Major Muscles of the Human Body: Locations and Movements

Muscular System Overview

Introduction

The muscular system consists of specialized tissues that contract to produce movement, maintain posture, and generate heat. Understanding the location and function of major muscles is essential for studying human anatomy and physiology, especially in relation to movement and biomechanics.

M uscles of Facial Expression and Mastication

Facial Muscles

These muscles are primarily responsible for facial expressions and some movements of the head.

• Corrugator supercilii: Draws eyebrows downward and medially, producing frowning.

• Orbicularis oculi: Closes the eyelids; involved in blinking and squinting.

• Zygomaticus major: Elevates the corners of the mouth, as in smiling.

• Orbicularis oris: Encircles the mouth; closes and protrudes lips (kissing muscle).

• Mentalis: Elevates and protrudes lower lip; wrinkles chin.

• Platysma: Tenses skin of neck; depresses mandible.

• Epicranius: Composed of two parts:

  • Frontal belly: Raises eyebrows, wrinkles forehead.

  • Occipital belly: Pulls scalp posteriorly.

Muscles of Mastication

• Temporalis: Elevates and retracts mandible.

• Buccinator: Compresses cheek; assists in chewing.

• Masseter: Elevates mandible; primary muscle for jaw closure.

• Pterygoids (medial and lateral): Move jaw side-to-side; assist in chewing.

Muscles of the Neck

Key Muscles

• Genioglossus, Styloglossus, Hyoglossus: Muscles of the tongue; control tongue movement.

• Sternocleidomastoid: Flexes and rotates the head.

• Scalenes: Elevate first two ribs; assist in neck flexion.

• Splenius: Extend and rotate the head.

• Semispinalis: Extend head and vertebral column.

Muscles of the Trunk

Thoracic and Abdominal Muscles

• Erector spinae: Extends vertebral column; maintains posture.

• External intercostals: Elevate ribs during inspiration.

• Internal intercostals: Depress ribs during forced expiration.

• Diaphragm: Prime mover of inspiration; flattens to increase thoracic cavity volume.

• Rectus abdominis: Flexes vertebral column; compresses abdomen.

• External oblique: Compresses abdomen; rotates trunk.

• Internal oblique: Compresses abdomen; rotates trunk.

Muscles of the Pelvic Floor

Key Muscles

• Levator ani: Supports pelvic organs; maintains continence.

• Coccygeus: Supports pelvic organs; pulls coccyx forward.

Muscles of the Shoulder and Upper Limb

Shoulder Muscles

• Pectoralis minor: Stabilizes scapula.

• Serratus anterior: Protracts scapula; assists in upward rotation.

• Subclavius: Stabilizes clavicle.

• Trapezius: Elevates, retracts, and rotates scapula.

• Levator scapulae: Elevates scapula.

• Rhomb oids: Retract scapula.

• Pectoralis major: Flexes, adducts, and medially rotates arm.

• Deltoid: Abducts arm; assists in flexion and extension.

• Latissimus dorsi: Extends, adducts, and medially rotates arm.

• Coracobrachialis: Flexes and adducts arm.

Rotator Cuff Muscles

• Teres major: Extends and medially rotates arm.

• Subscapularis: Medially rotates arm.

• Supraspinatus: Abducts arm.

• Infraspinatus: Laterally rotates arm.

• Teres minor: Laterally rotates arm.

Arm and Forearm Muscles

• Biceps brachii: Flexes elbow; supinates forearm.

• Anconeus: Assists in elbow extension.

• Brachialis: Flexes elbow.

• Brachioradialis: Flexes forearm.

• Pronator teres: Pronates forearm.

• Pronator quadratus: Pronates forearm.

• Supinator: Supinates forearm.

• Flexor carpi radialis: Flexes and abducts wrist.

• Flexor carpi ulnaris: Flexes and adducts wrist.

• Extensor carpi radialis: Extends and abducts wrist.

• Extensor carpi ulnaris: Extends and adducts wrist.

Muscles of the Hip and Lower Limb

Hip Flexors

• Iliopsoas: Composed of iliacus and psoas major; flexes thigh at hip.

• Sartorius: Flexes, abducts, and laterally rotates thigh; flexes knee.

Adductors

• Adductor magnus, longus, brevis: Adduct and medially rotate thigh.

• Pectineus: Adducts and flexes thigh.

• Gracilis: Adducts thigh; flexes leg.

Quadriceps Femoris

• Rectus femoris: Extends knee; flexes thigh at hip.

• Vastus lateralis, medialis, intermedius: Extend knee.

Gluteal Muscles

• Gluteus maximus: Extends and laterally rotates thigh.

• Gluteus medius: Abducts and medially rotates thigh.

• Gluteus minimus: Abducts and medially rotates thigh.

• Piriformis: Laterally rotates and abducts thigh.

Hamstrings

• Biceps femoris: Flexes knee; extends thigh.

• Semitendinosus: Flexes knee; extends thigh.

• Semimembranosus: Flexes knee; extends thigh.

Muscles of the Leg

• Tibialis anterior: Dorsiflexes and inverts foot.

• Fibularis longus, brevis: Evert and plantarflex foot.

• Gastrocnemius: Plantarflexes foot; flexes knee.

• Soleus: Plantarflexes foot.

• Popliteus: Unlocks knee by rotating femur.

• Flexor digitorum longus: Flexes toes; plantarflexes foot.

• Flexor hallucis longus: Flexes great toe; plantarflexes foot.

• Tibialis posterior: Inverts and plantarflexes foot.

Summary Table: Major Muscles and Their Actions

Muscle Group	Example Muscles	Main Actions
Facial Expression	Orbicularis oculi, Zygomaticus major	Close eyes, smile
Mastication	Masseter, Temporalis	Elevate mandible (chewing)
Neck	Sternocleidomastoid, Scalenes	Flex/rotate head, elevate ribs
Trunk	Rectus abdominis, Erector spinae	Flex/extend vertebral column
Shoulder	Deltoid, Trapezius	Abduct arm, elevate scapula
Arm	Biceps brachii, Triceps brachii	Flex/extend elbow
Forearm	Pronator teres, Supinator	Pronate/supinate forearm
Hip	Iliopsoas, Gluteus maximus	Flex/extend thigh
Thigh	Quadriceps, Hamstrings	Extend/flex knee
Leg	Tibialis anterior, Gastrocnemius	Dorsiflex/plantarflex foot

Key Terms and Concepts

• Prime mover (agonist): The muscle primarily responsible for a specific movement.

• Antagonist: Muscle that opposes the action of the prime mover.

• Synergist: Muscle that assists the prime mover.

• Origin: The fixed attachment point of a muscle.

• Insertion: The movable attachment point of a muscle.

Example: Elbow Flexion

• Prime mover: Biceps brachii

• Synergist: Brachialis

• Antagonist: Triceps brachii

Additional info:

• Students should be able to identify each muscle's location on a diagram and describe its major movement.

• Some muscles act as both agonists and antagonists depending on the movement.