Difficulty: Introductory | Prerequisites: Chapter 7 skeletal landmarks (humerus, scapula, radius, ulna), basic anatomical terminology. Part 1 of these notes (Head, Neck, and Trunk) covers the trapezius and pectoralis major, which also act on the upper limb.
This second set of notes covers the muscles of the shoulder and arm identified in the Chapter 8 muscles worksheet. The upper limb muscles here include the shoulder movers (deltoid, teres major, teres minor), the primary elbow flexors and extensors (biceps brachii, brachialis, triceps brachii), and forearm muscles involved in elbow and wrist movement (brachioradialis, flexor carpi ulnaris). Most of these are superficial and readily identifiable on anterior and posterior diagrams. The exam will expect you to know their locations, primary actions, and which view (anterior, posterior, or both) they appear in.
The deltoid caps the shoulder and abducts the arm. The biceps brachii and brachialis flex the elbow from the front; the triceps brachii extends it from the back. The teres minor and teres major sit on the posterior scapula with different roles (lateral vs. medial rotation). The brachioradialis flexes the elbow from the lateral forearm, and the flexor carpi ulnaris flexes and adducts the wrist.
Deltoid
The thick, triangular muscle capping the shoulder, visible from both anterior and posterior views. It has three parts: anterior (clavicular), middle (acromial), and posterior (spinal) fibres. Its main action is abduction of the arm. In simple terms, the deltoid is what lifts your arm out to the side.
Biceps brachii
The two-headed muscle on the anterior arm. The long head originates from the supraglenoid tubercle of the scapula; the short head from the coracoid process. It inserts on the radial tuberosity. It flexes the elbow and supinates the forearm. Think of it as the muscle you flex when someone asks you to "make a muscle."
Brachialis
A deep muscle lying beneath the biceps brachii on the anterior arm. It originates from the distal anterior humerus and inserts on the coronoid process and ulnar tuberosity. It is the primary flexor of the elbow, more powerful than the biceps for pure flexion because it pulls only on the ulna, which cannot rotate. In simple terms, the brachialis does most of the heavy lifting during elbow flexion, even though the biceps gets the credit.
Triceps brachii
The three-headed muscle on the posterior arm. Its long head originates from the infraglenoid tubercle of the scapula; the lateral and medial heads from the posterior humerus. All three converge on the olecranon process of the ulna. It is the primary extensor of the elbow. This is the muscle that straightens your arm.
Brachioradialis
A forearm muscle on the lateral (thumb) side, originating from the lateral supracondylar ridge of the humerus and inserting near the styloid process of the radius. It flexes the elbow, particularly when the forearm is in a neutral (midprone) position. Think of it as the muscle that helps you lift a drink to your mouth when your thumb is pointing up.
Teres minor
A small muscle on the posterior scapula, part of the rotator cuff. It originates from the lateral border of the scapula and inserts on the greater tubercle of the humerus. It laterally rotates the arm. In simple terms, it helps rotate your arm outward.
Teres major
Sits just below the teres minor on the posterior scapula but is not part of the rotator cuff. It originates from the inferior angle of the scapula and inserts on the intertubercular groove of the humerus. It medially rotates, adducts, and extends the arm. Think of it as doing roughly the opposite of the teres minor in terms of rotation.
Flexor carpi ulnaris
A superficial forearm muscle on the medial (pinky) side. It originates from the medial epicondyle of the humerus and the olecranon, and inserts on the pisiform, hamate, and fifth metacarpal. It flexes and adducts (ulnar deviates) the wrist. Visible on the posterior forearm diagram.
Deltoid is the most superficial shoulder muscle and a primary landmark
Anterior fibres: flex and medially rotate the arm
Middle fibres: abduct the arm (the classic action tested on exams)
Posterior fibres: extend and laterally rotate the arm
Common intramuscular injection site
Teres minor sits on the upper lateral border of the posterior scapula
One of the four rotator cuff muscles (along with supraspinatus, infraspinatus, subscapularis)
Action: lateral rotation of the arm at the shoulder
Teres major sits just below teres minor
Not a rotator cuff muscle, despite its proximity
Action: medial rotation, adduction, and extension of the arm
Sometimes called "lat's little helper" because it assists the latissimus dorsi
Biceps brachii is the superficial anterior arm muscle
Two heads: long and short
Actions: flexes the elbow, supinates the forearm, weakly flexes the shoulder
The supination function is clinically important: turning a doorknob or a screwdriver
Brachialis lies deep to the biceps
Crosses only the elbow joint (unlike the biceps, which crosses the shoulder too)
The true workhorse of elbow flexion
Partially visible on the lateral side of the arm, between biceps and triceps
Triceps brachii is the only muscle on the posterior arm in this worksheet
Three heads: long, lateral, medial
The long head crosses the shoulder joint; the other two do not
Primary action: extension of the elbow
The long head also weakly extends and adducts the shoulder
Brachioradialis is on the lateral (radial) forearm
Visible on the anterior view of the body
Flexes the elbow, especially in midprone position
A useful test: flex the elbow against resistance with the forearm in neutral, and the brachioradialis stands out prominently
Flexor carpi ulnaris is on the medial (ulnar) forearm
Visible on the posterior view of the body in the worksheet diagram
Flexes and adducts the wrist
Named for its position: "flexor" (action), "carpi" (wrist), "ulnaris" (ulnar side)
The rotator cuff, which includes the teres minor, is one of the most commonly injured structures in the shoulder. Athletes who throw overhand (cricket bowlers, baseball pitchers, tennis players) stress these muscles repeatedly, and tears often require surgical repair. Understanding the distinct roles of the teres minor (lateral rotation) versus teres major (medial rotation) helps explain why rehabilitation protocols target each one differently. The brachioradialis reflex (tapping the distal radius with a reflex hammer) is a standard neurological test for the C5-C6 spinal nerve levels.
Students frequently confuse teres minor and teres major. They sit next to each other on the posterior scapula, but teres minor laterally rotates the arm (and is a rotator cuff muscle), while teres major medially rotates it (and is not part of the rotator cuff). Their actions are essentially opposite.
The biceps brachii is often assumed to be the strongest elbow flexor. It is not. The brachialis generates more flexion force. The biceps is more superficial and more visible, which is why it gets the attention.
The triceps brachii has three heads, not two. Students sometimes confuse it with the biceps and assume "tri" refers to three functions rather than three origins.
Brachioradialis is a forearm muscle, not an arm muscle, even though it acts on the elbow. Its muscle belly is in the forearm, and it crosses the elbow joint from below.
⚠️ Know which muscles appear on the anterior view versus the posterior view. The deltoid and triceps appear on both. The biceps brachii, brachialis, and brachioradialis are anterior. Teres minor, teres major, and flexor carpi ulnaris appear on the posterior diagram in this worksheet.
⚠️ Teres minor vs. teres major is a very common exam distinction. Memorise that teres minor is rotator cuff and laterally rotates; teres major is not rotator cuff and medially rotates.
⚠️ Be prepared to explain why the brachialis is the primary elbow flexor despite being less visible than the biceps.
⚠️ Muscle-naming conventions are heavily tested. "Biceps" = two heads. "Triceps" = three heads. "Brachii" = of the arm. "Brachialis" = relating to the arm. "Brachioradialis" = arm-to-radius. "Flexor carpi ulnaris" = wrist flexor on the ulnar side.
True or false: The teres major is part of the rotator cuff. ___
The primary extensor of the elbow is the __________.
Which muscle is the strongest pure flexor of the elbow: biceps brachii or brachialis? ___
True or false: The deltoid has two distinct fibre groups. ___
Fill in the blank: The flexor carpi ulnaris flexes and __________ the wrist.
Answers: 1. False (teres minor is the rotator cuff member). 2. Triceps brachii. 3. Brachialis. 4. False (it has three: anterior, middle, posterior). 5. Adducts (ulnar deviation).
Q: A student identifies a muscle on the posterior scapula that laterally rotates the arm and is part of the rotator cuff. Name this muscle.
A: Teres minor.
Q: How many heads does the triceps brachii have, and where does it insert?
A: Three heads (long, lateral, medial). It inserts on the olecranon process of the ulna.
Q: Which forearm muscle flexes the elbow most effectively when the forearm is in a neutral (midprone) position?
A: Brachioradialis.
Q: Name the two heads of the biceps brachii and state one action besides elbow flexion.
A: Long head and short head. It also supinates the forearm (or weakly flexes the shoulder).
Q: A muscle on the posterior forearm is named for its action, the joint it acts on, and its side of the forearm. It flexes and adducts the wrist. What is it?
A: Flexor carpi ulnaris.
The upper limb muscles connect to the skeletal system (Chapter 7) through specific bony landmarks: the greater and lesser tubercles of the humerus, the radial tuberosity, the olecranon, and the scapular borders. The rotator cuff muscles link to the joint chapter, where glenohumeral stability and common shoulder injuries are discussed. Nerve supply matters too: the musculocutaneous nerve serves the biceps and brachialis, the radial nerve serves the triceps and brachioradialis, and the ulnar nerve serves the flexor carpi ulnaris. These nerve-muscle pairings are tested in neuroscience and clinical modules.
Deltoid, biceps brachii, brachialis, triceps brachii, brachioradialis, teres minor, teres major, flexor carpi ulnaris, rotator cuff, shoulder muscles, arm muscles, forearm muscles, elbow flexion, elbow extension, lateral rotation, medial rotation, supination, upper limb, appendicular musculature, Chapter 8, anatomy and physiology, UF, muscle identification, anterior arm, posterior arm