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