Muscles of the Shoulder Girdle
Describe the agonistic relationship of the upper trapezius muscle and lower trapezius muscle in upward scapular rotation.
As the upper trapezius muscle moves upward and inward (think line of pull), the lower trapezius moves downward and inward, causing the inferior angle of the scapula to move up and out (upward rotation).
What does reverse muscle action allow the shoulder girdle to do?
Assist in other joints, primarily the head and neck
In reverse muscle action, if the shoulder girdle is stabilized, how can the upper trapezius muscles assist in moving the head and neck?
Bilateral contraction of the upper trapezius muscles can assist in extending the head and neck Unilateral contraction of the upper trapezius can laterally bend the head and neck to the same side and rotate it to the opposite site
What is the rhomboids muscle line of pull?
Diagonal; good horizontal and vertical components
What is the lower trapezius' line of pull?
Diagonal; more downward (vertical) than inward (horizontal)
What is the upper trapezius' line of pull?
Diagonal; more vertical (upward) than horizontal (inward)
What is the levator scapula muscle's line of pull?
Diagonal; mostly vertical
What is the line of pull of pectoralis minor?
Diagonal; mostly vertical (downward)
What is the middle trapezius' line of pull?
Horizontal
What is the line of pull for serratus anterior?
Horizontal (outward)
What is reverse muscle action?
If the insertion is stabilized, the origin will move toward the insertion.
As serratus anterior crosses the lateral chest wall, what muscles can it be seen between?
Latissimus dorsi (posteriorly) and pectoralis major and external oblique (anteriorly)
Pectoralis Minor: OIAN
O: Anterior surface, third through fifth ribs I: Coracoid process of the scapula A: Scapular depression, protraction, downward rotation, and tilt N: Medial pectoral nerve
Serratus Anterior: OIAN
O: Lateral surface of the upper eight ribs I: Vertebral border of the scapula, anterior surface A: Scapular protraction and upward rotation N: Long thoracic nerve
Upper Trapezius: OIAN
O: Occipital bone, nuchal ligament on upper cervical spinous processes I: Outer third of clavicle, acromion process A: Scapular elevation and upward rotation N: Spinal accessory nerve
Middle Trapezius: OIAN
O: Spinous processes of C7 through T3 I: Scapular spine A: Scapular retraction N: Spinal accessory nerve
Rhomboids: OIAN
O: Spinous processes of C7 through T5 I: Vertebral border of scapula between the spine and inferior angle A: Scapular retraction, elevation, and downward rotation N: Dorsal scapular nerve
Lower Trapezius: OIAN
O: Spinous processes of middle and lower thoracic vertebrae I: Base of scapular spine A: Scapular depression and upward rotation N: Spinal accessory nerve
Levator Scapula: OIAN
O: Transverse processes of first four cervical vertebrae I: Vertebral border of scapula between the superior angle and spine A: Scapular elevation and downward rotation N: Third and fourth cervical nerves and dorsal scapular nerve (C5)
Pectoralis minor is deep to what muscle?
Pectoralis major
What are the prime movers of each joint motion of the shoulder girdle?
Retraction: Middle trapezius, rhomboids Protraction: Serratus anterior, pectoralis minor Elevation: Upper trapezius, levator scapula, rhomboids Depression: Lower trapezius, pectoralis minor Upward Rotation: Upper and lower trapezius, serratus anterior (lower fibers) Downward Rotation: Rhomboids, levator scapula, pectoralis minor Scapular Tilt: Pectoralis minor
What two muscles make up the rhomboids?
Rhomboid Major Rhomboid Minor
If you remove the trapezius muscle, what muscles lie deep to it?
Rhomboids Levator scapula
All three parts of the trapezius work together to perform what motion?
Scapular retraction The middle trapezius muscle is the prime mover. The upper and lower trapezius only assist.
Describe the force couple associated with downward scapula rotation.
The combined effects of pectoralis minor pulling down, the rhomboid muscles pulling in, and the levator scapula muscle pulling up is downward rotation of the scapula.
How do the origins of all five shoulder girdle muscles relate?
The origins of all five shoulder girdle muscles are located on the trunk: 3 posteriorly (trapezius, levator scapula, rhomboids), 1 laterally (serratus anterior), and 1 anteriorly (pectoralis minor).
Describe the force couple associated with upward scapula rotation.
The upper trapezius pulls up, the lower trapezius pulls down, and the lower fibers of the serratus anterior muscle pull outward in a horizontal direction
Of the three posterior muscles of the shoulder girdle, what muscle is most superficial?
Trapezius muscle
What are the muscles of the shoulder girdle?
Trapezius muscle Levator scapula muscle Rhomboids muscle Serratus anterior muscle Pectoralis minor muscle
What are the three divisions of the trapezius muscle and why is it separated this way?
Upper, middle, and lower trapezius There are three different lines of pull (upward, inward, and downward) resulting in three different muscle actions.
In reverse muscle action, if the scapula is stabilized, how can the levator scapula assist in moving the head and neck?
When the scapula is stabilized, the levator scapula can assist the splenius cervicis in rotating and laterally bending the neck ipsilaterally.
Describe the reverse muscle action of lower trapezius and pectoralis minor in crutch walking.
With the crutches planted on the floor and the hands bearing weight on the crutches, the scapula becomes stabilized, preventing the lower trapezius and pectoralis minor from depressing the scapula when they contract. Instead, their origins move the body upward toward the scapula, thus elevating the trunk as it swings through the crutches.
What is a force couple?
muscles pulling in different directions to accomplish the same motion
When can serratus anterior be palpated?
when the arm is overhead
What are some examples of motions accomplished through the force coupling associated with downward scapula rotation?
when the shoulder joint is forcefully extended as when chopping wood, paddling a canoe, or pulling down on an overhead exercise machine
When can the rhomboids be palpated?
when the trapezius muscle is relaxed
