dindin777

[princeofnazareth]

Here is your complete, raw muscle list organized into a clean, uniform, and
highly readable academic study guide. Tyrant typos, broken lines, and OCR
fragments have been corrected.

Part 1: Muscles of the Head, Neck & Cranial Region

Muscles of the Face

All muscles of facial expression are innervated by the facial nerve (CN VII).

• Occipitofrontalis (Frontal Belly)
  • Origin: Epicranial aponeurosis
  • Insertion: Skin and subcutaneous tissue of eyebrows and forehead
  • Action: Elevates eyebrows and wrinkles skin of forehead; protracts scalp
    (expresses surprise)
• Occipitofrontalis (Occipital Belly)
  • Origin: Lateral two-thirds of superior nuchal line
  • Insertion: Epicranial aponeurosis
  • Action: Retracts scalp
• Orbicularis Oculi
  • Origin: Medial orbital margin; medial palpebral ligament; lacrimal bone
  • Insertion: Skin around orbital margin; superior and inferior tarsal
    plates
  • Action:
    • Orbital part: Closes eyelids tightly (squinting)
    • Palpebral part: Closes eyelids gently (blinking)
    • Lacrimal part: Aids in draining tears
• Corrugator Supercilii
  • Origin: Medial end of superciliary arch
  • Insertion: Skin superior to the middle of the supraorbital margin and
    superciliary arch
  • Action: Draws eyebrows medially and inferiorly, creating vertical
    wrinkles above the nose (expresses concern or worry)
• Procerus
  • Origin: Fascia/aponeurosis covering the nasal bone and superior lateral
    nasal cartilage
  • Insertion: Skin of glabella; fibers of the frontal belly of
    occipitofrontalis
  • Action: Depresses medial end of eyebrow, wrinkling the skin over the
    glabella (expresses anger)
• Nasalis (Transverse Part)
  • Origin: Maxilla (superolateral to the incisive fossa)
  • Insertion: Merges with its counterpart at the dorsum of the nose
  • Action: Wrinkles the skin over the dorsum of the nose (expresses
    dislike/flaring)
• Nasalis (Alar Part)
  • Origin: Frontal process of maxilla (inferomedial to the orbital margin)
  • Insertion: Skin of the ala; major alar cartilage
  • Action: Depresses ala laterally, dilating the anterior nasal aperture
    (flares nostrils in anger or exertion)
• Levator Labii Superioris Alaeque Nasi
  • Origin: Frontal process of maxilla
  • Insertion: Blends with the muscles of the upper lip and the lateral
    nasal ala
  • Action: Elevates upper lip, dilates nostril, and exposes maxillary teeth
• Depressor Septi Nasi
  • Origin: Incisive fossa of maxilla
  • Insertion: Nasal septum and posterior aspect of the alar part of nasalis
  • Action: Depresses nasal septum and pulls the ala of the nose downward
• Orbicularis Oris
  • Origin: Medial maxilla and mandible; deep surface of perioral skin;
    angle of mouth (modiolus)
  • Insertion: Mucous membrane of the lips
  • Action: Tonic contraction closes the oral fissure; phasic contraction
    compresses and protrudes the lips (kissing/pouting) or resists
    distension (as when blowing)
• Levator Labii Superioris
  • Origin: Infraorbital margin (maxilla)
  • Insertion: Skin of the upper lip
  • Action: Retracts (elevates) and everts upper lip; deepens the nasolabial
    sulcus (expresses sadness or seriousness)
• Zygomaticus Minor
  • Origin: Anterior aspect of the zygomatic bone
  • Insertion: Skin of the upper lip (medial to corner of mouth)
  • Action: Elevates the upper lip (assists in exposing teeth)
• Buccinator
  • Origin: Alveolar processes of maxilla and mandible; pterygomandibular
    raphe
  • Insertion: Angle of the mouth (modiolus); orbicularis oris
  • Action: Presses the cheek against the molar teeth; works with the tongue
    to keep food between occlusal surfaces and out of the oral vestibule;
    resists distension (as when blowing)
• Zygomaticus Major
  • Origin: Lateral aspect of zygomatic bone
  • Insertion: Angle of the mouth (modiolus)
  • Action: Elevates the labial commissure (bilaterally to smile;
    unilaterally to sneer)
• Levator Anguli Oris
  • Origin: Infra-orbital maxilla (canine fossa)
  • Insertion: Angle of the mouth (modiolus)
  • Action: Widens the oral fissure (as when grinning or grimacing)
• Risorius
  • Origin: Parotid fascia and buccal skin (highly variable)
  • Insertion: Angle of the mouth (modiolus)
  • Action: Draws the corner of the mouth laterally (grimacing)
• Depressor Anguli Oris
  • Origin: Anterolateral base of the mandible
  • Insertion: Angle of the mouth (modiolus)
  • Action: Depresses labial commissure bilaterally to frown (expresses
    sadness)
• Depressor Labii Inferioris
  • Origin: Anterolateral body of the mandible
  • Insertion: Skin of the lower lip
  • Action: Retracts (depresses) and/or everts the lower lip (pouting,
    expressing sadness)
• Mentalis
  • Origin: Body of the mandible (anterior to the roots of the inferior
    incisors)
  • Insertion: Skin of the chin (mentolabial sulcus)
  • Action: Elevates and protrudes the lower lip; elevates the skin of the
    chin (expresses doubt)
• Temporalis (Muscle of Mastication - CN V₃)
  • Origin: Temporal fossa (up to the inferior temporal line) and temporal
    fascia
  • Insertion: Apex and medial surface of the coronoid process of the
    mandible
  • Action: Anterior fibers elevate the mandible; posterior part retracts
    the mandible
• Auricularis (Superior, Anterior, Posterior)
  • Origin: Temporal fascia and epicranial aponeurosis
  • Insertion: Cartilage of the ear
  • Action: Adjusts and wiggles the ear
• Masseter (Muscle of Mastication - CN V₃; does not participate in facial
  expression)
  • Origin:
    • Superficial part: Maxillary process of zygomatic bone; inferior
      border of zygomatic arch
    • Deep part: Inferior/deep surface of zygomatic arch
  • Insertion: Lateral surface of the ramus and angle of the mandible
  • Action: Elevates and protrudes the mandible (clenches teeth)

Cutaneous and Superficial Muscles of the Neck

• Platysma
  • Superior Attachment: Inferior border of the mandible; skin of cheek and
    lower lip; modiolus; orbicularis oris
  • Inferior Attachment: Fascia covering superior parts of the pectoralis
    major and deltoid muscles
  • Action: Draws the corners of the mouth inferiorly and widens it
    (expresses sadness/fright); draws skin of the neck superiorly when teeth
    are clenched; depresses mandible against resistance
• Sternocleidomastoid (SCM)
  • Superior Attachment: Lateral surface of mastoid process of temporal
    bone; lateral half of superior nuchal line
  • Inferior Attachment:
    • Sternal head: Anterior surface of the manubrium of the sternum
    • Clavicular head: Superior surface of the medial third of the
      clavicle
  • Action:
    • Unilateral: Tilts head to the same side (laterally flexes) and
      rotates face to the opposite side
    • Bilateral: Extends neck at atlanto-occipital joints; flexes cervical
      vertebrae (chin to chest); assists in deep respiration by elevating
      the manubrium and clavicles
• Trapezius (Cranial Nerve XI)
  • Superior Attachment: Medial third of superior nuchal line; external
    occipital protuberance; nuchal ligament; spinous processes of C7–T12
  • Inferior Attachment: Lateral third of clavicle; acromion; spine of
    scapula
  • Action: Elevates, retracts, and rotates scapulae superiorly; bilateral
    contraction extends the neck; unilateral contraction produces lateral
    flexion to the same side

Muscles of the Anterior Cervical Region (Extrinsic Muscles of Larynx)

Suprahyoid Muscles (Elevators of Hyoid/Larynx)

• Mylohyoid (Innervation: Nerve to mylohyoid, CN V₃)
  • Origin: Mylohyoid line of the mandible
  • Insertion: Mylohyoid raphe and body of the hyoid bone
  • Action: Elevates hyoid bone, floor of the mouth, and tongue during
    swallowing and speaking
• Geniohyoid (Innervation: C1 via hypoglossal nerve, CN XII)
  • Origin: Inferior mental spine of the mandible
  • Insertion: Body of the hyoid bone
  • Action: Pulls the hyoid anterosuperiorly; shortens the floor of the
    mouth; widens the pharynx
• Stylohyoid (Innervation: Facial nerve, CN VII)
  • Origin: Styloid process of the temporal bone
  • Insertion: Body of the hyoid bone
  • Action: Elevates and retracts the hyoid bone; elongates the floor of the
    mouth
• Digastric
  • Origin:
    • Anterior belly (CN V₃): Digastric fossa of the mandible
    • Posterior belly (CN VII): Mastoid notch of the temporal bone
  • Insertion: Intermediate tendon attached to the body and greater horn of
    the hyoid bone
  • Action: Depresses the mandible against resistance (with infrahyoids
    fixed); elevates hyoid during swallowing and speaking

Infrahyoid Muscles (Depressors of Hyoid/Larynx)

All are innervated by the ansa cervicalis (C1–C3), except the thyrohyoid.

• Sternohyoid
  • Origin: Manubrium of the sternum and medial end of the clavicle
  • Insertion: Body of the hyoid bone
  • Action: Depresses the hyoid bone after elevation during swallowing
• Omohyoid
  • Origin: Superior border of the scapula near the suprascapular notch
  • Insertion: Inferior border of the hyoid bone
  • Action: Depresses, retracts, and steadies the hyoid bone
• Thyrohyoid (Innervation: C1 via hypoglossal nerve, CN XII)
  • Origin: Oblique line of the thyroid cartilage
  • Insertion: Inferior border of the body and greater horn of the hyoid
    bone
  • Action: Depresses the hyoid bone and elevates the larynx
• Sternothyroid
  • Origin: Posterior surface of the manubrium of the sternum
  • Insertion: Oblique line of the thyroid cartilage
  • Action: Depresses the hyoid bone and the larynx

Suboccipital Muscles

Mainly innervated by the suboccipital nerve (posterior ramus of C1).

• Rectus Capitis Posterior Major
  • Origin: Spinous process of the axis (C2)
  • Insertion: Lateral part of the inferior nuchal line of the occipital
    bone
  • Action: Bilaterally extends the head; unilaterally rotates the head
    ipsilaterally
• Rectus Capitis Posterior Minor
  • Origin: Posterior tubercle of the atlas (C1)
  • Insertion: Medial part of the inferior nuchal line of the occipital bone
  • Action: Bilaterally extends the head at the atlanto-occipital joint
• Obliquus Capitis Inferior
  • Origin: Spinous process of the axis (C2)
  • Insertion: Transverse process of the atlas (C1)
  • Action: Bilaterally extends the head; unilaterally rotates the
    atlas/head ipsilaterally
• Obliquus Capitis Superior
  • Origin: Transverse process of the atlas (C1)
  • Insertion: Occipital bone (between the superior and inferior nuchal
    lines)
  • Action: Bilaterally extends the head; unilaterally flexes the head
    laterally to the same side

Prevertebral Muscles

Anterior Vertebral Muscles (Flexors)

• Longus Colli
  • Superior Attachment: Anterior tubercle of C1; bodies of C1–C3;
    transverse processes of C3–C6
  • Inferior Attachment: Bodies of C5–T3; transverse processes of C3–C5
  • Action: Flexes the neck; permits rotation to the opposite side if acting
    unilaterally
• Longus Capitis
  • Superior Attachment: Basilar part of the occipital bone
  • Inferior Attachment: Anterior tubercles of the transverse processes of
    C3–C6
  • Action: Flexes the head at the atlanto-occipital joints
• Rectus Capitis Anterior
  • Superior Attachment: Base of cranium, anterior to the occipital condyle
  • Inferior Attachment: Anterior surface of the lateral mass of C1 (atlas)
  • Action: Flexes the head at the atlanto-occipital joints
• Anterior Scalene
  • Superior Attachment: Transverse processes of C3–C6
  • Inferior Attachment: First rib
  • Action: Flexes the head and neck; elevates the first rib during deep
    respiration

Lateral Vertebral Muscles (Lateral Flexors & Stabilizers)

• Rectus Capitis Lateralis
  • Superior Attachment: Jugular process of the occipital bone
  • Inferior Attachment: Transverse process of C1 (atlas)
  • Action: Flexes the head laterally and helps stabilize it at the
    atlanto-occipital joint
• Splenius Capitis
  • Superior Attachment: Lateral aspect of mastoid process; lateral third of
    superior nuchal line
  • Inferior Attachment: Inferior half of nuchal ligament; spinous processes
    of C7–T6
  • Action: Laterally flexes and rotates the head/neck to the same side;
    bilaterally extends the head and neck
• Levator Scapulae
  • Superior Attachment: Posterior tubercles of transverse processes of
    C1–C4
  • Inferior Attachment: Superior part of the medial border of the scapula
  • Action: Rotates the scapula downward and tilts its glenoid cavity
    inferiorly; elevates the scapula
• Middle Scalene
  • Superior Attachment: Posterior tubercles of transverse processes of
    C5–C7
  • Inferior Attachment: Superior surface of the first rib
  • Action: Flexes the neck laterally; elevates the first rib during forced
    inspiration
• Posterior Scalene
  • Superior Attachment: Transverse processes of C5–C7
  • Inferior Attachment: External border of the second rib
  • Action: Flexes the neck laterally; elevates the second rib during forced
    inspiration

Part 2: Muscles of the Trunk, Thorax & Abdomen

Muscles of the Thoracic Wall

• Serratus Posterior Superior
  • Superior Attachment: Nuchal ligament; spinous processes of C7–T3
  • Inferior Attachment: Superior borders of the 2nd–4th ribs
  • Action: Elevates the ribs (assists in inspiration)
• Serratus Posterior Inferior
  • Superior Attachment: Spinous processes of T11–L2
  • Inferior Attachment: Inferior borders of the 8th–12th ribs
  • Action: Depresses the ribs (assists in expiration)
• Levatores Costarum
  • Superior Attachment: Transverse processes of C7 and T1–T11
  • Inferior Attachment: Subjacent ribs between the tubercle and angle
  • Action: Elevates the ribs, assisting in respiration; assists with
    lateral flexion of the vertebral column
• External Intercostals
  • Superior Attachment: Inferior border of the rib above
  • Inferior Attachment: Superior border of the rib below
  • Action: Elevates the ribs; most active during inspiration
• Internal Intercostals
  • Superior Attachment: Inferior border of the rib above
  • Inferior Attachment: Superior border of the rib below
  • Action:
    • Interosseous part: Depresses the ribs (active during expiration)
    • Interchondral part: Elevates the ribs
• Innermost Intercostals
  • Superior Attachment: Internal surface of the rib above
  • Inferior Attachment: Superior border of the rib below
  • Action: Act similarly to the internal intercostal muscles (depress ribs
    during expiration)
• Subcostals
  • Superior Attachment: Internal surface of lower ribs near their angles
  • Inferior Attachment: Superior borders of the 2nd or 3rd ribs below
  • Action: Act similarly to internal intercostal muscles
• Transversus Thoracis
  • Superior Attachment: Internal surface of costal cartilages 2–6
  • Inferior Attachment: Posterior surface of the lower sternum
  • Action: Weakly depresses the ribs

Muscles of the Anterolateral Abdominal Wall

• External Oblique
  • Origin: External surfaces of the 5th–12th ribs
  • Insertion: Linea alba; pubic tubercle; anterior half of the iliac crest
  • Action: Compresses and supports abdominal viscera; flexes and rotates
    the trunk (primary rotator)
• Internal Oblique
  • Origin: Thoracolumbar fascia; anterior two-thirds of the iliac crest;
    connective tissue deep to the lateral third of the inguinal ligament
  • Insertion: Inferior borders of the 10th–12th ribs; linea alba; pecten
    pubis (via conjoint tendon)
  • Action: Compresses and supports abdominal viscera; flexes and rotates
    the trunk
• Transversus Abdominis
  • Origin: Internal surfaces of the 7th–12th costal cartilages;
    thoracolumbar fascia; iliac crest; connective tissue deep to the lateral
    third of the inguinal ligament
  • Insertion: Linea alba (with aponeurosis of internal oblique); pubic
    crest; pecten pubis (via conjoint tendon)
  • Action: Compresses and supports abdominal viscera (does not rotate the
    trunk)
• Rectus Abdominis
  • Origin: Pubic symphysis and pubic crest
  • Insertion: Xiphoid process and 5th–7th costal cartilages
  • Action: Flexes the trunk (lumbar vertebrae) and compresses abdominal
    viscera; controls pelvic tilt (primary flexor of the trunk)
• Pyramidalis
  • Origin: Pubic crest and symphysis
  • Insertion: Linea alba
  • Action: Tenses the linea alba

Muscles of the Posterior Abdominal Wall

• Psoas Major
  • Origin: Transverse processes of lumbar vertebrae; sides of bodies of
    T12–L5 with their IV discs
  • Insertion: By a strong tendon to the lesser trochanter of the femur
  • Action: Flexes the thigh at the hip (acting with iliacus); flexes the
    vertebral column laterally (acting superiorly); flexes trunk when
    sitting
• Psoas Minor
  • Origin: Vertebral bodies of T12 and L1
  • Insertion: Iliopubic eminence and pectineal line of the pubis
  • Action: Assists in flexing the pelvis on the vertebral column (weak
    flexor)
• Iliacus
  • Origin: Superior two-thirds of the iliac fossa; ala of the sacrum;
    anterior sacro-iliac ligaments
  • Insertion: Lesser trochanter of the femur and the shaft inferior to it,
    joining the psoas major tendon
  • Action: Flexes the thigh at the hip joint and stabilizes the hip; works
    with the psoas major (collectively forming the iliopsoas, the chief
    flexor of the thigh)
• Quadratus Lumborum
  • Origin: Iliolumbar ligament and internal lip of the iliac crest
  • Insertion: Medial half of the inferior border of the 12th rib and tips
    of the lumbar transverse processes
  • Action: Extends and laterally flexes the vertebral column; fixes
    the 12th rib during inspiration

Intrinsic Back Muscles (Deep Back Muscles)

Superficial Layer

• Splenius Capitis
  • Origin: Lower half of the nuchal ligament; spinous processes of C7–T3/T4
  • Insertion: Lateral aspect of the mastoid process; lateral third of the
    superior nuchal line
  • Action: Acting alone: laterally flexes neck and rotates head
    ipsilaterally. Acting together: extends head and neck.
• Splenius Cervicis
  • Origin: Spinous processes of T3–T6
  • Insertion: Transverse processes (posterior tubercles) of C1–C3/C4
  • Action: Acting alone: laterally flexes neck and rotates neck
    ipsilaterally. Acting together: extends the neck.

Intermediate Layer (Erector Spinae)

All are acting bilaterally to extend the vertebral column and head, and
unilaterally to laterally flex the column.

• Iliocostalis (Lumborum, Thoracis, Cervicis)
  • Origin: Broad tendon from posterior part of iliac crest; posterior
    surface of sacrum; sacro-iliac ligaments; sacral and inferior lumbar
    spinous processes
  • Insertion: Angles of the lower ribs; cervical transverse processes
  • Action: Extends and laterally flexes the vertebral column
• Longissimus (Thoracis, Cervicis, Capitis)
  • Origin: Broad common tendon of erector spinae
  • Insertion: Ribs between tubercles and angles; transverse processes in
    thoracic and cervical regions; mastoid process of temporal bone
  • Action: Extends and laterally flexes the vertebral column; extends the
    head (capitis portion)
• Spinalis (Thoracis, Cervicis, Capitis)
  • Origin: Spinous processes in upper lumbar/lower thoracic regions
  • Insertion: Spinous processes in upper thoracic/cervical regions; cranium
  • Action: Extends the vertebral column and head

Deep Layer (Transversospinalis)

These muscles arise from transverse processes and insert onto spinous processes
of more superior vertebrae.

• Semispinalis (Thoracis, Cervicis, Capitis)
  • Origin: Transverse processes of C4–T12 vertebrae
  • Insertion: Occipital bone (between superior and inferior nuchal lines)
    and spinous processes in thoracic and cervical regions (spanning 4–6
    segments)
  • Action: Extends head and thoracic/cervical regions of vertebral column;
    rotates them contralaterally
• Multifidus
  • Origin: Posterior sacrum; PSIS; aponeurosis of erector spinae;
    sacro-iliac ligaments; mammillary processes of lumbar vertebrae;
    transverse processes of T1–T3; articular processes of C4–C7
  • Insertion: Spinous processes of vertebrae 2–4 segments superior to
    origin (thickest in the lumbar region)
  • Action: Stabilizes vertebrae during local movements of the vertebral
    column
• Rotatores (Brevis and Longus)
  • Origin: Transverse processes of vertebrae (best developed in the
    thoracic region)
  • Insertion: Junction of lamina and transverse process or spinous process
    of vertebra 1 segment superior (brevis) or 2 segments superior (longus)
    to origin
  • Action: Stabilize vertebrae and assist with local extension and rotatory
    movements of the vertebral column; function primarily in proprioception
• Interspinales
  • Origin: Superior surfaces of spinous processes of cervical and lumbar
    vertebrae
  • Insertion: Inferior surfaces of spinous processes of the vertebra
    directly superior to origin
  • Action: Aids in extension and rotation of the vertebral column
• Intertransversarii
  • Origin: Transverse processes of cervical and lumbar vertebrae
  • Insertion: Transverse processes of adjacent vertebrae
  • Action: Aids in lateral flexion of the vertebral column; acting
    bilaterally, stabilizes the vertebral column

Part 3: Muscles of the Upper Limb

Anterior Axio-Appendicular Muscles (Pectoral Group)

• Pectoralis Major
  • Origin:
    • Clavicular head: Medial half of clavicle
    • Sternocostal head: Sternum; superior 6 costal cartilages;
      aponeurosis of external oblique
  • Insertion: Lateral lip of intertubercular sulcus (bicipital groove) of
    the humerus
  • Action: Adducts and medially rotates the humerus; clavicular head flexes
    humerus; sternocostal head extends humerus from a flexed position
• Pectoralis Minor
  • Origin: 3rd–5th ribs near their costal cartilages
  • Insertion: Coracoid process of the scapula
  • Action: Stabilizes the scapula by drawing it inferiorly and anteriorly
    against the thoracic wall
• Subclavius
  • Origin: Junction of the 1st rib and its costal cartilage
  • Insertion: Inferior surface of the clavicle (subclavian groove)
  • Action: Anchors and depresses the clavicle; stabilizes the clavicle
    during movements of the shoulder girdle
• Serratus Anterior
  • Origin: External surfaces of lateral parts of the 1st–8th ribs
  • Insertion: Anterior medial border of the scapula
  • Action: Protracts the scapula and holds it against the thoracic wall;
    rotates the scapula superiorly (the "boxer's muscle")

Posterior Axio-Appendicular Muscles (Shoulder / Back Group)

Superficial Layer (Extrinsic Shoulder)

• Trapezius
  • Origin: Medial third of superior nuchal line; external occipital
    protuberance; nuchal ligament; spinous processes of C7–T12
  • Insertion: Lateral third of clavicle; acromion; spine of scapula
  • Action: Descending (superior) fibers elevate the scapula; transverse
    (middle) fibers retract the scapula; ascending (inferior) fibers depress
    the scapula; together they rotate the scapula superiorly
• Latissimus Dorsi
  • Origin: Spinous processes of inferior 6 thoracic vertebrae;
    thoracolumbar fascia; iliac crest; inferior 3 or 4 ribs
  • Insertion: Floor of the intertubercular sulcus (bicipital groove) of the
    humerus
  • Action: Extends, adducts, and medially rotates the humerus (works with
    pectoralis major to pull the trunk up during climbing)

Deep Layer (Extrinsic Shoulder)

• Levator Scapulae
  • Origin: Transverse processes of C1–C4 vertebrae
  • Insertion: Medial border of the scapula (above the spine)
  • Action: Elevates the scapula and rotates its glenoid cavity inferiorly
• Rhomboid Minor
  • Origin: Nuchal ligament; spinous processes of C7 and T1
  • Insertion: Medial end of the spine of the scapula
  • Action: Retracts and stabilizes the scapula; rotates its glenoid cavity
    inferiorly
• Rhomboid Major
  • Origin: Spinous processes of T2–T5 vertebrae
  • Insertion: Medial border of the scapula (below the spine)
  • Action: Retracts and stabilizes the scapula; rotates its glenoid cavity
    inferiorly

Scapulohumeral Muscles (Intrinsic Shoulder Group)

• Deltoid
  • Origin: Lateral third of the clavicle; acromion; spine of the scapula
  • Insertion: Deltoid tuberosity of the humerus
  • Action:
    • Clavicular (anterior) part: Flexes and medially rotates the arm
    • Acromial (middle/lateral) part: Abducts the arm (after the first 15°
      initiated by supraspinatus)
    • Spinal (posterior) part: Extends and laterally rotates the arm
• Teres Major
  • Origin: Posterior surface of the inferior angle of the scapula
  • Insertion: Medial lip of the intertubercular sulcus (bicipital groove)
    of the humerus
  • Action: Adducts and medially rotates the arm (humerus)
• Supraspinatus (Rotator Cuff)
  • Origin: Supraspinous fossa of the scapula
  • Insertion: Superior facet of the greater tubercle of the humerus
  • Action: Initiates and assists the deltoid in the first 15° of arm
    abduction; holds the humeral head in the glenoid cavity
• Infraspinatus (Rotator Cuff)
  • Origin: Infraspinous fossa of the scapula
  • Insertion: Middle facet of the greater tubercle of the humerus
  • Action: Laterally rotates the arm (humerus); holds the humeral head in
    the glenoid cavity
• Teres Minor (Rotator Cuff)
  • Origin: Middle part of the lateral border of the scapula
  • Insertion: Inferior facet of the greater tubercle of the humerus
  • Action: Laterally rotates the arm (humerus); holds the humeral head in
    the glenoid cavity
• Subscapularis (Rotator Cuff)
  • Origin: Subscapular fossa of the scapula
  • Insertion: Lesser tubercle of the humerus
  • Action: Medially rotates the arm (humerus); holds the humeral head in
    the glenoid cavity (Note: This is the only rotator cuff muscle inserting
    onto the lesser tubercle).

Muscles of the Arm (Brachium)

Anterior Compartment (Flexors)

Mainly innervated by the musculocutaneous nerve (C5–C7).

• Biceps Brachii
  • Origin:
    • Short head: Coracoid process of the scapula
    • Long head: Supraglenoid tubercle of the scapula (tendon runs through
      bicipital groove)
  • Insertion: Tuberosity of the radius; fascia of the forearm via the
    bicipital aponeurosis
  • Action: Supinates the forearm, and when it is supine, flexes the
    forearm; short head resists dislocation of the shoulder
• Coracobrachialis
  • Origin: Coracoid process of the scapula
  • Insertion: Medial surface of the middle third of the humerus
  • Action: Helps flex and adduct the arm; resists dislocation of the
    shoulder
• Brachialis
  • Origin: Distal half of the anterior surface of the humerus
  • Insertion: Coronoid process and tuberosity of the ulna
  • Action: Flexes the forearm in all positions (the "pure/workhorse" flexor
    of the elbow)

Posterior Compartment (Extensors)

Innervated by the radial nerve (C6–C8).

• Triceps Brachii
  • Origin:
    • Long head: Infraglenoid tubercle of the scapula
    • Lateral head: Posterior surface of the humerus, superior to the
      radial groove
    • Medial head: Posterior surface of the humerus, inferior to the
      radial groove
  • Insertion: Olecranon of the ulna
  • Action: Chief extensor of the forearm; long head resists dislocation of
    the humerus (especially important during adduction)
• Anconeus
  • Origin: Lateral epicondyle of the humerus
  • Insertion: Lateral surface of the olecranon and superior part of the
    posterior surface of the ulna
  • Action: Assists the triceps in extending the forearm; stabilizes the
    elbow joint; may abduct the ulna during pronation

Muscles of the Forearm (Antebrachium)

Anterior Compartment (Flexor-Pronator Group)

Mainly innervated by the median nerve, except for the flexor carpi ulnaris and
the medial half of the flexor digitorum profundus (which are supplied by the
ulnar nerve).

Superficial (First) Layer

• Pronator Teres
  • Origin: Medial epicondyle of the humerus (common flexor origin) and the
    coronoid process of the ulna
  • Insertion: Middle of the lateral surface of the radius
  • Action: Pronates and flexes the forearm at the elbow joint
• Flexor Carpi Radialis (FCR)
  • Origin: Medial epicondyle of the humerus (common flexor origin)
  • Insertion: Base of the 2nd metacarpal
  • Action: Flexes and abducts the hand at the wrist joint
• Palmaris Longus
  • Origin: Medial epicondyle of the humerus (common flexor origin)
  • Insertion: Distal half of flexor retinaculum and apex of the palmar
    aponeurosis
  • Action: Flexes the hand at the wrist and tenses the palmar aponeurosis
• Flexor Carpi Ulnaris (FCU) (Innervated by the Ulnar Nerve)
  • Origin: Medial epicondyle of the humerus (common flexor origin) and the
    olecranon/posterior border of the ulna
  • Insertion: Pisiform bone; hook of hamate; base of the 5th metacarpal
  • Action: Flexes and adducts the hand at the wrist joint

Intermediate (Second) Layer

• Flexor Digitorum Superficialis (FDS)
  • Origin: Medial epicondyle of the humerus; coronoid process of the ulna;
    superior half of the anterior border of the radius
  • Insertion: Shafts of the middle phalanges of the lateral four digits
    (digits 2–5)
  • Action: Flexes the middle phalanges at the proximal interphalangeal
    (PIP) joints of the lateral four digits; can also flex proximal
    phalanges at MCP joints

Deep (Third) Layer

• Flexor Digitorum Profundus (FDP)
  • Origin: Proximal three-quarters of the medial and anterior surfaces of
    the ulna and the interosseous membrane
  • Insertion: Bases of the distal phalanges of the lateral four digits
    (digits 2–5)
  • Action:
    • Medial part (Ulnar Nerve): Flexes distal phalanges of digits 4 and 5
      at DIP joints
    • Lateral part (Median Nerve): Flexes distal phalanges of digits 2
      and 3 at DIP joints
• Flexor Pollicis Longus (FPL)
  • Origin: Anterior surface of the radius and adjacent interosseous
    membrane
  • Insertion: Base of the distal phalanx of the thumb (1st digit)
  • Action: Flexes the phalanges of the thumb (IP and MCP joints)
• Pronator Quadratus
  • Origin: Distal quarter of the anterior surface of the ulna
  • Insertion: Distal quarter of the anterior surface of the radius
  • Action: Pronates the forearm (deepest muscle of the forearm; initiates
    pronation)

Posterior Compartment (Extensor-Supinator Group)

All are innervated by the radial nerve or its deep/posterior interosseous
branches.

Superficial (First) Layer

• Brachioradialis (Innervated by Radial Nerve before it crosses elbow)
  • Origin: Proximal two-thirds of the lateral supra-epicondylar ridge of
    the humerus
  • Insertion: Distal lateral surface of the radius, just proximal to the
    styloid process
  • Action: Weakly flexes the forearm when it is in the midproned position
• Extensor Carpi Radialis Longus (ECRL)
  • Origin: Lateral supra-epicondylar ridge of the humerus
  • Insertion: Dorsal aspect of the base of the 2nd metacarpal
  • Action: Extends and abducts the hand at the wrist joint (highly active
    during fist clenching)
• Extensor Carpi Radialis Brevis (ECRB)
  • Origin: Lateral epicondyle of the humerus (common extensor origin)
  • Insertion: Dorsal aspect of the base of the 3rd metacarpal
  • Action: Extends and abducts the hand at the wrist joint
• Extensor Digitorum
  • Origin: Lateral epicondyle of the humerus (common extensor origin)
  • Insertion: Extensor expansions of the lateral four digits (digits 2–5)
  • Action: Extends the lateral four digits, primarily at MCP joints,
    secondarily at IP joints
• Extensor Digiti Minimi
  • Origin: Lateral epicondyle of the humerus (common extensor origin)
  • Insertion: Extensor expansion of the 5th digit (little finger)
  • Action: Extends the 5th digit, primarily at MCP joint, secondarily at IP
    joints
• Extensor Carpi Ulnaris (ECU)
  • Origin: Lateral epicondyle of the humerus and the posterior border of
    the ulna
  • Insertion: Dorsal aspect of the base of the 5th metacarpal
  • Action: Extends and adducts the hand at the wrist joint

Deep Layer

• Supinator
  • Origin: Lateral epicondyle of the humerus; radial collateral and annular
    ligaments; supinator fossa and crest of the ulna
  • Insertion: Lateral, posterior, and anterior proximal surfaces of the
    radius
  • Action: Supinates the forearm (rotates radius to turn palm anteriorly)
• Extensor Indicis
  • Origin: Posterior surface of the distal third of the ulna and the
    interosseous membrane
  • Insertion: Extensor expansion of the 2nd digit (index finger)
  • Action: Extends the 2nd digit independently; helps extend the hand at
    the wrist

Outcropping Muscles of the Deep Layer (Act on the Thumb)

• Abductor Pollicis Longus (APL)
  • Origin: Posterior surface of proximal halves of the ulna, radius, and
    interosseous membrane
  • Insertion: Base of the 1st metacarpal (radial side)
  • Action: Abducts the thumb and extends it at the carpometacarpal (CMC)
    joint
• Extensor Pollicis Brevis (EPB)
  • Origin: Posterior surface of the distal third of the radius and the
    interosseous membrane
  • Insertion: Dorsal aspect of the base of the proximal phalanx of the
    thumb
  • Action: Extends the proximal phalanx of the thumb at the MCP joint
• Extensor Pollicis Longus (EPL)
  • Origin: Posterior surface of the middle third of the ulna and the
    interosseous membrane
  • Insertion: Dorsal aspect of the base of the distal phalanx of the thumb
  • Action: Extends the distal phalanx of the thumb at the IP joint; extends
    the MCP and CMC joints

Intrinsic Muscles of the Hand

Thenar Muscles (Ball of the Thumb)

Innervated by the recurrent branch of the median nerve (C8, T1) (except the deep
head of FPB and adductor pollicis).

• Opponens Pollicis
  • Origin: Flexor retinaculum and tubercles of the scaphoid and trapezium
    bones
  • Insertion: Lateral side of the 1st metacarpal
  • Action: Pulls the 1st metacarpal medially across the palm and rotates it
    medially (creates opposition)
• Abductor Pollicis Brevis (APB)
  • Origin: Flexor retinaculum and tubercles of the scaphoid and trapezium
    bones
  • Insertion: Lateral side of the base of the proximal phalanx of the thumb
  • Action: Abducts the thumb and assists in opposition
• Flexor Pollicis Brevis (FPB)
  • Origin:
    • Superficial head (Median Nerve): Flexor retinaculum and trapezium
    • Deep head (Ulnar Nerve): Capitate and trapezoid bones
  • Insertion: Lateral side of the base of the proximal phalanx of the thumb
  • Action: Flexes the thumb at the MCP joint
• Adductor Pollicis (Innervated by deep branch of Ulnar Nerve)
  • Origin:
    • Oblique head: Bases of the 2nd and 3rd metacarpals and capitate bone
    • Transverse head: Anterior surface of the shaft of the 3rd metacarpal
  • Insertion: Medial side of the base of the proximal phalanx of the thumb
  • Action: Adducts the thumb toward the lateral border of the palm

Hypothenar Muscles (Ball of the Little Finger)

All are innervated by the deep branch of the ulnar nerve (C8, T1).

• Abductor Digiti Minimi (ADM)
  • Origin: Pisiform bone and tendon of flexor carpi ulnaris
  • Insertion: Medial side of the base of the proximal phalanx of the 5th
    digit
  • Action: Abducts the 5th digit; assists in flexing its proximal phalanx
• Flexor Digiti Minimi Brevis (FDMB)
  • Origin: Hook of the hamate and the flexor retinaculum
  • Insertion: Medial side of the base of the proximal phalanx of the 5th
    digit
  • Action: Flexes the proximal phalanx of the 5th digit at the MCP joint
• Opponens Digiti Minimi
  • Origin: Hook of the hamate and the flexor retinaculum
  • Insertion: Medial border of the 5th metacarpal
  • Action: Draws the 5th metacarpal anteriorly and rotates it, bringing
    the 5th digit into opposition with the thumb

Short Muscles of the Hand

• Lumbricals (1st–4th)
  • Origin: Tendons of the flexor digitorum profundus (FDP)
    • 1st and 2nd (Median Nerve): Lateral two tendons (unipennate)
    • 3rd and 4th (Ulnar Nerve): Medial three tendons (bipennate)
  • Insertion: Lateral (radial) sides of the extensor expansions of
    digits 2–5
  • Action: Flex the MCP joints and extend the IP joints of the lateral four
    digits (digits 2–5)
• Dorsal Interossei (1st–4th) (Innervated by deep branch of Ulnar Nerve)
  • Origin: Adjacent sides of two metacarpal bones (bipennate)
  • Insertion: Bases of the proximal phalanges and extensor expansions of
    digits 2–4
  • Action: Abduct digits 2–4 from the axial line (middle finger); work with
    lumbricals to flex MCP and extend IP joints (Mnemonic: DAB)
• Palmar Interossei (1st–3rd) (Innervated by deep branch of Ulnar Nerve)
  • Origin: Palmar surfaces of the 2nd, 4th, and 5th metacarpal bones
    (unipennate)
  • Insertion: Bases of the proximal phalanges and extensor expansions of
    digits 2, 4, and 5
  • Action: Adduct digits 2, 4, and 5 toward the axial line (middle finger);
    assist lumbricals in flexing MCP and extending IP joints (Mnemonic: PAD)

Part 4: Muscles of the Lower Limb

Muscles of the Anterior Thigh

Flexors of the Hip Joint

• Pectineus (Innervation: Femoral nerve, sometimes obturator nerve)
  • Origin: Superior ramus of the pubis (pectineal line)
  • Insertion: Pectineal line of the femur, inferior to the lesser
    trochanter
  • Action: Adducts and flexes the thigh; assists with medial rotation of
    the thigh
• Iliopsoas (Iliacus, Psoas Major, Psoas Minor) (Innervation: Femoral nerve
  and ventral rami of L1–L3)
  • Origin:
    • Iliacus: Iliac fossa and ala of the sacrum
    • Psoas major: Transverse processes and bodies of T12–L5 vertebrae and
      their IV discs
  • Insertion: Lesser trochanter of the femur
  • Action: Chief flexor of the thigh (most powerful hip flexor with the
    longest range); bilateral contraction initiates flexion of the trunk on
    the fixed thigh
• Sartorius (Innervation: Femoral nerve)
  • Origin: Anterior superior iliac spine (ASIS)
  • Insertion: Superior part of the medial surface of the tibia (forms part
    of the pes anserinus)
  • Action: Flexes, abducts, and laterally rotates the thigh at the hip
    joint; flexes and medially rotates the leg at the knee joint (the
    "tailor's muscle")

Extensors of the Knee Joint (Quadriceps Femoris)

All are innervated by the femoral nerve (L2–L4).

• Rectus Femoris
  • Origin: Anterior inferior iliac spine (AIIS) and ilium superior to the
    acetabulum
  • Insertion: Base of the patella and via the patellar ligament onto the
    tibial tuberosity
  • Action: Extends the leg at the knee joint; assists the iliopsoas in
    flexing the thigh at the hip joint
• Vastus Lateralis
  • Origin: Greater trochanter and lateral lip of the linea aspera of the
    femur
  • Insertion: Base of the patella and via the patellar ligament onto the
    tibial tuberosity
  • Action: Extends the leg at the knee joint (largest component of the
    quadriceps)
• Vastus Medialis
  • Origin: Intertrochanteric line and medial lip of the linea aspera of the
    femur
  • Insertion: Base of the patella and via the patellar ligament onto the
    tibial tuberosity
  • Action: Extends the leg at the knee joint; crucial for proper patellar
    tracking
• Vastus Intermedius
  • Origin: Anterior and lateral surfaces of the shaft of the femur
  • Insertion: Base of the patella and via the patellar ligament onto the
    tibial tuberosity
  • Action: Extends the leg at the knee joint (Note: Gives rise to the
    articularis genu muscle, which pulls the synovial membrane superiorly
    during knee extension).

Muscles of the Medial Thigh (Adductors of the Thigh)

All are innervated by the obturator nerve (L2–L4) (except the hamstring part of
adductor magnus).

• Adductor Longus
  • Origin: Body of the pubis, inferior to the pubic crest
  • Insertion: Middle third of the linea aspera of the femur
  • Action: Adducts the thigh at the hip joint
• Adductor Brevis
  • Origin: Body and inferior ramus of the pubis
  • Insertion: Pectineal line and proximal part of the linea aspera of the
    femur
  • Action: Adducts the thigh; weakly assists in hip flexion
• Adductor Magnus
  • Origin:
    • Adductor part: Inferior ramus of the pubis and ramus of the ischium
    • Hamstrings part: Ischial tuberosity
  • Insertion:
    • Adductor part: Gluteal tuberosity, linea aspera, and medial
      supracondylar line of the femur
    • Hamstrings part (Innervated by Tibial Nerve): Adductor tubercle of
      the femur
  • Action: Adducts the thigh; adductor part flexes the thigh; hamstring
    part extends the thigh
• Gracilis
  • Origin: Body and inferior ramus of the pubis
  • Insertion: Superior part of the medial surface of the tibia (forms part
    of the pes anserinus)
  • Action: Adducts the thigh; flexes the leg at the knee joint and rotates
    it medially
• Obturator Externus
  • Origin: Margins of the obturator foramen and the external surface of the
    obturator membrane
  • Insertion: Trochanteric fossa of the femur
  • Action: Laterally rotates the thigh; steadies the head of the femur in
    the acetabulum

Muscles of the Gluteal Region

Superficial Layer (Abductors and Rotators)

• Gluteus Maximus (Innervation: Inferior gluteal nerve, L5–S2)
  • Origin: Ilium posterior to the posterior gluteal line; posterior surface
    of the sacrum and coccyx; sacrotuberous ligament
  • Insertion: Most fibers insert into the iliotibial (IT) tract; deeper
    fibers insert onto the gluteal tuberosity of the femur
  • Action: Chief extensor of the thigh at the hip joint; assists in lateral
    rotation of the thigh; assists in rising from a sitting position
• Gluteus Medius (Innervation: Superior gluteal nerve, L4–S1)
  • Origin: External surface of the ilium between the anterior and posterior
    gluteal lines
  • Insertion: Lateral surface of the greater trochanter of the femur
  • Action: Abducts and medially rotates the thigh; stabilizes the pelvis
    when the opposite foot is raised
• Gluteus Minimus (Innervation: Superior gluteal nerve, L4–S1)
  • Origin: External surface of the ilium between the anterior and inferior
    gluteal lines
  • Insertion: Anterior aspect of the greater trochanter of the femur
  • Action: Abducts and medially rotates the thigh; stabilizes the pelvis
• Tensor Fasciae Latae (TFL) (Innervation: Superior gluteal nerve, L4–S1)
  • Origin: Anterior superior iliac spine (ASIS) and anterior part of the
    iliac crest
  • Insertion: Iliotibial (IT) tract (which inserts on the lateral condyle
    of the tibia)
  • Action: Abducts, medially rotates, and flexes the thigh; helps keep the
    knee extended

Deep Layer (Lateral Rotators)

All are lateral rotators of the extended thigh and abductors of the flexed
thigh.

• Piriformis (Innervation: Ventral rami of S1–S2)
  • Origin: Anterior surface of the sacrum and sacrotuberous ligament
  • Insertion: Superior border of the greater trochanter of the femur
  • Action: Laterally rotates the extended thigh; abducts the flexed thigh;
    stabilizes the femoral head
• Obturator Internus (Innervation: Nerve to obturator internus, L5, S1)
  • Origin: Pelvic/internal surface of the obturator membrane and
    surrounding bones
  • Insertion: Medial surface of the greater trochanter of the femur
    (trochanteric fossa)
  • Action: Laterally rotates the extended thigh; abducts the flexed thigh
• Superior and Inferior Gemelli
  • Origin:
    • Superior (Nerve to obturator internus): Ischial spine
    • Inferior (Nerve to quadratus femoris): Ischial tuberosity
  • Insertion: Medial surface of the greater trochanter of the femur
    (trochanteric fossa)
  • Action: Assist the obturator internus in lateral rotation of the
    extended thigh and abduction of the flexed thigh
• Quadratus Femoris (Innervation: Nerve to quadratus femoris, L5, S1)
  • Origin: Lateral border of the ischial tuberosity
  • Insertion: Quadrate tubercle on the intertrochanteric crest of the femur
  • Action: Laterally rotates the thigh; stabilizes the femoral head

Muscles of the Posterior Thigh (Hamstrings)

All are innervated by the tibial division of the sciatic nerve (except the short
head of the biceps femoris).

• Semitendinosus
  • Origin: Ischial tuberosity
  • Insertion: Superior part of the medial surface of the tibia (forms part
    of the pes anserinus)
  • Action: Extends the thigh at the hip joint; flexes the leg at the knee
    joint and medially rotates it
• Semimembranosus
  • Origin: Ischial tuberosity
  • Insertion: Posterior part of the medial condyle of the tibia
  • Action: Extends the thigh at the hip joint; flexes the leg at the knee
    joint and medially rotates it
• Biceps Femoris
  • Origin:
    • Long head (Tibial Nerve): Ischial tuberosity
    • Short head (Common Fibular Nerve): Lateral lip of the linea aspera
      and lateral supracondylar line of the femur
  • Insertion: Lateral side of the head of the fibula
  • Action: Flexes the leg at the knee joint and laterally rotates it; long
    head extends the thigh at the hip joint

Muscles of the Leg (Crus)

Anterior Compartment (Dorsiflexors)

All are innervated by the deep fibular nerve (L4–S1).

• Tibialis Anterior
  • Origin: Lateral condyle and superior half of the lateral surface of the
    tibia; interosseous membrane
  • Insertion: Medial and inferior surfaces of the medial cuneiform and the
    base of the 1st metatarsal
  • Action: Dorsiflexes the foot at the ankle joint and inverts the foot
    (strongest dorsiflexor)
• Extensor Hallucis Longus (EHL)
  • Origin: Middle part of the anterior surface of the fibula and the
    interosseous membrane
  • Insertion: Dorsal aspect of the base of the distal phalanx of the great
    toe (hallux)
  • Action: Extends the great toe; dorsiflexes the foot at the ankle joint;
    assists in inversion
• Extensor Digitorum Longus (EDL)
  • Origin: Lateral condyle of the tibia; superior three-quarters of the
    anterior surface of the fibula; interosseous membrane
  • Insertion: Middle and distal phalanges of the lateral four digits
    (digits 2–5)
  • Action: Extends the lateral four digits; dorsiflexes the foot at the
    ankle joint
• Fibularis (Peroneus) Tertius
  • Origin: Inferior third of the anterior surface of the fibula and the
    interosseous membrane
  • Insertion: Dorsum of the base of the 5th metatarsal
  • Action: Dorsiflexes the foot at the ankle joint; assists in foot
    eversion

Lateral Compartment (Everters)

All are innervated by the superficial fibular nerve (L5–S2).

• Fibularis (Peroneus) Longus
  • Origin: Head and superior two-thirds of the lateral surface of the
    fibula
  • Insertion: Base of the 1st metatarsal and the medial cuneiform (passes
    obliquely across the sole)
  • Action: Everts the foot and weakly plantar flexes the foot at the ankle
    joint; supports transverse arch
• Fibularis (Peroneus) Brevis
  • Origin: Inferior two-thirds of the lateral surface of the fibula
  • Insertion: Tuberosity on the lateral side of the base of the 5th
    metatarsal
  • Action: Everts the foot and weakly plantar flexes the foot at the ankle
    joint

Posterior Compartment (Plantar Flexors)

All are innervated by the tibial nerve (L4–S3).

Superficial Layer (Calf Muscles)

• Gastrocnemius
  • Origin:
    • Lateral head: Lateral aspect of the lateral condyle of the femur
    • Medial head: Popliteal surface of the femur, superior to the medial
      condyle
  • Insertion: Posterior surface of the calcaneus via the calcaneal
    (Achilles) tendon
  • Action: Plantar flexes the foot at the ankle joint when the knee is
    extended; flexes the leg at the knee joint
• Soleus
  • Origin: Posterior aspect of head of the fibula; soleal line and medial
    border of the tibia
  • Insertion: Posterior surface of the calcaneus via the calcaneal
    (Achilles) tendon
  • Action: Plantar flexes the foot at the ankle joint (independent of knee
    position; the "workhorse" of plantar flexion)
• Plantaris
  • Origin: Inferior end of the lateral supracondylar line of the femur and
    the oblique popliteal ligament
  • Insertion: Posterior surface of the calcaneus (often merges with
    calcaneal tendon)
  • Action: Weakly assists the gastrocnemius in plantar flexing the ankle;
    acts primarily as a proprioceptive organ

Deep Layer

• Popliteus
  • Origin: Lateral surface of the lateral condyle of the femur and the
    lateral meniscus
  • Insertion: Posterior surface of the tibia, superior to the soleal line
  • Action: Weakly flexes the knee and unlocks the knee joint by rotating
    the femur laterally 5° on a fixed tibia (or medially rotating the tibia
    of an unplanted limb)
• Flexor Hallucis Longus (FHL)
  • Origin: Inferior two-thirds of the posterior surface of the fibula and
    the interosseous membrane
  • Insertion: Base of the distal phalanx of the great toe (hallux)
  • Action: Flexes the great toe at all joints; weakly plantar flexes the
    ankle; supports the medial longitudinal arch
• Flexor Digitorum Longus (FDL)
  • Origin: Posterior surface of the tibia, inferior to the soleal line
  • Insertion: Bases of the distal phalanges of the lateral four digits
    (digits 2–5)
  • Action: Flexes the lateral four digits; plantar flexes the foot at the
    ankle joint; supports longitudinal arches
• Tibialis Posterior
  • Origin: Posterior surface of the tibia (inferior to soleal line);
    posterior surface of the fibula; interosseous membrane
  • Insertion: Tuberosity of the navicular bone; cuneiforms; cuboid;
    sustentaculum tali of the calcaneus; bases of the 2nd–4th metatarsals
  • Action: Plantar flexes the foot at the ankle joint and inverts the foot

Muscles of the Foot

Muscles of the Dorsum of the Foot

Innervated by the lateral terminal branch of the deep fibular nerve (S1, S2).

• Extensor Digitorum Brevis
  • Origin: Superolateral surface of the calcaneus; stem of the inferior
    extensor retinaculum
  • Insertion: Long extensor tendons of digits 2–4
  • Action: Assists the extensor digitorum longus in extending the lateral
    three toes (digits 2–4) at the MTP and IP joints
• Extensor Hallucis Brevis
  • Origin: Superolateral surface of the calcaneus (medial part of the EDB
    muscle mass)
  • Insertion: Base of the proximal phalanx of the great toe (hallux)
  • Action: Assists the extensor hallucis longus in extending the great toe
    at the MTP joint

Intrinsic Muscles of the Sole of the Foot (Plantar Aspect)

Mainly innervated by the lateral plantar nerve, except for the four muscles
supplied by the medial plantar nerve (Abductor hallucis, Flexor digitorum
brevis, Flexor hallucis brevis, and 1st Lumbrical).

First Layer (Superficial)

• Abductor Hallucis (Medial Plantar Nerve)
  • Origin: Medial tubercle of the calcaneal tuberosity; plantar
    aponeurosis; flexor retinaculum
  • Insertion: Medial side of the base of the proximal phalanx of the great
    toe (hallux)
  • Action: Abducts and assists in flexing the great toe
• Flexor Digitorum Brevis (FDB) (Medial Plantar Nerve)
  • Origin: Medial tubercle of the calcaneal tuberosity; plantar aponeurosis
  • Insertion: Both sides of the middle phalanges of the lateral four digits
    (digits 2–4)
  • Action: Flexes the lateral four digits (toes 2–4) at the PIP joints
• Abductor Digiti Minimi (Lateral Plantar Nerve)
  • Origin: Medial and lateral tubercles of the calcaneal tuberosity;
    plantar aponeurosis
  • Insertion: Lateral side of the base of the proximal phalanx of the
    little toe (5th digit)
  • Action: Abducts and assists in flexing the little toe (5th digit)

Second Layer

• Quadratus Plantae (Flexor Accessorius) (Lateral Plantar Nerve)
  • Origin: Medial surface and lateral margin of the calcaneus
  • Insertion: Posterolateral margin of the tendon of the flexor digitorum
    longus (FDL)
  • Action: Assists the flexor digitorum longus in flexing digits 2–5 by
    pulling its tendons straight
• Lumbricals (1st–4th)
  • Origin: Tendons of the flexor digitorum longus (FDL)
  • Insertion: Medial aspect of the extensor expansions of digits 2–5
  • Action: Flex the proximal phalanges (at MTP joints) and extend the
    middle and distal phalanges of digits 2–5
  • Innervation:
    • 1st (Medialmost): Medial plantar nerve
    • 2nd, 3rd, and 4th: Lateral plantar nerve

Third Layer

• Flexor Hallucis Brevis (FHB) (Medial Plantar Nerve)
  • Origin: Plantar surface of the cuboid and lateral cuneiform bones
  • Insertion: Both sides of the base of the proximal phalanx of the great
    toe (hallux) via two sesamoid bones
  • Action: Flexes the proximal phalanx of the great toe
• Adductor Hallucis (Lateral Plantar Nerve)
  • Origin:
    • Oblique head: Bases of the 2nd–4th metatarsals
    • Transverse head: Plantar ligaments of the metatarsophalangeal (MTP)
      joints
  • Insertion: Lateral side of the base of the proximal phalanx of the great
    toe (hallux)
  • Action: Adducts the great toe; assists in maintaining the transverse
    arch of the foot
• Flexor Digiti Minimi Brevis (Lateral Plantar Nerve)
  • Origin: Base of the 5th metatarsal
  • Insertion: Base of the proximal phalanx of the little toe (5th digit)
  • Action: Flexes the proximal phalanx of the little toe

Fourth Layer (Deepest)

All are innervated by the lateral plantar nerve.

• Plantar Interossei (1st–3rd)
  • Origin: Medial shafts of the 3rd–5th metatarsals (unipennate)
  • Insertion: Medial sides of the bases of the proximal phalanges and
    extensor expansions of digits 3–5
  • Action: Adduct digits 3–5 toward the midline of the second toe; flex the
    MTP joints (Mnemonic: PAD)
• Dorsal Interossei (1st–4th)
  • Origin: Adjacent sides of the shafts of the 1st–5th metatarsals
    (bipennate)
  • Insertion:
    • 1st: Medial side of proximal phalanx of the 2nd digit
    • 2nd–4th: Lateral sides of proximal phalanges and extensor expansions
      of digits 2–4
  • Action: Abduct digits 2–4 from the midline of the second toe; flex the
    MTP joints (Mnemonic: DAB)

Part 5: Muscles of the Pelvic Cavity

• Obturator Internus (Lateral Wall)
  • Origin: Pelvic/internal surfaces of the ilium and ischium; obturator
    membrane
  • Insertion: Greater trochanter of the femur (trochanteric fossa)
  • Action: Rotates thigh laterally; assists in holding the head of the
    femur in the acetabulum
• Piriformis (Posterosuperior Wall)
  • Origin: Pelvic surface of the S2–S4 sacral segments; superior margin of
    the greater sciatic notch and sacrotuberous ligament
  • Insertion: Greater trochanter of the femur
  • Action: Rotates the extended thigh laterally; abducts the flexed thigh;
    assists in holding the femoral head in the acetabulum
• Coccygeus (Ischiococcygeus) (Pelvic Floor)
  • Origin: Ischial spine
  • Insertion: Inferior end of the sacrum and the coccyx
  • Action: Forms a small part of the pelvic diaphragm that supports the
    pelvic viscera; flexes the coccyx
• Levator Ani (Puborectalis, Pubococcygeus, and Iliococcygeus) (Pelvic Floor)
  • Origin: Body of the pubis; tendinous arch of the obturator fascia;
    ischial spine
  • Insertion: Perineal body; coccyx; anococcygeal ligament; walls of the
    prostate or vagina, rectum, and anal canal
  • Action: Forms the vast majority of the pelvic diaphragm, which helps
    support the pelvic viscera and actively resists increases in
    intra-abdominal pressure