Superficial muscles of the back

Question 1

Trapezius muscle

Answer 1

This is a superficial, large, fan like muscle found on the back. The muscle can be divided into three sets of fibers: upper, middle, and lower. The upper fibers act to extend the neck, elevate, and upwardly rotate. The middle fibers retract (adduct). The lower fibers are responsible for elevation and depression.
Origin: Superior nuchal line, external occipital protruberance, nuchal ligament, spinous processes of C7 to T12 vertebrae
Insertion: Lateral third of the clavicle, acromion and spine of the scapula
Innervation: Spinal accessory nerve; C3 and C4 spinal nerves
Function: Elevation, depression, and retraction of the scapula

Question 2

Rhomboid minor muscle

Answer 2

Origins: nuchal ligament, spinous processes of C7 and T1 vertebrae
Insertions: medial end of the scapular spine
Innervation: dorsal scapular nerve
Function: retraction and fixation of the scapula on the thoracic wall

Question 3

Rhomboid major muscle

Answer 3

Origins: spinous processes of T2 to T5
Insertions: medial border of scapula from the level of the spine to the inferior angle
Innervation: dorsal scapular nerve
Function: retraction and fixation of the scapula on the thoracic wall

Question 4

Levator scapulae muscle

Answer 4

Origins: Transverse process of the atlas and axis, posterior tubercles C3 and C4
Insertions: Posterior surface of the medial scapular border (from the superior angle to the root of the spine of the scapula)
Innervation: Anterior rami of the nerves C3 and C4, dorsal scapular nerve (branch of the C5)
Function: Elevation of the scapula

Question 5

Serratus anterior

Answer 5

Origins
Lateral parts of the 1st to 8th ribs
Insertions
Medial border of the scapula
Innervation
Long thoracic nerve
Function
Protraction and rotation of the scapula and stabiliser of the scapula
Clinical correlation: winged scapula

Question 6

Latissimus Dorsi muscle

Answer 6

Origins
Spinous processes of T7-L5 and sacrum, iliac crest, X-XII ribs. It blends into the thoracolumbar fascia which acts to stabilize the sacroiliac joints along the gluteus maximus muscle.
Insertions
Intertubercular groove of the humerus
Innervation
Thoracodorsal nerve (C6-C8)
Function
Contracting insertion->origin: adduction, extension, internal rotation of the arm
Contracting origin->insertion: rotation of the trunk

Question 7

Clinical Relevance: Testing the accessory nerve.

Answer 7

The most common cause of accessory nerve damage is iatrogenic (i.e. due to a medical procedure). In particular, operations such as cervical lymph node biopsy or cannulation of the internal jugular vein can cause trauma to the nerve.

To test the accessory nerve, trapezius function can be assessed. This can be done by asking the patient to shrug his/her shoulders. Other clinical features of accessory nerve damage include muscle wasting, partial paralysis of the sternocleidomastoid, and an asymmetrical neckline.