Muscular System: Surface Muscles Identification and Functions

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Muscular System Overview

The muscular system is responsible for movement, posture, and heat production in the human body. It consists of over 600 muscles, which are classified based on their location, function, and structure. This guide focuses on the identification and basic functions of major surface muscles, organized by anatomical region.

Head & Neck Muscles

Major Muscles and Their Functions

Epicranius: Raises the eyebrows and wrinkles the forehead.
Orbicularis oculi: Closes the eyelids; involved in blinking and squinting.
Zygomaticus: Elevates the corners of the mouth (as in smiling).
Buccinator: Compresses the cheek; assists in chewing and blowing.
Masseter: Elevates the mandible; primary muscle for chewing.
Orbicularis oris: Closes and protrudes the lips (as in kissing).
Temporalis: Elevates and retracts the mandible; assists in chewing.
Sternocleidomastoid: Flexes the neck; rotates the head to the opposite side.
Platysma: Tenses the skin of the neck; depresses the mandible.

Abdomen & Chest Muscles

Major Muscles and Their Functions

Rectus abdominis: Flexes the vertebral column; compresses abdominal contents.
Transversus abdominis: Compresses abdominal contents; stabilizes the trunk.
Internal oblique: Flexes and rotates the vertebral column; compresses abdomen.
External oblique: Flexes and rotates the vertebral column; compresses abdomen.
Pectoralis major: Adducts and medially rotates the arm; flexes the shoulder.
Pectoralis minor: Depresses and protracts the scapula.

Back Muscles

Major Muscles and Their Functions

Trapezius: Elevates, retracts, and rotates the scapula; extends the neck.
Latissimus dorsi: Extends, adducts, and medially rotates the arm.
Rhomboid: Retracts and elevates the scapula.
Supraspinatus: Abducts the arm; stabilizes the shoulder joint.
Infraspinatus: Laterally rotates the arm; stabilizes the shoulder joint.

Upper Arm Muscles

Major Muscles and Their Functions

Biceps brachii: Flexes the elbow; supinates the forearm.
Triceps brachii: Extends the elbow.
Brachialis: Flexes the elbow (primary mover).
Deltoid: Abducts the arm; assists in flexion and extension of the shoulder.

Forearm Muscles

Major Muscles and Their Functions

Brachioradialis: Flexes the elbow, especially during rapid movement or when the forearm is in mid-position.
Flexor carpi radialis: Flexes and abducts the wrist.
Palmaris longus: Flexes the wrist; tenses the palmar fascia.
Pronator teres: Pronates the forearm; assists in elbow flexion.
Flexor carpi ulnaris: Flexes and adducts the wrist.
Extensor carpi radialis: Extends and abducts the wrist.
Extensor digitorum: Extends the fingers and the wrist.
Extensor carpi ulnaris: Extends and adducts the wrist.

Buttocks & Posterior Upper Leg Muscles

Major Muscles and Their Functions

Gluteus maximus: Extends and laterally rotates the thigh; important for climbing stairs and rising from a sitting position.
Gluteus medius: Abducts and medially rotates the thigh.
Adductor magnus: Adducts, flexes, and extends the thigh.
Gracilis: Adducts the thigh; flexes and medially rotates the leg.
Biceps femoris: Extends the thigh; flexes the knee (part of the hamstrings).
Semitendinosus: Extends the thigh; flexes the knee (hamstring group).
Semimembranosus: Extends the thigh; flexes the knee (hamstring group).

Anterior Upper Leg Muscles

Major Muscles and Their Functions

Adductor longus: Adducts and flexes the thigh.
Iliopsoas: Flexes the thigh at the hip joint; important for walking and running.
Sartorius: Flexes, abducts, and laterally rotates the thigh; flexes the knee.
Rectus femoris: Extends the knee; flexes the thigh at the hip (part of quadriceps).
Vastus medialis: Extends the knee (quadriceps group).
Vastus intermedius: Extends the knee (quadriceps group).
Vastus lateralis: Extends the knee (quadriceps group).

Posterior Lower Leg Muscles

Major Muscles and Their Functions

Gastrocnemius: Plantar flexes the foot; flexes the knee.
Soleus: Plantar flexes the foot; important for standing and walking.
Fibularis longus: Everts and plantar flexes the foot.

Anterior Lower Leg Muscles

Major Muscles and Their Functions

Extensor digitorum longus: Extends the toes; dorsiflexes the foot.
Tibialis anterior: Dorsiflexes and inverts the foot.

Example: Muscle Identification in Practice

When asked to identify the biceps brachii on a model or diagram, look for the prominent muscle on the anterior upper arm responsible for elbow flexion.
The gastrocnemius forms the bulk of the calf and is easily identified by its two heads and its role in plantar flexion.

Additional info:

Muscles often work in pairs: for example, the biceps brachii (flexor) and triceps brachii (extensor) control elbow movement.
Surface muscles are those that can be palpated or seen under the skin, as opposed to deeper muscles.