Untitled Quiz

Muscles of the Shoulder Region & Front of Arm

• Learning Objectives (ILOs):
  • Recognize muscles of the shoulder region and front of arm.
  • Identify origin and insertion of each muscle in these regions.
  • List the nerve supply for each muscle.
  • Recall the actions of the various shoulder and arm muscles.

Shoulder Region Muscles

• Deltoid: A multipennate muscle shaping the shoulder.

  • Origin: Anterior fibers from the anterior border of the lateral one-third of the clavicle; middle fibers from the lateral edge of the acromion; posterior fibers from the lower lip of the crest of the scapular spine.
  • Insertion: Deltoid tuberosity on the middle of the anterolateral humerus surface.
  • Nerve Supply: Axillary nerve.
  • Actions:
    • Anterior fibers: Flexion and medial rotation of the arm.
    • Middle fibers: Abduct the arm from 15 to 90 degrees.
    • Posterior fibers: Extension and lateral rotation of the arm.

• Supraspinatus:

  • Origin: Medial two-thirds of the supraspinous fossa.
  • Insertion: Upper impression of the greater tubercle of the humerus.
  • Nerve Supply: Suprascapular nerve (C5,6).
  • Action: Abduction of the arm from 0 to 15 degrees. Helps stabilize the head of the humerus in the glenoid cavity.

• Infraspinatus:

  • Origin: Medial two-thirds of the infraspinatus fossa.
  • Insertion: Middle impression on the greater tuberosity of the humerus.
  • Nerve Supply: Suprascapular nerve (C5,6).
  • Action: Adduction and lateral rotation of the arm. Helps stabilize the head of the humerus in the glenoid cavity.

• Teres Minor:

  • Origin: Upper two-thirds of the dorsal aspect of the lateral border of the scapula.
  • Insertion: Lower impression of the greater tuberosity of the humerus.
  • Nerve Supply: Axillary nerve.
  • Action: Adduction and lateral rotation of the arm. Helps stabilize the head of the humerus in the glenoid cavity.

• Teres Major:

  • Origin: Oval area on the dorsal aspect of the inferior angle of the scapula and lower one-third of the back of the lateral border.
  • Insertion: Medial lip of the biceptal groove.
  • Nerve Supply: Lower subscapular nerve.
  • Action: Adduction and medial rotation of the arm.

• Subscapularis:

  • Origin: Medial two-thirds of the subscapular fossa.
  • Insertion: Lesser tuberosity of the humerus.
  • Nerve Supply: Upper and lower subscapular nerves (C5,6).
  • Action: Adduction and medial rotation of the arm. Helps stabilize the head of the humerus in the glenoid cavity.

Rotator Cuff Muscles

• Supraspinatus, Infraspinatus, Teres minor, and Subscapularis are intimately adhered to the shoulder joint capsule.
• They reinforce the capsule of the shoulder joint; their tone helps to stabilize the head of the humerus.

Muscles of the Arm

• Anterior Compartment:

  • Biceps Brachii:
    • Origin: Two heads (short head with coracobrachialis from tip of coracoid process; long head by tendon from supra-glenoid tubercle of scapula).
    • Insertion: Tendon into the rough posterior part of the radial tuberosity; bicipital aponeurosis descends and medially to the deep fascia of the upper medial side of the forearm.
    • Nerve Supply: Musculocutaneous nerve
    • Action: Supination of forearm; flexion of the supinated forearm; long head steadies humerus in glenoid cavity to prevent upward displacement.
  • Coracobrachialis:
    • Origin: Tip of coracoid process.
    • Insertion: Middle of medial border of humerus.
    • Nerve Supply: Musculocutaneous nerve (before piercing).
    • Action: Weak flexor of the arm.
  • Brachialis:
    • Origin: Lower 1.5 of front of humerus, including anteromedial, anterolateral surfaces and anterior border in between and front of medial and lateral intermuscular septa.
    • Insertion: Anterior surface of the coronoid process of the ulna.
    • Nerve Supply: Medial part by musculocutaneous nerve; lateral part by radial nerve.
    • Action: Main flexor of the elbow joint.

• Posterior Compartment: Triceps (described elsewhere).

Summary

• Muscles of shoulder region
• Rotator cuff muscles
• Muscles of front of arm (Biceps, coracobrachialis & brachialis)

Questions and Answers (Partial)

• Question 1: Which muscle does not insert into the intertubercular groove of the upper humerus?
  • Answer: Teres major
• Question 2: Which muscle is NOT part of the rotator cuff?
  • Answer: Teres major