12.2 Muscles of the Deep Back

Question 1

What nerves innervate the intrinsic muscles of the back?

Answer 1

Posterior rami of spinal nerves.

Question 2

Identify the splenius capitis muscle, its attachments, function, and innervation.

Answer 2

• Attachments: medially to nuchal ligament and spinous processes of C7-T3; superolaterally to mastoid process and superior nuchal line of occiput
• Action: unilateral – laterally flexes neck, rotates head; bilateral – extends head/neck
• Innervation: posterior rami of spinal nerves.

Question 3

Identify the Splenius cervicis muscle, its attachments, function, and innervation.

Answer 3

o Attachments: medially to nuchal ligament and spinous processes of C7-T4; superolaterally to posterior tubercles of C1-C4
o Action: unilateral – laterally flexes neck, rotates head; bilateral – extends head/neck
-Innervation: posterior rami of spinal nerves.

Question 4

Identify the 3 muscles that constitute the erector spinae muscles.
-Describe the attachments for each, as well as their general function and innervation.

Answer 4

• 3 columns that attach to a broad tendon from the posterior iliac crest, posterior sacrum, sacroiliac ligaments, lumbosacral spinous processes, and supraspinous ligaments
• Action: unilaterally, lateral flexion of vertebral column; bilaterally, extension of vertebral column and head
• Innervation: posterior rami of spinal nerves.

o Spinalis (capitis, cervicis, thoracis)
• Medial column
• Fibers rise up to spinous processes in upper thorax and cranium
o Longissimus (capitis, cervicis, thoracis)
• Intermediate column
• Fibers rise up to ribs between angle and tubercle, transverse processes, and mastoid processes
o Iliocostalis (cervicis, thoracis, lumborum)
• Lateral column
• Fibers rise up to angles of ribs and cervical transverse processes

Question 5

Identify the semispinalis muscles (capitis, cervicis, and thoracis).

• Describe the attachment plan and function of these muscles.
• Innervation?

Answer 5

-Attachments: Rise from vertebral transverse processes to spinous processes of superior vertebrae
-Function: extension of head and cervical and thoracic vertebral column; rotates thoracic and cervical vertebral column contralaterally
Innervation: Posterior rami of spinal nerves.

Question 6

Identify the rotatores longus and brevis muscles, their attachments, function, and innervation.

Answer 6

• Spans 1-2 segments
• Attachments: inferiorly to articular processes of C4-C7, transverse processes of T1-T3, ilium, sacrum; superomedially to root of spinous process of superior 1 or 2 vertebrae
• Action: mainly proprioception, also stabilizing and rotating vertebral column
-Innervation: Posterior rami of spinal nerves.

Question 7

Identify the multifidus muscle, its attachments, function, and innervation.

Answer 7

• Spans 2-4 segments
• Attachments: sacrum, PSIS, aponeurosis of erector spinae, lateral neural arch to spinous processes
• Action: unilaterally, rotation to contralateral side; bilaterally, stabilizes vertebrae during movements
• Innervation: Posterior rami of spinal nerves

Question 8

Identify the lavatores long and brevis muscles, their attachments, function, and innervation.

Answer 8

Attachments: Tips of transverse processes of C7-T11; inferolaterally to rib between tubercle and angle

• Action: Mainly proprioceptive. May elevates ribs, contributes to inspiration, contributes to lateral bending of VC
• Innervation: posterior rami of C8-T11