Comprehensive Study Guide: Major Muscles of the Human Body – Names, Actions, and Attachments

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Overview of Muscle Classification and Naming

Introduction to Muscle Classification

Muscles in the human body can be classified and named based on several characteristics, including the orientation of their fibers, location, size, shape, and attachments. Understanding these conventions aids in identifying and remembering muscle functions and locations.

Orientation of Muscle Fibers: Describes the direction of muscle fibers relative to the body's midline.
Location or Specific Body Region: Indicates the anatomical region where the muscle is found.
Muscle Size: Refers to the relative size of the muscle within a group.
Muscle Shape: Describes the geometric shape of the muscle.
Muscle Attachment: Names may reflect the origin and insertion points.

Characteristic	Examples	Examples in Humans
Orientation of muscle fibers	Rectus (parallel), Transverse (perpendicular), Oblique (45° angle), Orbicularis (circular)	Rectus abdominis, Transverse abdominis, External oblique, Orbicularis oculi
Location or specific body region	Frontal bone, Tibia, Oris	Frontalis, Tibialis anterior, Orbicularis oris
Muscle size	Maximus (largest), Longus (longest), Brevis (shortest)	Gluteus maximus, Adductor longus, Adductor brevis
Muscle shape	Deltoid (triangle), Trapezius (trapezoid), Serratus (saw-toothed), Orbicularis (circular)	Deltoid, Trapezius, Serratus anterior, Orbicularis oculi
Muscle attachment	Origin, Insertion, Ribs	Sternocleidomastoid (sternum, clavicle, mastoid), External intercostals

Example: The sternocleidomastoid muscle is named for its attachments: the sternum, clavicle, and mastoid process.

Muscles of Facial Expression

Overview

Facial muscles control expressions by moving the skin rather than bones. Most originate from the skull or fascia and insert into the skin.

Muscle	Action	Origin	Insertion
Frontalis	Elevates eyebrows, wrinkles forehead horizontally	Epicranial aponeurosis	Skin of eyebrows
Corrugator supercilii	Pulls eyebrows medially	Frontal bone	Skin of eyebrows
Orbicularis oculi	Closes eye	Frontal bone and maxilla	Skin of orbital area
Levator labii superioris	Elevates upper lip	Zygomatic bone and maxilla	Skin of upper lip
Zygomaticus major	Elevates corners of mouth, pulls laterally	Zygomatic bone	Skin of corner of mouth
Zygomaticus minor	Elevates lateral portion of upper lip	Zygomatic bone	Skin of lateral upper lip
Risorius	Pulls angle of mouth laterally	Connective tissue near ear	Angle of mouth
Orbicularis oris	Closes and protrudes lips	Maxilla and mandible	Skin near lips
Depressor anguli oris	Draws corners of mouth inferiorly	Mandible	Angle of mouth
Depressor labii inferioris	Protrudes lower lip	Mandible	Skin of lower lip
Mentalis	Protrudes lower lip	Mandible	Skin of the chin
Buccinator	Pulls cheeks in	Maxilla and mandible	Connective tissue of cheeks and lips
Platysma	Depresses lower lip, depresses mandible (slightly), tenses skin on the neck	Connective tissue of shoulder	Mandible

Example: The orbicularis oculi allows you to close your eyes tightly.

Muscles of Mastication

Overview

These muscles are responsible for movements of the jaw during chewing.

Muscle	Action	Origin	Insertion
Masseter	Elevates mandible	Zygomatic arch	Mandible
Temporalis	Elevates and retracts mandible	Lateral skull	Mandible
Medial pterygoid	Elevates and protracts mandible	Sphenoid bone	Mandible
Lateral pterygoid	Depresses and protracts mandible	Sphenoid bone	Mandible

Example: The masseter is one of the strongest muscles relative to its size and is essential for biting and chewing.

Muscles that Move the Neck and Trunk

Overview

These muscles are involved in movements such as flexion, extension, lateral flexion, and rotation of the neck and trunk.

Muscle	Action	Origin	Insertion
Sternocleidomastoid	Flexes neck, contralateral rotation	Sternum and clavicle	Mastoid process
Scalenes (anterior, middle, posterior)	Laterally flex neck, elevate ribs	Cervical spine	Upper ribs
Trapezius (upper)	Extends neck	External occipital protuberance, cervical spine	Clavicle
Erector spinae group (Iliocostalis, Longissimus, Spinalis)	Extends and laterally flexes trunk	Pelvis, ribs, vertebrae	Ribs, vertebrae
Quadratus lumborum	Extends and laterally flexes trunk	Ilium	Rib 12, lumbar spine

Example: The sternocleidomastoid is easily visible when turning the head to the side.

Muscles of Respiration

Overview

These muscles facilitate breathing by altering the volume of the thoracic cavity.

Muscle	Action	Origin	Insertion
Diaphragm	Flattens, lowers floor of thoracic cavity	Ribs, vertebrae	Central tendon of diaphragm
External intercostals	Elevate ribs	Ribs	Ribs
Internal intercostals	Depress ribs	Ribs	Ribs

Example: The diaphragm is the primary muscle of inspiration.

Muscles of the Abdominal Wall

Overview

The four abdominal muscles compress the abdominal cavity and contribute to trunk movements.

Muscle	Action	Origin	Insertion
Rectus abdominis	Flexes trunk	Pubic bone	Ribs
External oblique	Flexes trunk, laterally flexes trunk, contralateral rotation	Ribs	Pelvis
Internal oblique	Flexes trunk, laterally flexes trunk, ipsilateral rotation	Pelvis	Ribs
Transverse abdominis	Compresses abdominal cavity	Pelvis, costal cartilage, thoracolumbar fascia	Pelvis

Example: The rectus abdominis is commonly known as the "six-pack" muscle.

Muscles that Move the Scapula

Overview

These muscles control the position and movement of the scapula, which is essential for upper limb mobility.

Muscle	Action	Origin	Insertion
Levator scapulae	Elevates scapula	Cervical spine	Superior angle of scapula
Rhomboid major and minor	Retract and elevate scapula	Thoracic spine	Medial border of scapula
Trapezius (superior)	Elevates scapula	External occipital protuberance, cervical spine	Clavicle
Trapezius (middle and inferior)	Retracts and depresses scapula	Spinous process of thoracic spine	Scapula spine and acromion
Pectoralis minor	Protracts and depresses scapula	Ribs	Coracoid process
Serratus anterior	Protracts scapula	Ribs	Medial border of scapula

Example: The serratus anterior is essential for the upward rotation of the scapula during arm elevation.

Muscles that Move the Humerus

Overview

These muscles are responsible for movements of the shoulder joint, including flexion, extension, abduction, adduction, and rotation.

Muscle	Action	Origin	Insertion
Pectoralis major	Flexes, adducts, and internally rotates shoulder	Sternum, costal cartilage	Proximal humerus
Latissimus dorsi	Extends, adducts, and internally rotates shoulder	Iliac crest, lumbar and lower thoracic spine	Humerus
Deltoid	Abducts, flexes (anterior), and extends (posterior) shoulder	Scapula	Humerus
Teres major	Adducts, extends, and internally rotates shoulder	Scapula	Humerus
Coracobrachialis	Flexes and adducts shoulder	Coracoid process	Humerus
Rotator Cuff Muscles	Stabilize glenohumeral joint
Supraspinatus	Abducts shoulder	Supraspinous fossa	Humerus
Infraspinatus	Externally rotates shoulder	Infraspinous fossa	Humerus
Teres minor	Externally rotates shoulder	Posterior scapula	Humerus
Subscapularis	Internally rotates shoulder	Subscapular fossa	Humerus

Example: The deltoid is the main muscle responsible for arm abduction.

Muscles that Move the Elbow

Overview

These muscles control flexion, extension, and rotation of the forearm at the elbow joint.

Muscle	Action	Origin	Insertion
Biceps brachii	Flexes and supinates elbow	Supraglenoid tubercle (long head), coracoid process (short head)	Radial tuberosity
Brachialis	Flexes elbow	Humerus	Ulna
Brachioradialis	Flexes elbow	Distal humerus	Distal radius
Triceps brachii	Extends elbow	Infraglenoid tubercle, posterior humerus	Olecranon process
Anconeus	Extends elbow	Lateral epicondyle of humerus	Olecranon process
Pronator teres	Pronates elbow	Medial epicondyle of humerus	Radius

Example: The biceps brachii is prominent when flexing the forearm.

Muscles that Move the Wrist and Fingers

Overview

These muscles control the complex movements of the wrist and fingers, allowing for gripping, writing, and other fine motor skills.

Muscle	Action	Origin	Insertion
Flexor carpi radialis	Flexes wrist	Medial epicondyle of humerus	Metacarpals
Flexor carpi ulnaris	Flexes wrist	Medial epicondyle of humerus	Metacarpals
Palmaris longus	Flexes wrist	Medial epicondyle of humerus	Flexor retinaculum
Extensor carpi radialis longus	Extends wrist	Humerus	Posterior metacarpal #2
Extensor carpi radialis brevis	Extends wrist	Humerus	Posterior metacarpal #3
Extensor carpi ulnaris	Extends wrist	Humerus	Metacarpal #5
Extensor digitorum	Extends digits 2-5	Humerus	Phalanges of digits 2-5
Flexor digitorum superficialis	Flexes digits 2-5 (proximal interphalangeal joint)	Medial epicondyle of humerus	Middle phalanges of digits 2-5
Flexor digitorum profundus	Flexes digits 2-5 (distal interphalangeal joint)	Anterior ulna	Distal phalanges of digits 2-5

Example: The extensor digitorum is responsible for extending the fingers.

Muscles that Move the Thumb

Overview

These muscles allow for the unique range of motion of the thumb, including flexion, extension, and abduction.

Muscle	Action	Origin	Insertion
Flexor pollicis longus	Flexes thumb	Radius	Distal phalanx of digit #1
Abductor pollicis longus	Abducts thumb	Radius and ulna	Metacarpal #1
Extensor pollicis longus	Extends thumb	Ulna	Distal phalanx of digit #1

Example: The abductor pollicis longus is essential for thumb abduction, a movement unique to primates.

Muscles that Move the Hip

Overview

These muscles control movements of the thigh at the hip joint, including flexion, extension, abduction, adduction, and rotation.

Muscle	Action	Origin	Insertion
Iliacus	Flexes hip	Iliac fossa	Lesser trochanter of femur
Psoas major	Flexes thigh and trunk, laterally flexes trunk	Transverse process and bodies of T12 and lumbar vertebrae	Lesser trochanter
Sartorius	Flexes hip and knee, abducts and laterally rotates hip	ASIS	Medial proximal tibia
Tensor fascia lata	Flexes and abducts hip, medially rotates hip	Iliac crest and ASIS	Iliotibial tract
Adductor magnus/longus/brevis	Adducts and flexes hip	Pelvis	Femur
Pectineus	Adducts and flexes hip	Pelvis	Femur
Gracilis	Adducts hip, flexes knee	Pelvis	Tibia
Gluteus maximus	Extends, laterally rotates, and abducts hip	Posterolateral ilium, sacrum, coccyx	Gluteal tuberosity of femur
Gluteus medius/minimus	Abducts and medially rotates hip, stabilizes pelvis	Outer surface of ilium	Greater trochanter
Piriformis	Laterally rotates and abducts hip	Anterolateral sacrum	Greater trochanter

Example: The iliopsoas (iliacus + psoas major) is the primary hip flexor.

Muscles that Move the Knee

Overview

These muscles are responsible for flexion and extension of the knee joint.

Muscle	Action	Origin	Insertion
Popliteus	Flexes and internally rotates knee	Lateral condyle of femur	Tibia
Quadriceps femoris group	Extends knee (rectus femoris also flexes hip)	Femur, AIIS (rectus femoris)	Patella → tibial tuberosity
Hamstring group (biceps femoris, semitendinosus, semimembranosus)	Extends hip, flexes knee	Ischial tuberosity	Fibular head (biceps femoris), proximal tibia (others)

Example: The quadriceps femoris is the main extensor of the knee.

Muscles that Move the Ankle and Toes

Overview

These muscles control dorsiflexion, plantarflexion, inversion, eversion, and movements of the toes.

Muscle	Action	Origin	Insertion
Tibialis anterior	Ankle dorsiflexion, inversion	Anterior tibia	First metatarsal
Extensor digitorum longus	Extends toes 2-5, ankle dorsiflexion	Tibia and fibula	Phalanges of toes 2-5
Extensor hallucis longus	Extends hallux, ankle dorsiflexion	Fibula	Hallux
Fibularis longus/brevis	Ankle eversion, plantarflexion	Fibula	First metatarsal (longus), 5th metatarsal (brevis)
Gastrocnemius	Ankle plantarflexion, knee flexion	Femoral condyles	Calcaneus
Soleus	Ankle plantarflexion	Fibular head, tibia	Calcaneus
Plantaris	Ankle plantarflexion	Posterior femur	Calcaneus
Tibialis posterior	Ankle inversion, plantarflexion	Posterior tibia, fibula	Metatarsals 2-4
Flexor digitorum longus	Flexes toes 2-5	Posterior tibia	Distal phalanges of toes 2-5
Flexor hallucis longus	Flexes hallux	Fibula	Distal phalanx of hallux

Example: The gastrocnemius forms the bulk of the calf and is important for jumping and running.

Summary Table: Major Muscle Groups and Actions

Region	Key Muscles	Main Actions
Face	Frontalis, Orbicularis oculi, Zygomaticus major	Facial expression
Jaw	Masseter, Temporalis	Mastication
Neck	Sternocleidomastoid, Scalenes	Neck movement
Trunk	Rectus abdominis, Erector spinae	Trunk flexion/extension
Shoulder	Deltoid, Rotator cuff	Arm movement
Elbow	Biceps brachii, Triceps brachii	Forearm flexion/extension
Wrist/Hand	Flexor carpi radialis, Extensor digitorum	Wrist/finger movement
Hip	Gluteus maximus, Iliopsoas	Thigh movement
Knee	Quadriceps, Hamstrings	Leg flexion/extension
Ankle/Foot	Gastrocnemius, Tibialis anterior	Foot movement

Additional info:

Muscles often cross more than one joint and may have multiple actions depending on joint position.
Learning muscle groups by function (e.g., flexors, extensors) can aid in memorization.
Origin refers to the fixed attachment, while insertion moves with contraction.