Muscular System — revision sheet

More than 600 skeletal muscles, with their tendons and the motor and sensory apparatus that controls them, make up roughly 40% of adult body mass. Skeletal muscle turns the chemical energy of ATP into force by sliding actin past myosin. That force moves and stabilises the skeleton, maintains posture, guards body openings and generates most of the body's heat.

Number of skeletal muscles: >600Proportion of body mass: ≈40% skeletal muscle (+≈10% smooth and cardiac)Largest muscle (mass): Gluteus maximusLongest muscle: Sartorius (fibres up to ≈30 cm)Smallest skeletal muscle: Stapedius (middle ear)Skeletal fibre diameter: ≈10–100 µmSarcomere length (rest): ≈2.0–2.5 µmThick filament (= A band) length: ≈1.6 µmResting membrane potential: ≈ −85 to −90 mVMuscle action potential: ≈1–5 ms; conducted at ≈3–5 m/sMaximum isometric stress: ≈30–40 N per cm² of physiological cross-sectional areaMotor unit size: ≈10 fibres (extraocular) to ≈2,000 (gastrocnemius)

Muscle tissue & ultrastructure

Skeletal muscle tissue Tissue: Striated, voluntary muscle made of long, multinucleated fibres arranged in bundles. It forms the named muscles that move the skeleton.
Cardiac muscle tissue Tissue: Striated, involuntary muscle of the heart wall. It is made of branched cells with one or two central nuclei, joined end-to-end by intercalated discs.
Smooth muscle tissue Tissue: Non-striated, involuntary muscle of spindle-shaped cells with a single central nucleus. It forms the walls of hollow organs and blood vessels.
Tendon Tendon: A cord or sheet of dense regular collagenous tissue that transmits the force of muscle to bone. A flat, sheet-like tendon is called an aponeurosis.
Muscle fascicle Tissue: A bundle of tens to hundreds of muscle fibres wrapped in perimysium. It is the visible "grain" of a muscle.
Skeletal muscle fibre Cell: A long, cylindrical, multinucleated syncytium formed by the fusion of myoblasts. It is packed with myofibrils and specialised membranes for rapid, synchronous contraction.
Myofibril Organelle: A rod-like contractile organelle, ≈1–2 µm in diameter, made of thousands of sarcomeres joined end-to-end. It runs the full length of the muscle fibre.
Sarcomere Organelle: The repeating contractile unit of striated muscle, running from one Z disc to the next (≈2.0–2.5 µm at rest). Overlapping thick and thin filaments slide past each other to shorten it.
Thick filament (myosin) Molecule: A bipolar filament of ≈300 myosin II molecules (≈1.6 µm long) whose heads form cross-bridges with actin and hydrolyse ATP to generate force.
Thin filament (actin) Molecule: A ≈1.0–1.3 µm filament of double-helical F-actin carrying the regulatory proteins tropomyosin and troponin. It is anchored at the Z disc.
Troponin complex Molecule: A three-subunit, Ca²⁺-sensing regulatory complex on the thin filament of striated muscle. When it binds Ca²⁺ it shifts tropomyosin and allows cross-bridges to form.
Tropomyosin Molecule: A long α-helical coiled-coil protein that lies in the grooves of F-actin. At rest it blocks the myosin-binding sites.
Titin Molecule: The largest known protein (≈3–4 MDa). Each molecule spans half a sarcomere from the Z disc to the M line, acting as a molecular spring and a template for the thick filament.
Sarcoplasmic reticulum Organelle: A specialised smooth endoplasmic reticulum that sleeves every myofibril. It stores Ca²⁺ and releases and recaptures it to switch contraction on and off.
T-tubules (transverse tubules) Organelle: Tube-shaped inward folds of the sarcolemma that carry the action potential into the depth of the fibre. In skeletal muscle they lie at every A–I junction.

Neuromuscular control

Neuromuscular junction Organ part: The chemical synapse between an α-motor neuron terminal and a skeletal muscle fibre. Acetylcholine acting on nicotinic receptors produces an end-plate potential that reliably triggers a muscle action potential.
Motor unit Physiological process: One α-motor neuron and all the skeletal muscle fibres it supplies. It is the smallest unit of force the nervous system can control.
Muscle spindle Receptor: An encapsulated stretch receptor that lies parallel to the ordinary muscle fibres. It signals muscle length and its rate of change, and it drives the stretch reflex.
Golgi tendon organ Receptor: An encapsulated tension receptor at the musculotendinous junction. It lies in series with the muscle fibres and signals active force through Ib afferents.

Head — facial expression

Muscles of facial expression Muscle group: Thin subcutaneous muscles derived from the 2nd pharyngeal arch. They move the skin of the face and scalp, open and close the eyes and mouth, and create facial expression. All are supplied by the facial nerve (CN VII).
Occipitofrontalis Muscle: A scalp muscle with frontal and occipital bellies joined by the epicranial aponeurosis (galea). It raises the eyebrows and wrinkles the forehead.O Frontal belly: epicranial aponeurosis. Occipital belly: lateral two-thirds of the superior nuchal line of the occipital bone and the…I Frontal belly: skin and superficial fascia of the eyebrows and forehead. Occipital belly: epicranial aponeurosis.A Elevates the eyebrows and wrinkles the forehead (frontal belly); retracts the scalp (occipital belly).N Facial nerve (CN VII): temporal branch (frontal belly) and posterior auricular nerve (occipital belly).
Corrugator supercilii Muscle: A small pyramidal muscle deep to frontalis. It pulls the eyebrows medially and down, producing vertical frown lines.O Medial end of the superciliary arch of the frontal bone.I Deep surface of the skin above the middle of the supraorbital margin.A Pulls the eyebrows medially and down, producing vertical glabellar wrinkles.N Facial nerve (CN VII), temporal branch.
Orbicularis oculi Muscle: The sphincter of the eyelids, encircling the orbit. Its palpebral part closes the eye gently (blinking) and its orbital part screws the eye shut.O Nasal part of the frontal bone, frontal process of the maxilla, medial palpebral ligament and lacrimal bone (posterior lacrimal crest).I Skin around the orbital margin, the lateral palpebral raphe and the superior and inferior tarsal plates.A Closes the eyelids. The palpebral part closes them gently, the orbital part closes them tightly, and the lacrimal part assists tear…N Facial nerve (CN VII), temporal and zygomatic branches.
Nasalis Muscle: The main muscle of the nose. Its transverse part compresses the nostril and its alar part flares it.O Maxilla, superior to the incisor and canine teeth, lateral to the nasal notch.I Nasal aponeurosis over the bridge of the nose (transverse part) and the alar cartilage (alar part).A Compresses (transverse part) or dilates (alar part) the anterior nasal aperture.N Facial nerve (CN VII), buccal (and zygomatic) branches.
Levator labii superioris Muscle: A flat muscle from the infraorbital margin to the upper lip. It elevates and everts the upper lip and deepens the nasolabial fold.O Infraorbital margin of the maxilla, above the infraorbital foramen.I Skin and muscle of the upper lip (blending with orbicularis oris).A Raises and everts the upper lip, exposing the maxillary teeth (sadness, disdain).N Facial nerve (CN VII), zygomatic and buccal branches.
Zygomaticus major Muscle: The principal smiling muscle. It runs from the zygomatic bone to the modiolus and draws the angle of the mouth upward and laterally.O Lateral surface of the zygomatic bone, in front of the zygomaticotemporal suture.I Modiolus at the angle of the mouth (skin and orbicularis oris).A Elevates and draws back the angle of the mouth.N Facial nerve (CN VII), zygomatic and buccal branches.
Orbicularis oris Muscle: The complex sphincter of the mouth, forming most of the lips. It closes, purses and protrudes the lips.O Maxilla and mandible near the midline (incisive slips), the deep surface of the skin, and the modiolus (fibres from buccinator and other…I Mucous membrane and skin of the lips.A Closes the oral fissure, compresses the lips against the teeth, and purses and protrudes the lips.N Facial nerve (CN VII), buccal and marginal mandibular branches.
Buccinator Muscle: A thin quadrilateral muscle forming the muscular wall of the cheek. It presses the cheek against the teeth to keep food between the molars and to expel air.O Alveolar processes of the maxilla and mandible opposite the molar teeth, and the pterygomandibular raphe.I Modiolus at the angle of the mouth, blending with orbicularis oris.A Compresses the cheek against the molars, keeping food on the occlusal surfaces, and expels air.N Facial nerve (CN VII), buccal branch. Not supplied by the buccal nerve of V3, which is sensory.
Depressor anguli oris Muscle: A triangular muscle from the oblique line of the mandible to the modiolus. It pulls the corner of the mouth down (frowning, sadness).O Oblique line of the mandible.I Modiolus at the angle of the mouth.A Draws the angle of the mouth inferolaterally.N Facial nerve (CN VII), marginal mandibular (and buccal) branches.
Mentalis Muscle: A small paired muscle of the chin. It elevates and wrinkles the chin skin and protrudes the lower lip (pouting, doubt).O Incisive fossa of the mandible.I Skin of the chin.A Raises the chin skin and protrudes the lower lip.N Facial nerve (CN VII), marginal mandibular branch.
Platysma Muscle: A broad, thin sheet of muscle in the superficial fascia of the neck. It tenses the neck skin and depresses the mandible and the corners of the mouth.O Superficial fascia over the superior parts of pectoralis major and deltoid.I Inferior border of the mandible, the skin of the lower face and the modiolus.A Draws the angles of the mouth and the lower lip down; tenses the skin of the neck (grimacing, "strained" expression).N Facial nerve (CN VII), cervical branch.

Head — mastication

Temporalis Muscle: A fan-shaped muscle filling the temporal fossa. It elevates the mandible, and its posterior fibres retract it.O Floor of the temporal fossa and the deep surface of the temporal fascia.I Tip and medial surface of the coronoid process and the anterior border of the ramus of the mandible.A Elevates the mandible (closes the jaw); posterior fibres retract it.N Deep temporal nerves (anterior division of the mandibular nerve, CN V3).
Masseter Muscle: A thick quadrilateral muscle from the zygomatic arch to the angle of the mandible. It is the most powerful elevator of the jaw and one of the strongest muscles for its size.O Superficial part: zygomatic process of the maxilla and the anterior two-thirds of the inferior border of the zygomatic arch.…I Angle and lateral surface of the ramus of the mandible, up to the coronoid process.A Elevates the mandible (closes the jaw). Superficial part assists protrusion; deep part assists retraction.N Masseteric nerve (anterior division of the mandibular nerve, CN V3).
Medial pterygoid Muscle: A thick quadrilateral muscle on the inner side of the ramus that mirrors masseter. It elevates and protrudes the mandible and produces side-to-side grinding movements.O Deep head: medial surface of the lateral pterygoid plate and the pyramidal process of the palatine bone.…I Medial surface of the ramus and angle of the mandible, below the mandibular foramen.A Elevates and protrudes the mandible. Unilateral contraction moves the chin to the opposite side.N Nerve to medial pterygoid (main trunk of the mandibular nerve, CN V3).
Lateral pterygoid Muscle: A short, two-headed muscle running horizontally from the sphenoid to the neck of the mandible and the TMJ disc. It is the only muscle of mastication that opens (depresses and protrudes) the jaw.O Superior head: infratemporal surface and infratemporal crest of the greater wing of the sphenoid.…I Pterygoid fovea on the neck of the mandible; capsule and articular disc of the TMJ.A Bilaterally: protrudes the mandible and depresses the chin (opening). Unilaterally: moves the chin to the opposite side.N Nerve to lateral pterygoid (anterior division of the mandibular nerve, CN V3).

Neck

Sternocleidomastoid Muscle: A prominent two-headed strap muscle running obliquely from the sternum and clavicle to the mastoid process. It divides the neck into anterior and posterior triangles.O Sternal head: anterior surface of the manubrium of the sternum. Clavicular head: superior surface of the medial third of the clavicle.I Lateral surface of the mastoid process and the lateral half of the superior nuchal line.A Unilaterally: lateral flexion of the neck to the same side and rotation of the face to the opposite side.…N Spinal accessory nerve (CN XI) for motor supply; branches of C2–C3 (cervical plexus), mainly proprioceptive.
Scalene muscles Muscle group: Three paired lateral neck muscles running from the cervical transverse processes to the 1st and 2nd ribs. They raise the upper ribs in inspiration and flex the neck to the side.
Suprahyoid muscles Muscle group: Four muscles above the hyoid (digastric, stylohyoid, mylohyoid and geniohyoid). They raise the hyoid and larynx in swallowing and depress the mandible.
Digastric Muscle: A suprahyoid muscle with two bellies joined by an intermediate tendon that is slung to the hyoid bone. Each belly has a different nerve supply.O Anterior belly: digastric fossa of the mandible. Posterior belly: mastoid notch of the temporal bone.I Intermediate tendon attached to the body and greater horn of the hyoid.A Depresses the mandible against resistance; raises and steadies the hyoid.N Anterior belly: nerve to mylohyoid (inferior alveolar branch of CN V3). Posterior belly: facial nerve (CN VII).
Mylohyoid Muscle: A flat, triangular sheet that, with its partner, forms the muscular floor of the mouth. It raises the floor of the mouth and the tongue during swallowing.O Mylohyoid line of the mandible.I Median raphe and the body of the hyoid bone.A Raises the floor of the mouth, the tongue and the hyoid; depresses the mandible.N Nerve to mylohyoid (branch of the inferior alveolar nerve, CN V3).
Infrahyoid (strap) muscles Muscle group: Four flat "strap" muscles below the hyoid (sternohyoid, omohyoid, sternothyroid and thyrohyoid). They depress and steady the hyoid and larynx.
Omohyoid Muscle: A long, slender two-bellied infrahyoid muscle running from the scapula to the hyoid. Its intermediate tendon is tethered to the clavicle.O Superior border of the scapula, near the suprascapular notch.I Inferior border of the body of the hyoid bone.A Depresses, retracts and stabilises the hyoid.N Ansa cervicalis (cervical plexus).

Back — deep (intrinsic)

Splenius capitis Muscle: A broad, bandage-like muscle of the back of the neck. It runs from the nuchal ligament and upper thoracic spines to the mastoid process, and it extends and rotates the head to the same side.O Inferior half of the nuchal ligament and the spinous processes of C7–T3 (T4).I Mastoid process and the lateral third of the superior nuchal line.A Bilaterally: extends the head and neck. Unilaterally: laterally flexes the neck and rotates the face to the same side.N Dorsal rami of the middle cervical spinal nerves.
Erector spinae Muscle group: A massive column of intrinsic back muscle on either side of the spine, made up of iliocostalis, longissimus and spinalis. It is the chief extensor of the vertebral column.
Multifidus Muscle: The middle layer of the transversospinalis group. Its short fascicles span 2–4 vertebrae, and it is thickest in the lumbar region, where it is a key segmental stabiliser of the spine.O Posterior sacrum, posterior superior iliac spine, erector spinae aponeurosis, mammillary processes of the lumbar vertebrae, transverse…I Spinous processes of vertebrae 2–4 segments above the origin (up to C2).A Stabilises the vertebral segments; extends the spine; rotates it to the opposite side (unilaterally).N Medial branches of the dorsal rami of the spinal nerves.

Back — superficial (axio-appendicular)

Trapezius Muscle: A large, flat, triangular muscle of the upper back and neck. The two trapezius muscles together form a trapezoid shape. It elevates, retracts, depresses and upwardly rotates the scapula.O Medial third of the superior nuchal line, external occipital protuberance, nuchal ligament, and spinous processes and supraspinous…I Lateral third of the clavicle, acromion and spine of the scapula.A Upper fibres elevate the scapula; middle fibres retract it; lower fibres depress it.…N Spinal accessory nerve (CN XI) for motor supply; C3–C4 anterior rami (cervical plexus), mainly proprioceptive.
Latissimus dorsi Muscle: The broadest muscle of the back. It sweeps from the lower spine, thoracolumbar fascia and iliac crest to the floor of the intertubercular groove, and it extends, adducts and medially rotates the humerus.O Spinous processes of T7–T12, thoracolumbar fascia, posterior third of the iliac crest, inferior 3–4 ribs and (often) the inferior angle of…I Floor of the intertubercular sulcus (bicipital groove) of the humerus.A Extension, adduction and medial rotation of the humerus at the shoulder; elevates the trunk toward the arms when the arms are fixed.N Thoracodorsal nerve (posterior cord of the brachial plexus).
Levator scapulae Muscle: A strap-like muscle from the upper cervical transverse processes to the superior angle of the scapula. It elevates the scapula and rotates it downward.O Posterior tubercles of the transverse processes of C1–C4.I Superior angle and medial border of the scapula, above the root of the spine.A Elevates the scapula and rotates it downward; laterally flexes the neck to the same side.N Dorsal scapular nerve (C5) and direct branches of the C3–C4 cervical spinal nerves.
Rhomboid major Muscle: A flat, quadrilateral muscle from the T2–T5 spinous processes to the medial border of the scapula below the spine. It retracts the scapula and rotates it downward.O Spinous processes of T2–T5 and the supraspinous ligaments.I Medial border of the scapula, from the level of the spine to the inferior angle.A Retracts and downwardly rotates the scapula; holds it against the thoracic wall.N Dorsal scapular nerve (from the C5 root of the brachial plexus).
Rhomboid minor Muscle: A small, cylindrical muscle above rhomboid major. It runs from the C7–T1 spines to the medial border of the scapula at the root of the spine.O Nuchal ligament and the spinous processes of C7–T1.I Medial border of the scapula at the root of the spine.A Retracts and downwardly rotates the scapula; fixes it to the thoracic wall.N Dorsal scapular nerve.

Pectoral region & thoracic wall

Pectoralis major Muscle: A large, fan-shaped muscle of the anterior chest with clavicular and sternocostal heads. It adducts and medially rotates the humerus, flexes it (clavicular head) and extends it from flexion (sternocostal head).O Clavicular head: anterior surface of the medial half of the clavicle.…I Lateral lip of the intertubercular sulcus (crest of the greater tubercle) of the humerus.A Adduction and medial rotation of the humerus; flexion (clavicular head) and extension from flexion (sternocostal head).N Lateral pectoral nerve (lateral cord) and medial pectoral nerve (medial cord).
Pectoralis minor Muscle: A small, triangular muscle deep to pectoralis major, running from ribs 3–5 to the coracoid process. It stabilises the scapula by pulling it down and forward against the chest wall.O Outer surfaces of ribs 3–5, near the costal cartilages.I Medial border and superior surface of the coracoid process of the scapula.A Depresses, protracts and downwardly rotates the scapula; raises ribs 3–5 in forced inspiration.N Medial pectoral nerve (and lateral pectoral nerve).
Subclavius Muscle: A small, round muscle beneath the clavicle. It anchors and depresses the clavicle and protects the subclavian vessels in clavicle fractures.O Junction of the 1st rib and its costal cartilage.I Inferior surface of the middle third of the clavicle (subclavian groove).A Anchors and depresses the clavicle.N Nerve to subclavius (from the upper trunk of the brachial plexus).
Serratus anterior Muscle: A broad, saw-toothed muscle on the lateral chest wall, running from ribs 1–8 to the medial border of the scapula. It protracts the scapula and upwardly rotates it, and holds it against the thorax.O External surfaces of the lateral parts of ribs 1–8 (9).I Anterior (costal) surface of the medial border of the scapula, from the superior angle to the inferior angle.A Protracts the scapula and rotates it upward; holds it against the thoracic wall; can elevate the ribs when the scapula is fixed.N Long thoracic nerve (from the roots of the brachial plexus).
Intercostal muscles Muscle group: Three thin layers of muscle filling each of the 11 intercostal spaces (external, internal and innermost). They stiffen the chest wall and move the ribs during breathing.

Abdominal wall

Rectus abdominis Muscle: A long, strap-like vertical muscle on either side of the linea alba, enclosed in the rectus sheath. It flexes the trunk, tenses the abdominal wall and raises intra-abdominal pressure.O Pubic crest and pubic symphysis.I Xiphoid process and the costal cartilages of ribs 5–7.A Flexes the trunk; compresses the abdominal viscera; tilts the pelvis posteriorly; assists forced expiration.N Thoraco-abdominal nerves (anterior rami of T7–T11) and the subcostal nerve (T12).
Rectus sheath Membrane: The strong aponeurotic compartment enclosing rectus abdominis, formed by the aponeuroses of the three flat abdominal muscles. Its structure changes at the arcuate line.
External oblique Muscle: The largest and most superficial flat abdominal muscle. Its fibres run inferomedially ("hands in pockets"), and its aponeurosis forms the inguinal ligament and the superficial inguinal ring.O External surfaces of ribs 5–12.I Linea alba, pubic tubercle and the anterior half of the iliac crest (via the aponeurosis and inguinal ligament).A Compresses the abdomen; flexes the trunk; laterally flexes it to the same side and rotates it to the opposite side.N Thoraco-abdominal nerves (anterior rami of T7–T11) and the subcostal nerve (T12).
Internal oblique Muscle: The intermediate flat abdominal muscle, with fibres at right angles to the external oblique (superomedially). Its lowest fibres form the cremaster and, with transversus, the conjoint tendon.O Thoracolumbar fascia, anterior two-thirds of the iliac crest and the lateral half of the inguinal ligament.I Inferior borders of ribs 10–12, linea alba (via the aponeurosis) and the pubic crest and pecten pubis (via the conjoint tendon).A Compresses the abdomen; flexes the trunk; laterally flexes it and rotates it to the same side.N Thoraco-abdominal nerves (T7–T11), subcostal nerve (T12), iliohypogastric and ilioinguinal nerves (L1).
Transversus abdominis Muscle: The deepest flat abdominal muscle. Its fibres run horizontally like a corset, compressing the abdomen and stiffening the lumbar spine.O Internal surfaces of costal cartilages 7–12, thoracolumbar fascia, anterior two-thirds of the iliac crest and the lateral third of the…I Linea alba (via the aponeurosis), pubic crest and pecten pubis (via the conjoint tendon).A Compresses and supports the abdominal viscera; stabilises the trunk.N Thoraco-abdominal nerves (T7–T11), subcostal nerve (T12), iliohypogastric and ilioinguinal nerves (L1).
Quadratus lumborum Muscle: A quadrilateral muscle of the posterior abdominal wall between the 12th rib and the iliac crest. It laterally flexes the trunk, "hikes" the hip and fixes the 12th rib during inspiration.O Iliolumbar ligament and the internal lip of the iliac crest.I Medial half of the inferior border of the 12th rib and the tips of the transverse processes of L1–L4.A Lateral flexion of the trunk; elevation of the hip; fixes the 12th rib; extension of the lumbar spine (bilaterally).N Anterior rami of T12 (subcostal nerve) and L1–L4.

Pelvic floor

Levator ani Muscle group: A broad, funnel-shaped muscular sheet that, with coccygeus, forms the pelvic diaphragm. It supports the pelvic organs, maintains faecal and urinary continence and resists rises in intra-abdominal pressure.
Coccygeus Muscle: A small triangular muscle forming the posterior part of the pelvic diaphragm. It runs from the ischial spine to the side of the lower sacrum and coccyx.O Ischial spine (and sacrospinous ligament).I Lateral margins of the inferior sacrum and the coccyx.A Supports the pelvic floor; pulls the coccyx forward.N Direct branches of the anterior rami of S4–S5.

Shoulder (scapulohumeral)

Deltoid Muscle: A thick, triangular muscle that caps the shoulder and gives it its rounded contour. Its three parts abduct (15–90°), flex and extend the arm.O Lateral third of the clavicle, acromion and spine of the scapula.I Deltoid tuberosity of the humerus.A Abduction of the arm beyond the first 15°; anterior part flexes and medially rotates; posterior part extends and laterally rotates.N Axillary nerve (posterior cord of the brachial plexus).
Rotator cuff Muscle group: Four scapulohumeral muscles (supraspinatus, infraspinatus, teres minor and subscapularis) whose tendons blend with the shoulder joint capsule. They hold the humeral head in the shallow glenoid and rotate the arm.
Supraspinatus Muscle: A rotator cuff muscle filling the supraspinous fossa. Its tendon passes under the acromion to the greater tubercle. It initiates abduction and is the most commonly torn cuff tendon.O Medial two-thirds of the supraspinous fossa of the scapula.I Superior facet of the greater tubercle of the humerus; glenohumeral joint capsule.A Initiates abduction of the arm; acts with the rotator cuff to stabilise the joint.N Suprascapular nerve (upper trunk of the brachial plexus).
Infraspinatus Muscle: A thick, triangular rotator cuff muscle occupying the infraspinous fossa. It is the main lateral rotator of the humerus.O Medial two-thirds of the infraspinous fossa and the infraspinous fascia.I Middle facet of the greater tubercle of the humerus.A Lateral rotation of the arm; holds the humeral head in the glenoid.N Suprascapular nerve.
Teres minor Muscle: A narrow, cylindrical rotator cuff muscle along the lateral border of the scapula. It laterally rotates the arm and is supplied by the axillary nerve.O Upper two-thirds of the posterior surface of the lateral border of the scapula.I Inferior facet of the greater tubercle of the humerus.A Lateral rotation of the arm; stabilises the glenohumeral joint.N Axillary nerve (posterior cord).
Subscapularis Muscle: The largest and strongest rotator cuff muscle. It fills the subscapular fossa on the costal surface of the scapula and is the main medial rotator of the humerus.O Subscapular fossa (most of the anterior surface of the scapula).I Lesser tubercle of the humerus and the anterior joint capsule.A Medial rotation and adduction of the arm; holds the humeral head in the glenoid.N Upper and lower subscapular nerves (posterior cord).
Teres major Muscle: A thick, rounded muscle from the inferior angle of the scapula to the medial lip of the intertubercular sulcus. It adducts, medially rotates and extends the arm. It is not part of the rotator cuff.O Posterior surface of the inferior angle of the scapula.I Medial lip of the intertubercular sulcus of the humerus.A Adduction, medial rotation and extension of the humerus.N Lower subscapular nerve (posterior cord).

Arm — anterior compartment

Coracobrachialis Muscle: A slender muscle from the coracoid process to the middle of the medial humerus. It flexes and adducts the arm and is pierced by the musculocutaneous nerve.O Tip of the coracoid process of the scapula.I Middle third of the medial surface of the humerus.A Flexion and adduction of the arm.N Musculocutaneous nerve (lateral cord), which pierces it.
Biceps brachii Muscle: A two-headed muscle of the front of the arm. It crosses the shoulder and elbow and is the most powerful supinator of the forearm and a strong elbow flexor.O Short head: tip of the coracoid process. Long head: supraglenoid tubercle of the scapula.I Radial tuberosity and, via the bicipital aponeurosis, the deep fascia of the medial forearm.A Supination of the forearm; flexion of the elbow (strongest in supination); weak flexion of the arm at the shoulder.N Musculocutaneous nerve (lateral cord).
Brachialis Muscle: A broad muscle deep to biceps from the anterior distal humerus to the coronoid process of the ulna. It is the main flexor of the elbow in every forearm position.O Distal half of the anterior surface of the humerus and the medial and lateral intermuscular septa.I Coronoid process and tuberosity of the ulna.A Flexion of the forearm at the elbow.N Musculocutaneous nerve; small lateral part supplied by the radial nerve.

Arm — posterior compartment

Triceps brachii Muscle: The three-headed muscle of the back of the arm. It is the main extensor of the elbow, and its long head also extends and adducts the shoulder.O Long head: infraglenoid tubercle of the scapula. Lateral head: posterior humerus above the radial groove.…I Proximal end of the olecranon of the ulna and the posterior capsule of the elbow.A Extension of the forearm at the elbow; long head also extends and adducts the arm at the shoulder.N Radial nerve (posterior cord).
Anconeus Muscle: A small triangular muscle on the back of the elbow, from the lateral epicondyle to the olecranon. It assists extension and stabilises the elbow.O Posterior surface of the lateral epicondyle of the humerus.I Lateral surface of the olecranon and the upper posterior surface of the ulna.A Assists triceps in elbow extension; abducts the ulna during pronation; stabilises the elbow.N Radial nerve (branch to anconeus via the medial head of triceps).

Forearm — anterior compartment

Forearm flexors (anterior compartment) Muscle group: The eight muscles of the anterior compartment of the forearm, arranged in three layers. They flex the wrist and digits and pronate the forearm, and nearly all are supplied by the median nerve.
Pronator teres Muscle: The most lateral superficial forearm flexor. It runs obliquely from the medial epicondyle and coronoid process to the middle of the radius, pronates the forearm and assists elbow flexion.O Humeral head: medial epicondyle (common flexor origin) and the medial supracondylar ridge. Ulnar head: coronoid process of the ulna.I Middle of the lateral surface of the radius (pronator tuberosity).A Pronation of the forearm; flexion of the elbow.N Median nerve.
Flexor carpi radialis Muscle: A superficial forearm flexor from the medial epicondyle to the base of the 2nd metacarpal. It flexes and radially deviates the wrist.O Medial epicondyle of the humerus (common flexor origin).I Base of the 2nd metacarpal (and 3rd).A Flexion and abduction (radial deviation) of the wrist.N Median nerve.
Palmaris longus Muscle: A small, variable superficial flexor with a long, thin tendon to the palmar aponeurosis. It is absent in about 14% of people and is a popular tendon graft.O Medial epicondyle of the humerus (common flexor origin).I Distal half of the flexor retinaculum and the apex of the palmar aponeurosis.A Flexion of the wrist; tensing of the palmar aponeurosis.N Median nerve.
Flexor carpi ulnaris Muscle: The most medial superficial flexor. It flexes and adducts (ulnar deviates) the wrist, and it is one of only "one and a half" forearm muscles supplied by the ulnar nerve.O Humeral head: medial epicondyle. Ulnar head: medial olecranon and posterior border of the ulna.I Pisiform, hook of the hamate (pisohamate ligament) and the base of the 5th metacarpal (pisometacarpal ligament).A Flexion and adduction of the wrist.N Ulnar nerve.
Flexor digitorum superficialis Muscle: The large intermediate-layer flexor. Its four tendons split to insert on the middle phalanges of digits 2–5, and it is the main flexor of the PIP joints.O Humero-ulnar head: medial epicondyle and coronoid process. Radial head: anterior oblique line of the radius.I Sides of the middle phalanges of digits 2–5.A Flexion of the PIP joints, then the MCP joints and the wrist.N Median nerve.
Flexor digitorum profundus Muscle: A deep forearm flexor whose four tendons pierce the FDS tendons to reach the distal phalanges. It is the only muscle that flexes the DIP joints and has dual (median and ulnar) innervation.O Upper three-quarters of the anterior and medial surfaces of the ulna and the interosseous membrane.I Bases of the distal phalanges of digits 2–5.A Flexion of the DIP joints, then the PIP and MCP joints and the wrist.N Lateral half (digits 2–3): anterior interosseous nerve (median). Medial half (digits 4–5): ulnar nerve.
Flexor pollicis longus Muscle: A deep forearm flexor from the anterior radius to the distal phalanx of the thumb. It is the only muscle that flexes the thumb's interphalangeal joint.O Anterior surface of the radius and the adjacent interosseous membrane.I Base of the distal phalanx of the thumb (palmar surface).A Flexion of the phalanges of the thumb.N Anterior interosseous nerve (median nerve).
Pronator quadratus Muscle: A flat, square muscle joining the distal quarters of the ulna and radius. It is the prime mover of pronation and binds the two bones together.O Distal quarter of the anterior surface of the ulna.I Distal quarter of the anterior surface of the radius.A Pronation of the forearm; stabilises the distal radio-ulnar joint.N Anterior interosseous nerve (median nerve).

Forearm — posterior compartment

Forearm extensors (posterior compartment) Muscle group: The twelve muscles of the posterior compartment of the forearm. They extend the wrist and digits, abduct the thumb and supinate the forearm, and all are supplied by the radial nerve or its posterior interosseous branch.
Brachioradialis Muscle: A superficial muscle of the lateral forearm from the lateral supracondylar ridge to the radial styloid. Although it lies in the extensor compartment and is supplied by the radial nerve, it flexes the elbow, especially in mid-pronation.O Proximal two-thirds of the lateral supracondylar ridge of the humerus.I Lateral surface of the distal radius, just proximal to the styloid process.A Flexion of the elbow (strongest with the forearm mid-prone); semi-pronation or semi-supination to the neutral position.N Radial nerve (before its division).
Extensor carpi radialis longus Muscle: A superficial extensor from the lateral supracondylar ridge to the base of the 2nd metacarpal. It extends and abducts the wrist and is essential for a firm grip.O Distal third of the lateral supracondylar ridge of the humerus.I Dorsal surface of the base of the 2nd metacarpal.A Extension and abduction (radial deviation) of the wrist.N Radial nerve.
Extensor carpi radialis brevis Muscle: A wrist extensor from the common extensor origin to the base of the 3rd metacarpal. It is the tendon most often involved in tennis elbow.O Lateral epicondyle of the humerus (common extensor origin).I Dorsal surface of the base of the 3rd metacarpal.A Extension and (weak) abduction of the wrist.N Deep branch of the radial nerve.
Extensor digitorum Muscle: The main extensor of the medial four fingers. It arises from the lateral epicondyle and forms the extensor expansions (dorsal hoods) of digits 2–5.O Lateral epicondyle of the humerus (common extensor origin).I Extensor expansions of digits 2–5 (central slip → middle phalanx; lateral bands → distal phalanx).A Extension of the MCP joints (and, with the intrinsic muscles, the IP joints) of the medial four digits; assists wrist extension.N Posterior interosseous nerve (deep branch of the radial nerve).
Extensor digiti minimi Muscle: A slender muscle, often partly fused with extensor digitorum, that extends the little finger. It occupies its own (5th) extensor compartment.O Lateral epicondyle of the humerus (common extensor origin).I Extensor expansion of the 5th digit.A Extension of the little finger.N Posterior interosseous nerve.
Extensor carpi ulnaris Muscle: The most medial superficial extensor, running from the lateral epicondyle and ulna to the base of the 5th metacarpal. It extends and adducts (ulnar deviates) the wrist.O Lateral epicondyle of the humerus and the posterior border of the ulna.I Base of the 5th metacarpal (medial side).A Extension and adduction of the wrist.N Posterior interosseous nerve.
Supinator Muscle: A deep, sheet-like muscle that wraps around the upper radius. It supinates the forearm, and the deep branch of the radial nerve passes between its two layers.O Lateral epicondyle of the humerus, radial collateral and annular ligaments, supinator crest and fossa of the ulna.I Lateral, posterior and anterior surfaces of the proximal third of the radius.A Supination of the forearm.N Deep branch of the radial nerve.
Abductor pollicis longus Muscle: A deep "outcropping" muscle of the posterior forearm that abducts the thumb at the carpometacarpal joint. It forms part of the anterior boundary of the anatomical snuffbox.O Posterior surfaces of the ulna, radius and interosseous membrane.I Lateral base of the 1st metacarpal.A Abduction (and extension) of the thumb at the carpometacarpal joint.N Posterior interosseous nerve.
Extensor pollicis brevis Muscle: A deep posterior forearm muscle that extends the thumb at the MCP joint. With APL, it forms the anterior (radial) border of the anatomical snuffbox.O Posterior surface of the radius and the interosseous membrane.I Dorsal base of the proximal phalanx of the thumb.A Extension of the thumb at the metacarpophalangeal joint.N Posterior interosseous nerve.
Extensor pollicis longus Muscle: A deep extensor whose tendon hooks around Lister's tubercle to reach the distal phalanx of the thumb. It extends all the thumb joints and forms the posterior (ulnar) border of the anatomical snuffbox.O Posterior surface of the middle third of the ulna and the interosseous membrane.I Dorsal base of the distal phalanx of the thumb.A Extension of the distal phalanx of the thumb (and the MCP and CMC joints).N Posterior interosseous nerve.
Extensor indicis Muscle: A small deep extensor that allows the index finger to be extended independently, as in pointing. It is a common donor for tendon transfer.O Posterior surface of the distal ulna and the interosseous membrane.I Extensor expansion of the index finger.A Extension of the index finger (pointing); assists wrist extension.N Posterior interosseous nerve.
Anatomical snuffbox Region: A triangular hollow on the radial side of the wrist, seen when the thumb is extended. It is bounded by the APL/EPB and EPL tendons and floored by the scaphoid and trapezium.

Hand — intrinsic muscles

Thenar muscles Muscle group: Three short muscles that form the thenar eminence at the base of the thumb (abductor pollicis brevis, flexor pollicis brevis and opponens pollicis). They produce opposition, and the recurrent branch of the median nerve supplies them.
Hypothenar muscles Muscle group: Three short muscles that form the hypothenar eminence on the ulnar side of the palm (abductor, flexor and opponens digiti minimi). All are supplied by the deep branch of the ulnar nerve.
Adductor pollicis Muscle: A deep, fan-shaped two-headed muscle of the palm that adducts the thumb, providing a powerful key-pinch. It is supplied by the ulnar nerve and tested with Froment's sign.O Oblique head: capitate and the bases of the 2nd and 3rd metacarpals. Transverse head: anterior surface of the shaft of the 3rd metacarpal.I Medial side of the base of the proximal phalanx of the thumb (via the ulnar sesamoid) and the extensor expansion.A Adduction of the thumb at the CMC and MCP joints.N Deep branch of the ulnar nerve.
Lumbricals (hand) Muscle group: Four small worm-like muscles arising from the FDP tendons and inserting into the extensor expansions. They flex the MCP joints while extending the interphalangeal joints.
Interossei (hand) Muscle group: Small muscles between the metacarpals: four dorsal (abductors) and three palmar (adductors). They spread and close the fingers and, like the lumbricals, flex the MCP joints and extend the IP joints.

Hip & gluteal region

Iliopsoas Muscle group: The composite of psoas major and iliacus, which share a tendon inserting on the lesser trochanter. It is the most powerful flexor of the hip.
Psoas major Muscle: A long, fusiform muscle running alongside the lumbar spine to the lesser trochanter. With iliacus it forms iliopsoas, and the lumbar plexus is embedded within it.O Bodies of T12–L5 and the intervening discs; transverse processes of L1–L5.I Lesser trochanter of the femur (with iliacus).A Flexion of the hip; lateral flexion of the lumbar spine; flexion of the trunk.N Direct branches from the anterior rami of the lumbar spinal nerves.
Iliacus Muscle: A fan-shaped muscle filling the iliac fossa. It joins the psoas tendon to insert on the lesser trochanter and is supplied by the femoral nerve.O Iliac fossa, iliac crest, ala of the sacrum and the anterior sacroiliac ligaments.I Lesser trochanter of the femur (via the psoas tendon) and the shaft below it.A Flexion of the hip; flexion of the trunk on the thigh.N Femoral nerve.
Gluteus maximus Muscle: The largest and most superficial gluteal muscle, and by mass the largest muscle in the body. It is a powerful extensor and lateral rotator of the hip, used for rising, climbing and running.O Outer surface of the ilium posterior to the posterior gluteal line, dorsal surface of the sacrum and coccyx, sacrotuberous ligament and…I Most fibres: iliotibial tract (to the lateral condyle of the tibia). Deep inferior fibres: gluteal tuberosity of the femur.A Extension (from the flexed position) and lateral rotation of the hip; steadies the femur and pelvis;…N Inferior gluteal nerve (sacral plexus).
Gluteus medius Muscle: A thick fan-shaped muscle on the outer ilium, partly covered by gluteus maximus. It is the main abductor of the hip, and in single-leg stance it keeps the pelvis level.O External surface of the ilium between the anterior and posterior gluteal lines.I Lateral surface of the greater trochanter of the femur.A Abduction and medial rotation of the thigh; stabilises the pelvis on the stance limb.N Superior gluteal nerve.
Gluteus minimus Muscle: The smallest and deepest of the three gluteal muscles. It lies beneath gluteus medius and acts with it to abduct and medially rotate the thigh and to stabilise the pelvis.O External surface of the ilium between the anterior and inferior gluteal lines.I Anterior surface of the greater trochanter of the femur.A Abduction and medial rotation of the thigh; pelvic stabilisation in single-leg stance.N Superior gluteal nerve.
Tensor fasciae latae Muscle: A short, flat muscle at the front of the hip enclosed in the fascia lata. It flexes, abducts and medially rotates the hip and tenses the iliotibial tract to stabilise the knee.O Anterior superior iliac spine and the anterior part of the outer lip of the iliac crest.I Iliotibial tract, and through it the lateral condyle of the tibia (Gerdy's tubercle).A Flexion, abduction and medial rotation of the hip; tensing of the fascia lata to stabilise the knee.N Superior gluteal nerve.
Iliotibial tract Tendon: A thick lateral band of the fascia lata running from the iliac crest to Gerdy's tubercle on the tibia. It serves as the shared aponeurotic tendon of gluteus maximus and TFL.
Piriformis Muscle: A pear-shaped muscle from the anterior sacrum, through the greater sciatic foramen, to the greater trochanter. It is the key landmark of the gluteal region.O Anterior surface of the sacrum (S2–S4) and the sacrotuberous ligament.I Superior border of the greater trochanter of the femur.A Lateral rotation of the extended hip; abduction of the flexed hip.N Nerve to piriformis (anterior rami of S1–S2).
Deep lateral rotators of the hip Muscle group: A group of short muscles behind the hip joint (piriformis, superior and inferior gemelli, obturator internus, quadratus femoris and obturator externus). They laterally rotate the thigh and act like a rotator cuff of the hip.

Thigh — anterior compartment

Sartorius Muscle: The longest muscle in the body, a narrow strap running obliquely across the thigh from the ASIS to the medial tibia. It flexes, abducts and laterally rotates the hip and flexes the knee (the cross-legged "tailor's" position).O Anterior superior iliac spine.I Superior part of the medial surface of the tibia (pes anserinus).A Flexion, abduction and lateral rotation of the thigh; flexion of the leg at the knee.N Femoral nerve.
Quadriceps femoris Muscle group: The great extensor of the knee: rectus femoris and the three vasti. Their common tendon contains the patella and continues as the patellar ligament to the tibial tuberosity.
Rectus femoris Muscle: The only part of the quadriceps that crosses the hip. This bipennate muscle flexes the hip and extends the knee, as in kicking a ball.O Straight head: anterior inferior iliac spine. Reflected head: ilium above the acetabulum.I Base of the patella (via the quadriceps tendon), then the tibial tuberosity via the patellar ligament.A Extension of the knee; flexion of the hip.N Femoral nerve.
Vastus lateralis Muscle: The largest part of the quadriceps, forming the lateral bulk of the thigh. It extends the knee and is a common site for intramuscular injection and muscle biopsy.O Greater trochanter, intertrochanteric line, gluteal tuberosity and the lateral lip of the linea aspera of the femur.I Lateral border of the patella and the quadriceps tendon, then the tibial tuberosity via the patellar ligament.A Extension of the leg at the knee.N Femoral nerve.
Vastus medialis Muscle: The teardrop-shaped medial part of the quadriceps. Its lowest, oblique fibres (VMO) resist lateral displacement of the patella during extension.O Intertrochanteric line, medial lip of the linea aspera, medial supracondylar line and the adductor tendons.I Medial border of the patella and the quadriceps tendon, then the tibial tuberosity via the patellar ligament.A Extension of the leg at the knee; medial stabilisation of the patella.N Femoral nerve.
Vastus intermedius Muscle: The deepest part of the quadriceps, lying on the anterior femoral shaft beneath rectus femoris. It extends the knee, and its deep slip (articularis genus) retracts the suprapatellar bursa.O Anterior and lateral surfaces of the femoral shaft (upper two-thirds).I Deep surface of the quadriceps tendon and the base of the patella, then the tibial tuberosity via the patellar ligament.A Extension of the leg at the knee.N Femoral nerve.

Thigh — medial compartment

Adductor group (medial thigh) Muscle group: The muscles of the medial thigh compartment (pectineus, adductor longus, adductor brevis, adductor magnus, gracilis and obturator externus). They adduct the thigh and are supplied mainly by the obturator nerve.
Pectineus Muscle: A flat quadrangular muscle at the top of the medial thigh, in the floor of the femoral triangle. It adducts and flexes the hip and often has dual (femoral and obturator) innervation.O Pecten pubis (superior ramus of the pubis).I Pectineal line of the femur, below the lesser trochanter.A Adduction and flexion of the thigh at the hip.N Femoral nerve; sometimes also the obturator or accessory obturator nerve.
Adductor longus Muscle: The most anterior adductor, a fan-shaped muscle from the body of the pubis to the middle third of the linea aspera. Its tendon is the commonest site of groin strain.O Body of the pubis, inferior to the pubic crest.I Middle third of the linea aspera of the femur.A Adduction of the thigh; assists flexion.N Obturator nerve (anterior division).
Adductor brevis Muscle: A short triangular adductor lying behind pectineus and adductor longus. The anterior and posterior divisions of the obturator nerve pass in front of and behind it.O Body and inferior ramus of the pubis.I Pectineal line and the proximal part of the linea aspera.A Adduction and some flexion of the thigh.N Obturator nerve (anterior division).
Adductor magnus Muscle: The largest and deepest adductor, a composite muscle with an adductor part (obturator nerve) and a hamstring part (tibial nerve). The adductor hiatus in its tendon transmits the femoral vessels to the popliteal fossa.O Adductor part: inferior ramus of the pubis and ramus of the ischium. Hamstring part: ischial tuberosity.I Adductor part: gluteal tuberosity, linea aspera and medial supracondylar line. Hamstring part: adductor tubercle of the femur.A Adduction of the thigh; adductor part flexes and hamstring part extends the hip.N Adductor part: obturator nerve (posterior division). Hamstring part: tibial division of the sciatic nerve.
Gracilis Muscle: A long, slender strap muscle on the medial side of the thigh, the most superficial adductor. It adducts the thigh and flexes and medially rotates the knee.O Body and inferior ramus of the pubis.I Superior part of the medial surface of the tibia (pes anserinus).A Adduction of the thigh; flexion and medial rotation of the leg at the knee.N Obturator nerve (anterior division).

Thigh — posterior compartment

Hamstrings Muscle group: The three posterior thigh muscles (biceps femoris long head, semitendinosus and semimembranosus) arising from the ischial tuberosity. They cross the hip and knee to extend the hip and flex the knee.
Biceps femoris Muscle: The lateral hamstring, with a long head from the ischial tuberosity and a short head from the femur. It inserts on the head of the fibula, extends the hip (long head), flexes the knee and laterally rotates the flexed leg.O Long head: ischial tuberosity (and sacrotuberous ligament). Short head: lateral lip of the linea aspera and the lateral supracondylar line.I Lateral side of the head of the fibula (and the lateral tibial condyle).A Flexion of the knee; lateral rotation of the flexed knee; extension of the hip (long head).N Long head: tibial division of the sciatic nerve. Short head: common fibular division.
Semitendinosus Muscle: A superficial medial hamstring with a fusiform belly and a long cord-like tendon (hence "half-tendon"). It inserts in the pes anserinus.O Ischial tuberosity (inferomedial impression, common tendon with the long head of biceps femoris).I Superior part of the medial surface of the tibia (pes anserinus).A Extension of the thigh; flexion of the leg; medial rotation of the flexed knee.N Tibial division of the sciatic nerve.
Semimembranosus Muscle: The deep medial hamstring, broad and flat with a membranous origin (hence "half-membrane"). It inserts on the posteromedial tibial condyle and reinforces the back of the knee capsule.O Ischial tuberosity (superolateral impression).I Posterior part of the medial condyle of the tibia; the reflected expansion forms the oblique popliteal ligament.A Extension of the thigh; flexion of the leg; medial rotation of the flexed knee.N Tibial division of the sciatic nerve.

Leg — anterior compartment

Tibialis anterior Muscle: The strongest dorsiflexor of the ankle, lying along the lateral side of the tibial shin. It dorsiflexes and inverts the foot, and its weakness causes foot drop.O Lateral condyle and the upper half of the lateral surface of the tibia; interosseous membrane.I Medial and inferior surfaces of the medial cuneiform and the base of the 1st metatarsal.A Dorsiflexion of the ankle and inversion of the foot.N Deep fibular (peroneal) nerve.
Extensor hallucis longus Muscle: A thin anterior-compartment muscle between tibialis anterior and EDL. It extends the great toe and assists dorsiflexion, and it is the classic test of the L5 myotome.O Middle part of the anterior surface of the fibula and the interosseous membrane.I Dorsal aspect of the base of the distal phalanx of the great toe.A Extension of the hallux; dorsiflexion of the ankle.N Deep fibular nerve.
Extensor digitorum longus Muscle: The most lateral anterior-compartment muscle, a unipennate muscle that extends the lateral four toes and dorsiflexes the ankle. Its lateral slip often forms fibularis tertius.O Lateral condyle of the tibia, upper three-quarters of the anterior surface of the fibula and the interosseous membrane.I Middle and distal phalanges of the lateral four toes (via the extensor expansions).A Extension of the lateral four toes; dorsiflexion of the ankle.N Deep fibular nerve.

Leg — lateral compartment

Fibularis longus Muscle: The superficial lateral-compartment muscle. Its tendon turns under the cuboid and crosses the sole to the 1st metatarsal and medial cuneiform. It everts and plantarflexes the foot and supports the transverse arch.O Head and upper two-thirds of the lateral surface of the fibula.I Plantar surfaces of the base of the 1st metatarsal and the medial cuneiform.A Eversion of the foot and plantarflexion of the ankle; supports the arches.N Superficial fibular (peroneal) nerve.
Fibularis brevis Muscle: The deep lateral-compartment muscle, running from the lower lateral fibula to the tuberosity of the 5th metatarsal. It is the main evertor of the foot.O Lower two-thirds of the lateral surface of the fibula.I Tuberosity on the lateral side of the base of the 5th metatarsal.A Eversion of the foot; plantarflexion of the ankle.N Superficial fibular nerve.

Leg — posterior compartment

Gastrocnemius Muscle: The most superficial calf muscle, with two heads from the femoral condyles. It joins soleus in the calcaneal tendon. It powerfully plantarflexes the ankle and flexes the knee, giving the push-off in walking, running and jumping.O Medial head: popliteal surface of the femur above the medial condyle. Lateral head: lateral surface of the lateral femoral condyle.I Posterior surface of the calcaneus via the calcaneal tendon.A Plantarflexion of the ankle when the knee is extended; flexion of the knee; raises the heel during walking.N Tibial nerve.
Soleus Muscle: A broad, flat, powerful plantarflexor lying deep to gastrocnemius. It is mostly slow (type I) fibres, keeps us upright against forward sway, and is the main pump of venous return from the leg.O Posterior aspect of the head and upper quarter of the fibula, the soleal line and medial border of the tibia, and the tendinous arch…I Posterior surface of the calcaneus via the calcaneal tendon.A Plantarflexion of the ankle; steadies the leg on the foot in standing.N Tibial nerve.
Plantaris Muscle: A small, vestigial muscle with a short belly and the longest tendon in the body. It weakly assists gastrocnemius, is absent in ≈7–10% of people and is a useful tendon graft.O Inferior end of the lateral supracondylar line of the femur and the oblique popliteal ligament.I Posterior surface of the calcaneus (medial to, or with, the calcaneal tendon).A Weak plantarflexion of the ankle and flexion of the knee.N Tibial nerve.
Calcaneal tendon Tendon: The thickest and strongest tendon in the body, formed by gastrocnemius and soleus. It inserts on the posterior calcaneus and transmits the force of plantarflexion.
Popliteus Muscle: A thin, triangular muscle in the floor of the popliteal fossa. It "unlocks" the fully extended knee by laterally rotating the femur on the tibia.O Lateral surface of the lateral femoral condyle (popliteal groove) and the lateral meniscus.I Posterior surface of the tibia, above the soleal line.A Lateral rotation of the femur on the fixed tibia (unlocking the knee); weak knee flexion.N Tibial nerve.
Tibialis posterior Muscle: The deepest muscle of the posterior compartment. It is the main invertor of the foot and the key dynamic support of the medial longitudinal arch.O Interosseous membrane and the posterior surfaces of the tibia (below the soleal line) and fibula.I Tuberosity of the navicular, with slips to the cuneiforms, cuboid, sustentaculum tali and the bases of metatarsals 2–4.A Inversion of the foot; plantarflexion of the ankle; support of the medial arch.N Tibial nerve.
Flexor digitorum longus Muscle: A deep posterior-compartment muscle that flexes the lateral four toes. Its tendon crosses tibialis posterior in the leg and FHL in the sole.O Medial part of the posterior surface of the tibia, below the soleal line.I Plantar bases of the distal phalanges of the lateral four toes.A Flexion of toes 2–5; plantarflexion of the ankle; inversion of the foot.N Tibial nerve.
Flexor hallucis longus Muscle: A powerful deep muscle from the posterior fibula to the distal phalanx of the great toe. It provides the final push-off in gait and supports the medial arch.O Inferior two-thirds of the posterior surface of the fibula and the interosseous membrane.I Plantar base of the distal phalanx of the great toe.A Flexion of the hallux; plantarflexion of the ankle; supports the medial arch.N Tibial nerve.

Foot

Plantar intrinsic muscles of the foot Muscle group: Ten short muscles in four layers in the sole of the foot, plus extensor digitorum brevis and extensor hallucis brevis on the dorsum. They support the arches and fine-tune toe position for balance and gait.

Mnemonics

Rotator cuff (SITS): Supraspinatus, Infraspinatus, Teres minor (all on the greater tubercle, superior → inferior facets), Subscapularis (lesser tubercle).
Erector spinae, lateral → medial: "I Love Spaghetti": Iliocostalis, Longissimus, Spinalis.
Pes anserinus (anterior → posterior): "Say Grace before Tea": Sartorius (femoral nerve), Gracilis (obturator nerve), semiTendinosus (tibial nerve). Three muscles, three compartments, three nerves.
Behind the medial malleolus (tarsal tunnel): "Tom, Dick And Very Nervous Harry": Tibialis posterior, flexor Digitorum longus, posterior tibial Artery, Vein(s), tibial Nerve, flexor Hallucis longus.
Interossei of the hand: PAD (Palmar interossei ADduct) and DAB (Dorsal interossei ABduct), relative to the axis of the middle finger.
Median-nerve muscles of the hand (LOAF): Lateral two lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (superficial head). Every other intrinsic hand muscle is supplied by the ulnar nerve.
Branches of the facial nerve (muscles of facial expression): "Two Zebras Bit My Cookie": Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical.
Tendon reflex roots: "S1–2 buckle my shoe" (ankle jerk), "L3–4 kick the door" (knee jerk), "C5–6 pick up sticks" (biceps and brachioradialis), "C7–8 lay them straight" (triceps).

From the Corpus anatomy atlas — for education only.