TBL2 - Extrinsic Shoulder & Intrinsic Back Muscles

Question 1

What is the difference between adduction and abduction?

Answer 1

1) Abduction - away from the median plane

2) Adduction - towards the median plane

Question 2

How do muscles contract in relation to their origin and insertion points?

Answer 2

Contraction of a skeletal muscle pulls its distal bony attachment (aka insertion) toward its proximal bony attachment (aka origin)

Question 3

What is the role of muscle tone and when is it absence?

Answer 3

1) Even when “relaxed,” the muscles of a conscious individual are almost always slightly contracted. This slight contraction, called muscle tone (tonus), does not produce movement or active resistance (as phasic contraction does) but gives the muscle a certain firmness, assisting the stability of joints and the maintenance of posture, while keeping the muscle ready to respond to appropriate stimuli
2) Muscle tone is usually absent only when unconscious (as during deep sleep or under general anesthesia) or after a nerve lesion resulting in paralysis

Question 4

What are the superficial and deep extrinsic shouder muscles?

Answer 4

1) The trapezius and latissimus dorsi constitute the superficial extrinsic shoulder muscles
2) The levator scapulae and rhomboids constitute the deep extrinsic shoulder muscles

Question 5

How does the trapezius function with the scapula?

Answer 5

1) The trapezius attaches proximally to the cervical and thoracic vertebrae and distally to the scapula and clavicle
2) When the superior and inferior parts work together, the scapula is rotated upward to assist full abduction of the upper limb
3) Descending part elevates; ascending part depresses; and middle part (or all parts together) retracts scapula; descending and ascending parts act together to rotate glenoid cavity superiorly

Question 6

What spinal nerves innervate the trapezius?

Answer 6

Spinal accessory nerve (CN XI) (motor fibers) and C3, C4 spinal nerves (pain and proprioceptive fibers)

Question 7

Where does the trapezius attach?

Answer 7

The trapezius attaches proximally to the cervical and thoracic vertebrae and distally to the scapula and clavicle

Question 8

Where do the latissimus dorsi attach?

Answer 8

The latissimus dorsi attaches proximally via the thoracolumbar fascia to the inferior six thoracic vertebrae and distally to the medial side of the humerus

Question 9

What spinal nerves innervate the latissimus dorsi?

Answer 9

Thoracodorsal nerve (C6, C7, C8)

Question 10

What do the latissimus dorsi do?

Answer 10

1) Extends, adducts, and medially rotates humerus; raises body toward arms during climbing
2) It is a powerful adductor of the upper limb, especially from the fully abducted position as when swimming or climbing

Question 11

What is the visible clinical manifestation in patients with ipsilateral trapezius muscle weakness?

Answer 11

The primary clinical manifestation of spinal accessory nerve palsy is a marked ipsilateral weakness when the shoulders are elevated (shrugged) against resistance

Question 12

Why is the use of crutches difficult by an adult with latissimus dorsi weakness, and how would the weakness affect a 1-year old infant?

Answer 12

1) The thoracodorsal nerve passes inferiorly along the posterior wall of the axilla, and enters the medial surface of the latissimus dorsi close to where it becomes tendinous
2) The latissimus dorsi and the inferior part of the pectoralis major form an anteroposterior muscular sling between the trunk and the arm; however, the latissimus dorsi forms the more powerful part of the sling. With paralysis of the latissimus dorsi, the person is unable to raise the trunk with the upper limbs, as occurs during climbing
3) Furthermore, the person cannot use an axillary crutch because the shoulder is pushed superiorly by it. These are the primary activities for which active depression of the scapula is required; the passive depression provided by gravity is adequate for most activities
4) An infant would have difficulty crawling

Question 13

Where do the levator scapulae muscles attach to?

Answer 13

Levator scapulae muscle attaches proximally to the superior four cervical vertebrae and distally to the superior angle of the scapula

Question 14

What do the levator scapulae muscles do?

Answer 14

It acts synergistically with the superior part of the trapezius during elevation of the scapula

Question 15

Where does the rhomboid muscle attach?

Answer 15

The rhomboid muscle attaches proximally to the last cervical and superior five thoracic vertebrae and distally to the medial border of the scapula

Question 16

What is the rhomboid used for?

Answer 16

1) The rhomboids retract and rotate the scapula, depressing its glenoid cavity
2) They also assist the serratus anterior in holding the scapula against the thoracic wall, and fixing the scapula during movements of the upper limb
3) The rhomboids are used when forcibly lowering the raised upper limbs (e.g., when driving a stake with a sledge hammer)

Question 17

What is the function of the dorsal scapular nerve?

Answer 17

The dorsal scapular nerve innervates the levator scapulae and rhomboid muscles

Question 18

What is the segmental origin of the dorsal scapular nerve in the spinal cord?

Answer 18

Dorsal scapular nerve (C4, C5)

Question 19

Where does the erector spinae muscle attach?

Answer 19

The erector spinae muscle attaches proximally to the sacrum and distally to posterior aspects of the ribs and the thoracic and cervical vertebrae

Question 20

What spinal nerves innervate the erector spinae muscle?

Answer 20

Posterior rami of spinal nerves (sensory nerves in the skin of the back)

Question 21

What does the erector spinae muscle do?

Answer 21

1) Bilateral and unilateral contractions of the erector spinae move the vertebral column
2) Acting bilaterally: extend vertebral column and head; as back is flexed, control movement via eccentric contraction
3) Acting unilaterally: laterally flex vertebral column