Study Guide: Major Muscles of the Human Body – Head, Torso, Arm, and Leg

Overview of Human Muscular System

The human muscular system is composed of specialized tissues that enable movement, maintain posture, and support bodily functions. This guide summarizes the major skeletal muscles, their locations, and primary actions, organized by anatomical regions.

Facial Expression Muscles

Muscles of Facial Expression

These muscles are responsible for producing facial movements and expressions by moving the skin rather than joints.

• Frontalis (Occipitofrontalis): Raises eyebrows and wrinkles the forehead.

• Orbicularis oculi: Closes the eyelids.

• Orbicularis oris: Closes and protrudes the lips (as in kissing).

• Buccinator: Compresses the cheek (as in blowing or sucking).

• Zygomaticus minor and major: Elevate the corners of the mouth (as in smiling).

• Masseter: Elevates the mandible (main muscle of mastication).

• Temporalis: Elevates and retracts the mandible.

• Platysma: Tenses the skin of the neck and depresses the mandible.

Neck Muscles: Move Head and the Neck

Muscles Involved in Head and Neck Movement

These muscles control head rotation, flexion, and extension.

• Sternocleidomastoid: Flexes the neck and rotates the head to the opposite side.

• Splenius capitis: Extends and rotates the head.

• Splenius cervicis: Extends and rotates the cervical spine.

• Semispinalis: Extends the head and vertebral column.

• Scalenes: Flex and slightly rotate the neck; assist in breathing by elevating the first two ribs.

Anterior Trunk: Deep Thoracic Muscles

Muscles of the Thorax

These muscles are essential for respiration and movement of the rib cage.

• Diaphragm: Main muscle of inspiration; contracts to enlarge the thoracic cavity.

• External intercostals: Elevate the ribs during inspiration.

• Internal intercostals: Depress the ribs during forced expiration.

Abdominal Muscles

Muscles of the Abdominal Wall

These muscles support abdominal organs, flex and rotate the trunk, and assist in breathing.

• Rectus abdominis: Flexes the vertebral column and compresses abdominal contents.

• External abdominal oblique: Rotates and laterally flexes the trunk.

• Internal abdominal oblique: Rotates and laterally flexes the trunk (deep to external oblique).

• Transversus abdominis: Compresses abdominal contents (deepest abdominal muscle).

Upper Limb Movement

Muscles of the Shoulder and Arm

These muscles move the upper limb at the shoulder and elbow joints.

• Levator scapulae: Elevates the scapula.

• Rhomboid major and minor: Retract and stabilize the scapula.

• Serratus anterior: Protracts and holds the scapula against the thoracic wall.

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

• Pectoralis minor (deep): Stabilizes the scapula.

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

• Deltoid: Abducts, flexes, and extends the arm at the shoulder.

Shoulder Joint (Rotator Cuff)

The rotator cuff stabilizes the shoulder joint and allows rotation and lifting of the arm.

• Supraspinatus: Abducts the arm.

• Infraspinatus: Laterally rotates the arm.

• Subscapularis: Medially rotates the arm.

• Teres minor: Laterally rotates the arm.

• Teres major: Adducts and medially rotates the arm.

Arm: Anterior Compartment (Flexors)

• Biceps brachii: Flexes the elbow and supinates the forearm.

• Brachialis: Primary flexor of the elbow.

• Brachioradialis: Flexes the forearm at the elbow.

Arm: Posterior Compartment (Extensors)

• Triceps brachii: Main extensor of the elbow.

Forearm Muscles: Move Wrist, Hand, and Fingers

• Anterior Flexors: Flex the wrist and fingers (e.g., flexor digitorum, palmaris longus, flexor carpi ulnaris).

• Posterior Extensors: Extend the wrist and fingers (e.g., extensor carpi radialis, extensor digitorum, extensor carpi ulnaris).

Hip Muscles and Thigh Movement

Posterior Extensors

• Gluteus maximus: Extends and laterally rotates the thigh.

• Gluteus medius: Abducts and medially rotates the thigh.

• Gluteus minimus: Abducts and medially rotates the thigh (deepest gluteal muscle).

Anterior Flexors

• Psoas: Flexes the hip.

• Tensor fasciae latae: Abducts and medially rotates the thigh; stabilizes the iliotibial band.

Thigh and Leg Compartments

• Anterior compartment: Hip flexion, knee extension, ankle dorsiflexion.

• Posterior compartment: Hip extension, knee flexion, ankle plantarflexion.

• Medial compartment: Adducts the thigh.

Additional info: The fascia lata is a deep fascia that encloses the thigh muscles, separating them into compartments.

Thigh Muscles and Leg Movement

Anterior Compartment: Quadriceps Group

• Rectus femoris: Extends the knee and flexes the hip.

• Vastus medialis: Extends the knee.

• Vastus intermedius: Extends the knee.

• Vastus lateralis: Extends the knee.

Posterior Compartment: Hamstring Group

• Biceps femoris: Flexes the knee and extends the hip (lateral side).

• Semitendinosus: Flexes the knee and extends the hip (medial side).

• Semimembranosus: Flexes the knee and extends the hip (medial side, deeper).

Medial Adductors

• Pectineus: Adducts and flexes the thigh.

• Adductor brevis, longus, magnus: Adduct the thigh.

• Gracilis: Adducts the thigh and flexes the knee.

Leg Muscles and Ankle, Foot, and Toe Movement

Anterior Compartment

• Tibialis anterior: Dorsiflexes and inverts the foot.

• Extensor digitorum: Extends the toes.

• Fibularis longus (Peroneus): Everts and plantarflexes the foot.

Posterior Compartment

• Gastrocnemius: Plantarflexes the foot and flexes the knee.

• Soleus: Plantarflexes the foot (deep to gastrocnemius).

• Achilles tendon: Common tendon of gastrocnemius and soleus, attaches to the calcaneus.

Summary Table: Major Muscle Groups and Actions

Region	Muscle Group	Main Actions
Head/Face	Facial expression muscles	Facial movement, mastication
Neck	Sternocleidomastoid, scalenes, splenius	Head/neck flexion, rotation, extension
Thorax	Intercostals, diaphragm	Respiration
Abdomen	Rectus abdominis, obliques, transversus	Trunk flexion, rotation, compression
Upper limb	Deltoid, pectoralis, rotator cuff, biceps, triceps	Shoulder/arm movement, elbow flexion/extension
Thigh	Quadriceps, hamstrings, adductors	Knee extension/flexion, hip movement
Leg	Tibialis anterior, gastrocnemius, soleus	Ankle dorsiflexion/plantarflexion, toe movement

Additional info: Understanding the location and function of these muscles is essential for clinical assessment, injury diagnosis, and physical therapy in anatomy and physiology.