Muscles of the Human Body

Overview

The human body contains over 600 skeletal muscles, each with specific origins, insertions, and actions. Understanding these muscles is essential for comprehending movement, posture, and the mechanics of the musculoskeletal system. This guide summarizes key muscles by region, their primary actions, and anatomical attachments.

Muscles of the Scalp, Face, and Neck

Major Muscles and Their Functions

• Occipitalis (Occipital belly of occipitofrontalis/epicranius): Pulls scalp posteriorly. Origin: Occipital and temporal bones. Insertion: Epicranial aponeurosis.

• Frontalis (Frontal belly of occipitofrontalis/epicranius): Elevates eyebrows. Origin: Epicranial aponeurosis. Insertion: Skin of eyebrows.

• Epicranial aponeurosis: Tendinous sheet connecting the frontal and occipital bellies.

• Temporalis: Closes jaw. Origin: Zygomatic bone. Insertion: Angle & ramus of mandible.

• Buccinator: Compresses cheeks (as in blowing or sucking). Origin: Alveolar processes of maxilla and mandible. Insertion: Orbicularis oris.

• Mentalis: Elevates lower lip. Origin: Incisive fossa of mandible. Insertion: Skin of chin.

• Orbicularis oculi: Closes eyes. Origin: Orbit. Insertion: Skin around eyes.

• Orbicularis oris: Purses lips. Origin: Mandible. Insertion: Lips.

• Levator labii superioris: Elevates upper lip. Origin: Inferior margin of orbit. Insertion: Orbicularis oris.

• Masseter: Closes jaw. Origin: Zygomatic arch. Insertion: Mandibular ramus.

• Zygomaticus (major and minor): Retracts and elevates corners of mouth (smiling). Origin: Zygomatic bone. Insertion: Angle of the mouth.

• Sternocleidomastoid: Together: flexes neck; Alone: turns face to opposite side. Origin: Sternal end of clavicle and manubrium. Insertion: Mastoid process.

• Digastric: Depresses mandible. Origin: Inferior surface of mandible/temporal bone. Insertion: Hyoid bone.

• Platysma: Depresses mandible. Origin: Acromion of scapula. Insertion: Mandible.

• Depressor labii inferioris: Depresses lower lip. Origin: Mandible. Insertion: Skin of lower lip.

• Mylohyoid: Elevates hyoid bone. Origin: Mandible. Insertion: Hyoid bone.

• Omohyoid (superior and inferior belly): Depresses and retracts hyoid bone. Origin: Superior surface of scapula. Insertion: Hyoid bone.

• Sternohyoid: Depresses larynx and hyoid bone. Origin: Manubrium and medial end of clavicle. Insertion: Lower margin of hyoid.

• Sternothyroid: Depresses larynx and hyoid bone. Origin: Posterior surface of manubrium. Insertion: Thyroid cartilage.

Muscles of the Thorax and Back

Superficial Muscles

• Pectoralis major: Prime mover of arm flexion. Origin: Sternal end of clavicle. Insertion: Greater tubercle of humerus.

• Trapezius: Stabilizes, elevates, and rotates scapula. Origin: Occipital bone. Insertion: Acromion and spine of scapula.

Deep Muscles

• Internal intercostals: Depress rib cage (forced expiration). Origin: Superior border of rib. Insertion: Inferior border of rib above.

• External intercostals: Elevate rib cage (inspiration). Origin: Inferior border of rib. Insertion: Superior border of rib below.

• Diaphragm: Prime mover of inspiration. Origin: Inferior surface of rib cage. Insertion: Central tendon.

• Serratus anterior: Rotates scapula upward. Origin: Vertebral surface of scapula. Insertion: Anterior surface of scapula.

• Rhomboideus (rhomboids): Stabilizes scapula. Origin: Spinous process of C7 to T1. Insertion: Medial border of scapula.

• Pectoralis minor: Protracts and rotates scapula downward. Origin: Ribs 3-5. Insertion: Coracoid process of scapula.

Muscles of the Abdominal Region

• Rectus abdominis: Flexes and rotates lumbar region of vertebral column. Origin: Pubic bone. Insertion: Xiphoid process of sternum.

• Internal oblique: Compresses abdominal wall. Origin: Linea alba, pubic crest. Insertion: Inferior ribs, linea alba.

• External oblique: Compresses abdominal wall. Origin: Lower eight ribs. Insertion: Linea alba, iliac crest.

• Transverse abdominis: Compresses abdomen. Origin: Inguinal ligament, iliac crest, cartilages of last six ribs. Insertion: Linea alba, pubic crest.

• Linea alba: Fibrous structure running down the midline of the abdomen, serving as an attachment for abdominal muscles.

Muscles Crossing the Shoulder Joint

• Pectoralis major: Prime mover of arm flexion. Origin: Sternal end of clavicle. Insertion: Greater tubercle of humerus.

• Subscapularis: Medial rotation of arm. Origin: Subscapular fossa of scapula. Insertion: Lesser tubercle of humerus.

• Latissimus dorsi: Prime mover of arm extension. Origin: Iliac crest, thoracic and lumbar vertebrae. Insertion: Intertubercular sulcus of humerus.

• Supraspinatus: Initiates abduction of arm. Origin: Supraspinous fossa of scapula. Insertion: Greater tubercle of humerus.

• Infraspinatus: Laterally rotates arm. Origin: Infraspinous fossa of scapula. Insertion: Greater tubercle of humerus.

• Teres minor: Lateral rotation of humerus. Origin: Lateral margin of scapula. Insertion: Greater tubercle of humerus.

• Teres major: Extends, medially rotates, and adducts arm. Origin: Posterior surface of scapula. Insertion: Lesser tubercle of humerus.

• Deltoid: Prime mover of arm abduction. Origin: Acromion and spine of scapula. Insertion: Deltoid tuberosity of humerus.

Muscles of the Arm

• Coracobrachialis: Flexion and adduction of arm. Origin: Coracoid process of scapula. Insertion: Medial surface of humerus.

• Biceps brachii: Flexion of forearm. Origin: Scapula (short and long heads). Insertion: Radial tuberosity.

• Brachialis: Flexes forearm. Origin: Humerus. Insertion: Coronoid process of ulna.

• Brachioradialis: Forearm flexion. Origin: Humerus. Insertion: Styloid process of radius.

• Triceps brachii: Forearm extension. Origin: Scapula and humerus (three heads). Insertion: Olecranon of ulna.

Muscles of the Forearm

• Pronator teres: Pronates forearm. Origin: Medial epicondyle of humerus. Insertion: Radius.

• Palmaris longus: Tenses skin of palm during hand movement. Origin: Medial epicondyle of humerus. Insertion: Fascia of palm.

• Flexor carpi radialis: Flexion of hand. Origin: Medial epicondyle of humerus. Insertion: Palmar aponeurosis.

• Flexor carpi ulnaris: Flexes and adducts hand. Origin: Medial epicondyle of humerus. Insertion: Pisiform and hamate.

• Extensor carpi radialis longus: Extends hand. Origin: Humerus. Insertion: Base of second metacarpal.

• Extensor carpi radialis brevis: Extends and abducts hand. Origin: Lateral epicondyle of humerus. Insertion: Base of third metacarpal.

• Extensor carpi ulnaris: Extends hand. Origin: Lateral epicondyle of humerus. Insertion: Base of fifth metacarpal.

• Extensor digitorum: Prime mover of finger extension. Origin: Lateral epicondyle of humerus. Insertion: Distal phalanges.

• Abductor pollicis longus: Abducts thumb. Origin: Posterior surface of radius and ulna. Insertion: Base of first metacarpal.

• Extensor pollicis brevis: Extends thumb. Origin: Dorsal shaft of radius. Insertion: Proximal phalanx of thumb.

Muscles of the Thigh

Anterior Thigh

• Sartorius: Flexes and abducts thigh. Origin: Anterior superior iliac spine. Insertion: Medial aspect of proximal tibia.

• Pectineus: Adducts and medially rotates thigh. Origin: Pubis. Insertion: Lesser trochanter of femur.

• Adductor longus: Adducts and medially rotates thigh. Origin: Near pubic symphysis. Insertion: Linea aspera of femur.

• Adductor magnus: Adducts, medially rotates, and flexes thigh. Origin: Ischial and pubic ramus. Insertion: Linea aspera of femur.

• Gracilis: Adducts thigh, flexes and medially rotates leg. Origin: Inferior ramus and body of pubis. Insertion: Medial surface of tibia.

• Rectus femoris: Extends leg and flexes thigh. Origin: Anterior inferior iliac spine. Insertion: Patella and tibial tuberosity.

• Vastus lateralis: Extends leg and stabilizes knee. Origin: Greater trochanter. Insertion: Patella and tibial tuberosity.

• Vastus intermedius: Extends leg. Origin: Anterior and lateral surfaces of proximal femur. Insertion: Patella and tibial tuberosity.

• Vastus medialis: Extends leg. Origin: Linea aspera. Insertion: Patella and tibial tuberosity.

• Tensor fasciae latae: Steadies the leg and trunk. Origin: Iliac crest. Insertion: Iliotibial tract.

Posterior Thigh

• Gluteus maximus: Extends thigh. Origin: Sacrum, coccyx. Insertion: Gluteal tuberosity of femur.

• Gluteus medius: Abducts and medially rotates thigh. Origin: Lateral surface of ilium. Insertion: Greater trochanter of femur.

• Biceps femoris: Extends thigh and flexes leg. Origin: Ischial tuberosity. Insertion: Head of fibula.

• Semitendinosus: Extends thigh and flexes leg. Origin: Ischial tuberosity. Insertion: Medial aspect of tibial shaft.

• Semimembranosus: Extends thigh and flexes leg. Origin: Ischial tuberosity. Insertion: Medial aspect of tibial shaft.

Muscles of the Leg

Anterior Leg

• Tibialis anterior: Prime mover of dorsiflexion. Origin: Lateral condyle of tibia. Insertion: Cuneiform.

• Extensor digitorum longus: Extends toes. Origin: Lateral condyle of tibia. Insertion: Middle and distal phalanges of toes.

Posterior Leg

• Gastrocnemius: Plantar flexes foot. Origin: Condyles of femur. Insertion: Posterior of calcaneus.

• Soleus: Plantar flexes foot. Origin: Superior portion of tibia and fibula. Insertion: Posterior of calcaneus.

Summary Table: Selected Muscles, Actions, Origins, and Insertions

Key Terms and Concepts

• Origin: The fixed attachment point of a muscle, usually proximal or closer to the trunk.

• Insertion: The movable attachment point, usually distal or further from the trunk.

• Action: The movement produced when the muscle contracts.

• Prime mover (agonist): The main muscle responsible for a specific movement.

• Antagonist: Muscle that opposes the action of the prime mover.

• Synergist: Muscle that assists the prime mover.

• Fixator: Muscle that stabilizes the origin of the prime mover.

Examples and Applications

• Chewing: The masseter and temporalis muscles work together to close the jaw during mastication.

• Breathing: The diaphragm contracts to increase thoracic volume, drawing air into the lungs.

• Walking: The gluteus maximus, quadriceps femoris group, and gastrocnemius coordinate to extend the hip, knee, and ankle, respectively.

Additional info:

• Some muscle origins and insertions were inferred based on standard anatomical knowledge where the original notes were incomplete.

• Muscle actions may vary slightly depending on joint position and synergistic muscle activity.