to T6
ii. I – Transverse processes of C1 to C4
iii. N – dorsal primary rami
iv. A – rotate the head and neck to the same side; extend head and neck

Question 10

The Erector Spinae Muscles

Answer 10

i. Origin – broad tendon that attaches to the iliac crest, sacrum, sacroiliac ligaments, and sacral and inferior lumbar spinous processes
ii. Innervation – dorsal primary rami
iii. The three vertical columns from lateral to medial are:
1. Iliocostalis – lateral column
2. Longissimus – intermediate column
3. Spinalis – medial column

Question 11

iv. Iliocostalis – 3 parts

Answer 11

1. Lumborum – iliac crest and attaches into the angles of the inferior six ribs
2. Thoracis – arises from the six lower ribs and attaches to the six upper ribs
3. Cervicis - arises from the six upper ribs and attaches to the transverse processes of the lower cervical vertebrae 4 to 6

Question 12

v. Longissimus - 3 parts

Answer 12

1. Thoracis - arises from the lower lumbar spinous processes and sacrum and attaches to the lower nine ribs and associated transverse processes
2. Cervicis - arises from transverse processes of T1-4 or 6 and attaches to transverse processes of C2-6
3. Capitis - arises from lower four cervical vertebrae and attach to the mastoid process of the temporal bone

Question 13

vi. Spinalis

Answer 13

1. Origin – spinous processes of T11-L2
2. Insertion – spinous process of the upper 4 to 8 thoracic vertebrae
3. Action – extensors of the vertebral column

Question 14

c. Semispinalis

Answer 14

i. Divided into three parts: thoracis, cervicis, capitis
ii. It is best developed in the cervical region. Semispinalis Capitis arises from the transverse processes of T1 to T6 and inserts on occipital bone
iii. The fibers of the Semispinalis tend to span 5 to 6 segments
iv. Action – Semispinalis capitis bilaterally extends the head, and unilaterally it rotates the head to the same side
v. Innervation – dorsal rami of the cervical spinal nerves

Question 15

d. Multifidus

Answer 15

i. Muscles are found from C2 to S4 vertebrae. Most prominent (and most topical) in the lumbar region
ii. They originate from the vertebral arches and insert on the spinous processes, spanning 1 to 3 vertebrae
iii. Action – unilaterally – flexes the trunk laterally, rotates vertebra to the opposite side. Bilaterally – extends the trunk
iv. innervation – dorsal rami of the spinal nerves

Question 16

e. Rotatores

Answer 16

i. They are found along the entire length of the vertebral column. Easiest to observe in the thoracic region
ii. Arise from the transverse process of one vertebrae and insert into the base of the spinous process of the superior vertebrae
iii. Action – rotation of the superior vertebrae to opposite side (Functionally, they probably serve a proprioceptive role rather than biomechanical role)
iv. Innervation – dorsal rami of spinal nerves