Gross Anatomy of the Muscular System: Study Guide

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Gross Anatomy of the Muscular System

Introduction to Muscular System Anatomy

The muscular system is responsible for producing movement, maintaining posture, and stabilizing joints. Skeletal muscles attach to bones via tendons and are responsible for voluntary movements. Understanding the origin, insertion, and action of each muscle is essential for comprehending how body movements are produced and coordinated.

Origin: The fixed attachment point of a muscle, usually proximal and less movable.
Insertion: The movable attachment point, usually distal; movement occurs here when the muscle contracts.
Agonists: Muscles that produce a specific movement.
Antagonists: Muscles that oppose the action of agonists.

Types of Muscle Movements

Muscle actions are defined by the movement they produce at joints. These movements are described relative to the anatomical position:

Flexion: Decreases the angle between two bones (e.g., bending the elbow).
Extension: Increases the angle between two bones (e.g., straightening the elbow).
Hyperextension: Extension beyond the anatomical position (e.g., tilting the head backward).
Dorsiflexion: Flexing the foot upward at the ankle.
Plantarflexion: Pointing the toes downward.
Abduction: Moving a limb away from the midline (e.g., raising arms sideways).
Adduction: Moving a limb toward the midline.
Rotation: Turning a bone around its own axis (medial or lateral).
Circumduction: Circular movement combining flexion, extension, abduction, and adduction.
Inversion: Turning the sole of the foot inward.
Eversion: Turning the sole of the foot outward.
Pronation: Rotating the forearm so the palm faces posteriorly.
Supination: Rotating the forearm so the palm faces anteriorly.

Study Tips for Muscular Anatomy

Review skeletal bone anatomy to understand muscle attachments.
Use anatomical models and digital resources to locate muscles.
Visualize muscle actions using elastic bands on skeleton models.
Study in manageable sections and use repetition for memorization.
Quiz with a partner for reinforcement.

Major Muscles of the Face and Neck

Facial Muscles

Facial muscles control expressions, mastication, and movements of the head. They are often attached to skin and other muscles rather than bones.

Muscle Name	Origin	Insertion	Action
Frontalis	Epicranial aponeurosis	Fascia of facial muscles and skin above nose and eyes	Draws back scalp, wrinkles forehead, raises eyebrows
Masseter	Maxilla and zygomatic arch	Angle and ramus of mandible	Elevates mandible (closes jaw), clenches teeth
Temporalis	Temporal bone	Coronoid process and ramus of mandible	Elevates mandible, assists with side-to-side movement
Orbicularis oculi	Frontal and maxilla bone	Skin of eyelids	Closes eye
Orbicularis oris	Maxilla and mandible	Skin of upper and lower lips	Closes and protrudes lips
Sternocleidomastoid	Sternum and clavicle	Mastoid process of temporal bone	Flexes head (both sides), rotates head to opposite side (one side)

Labeled diagram of facial muscles, anterior and lateral views

Muscles Involved in Ventilation

Thoracic Muscles

These muscles control the size of the thoracic cavity, facilitating breathing. The diaphragm is the primary muscle for inspiration, while intercostal muscles assist in both inspiration and forced expiration.

Muscle Name	Origin	Insertion	Action
Diaphragm	Xiphoid process, inferior rib cage, lumbar vertebrae	Central tendon	Contraction flattens muscle, increases thoracic volume (inspiration)
External intercostals	Inferior border of superior rib	Superior border of inferior rib	Elevates ribs during inspiration
Internal intercostals	Superior border of inferior rib	Inferior border of superior rib	Depresses ribs during forced exhalation

Muscles of the thoracic wall, including intercostals and pectoralis major

Muscles of the Abdominal Wall

Abdominal Muscles

The abdominal wall consists of four main muscles: rectus abdominis (anterior), and the external oblique, internal oblique, and transversus abdominis (lateral). These muscles flex, rotate, and compress the abdominal contents.

Muscle Name	Origin	Insertion	Action
Rectus abdominis	Pubic crest and symphysis	Xiphoid process, cartilage of 5th-7th ribs	Flexes and rotates vertebral column
External oblique	5th-12th ribs	Iliac crest, linea alba	Flexes, rotates vertebral column
Internal oblique	Iliac crest, inguinal ligament, thoracolumbar fascia	Linea alba, cartilage of 7th-10th ribs	Flexes, rotates vertebral column
Transversus abdominis	Iliac crest, inguinal ligament, lumbar fascia, cartilage of 5th-10th ribs	Xiphoid process, linea alba, pubis	Compresses abdominal contents

Superficial and deep abdominal muscles, anterior lateral view

Muscles that Act on the Pectoral (Shoulder) Girdle

Scapular Stabilizers

These muscles stabilize and move the scapula, aiding in arm movements. The trapezius is especially versatile due to its size and multiple fiber directions.

Muscle Name	Origin	Insertion	Action
Trapezius	Occipital bone, ligamentum nuchae, spinous processes of C7 and thoracic vertebrae	Clavicle, acromion, spine of scapula	Elevates, depresses, adducts, laterally rotates scapula
Rhomboid major	Spinous processes of T2-T5	Medial border of scapula (inferior to spine)	Adducts, medially rotates scapula
Rhomboid minor	Spinous processes of C7, T1	Medial border of scapula (superior to spine)	Adducts, medially rotates scapula

Muscles of the neck and upper back, including trapezius and rhomboids

Major Muscles that Act on the Humerus

Shoulder and Arm Movers

These muscles move the humerus at the shoulder joint. They include both superficial and deep muscles, with most originating on the scapula.

Muscle Name	Origin	Insertion	Action
Pectoralis major	Clavicle, sternum, cartilage of 2nd-6th ribs	Greater tubercle, intertubercular sulcus of humerus	Flexes, adducts, medially rotates arm
Latissimus dorsi	Spinous processes of T7-L5, sacrum, ilium, ribs	Intertubercular sulcus of humerus	Extends, adducts, medially rotates arm
Deltoid	Clavicle, acromion, spine of scapula	Deltoid tuberosity of humerus	Flexes, extends, abducts, rotates arm
Subscapularis	Subscapular fossa of scapula	Lesser tubercle of humerus	Medially rotates arm
Supraspinatus	Supraspinous fossa of scapula	Greater tubercle of humerus	Abducts arm
Infraspinatus	Infraspinous fossa of scapula	Greater tubercle of humerus	Abducts, laterally rotates arm
Teres minor	Inferior lateral border of scapula	Greater tubercle of humerus	Extends, adducts, laterally rotates arm
Teres major	Inferior angle of scapula	Intertubercular sulcus of humerus	Extends, adducts, medially rotates arm

Pectoralis major and latissimus dorsi, anterior and posterior views Deep muscles of the left shoulder, anterior and posterior views

Muscles that Act on the Forearm

Elbow Flexors and Extensors

The main muscles moving the forearm at the elbow are the biceps brachii, brachialis, brachioradialis (flexors), and triceps brachii (extensor). Some also cross the shoulder joint, affecting arm movement.

Muscle Name	Origin	Insertion	Action
Biceps brachii	Long head: supraglenoid tubercle; Short head: coracoid process of scapula	Radial tuberosity, bicipital aponeurosis	Flexes arm, flexes and supinates forearm
Brachialis	Distal anterior humerus	Ulnar tuberosity, coronoid process of ulna	Flexes forearm
Brachioradialis	Distal lateral humerus	Styloid process of radius	Flexes forearm
Triceps brachii	Long head: infraglenoid tubercle; Lateral/medial heads: posterior humerus	Olecranon process of ulna	Extends arm and forearm

Left upper arm muscles, anterior and posterior views

Muscles that Act on the Upper Leg (Thigh)

Gluteal and Adductor Muscles

These muscles originate on the pelvis and move the thigh at the hip joint. The iliotibial tract serves as an insertion for the gluteus maximus.

Muscle Name	Origin	Insertion	Action
Gluteus maximus	Iliac crest, sacrum, coccyx	Iliotibial tract, gluteal tuberosity	Extends, laterally rotates thigh
Gluteus medius	Iliac crest	Greater trochanter of femur	Abducts, medially rotates thigh
Adductor magnus	Inferior pubis	Linea aspera of femur	Adducts, flexes, extends, laterally rotates thigh
Adductor longus	Anterior pubis	Linea aspera of femur	Adducts, flexes, laterally rotates thigh
Iliopsoas	T12-L5 vertebrae, sacrum, iliac fossa	Lesser trochanter of femur	Flexes, laterally rotates thigh

Superficial pelvic and thigh muscles, anterior view Deep pelvic and thigh muscles, anterior and posterior views

Muscles that Act on the Upper and Lower Leg

Quadriceps and Hamstrings

The quadriceps group (anterior thigh) extends the lower leg, while the hamstrings (posterior thigh) flex the lower leg and extend the thigh.

Muscle Name	Origin	Insertion	Action
Rectus femoris	Anterior inferior iliac spine	Tibial tuberosity	Extends lower leg, flexes thigh
Vastus lateralis/medialis/intermedius	Femur (various locations)	Tibial tuberosity	Extends lower leg
Biceps femoris	Ischial tuberosity, linea aspera	Head of fibula, lateral condyle of tibia	Flexes lower leg, extends thigh
Semitendinosus	Ischial tuberosity	Medial proximal tibia	Flexes lower leg, extends thigh
Semimembranosus	Ischial tuberosity	Medial condyle of tibia	Flexes lower leg, extends thigh

Other Thigh and Leg Muscles

Muscle Name	Origin	Insertion	Action
Sartorius	Anterior superior iliac spine	Medial proximal tibia	Flexes lower leg, flexes and laterally rotates thigh
Gracilis	Inferior pubis	Medial proximal tibia	Flexes lower leg, adducts thigh
Adductor longus/magnus	Pubis/ischial tuberosity	Linea aspera, medial condyle of femur	Adducts, flexes, extends thigh, assists with lateral rotation

Muscles that Act on the Foot and Lower Leg

Anterior and Posterior Leg Muscles

These muscles control movements of the foot and toes, as well as plantarflexion and dorsiflexion at the ankle.

Muscle Name	Origin	Insertion	Action
Tibialis anterior	Lateral condyle of tibia	Medial cuneiform, 1st metatarsal	Dorsiflexes, inverts foot
Gastrocnemius	Posterior femoral condyles	Calcaneus via Achilles tendon	Plantarflexes foot, flexes lower leg
Soleus	Head of fibula, medial tibia	Calcaneus via Achilles tendon	Plantarflexes foot

Superficial and deep muscles of the lower leg, anterior and posterior views

Additional info: For exam preparation, focus on understanding muscle actions and their anatomical relationships rather than rote memorization of origins and insertions. Practice identifying muscles on models and diagrams, and reinforce learning through active recall and repetition.