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Human Musculoskeletal Anatomy: A Complete Overview

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1. SKULL

Subdivisions of the Cranium

Key Skull Features

• Fontanelles (in newborns): membranous unossified gaps that allow head deformation during birth and postnatal growth
• Sutures: coronal, sagittal, lambdoid, squamous — all immovable fibrous joints
• Synovial joints in the head (only 3 pairs):
  • Temporomandibular joints (TMJ) — between mandible and temporal bone
  • Between the 3 ossicles of the middle ear (malleus–incus–stapes)
• Key foramina: supra-orbital (CN V1), infra-orbital (CN V2), mental (CN V3), foramen magnum (brainstem)

Named Skull Bones at a Glance

• Frontal — forehead, superior orbital rim
• Parietal (×2) — sides and roof of cranium
• Temporal (×2) — sides of skull, houses middle/inner ear
• Occipital — posterior skull, foramen magnum
• Sphenoid — central skull base, "keystone bone," forms part of all cranial fossae
• Ethmoid — between eye sockets, forms part of nasal septum
• Zygomatic (×2) — cheekbones
• Maxilla (×2) — upper jaw, floor of orbit
• Nasal (×2) — bridge of nose

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2. VERTEBRAL COLUMN & VERTEBRAE

Regions

Spinal Curvatures

• Cervical lordosis — anterior convexity
• Thoracic kyphosis — posterior convexity
• Lumbar lordosis — anterior convexity
• Sacrococcygeal kyphosis — posterior convexity

Special Cervical Vertebrae

• Atlas (C1): ring-shaped, no body, no spinous process — supports the skull on two lateral masses
• Axis (C2): has the dens (odontoid process) that projects superiorly into C1, forming the pivot joint for head rotation

Typical Vertebra — Parts

• Body — weight-bearing anterior cylinder
• Vertebral arch — pedicles + laminae, forms the spinal canal
• Spinous process — posterior midline projection
• Transverse processes (×2) — lateral projections for muscle/rib attachment
• Superior & inferior articular processes — form facet joints between vertebrae
• Intervertebral discs — fibrocartilaginous shock absorbers between bodies (nucleus pulposus + annulus fibrosus)

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3. JOINTS

A. Synovial Joints (Diarthroses)

• Articular cartilage (hyaline) covers bone surfaces — prevents direct bone contact
• Joint capsule = inner synovial membrane (produces synovial fluid for lubrication) + outer fibrous membrane
• Ligaments — thickenings of the fibrous membrane or separate bands
• Bursae — closed sacs of synovial membrane that reduce friction
• Intra-articular structures — articular discs (fibrocartilage), fat pads, tendons

B. Solid Joints (Synarthroses)

• Fibrous joints — sutures (skull), syndesmoses (interosseous membranes), gomphoses (teeth in sockets)
• Cartilaginous joints — primary (synchondroses, growth plates) and secondary (symphyses, e.g., pubic symphysis, intervertebral discs)

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4. UPPER LIMB

Bones of the Upper Limb (64 total per limb)

• Clavicle — S-shaped, only bony link between upper limb and axial skeleton
• Scapula — triangular flat bone with glenoid cavity, acromion, coracoid process, spine

• Humerus — head articulates with glenoid (glenohumeral joint); has greater & lesser tubercles (rotator cuff insertions), deltoid tuberosity, medial/lateral epicondyles

• Radius — lateral; broader distally; articulates with scaphoid & lunate (wrist)
• Ulna — medial; has olecranon (forms point of elbow); trochlear notch articulates with humerus

• Proximal: Scaphoid, Lunate, Triquetrum, Pisiform
• Distal: Trapezium, Trapezoid, Capitate, Hamate
• Mnemonic: "Some Lovers Try Positions That They Can't Handle"

• Metacarpals (5) — numbered I–V (thumb to little finger)
• Phalanges (14) — thumb has 2 (proximal, distal); fingers 2–5 have 3 each (proximal, middle, distal)

Key Upper Limb Joints

Muscles of the Upper Limb

The supraspinatus, infraspinatus, teres minor, and subscapularis form the SITS rotator cuff — they stabilize the glenohumeral joint.

• Superficial: Pronator teres, Flexor carpi radialis, Palmaris longus, Flexor carpi ulnaris, Flexor digitorum superficialis
• Deep: Flexor digitorum profundus, Flexor pollicis longus, Pronator quadratus
• Nerve supply: Median nerve (mostly) + Ulnar nerve (FCU, medial FDP)

• Extensor carpi radialis longus & brevis, Extensor digitorum, Extensor digiti minimi, Extensor carpi ulnaris
• Deep: Supinator, Abductor pollicis longus, Extensor pollicis brevis & longus, Extensor indicis
• Nerve supply: Radial nerve (posterior interosseous branch)

• Thenar group (thumb): Abductor pollicis brevis, Flexor pollicis brevis, Opponens pollicis — Median nerve
• Hypothenar group (little finger): Abductor digiti minimi, Flexor digiti minimi, Opponens digiti minimi — Ulnar nerve
• Lumbricals (4): Flex MCP, extend IP joints — Median (1st & 2nd), Ulnar (3rd & 4th)
• Interossei: Dorsal (abduct fingers), Palmar (adduct fingers) — all Ulnar nerve
• Adductor pollicis — Ulnar nerve

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5. LOWER LIMB

Bones of the Lower Limb (62 total per limb)

• Hip bone (os coxae) — formed by 3 fused bones: ilium (upper wing), ischium (posterior/inferior), pubis (anterior). Together with the sacrum they form the bony pelvis.
• Acetabulum — deep socket formed by the union of all three bones; articulates with femoral head

• Femur — longest/strongest bone in body. Head, neck, greater & lesser trochanters; shaft; medial & lateral condyles distally
• Patella — sesamoid bone within quadriceps tendon; sits in front of knee

• Tibia — medial, weight-bearing; has medial condyle, tibial tuberosity, medial malleolus
• Fibula — lateral, non-weight-bearing (thin); lateral malleolus forms lateral ankle

• Talus — articulates with tibia/fibula above (ankle joint)
• Calcaneus — heel bone, largest tarsal
• Navicular, Cuboid, 3 Cuneiforms (medial, intermediate, lateral)

• Metatarsals (5) — I–V
• Phalanges (14) — big toe has 2; toes 2–5 have 3 each

Key Lower Limb Joints

Muscles of the Lower Limb

• Adductor longus, brevis, magnus; Gracilis; Pectineus
• Action: hip adduction — Obturator nerve (L2–L4)

• Tibialis anterior (dorsiflexion + inversion), Extensor digitorum longus, Extensor hallucis longus, Fibularis tertius
• Nerve: Deep fibular (peroneal) nerve

• Fibularis longus & brevis — eversion of foot
• Nerve: Superficial fibular nerve

• Superficial: Gastrocnemius + Soleus (= triceps surae) → plantarflexion via calcaneal (Achilles) tendon; also Plantaris
• Deep: Tibialis posterior (inversion), Flexor digitorum longus, Flexor hallucis longus
• Nerve: Tibial nerve

• Plantar surface: abductors/flexors of toes, lumbricals, interossei — primarily medial & lateral plantar nerves (branches of tibial nerve)
• Support longitudinal and transverse arches of the foot

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Summary Comparison

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