Appendicular Muscles

Introduction

The appendicular muscles are responsible for movement and stabilization of the limbs and girdles. They are essential for locomotion, posture, and various voluntary movements. This guide summarizes the major muscle groups, their anatomical locations, and their functions, as well as key concepts for understanding muscle organization and action.

Muscles of the Head, Neck, and Torso

Muscles of Facial Expression

• Epicranius (occipitofrontalis): Includes the occipitalis and frontalis; raises eyebrows and wrinkles forehead.

• Orbicularis oculi: Closes eyelids.

• Orbicularis oris: Closes and protrudes lips.

• Buccinator: Compresses cheek.

• Depressor anguli oris: Depresses corner of mouth.

• Depressor labii inferioris: Depresses lower lip.

• Levator labii superioris: Elevates upper lip.

• Levator anguli oris: Elevates corner of mouth.

• Risorius: Draws corner of mouth laterally.

• Zygomaticus major/minor: Elevates corner of mouth (smiling).

• Platysma: Tenses skin of neck.

• Orbicularis oculi: Closes eyelids.

Extrinsic Eye Muscles

• Medial rectus

• Lateral rectus

• Inferior rectus

• Superior rectus

• Inferior oblique

• Superior oblique

Muscles of Mastication

• Temporalis: Elevates and retracts mandible.

• Masseter: Elevates mandible (primary chewing muscle).

Muscles of the Anterior Neck

• Digastric

• Mylohyoid

• Sternohyoid

• Thyrohyoid

Muscles that Move the Head, Neck, Torso

• Sternocleidomastoid: Rotates and flexes neck.

• Scalene muscles: Anterior, middle, and posterior; flex and rotate neck, elevate ribs during inspiration.

• Splenius capitis/cervicis: Extend and rotate head.

• Semispinalis capitis: Extends head and neck.

Muscles of Respiration

• Serratus posterior inferior/superior: Assist in respiration.

• External and internal intercostals: Elevate and depress ribs.

• Diaphragm: Main muscle of inspiration.

Muscles of the Abdominal Wall

• External oblique

• Internal oblique

• Transverse abdominis

• Rectus abdominis

Muscles of the Appendicular Skeleton

Muscles that Move the Pectoral Girdle

• Pectoralis minor

• Serratus anterior

• Subclavius

• Levator scapulae

• Rhomboid major/minor

• Trapezius

Muscles that Move the Shoulder/Arm

• Latissimus dorsi

• Pectoralis major

• Deltoid

• Coracobrachialis

• Teres major/minor

• Subscapularis

• Supraspinatus

• Infraspinatus

Muscles that Move the Forearm, Wrist, Hand

• Brachialis

• Brachioradialis

• Pronator teres

• Flexor carpi radialis

• Flexor carpi ulnaris

• Flexor digitorum superficialis

• Extensor carpi radialis longus/brevis

• Extensor digitorum

• Extensor carpi ulnaris

Muscle Groups

• Rotator cuff: Supraspinatus, infraspinatus, teres minor, subscapularis; stabilize shoulder joint.

• Hamstrings: Biceps femoris, semitendinosus, semimembranosus; flex knee, extend hip.

• Quadriceps: Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius; extend knee.

• Triceps surae: Gastrocnemius, soleus; plantar flex foot.

Muscles that Move the Hip/Thigh

• Psoas major

• Iliacus

• Sartorius

• Rectus femoris

• Adductor longus

• Adductors

• Gracilis

• Pectineus

• Gluteus maximus/medius/minimus

• Tensor fasciae latae

• Hamstrings: Biceps femoris, semitendinosus, semimembranosus

Muscles that Move the Knee, Leg, Foot

• Quadriceps tendon

• Rectus femoris

• Vastus intermedius/lateralis/medialis

• Extensor digitorum longus

• Extensor hallucis longus

• Fibularis (peroneus) brevis/longus

• Gastrocnemius

• Soleus

• Plantaris

• Flexor digitorum longus

• Flexor hallucis longus

• Tibialis anterior/posterior

Key Concepts in Muscle Anatomy

Origin and Insertion

• Origin: The fixed attachment point of a muscle.

• Insertion: The movable attachment point where the muscle exerts force.

• Example: The biceps brachii originates at the scapula and inserts on the radius, allowing forearm flexion.

Muscle Actions and Organizational Patterns

• Agonist (prime mover): Muscle primarily responsible for movement.

• Antagonist: Muscle that opposes the action of the agonist.

• Synergist: Muscle that assists the agonist.

• Organizational patterns: Muscles can be parallel, convergent, pennate, or circular, affecting force and range of motion.

Classification Table: Muscle Roles

Muscle Naming Conventions

• Muscles are often named based on location, shape, size, direction of fibers, number of origins, or action.

• Example: Rectus femoris is named for its straight (rectus) orientation and location in the femur region.

Formulas and Equations

• Muscle Force Equation:

• Where F is force, m is mass, and a is acceleration. This basic physics equation applies to muscle contraction and movement.

Summary Table: Major Muscle Groups and Actions

Additional info:

• Muscle actions are often coordinated by groups, with agonists, antagonists, and synergists working together for smooth movement.

• Understanding muscle origin and insertion is crucial for predicting movement and diagnosing injuries.

• Muscle organization (parallel, pennate, etc.) affects strength and range of motion.