Muscles of the shoulder Flashcards
What are the two groups of muscles that make up the shoulder?
Extrinsic – originate from the torso, and attach to the bones of the shoulder (clavicle, scapula or humerus).
Intrinsic – originate from the scapula and/or clavicle, and attach to the humerus.
What does the deltoid muscle attach to?
Originate from the lateral third of the clavicle, the acromion and the spine of the scapula. It attaches to the deltoid tuberosity on the lateral aspect of the humerus.
What does the deltoid muscle innervate?
Axillary nerve.
What are the actions of the deltoid?
Anterior fibres – flexion and medial rotation.
Posterior fibres – extension and lateral rotation.
Middle fibres – the major abductor of the arm (takes over from the supraspinatus, which abducts the first 15 degrees).
What does teres major attach to?
Originates from the posterior surface of the inferior angle of the scapula. It attaches to the medial lip of the intertubercular groove of the humerus.
What innervates terers major?
Lower subscapular nerve.
What are the actions of teres major?
Adducts and extends at the shoulder, and medially rotates the arm.
Where do the rotator muscles originate and attach to?
The rotator cuff muscles are a group of four muscles that originate from the scapula and attach to the humeral head. Collectively, the resting tone of these muscles acts to ‘pull’ the humeral head into the glenoid fossa. This gives the glenohumeral joint a lot of additional stability.
What are the attachments, innervations and actions of the rotator cuff muscles?
Supraspinatus
Attachments: Originates from the supraspinous fossa of the scapula, attaches to the greater tubercle of the humerus.
Innervation: Suprascapular nerve.
Actions: Abducts the arm 0-15o, and assists deltoid for 15-90o
Infraspinatus
Attachments: Originates from the infraspinous fossa of the scapula, attaches to the greater tubercle of the humerus.
Innervation: Suprascapular nerve.
Actions: Laterally rotates the arm.
Subscapularis
Attachments: Originates from the subscapular fossa, on the costal surface of the scapula. It attaches to the lesser tubercle of the humerus.
Innervation: Upper and lower subscapular nerves.
Actions: Medially rotates the arm.
Teres Minor
Attachments: Originates from the posterior surface of the scapula, adjacent to its lateral border. It attaches to the greater tubercle of the humerus.
Innervation: Axillary nerve.
Actions: Laterally rotates the arm.
How many superficial extrinsic muscles are there?
2
What does the Trapezius attach to?
What is the function?
What is it innervated by?
The trapezius is a broad, flat, and triangular muscle. The muscles on each side form a trapezoid shape. It is the most superficial of all the back muscles.
Attachments: Originates from the skull, nuchal ligament and the spinous processes of C7-T12. The fibres attach to the clavicle, acromion, and the scapula spine.
Innervation: Motor innervation is from the accessory nerve. It also receives proprioceptor fibres from C3 and C4 spinal nerves.
Actions: The upper fibres of the trapezius elevate the scapula and rotates it during abduction of the arm. The middle fibres retract the scapula and the lower fibres pull the scapula inferiorly.
What does the Latissimus Dorsi do?
What is the function
What is it innervated by?
The latissimus dorsi originates from the lower part of the back, where it covers a wide area.
Attachments: Has a broad origin – arising from the spinous processes of T7-T12, iliac crest, thoracolumbar fascia and the inferior three ribs. The fibres converge into a tendon that attaches to the intertubercular sulcus of the humerus.
Innervation: Thoracodorsal nerve.
Actions: Extends, adducts, and medially rotates the upper limb.
What are the deep extrinsic shoulder muscles?
What are there attachments and innervations?
Deep
There are three muscles in this group – the levator scapulae and the two rhomboids. They are situated in the upper back, underneath the trapezius.
Levator Scapulae
The levator scapulae is a small strap-like muscle. It begins in the neck, and descends to attach to the scapula.
Attachments: Originates from the transverse processes of the C1-C4 vertebrae and attaches to the medial border of the scapula.
Innervation: Dorsal scapular nerve.
Actions: Elevates the scapula.
Rhomboids
There are two rhomboid muscles – major and minor. The rhomboid minor is situated superiorly to the major.
Rhomboid Major
Attachments: Originates from the spinous processes of T2-T5 vertebrae. Attaches to the medial border of the scapula, between the scapula spine and inferior angle.
Innervation: Dorsal scapular nerve.
Actions: Retracts and rotates the scapula.
Rhomboid Minor
Attachments: Originates from the spinous processes of C7-T1 vertebrae. Attaches to the medial border of the scapula, at the level of the spine of scapula.
Innervation: Dorsal scapular nerve.
Actions: Retracts and rotates the scapula.
