Gross Anatomy of Muscles

Head and Neck Muscles

Face Muscles:

  • Cranial Aponeurosis – Connects to the frontalis and occipitalis; forms the scalp.

  • Occipitalis – Located at the back of the head; immovable.

  • Frontalis – Raises eyebrows and wrinkles the forehead.

  • Temporalis – Closes the jaw; elevates the mandible.

  • Orbicularis Oculi – Responsible for blinking, squinting, and winking.

  • Nasalis – Flares nostrils; used when smelling deeply.

  • Zygomaticus (major and minor) – Runs diagonally; helps with smiling.

  • Buccinator – Runs horizontally across the cheek; compresses cheek to keep food between teeth.

  • Masseter – Strongest jaw muscle; helps with chewing and elevates the mandible.

  • Orbicularis Oris – Closes the lips; used in kissing.

Neck Muscles:

  • Platysma – Pulls mouth downward (sad face expression); superficial muscle.

  • Sternocleidomastoid – Rotates head and helps lift head when lying down (one side at a time).

  • Trapezius – Moves the scapula (elevation and retraction); located in the upper back.

Trunk Muscles

Arm Muscles:

  • Deltoid – Covers the shoulder; abducts the arm.

  • Pectoralis Major – Located in the chest; responsible for shoulder flexion and arm adduction.

  • Biceps Brachii – Main muscle for elbow flexion; works when arm is supinated (palm up).

  • Brachialis – Lies deep to the biceps; works in both supination and pronation.

  • Triceps Brachii – Main muscle for elbow extension.

  • Brachioradialis – Assists in wrist flexion and helps stabilize the elbow.

Abdominal Muscles:

  • External Oblique – Runs diagonally; involved in trunk rotation and flexion (intermediate layer).

  • Internal Oblique – Also runs diagonally (opposite direction); deeper than external.

  • Transversus Abdominis – Runs horizontally; deepest abdominal muscle; compresses abdomen.

  • Rectus Abdominis – Runs vertically (“six-pack”); flexes the spine and stabilizes the pelvis.

  • Serratus Anterior – Located on the ribs; abducts and stabilizes the scapula (think: boxing motion).

Back Muscles:

  • Latissimus Dorsi – Large lower back muscle; helps with arm adduction and extension (think: swimming).

  • Erector Spinae (3 muscles) – Runs from skull to pelvis; helps with back extension and posture.

  • Quadratus Lumborum – Located in the lower back (lumbar region); helps stabilize and extend the spine.