Gross Anatomy of the Muscular System: Study Notes

Gross Anatomy of the Muscular System

Introduction to Skeletal Muscle Anatomy

The muscular system is responsible for movement, posture, and heat production in the human body. Understanding the structure, classification, and naming of muscles is essential for studying anatomy and physiology.

• Origin: The fixed attachment point of a muscle.

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

• Action: The specific movement produced when a muscle contracts.

Classification of Muscles by Function

• Prime Movers (Agonists): Muscles primarily responsible for a specific movement.

• Antagonists: Muscles that oppose or reverse a movement.

• Synergists: Muscles that assist the prime mover by adding force or reducing unnecessary movement.

• Fixators: Specialized synergists that immobilize the origin of a prime mover for stability.

Criteria for Naming Muscles

• Location: e.g., Temporalis (temporal bone)

• Shape: e.g., Deltoid (triangular)

• Size: e.g., Gluteus maximus (largest gluteal muscle)

• Direction of fibers: e.g., Rectus abdominis (straight fibers)

• Number of origins: e.g., Biceps brachii (two origins)

• Location of attachments: e.g., Sternocleidomastoid (sternum, clavicle, mastoid process)

• Action: e.g., Flexor carpi ulnaris (flexes wrist on ulnar side)

Major Muscles of the Head and Neck

These muscles control facial expressions, mastication, and movements of the head and neck.

Muscle	Action	Origin	Insertion
Frontalis	Raises eyebrows	Epicranial aponeurosis	Skin of eyebrows
Occipitalis	Pulls scalp back	Epicranial aponeurosis	Occipital bone
Orbicularis oculi	Blinks, closes eye	Frontal and maxillary bones	Tissue of eyelid
Orbicularis oris	Closes lips, kissing	Maxillary and mandible bones	Skin of mouth
Zygomaticus minor/major	Smiling	Zygomatic bone	Skin/muscle at mouth corner
Masseter	Elevates mandible	Zygomatic arch	Mandible
Temporalis	Elevates/retracts mandible	Temporal fossa	Coronoid process of mandible
Risorius	Draws lips laterally	Connective tissue anterior to ear	Skin of mouth angle
Buccinator	Compresses cheeks, aids chewing/whistling	Molar region of maxilla/mandible	Orbicularis oris
Platysma	Opens mouth, depresses mandible	Connective tissue of pectoral/deltoid muscles	Lower border of mandible, skin
Sternocleidomastoid	Neck flexion, head rotation	Sternum and clavicle	Mastoid process of temporal bone

Muscles of the Trunk

Anterior Muscles

Muscle	Action	Origin	Insertion
Diaphragm	Lowers thoracic cavity floor	Sternum, lower ribs, lumbar vertebrae	Central tendon of diaphragm
Rectus abdominis	Flexes trunk, compresses abdomen	Superior pubic bones	Costal cartilage of ribs 5-7
Transversus abdominis	Compresses abdominal cavity	Lower six costal cartilages	Pubic bone
Internal oblique	Flexes/rotates vertebral column, compresses abdomen	Iliac crest	Lower four ribs
External oblique	Flexes/rotates vertebral column, compresses abdomen	Lower eight ribs	Pubic and iliac crests

Posterior Muscles

Muscle	Action	Origin	Insertion
Trapezius	Extends head, elevates scapula	Occipital bone, cervical vertebrae	Clavicle
Rhomboids (major/minor)	Retracts scapula	Spinous processes C7-T1/T1-T5	Scapula
Teres major	Adducts, extends, rotates arm laterally	Posterior/inferior scapula	Medial sulcus of humerus

Muscles of the Rotator Cuff

The rotator cuff stabilizes the shoulder joint and allows for a wide range of arm movements.

Muscle	Action	Origin	Insertion
Supraspinatus	Abducts humerus	Supraspinous fossa of scapula	Greater tubercle of humerus
Infraspinatus	Laterally rotates humerus	Infraspinous fossa of scapula	Greater tubercle of humerus
Teres minor	Laterally rotates humerus, stabilizes shoulder	Posterior/lateral scapula	Greater tubercle of humerus
Subscapularis	Medially rotates humerus	Subscapular fossa of scapula	Lesser tubercle of humerus

Muscles of the Upper Limb

Muscle	Action	Origin	Insertion
Pectoralis major	Flexes, adducts, rotates arm	Clavicle, sternum, costal cartilage (ribs 1-7)	Intertubercular sulcus of humerus
Latissimus dorsi	Adducts, extends arm	Spinous processes of lower thoracic/lumbar vertebrae	Humerus
Deltoid	Abducts arm	Acromion, spine of scapula, clavicle	Deltoid tuberosity of humerus
Biceps brachii	Flexes arm at elbow	Glenoid cavity	Radial tuberosity
Brachialis	Flexes arm at elbow	Distal anterior humerus	Proximal ulna
Triceps brachii	Extends arm, stabilizes elbow	Glenoid cavity, head of humerus	Olecranon process of ulna
Flexor carpi ulnaris	Flexes wrist, adducts hand	Medial epicondyle humerus/olecranon ulna	Metacarpal V, carpals
Flexor carpi radialis	Flexes wrist, abducts hand	Medial epicondyle humerus	Metacarpal II, III
Flexor digitorum superficialis	Flexes fingers, wrist	Medial epicondyle humerus	Middle phalanges II-V
Flexor pollicis longus	Flexes thumb	Anterior diaphysis of radius	Distal phalange of thumb
Extensor carpi ulnaris	Extends wrist, adducts hand	Lateral epicondyle humerus	Metacarpal V, carpals
Extensor carpi radialis longus	Extends wrist, abducts hand	Lateral epicondyle humerus	Metacarpal II
Extensor digitorum	Extends fingers	Lateral epicondyle humerus	Posterior phalanges II-V
Extensor pollicis longus	Extends thumb	Posterior diaphysis of ulna	Distal phalange of thumb

Muscles of the Lower Limb

Muscle	Action	Origin	Insertion
Gluteus maximus	Extends thigh	Ilium	Tuberosity of femur
Gluteus medius	Abducts, rotates thigh	Ilium	Greater trochanter of femur
Hamstrings (Biceps femoris, Semitendinosus, Semimembranosus)	Flex knee, extend thigh	Ischial tuberosity	Tibia, fibula
Gastrocnemius	Plantar flexes foot	Condyles of femur	Calcaneus
Soleus	Plantar flexion	Proximal tibia, fibula	Calcaneus
Sartorius	Flexes, abducts, rotates thigh (cross-legged)	Iliac spine	Proximal tibia
Quadriceps (Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius)	Extend leg, stabilize knee	Pelvis, proximal femur	Tibia, patella
Tibialis anterior	Dorsiflexes foot	Lateral condyle of tibia	Cuneiform, first metatarsal

Muscle Action Demonstration and Measurement

Hand Dynamometer Activity

The hand dynamometer is used to measure grip strength, an indicator of muscular function in the hand and forearm.

1. Adjust the handle to fit your hand size using the adjustment knob.

2. Power on the device and set parameters (gender, age).

3. Grip and squeeze the dynamometer; the device displays your strength measurement and category.

Application: Grip strength is used in clinical and sports settings to assess muscular health and rehabilitation progress.

Muscle Action Demonstration Models

• Models such as the Large Muscle Man, torso, and muscle fiber models help visualize muscle structure and function.

• Demonstration models illustrate muscle actions, attachments, and movements.

Additional info: Understanding muscle origins, insertions, and actions is fundamental for clinical assessments, injury diagnosis, and physical therapy. The arrangement of muscle fibers and their attachments determines the range and strength of movement produced.