SKELETAL SYSTEM

SKELETAL SYSTEM

EXOSKELETON & ENDOSKELETON

  • ENDOSKELETON: from mesodermal, cartilages, dermis, etc
  • EXOSKELETON: integumentary origin

ORIGINS

  • MESODERMAL: mesenchymal cells
  • ENDOCHONDRAL OSSIFICATION
  • INTEGUMENTARY
  • SESAMOID BONES: formation from within tendons

THE SKULL

CRANIAL STRUCTURE OF VERTEBRATES

  • CHONDROCRANIUM / NEUROCRANIUM
    • cartilaginous
    • FUNCTIONS:
      • Protects the brain and other sense organs
      • Provide attachment sites for jaw muscles
    • mostly seen only embryonically except in some fish
    • brain platform
      • ELASMOBRANCHII: support
      • Others: embryonic
    • FATE:
      • ossification in bony fish and tetrapods
      • adult form in elasmobranchii
  • SPLANCHNOCRANIUM
    • ancient chordates - feeding structure
    • vertebrates:
      • supports gills and some respiratory structures
      • develop into jaws and hyoid apparatus

  • DERMATOCRANIUM
    • derived from the dermis
    • Covers and protects the underside of the chondrocranium

DERMAL BONE SERIES

FACIAL SERIES

  • snout series
  • premaxilla, maxilla, nasal

ORBITAL SERIES

  • surrounds the eye sockets
  • lacrimal, prefrontal, postfrontal, postorbital, jugal (aka mallar)

TEMPORAL SERIES

  • beside the orbit
  • intertemporal, supratemporal, tabular, squamosal, quadratojugal

VAULT SERIES

  • covers the brain (roof of the head)
  • frontal, parietal, postparietal

PALATAL SERIES

  • roof of the mouth
  • vomer, palatine, ectopterygoid, pterygoid, parasphenoid

MANDIBULAR SERIES

  • lower jaw
  • lateral, dentary, splenials, angular, strangulation, prearticular, coronoid

NOTE:

bones fuse tgt as the organism develops to lessen the gaps btw them, thereby reducing risk of injury. this protects them from external forces.

SKULL PHYLOGENY

FISH

  • cartilaginous in chondrichthyes
    • no dermatocranium, expanded chondrocranium
  • bony skeleton in actinopterygians
    • major presence of dermal bones (dermatocranium)
    • presence of opercular bones (protect the gills)

DISADVANTAGE: since more articulate, more vulnerable to injury

ADVANTAGES:

  • more attachment points to the muscles, which pulls the muscles downward, allowing movement. creates lower pressure inside the mouth, allowing more water to rush in (along with food).
      • thus, fish take in water through their mouths, run it through their gills and expel them through their opercular bones.
  • puzzle-like arrangement allows for more efficient feeding

AMPHIBIA

  • disappearance of operculum
  • reduction of neurocranial mobility
  • fusion of bones

REPTILIA

  • temporal fenestrae: anapsid, diapsid, synapsid

AVIALAE

  • diapsid
  • mostly dermatocranial
  • braincase is much larger
    • have bigger brains
  • highly elongated jaw, keratinized (for protection)

MAMMALIAN

  • synapsid
  • mostly dermatocranial
  • fusion and loss of numerous bones
  • secondary palate formation
    • separates the nasal cavity and oral cavity

AXIAL SKELETON (trunk, back)

MAIN COMPONENTS

  • ribs
  • Sternum (aka breastbone)
  • vertebrae

FUNCTIONS

  • Protection (ribs protect internal organs)
  • Streamlining (ex. In fish, allows them to move better in water)
  • Stability (vertebral column)
  • maintaining body form and posture (vertebral column)
  • Locomotion (undulating movements from side to side of the axial skeleton allows organism to swim better underwater)
  • weight suspension (in quadruped animals; enables suspension of animal's weight)

VERTEBRAL COLUMN - SEGMENTS IN HUMANS

  • Cervical (neck bones)
  • Thoracic (upper back; attached to the ribs)
  • Lumbar (lower back)
  • Sacral (attached to the pelvic girdle)
  • Caudal (tailbone; reduced in humans, elongated to make up the tail in other organisms)

RIBS

  • FUNCTIONS:
    • muscle attachment
    • protection
    • respiration
  • true, false, floating ribs
    • TRUE: dorsally attached to vertebral column and ventrally attached to breastbone
    • FALSE: dorsally attached to vertebral column, can be ventrally attached to another rib
    • FLOATING: dorsally anchored to the vertebral column but not attached to anything else on the other end

STERNUM

  • attachment point for chest muscles (aids in movement of forelimbs)
  • FUNCTIONS:
    • Protection (shields internal organs: thoracic cavity)
    • Stability (movement, structurally)
  • part of the rib cage
  • absent in fish, testudines, limbless lizards, snakes, and primitive tetrapods
  • highly modified in avialae (KEEL/CARINA)
    • Flattened structure found in the ventral side that allows more muscles to attach. Modification for flight

APPENDICULAR SKELETON

COMPONENTS

  • pectoral and pelvic girdles (support arms, legs, fins)
  • limbs
  • Fins (can be attached to the pectoral or pelvic girdles)

PECTORAL GIRDLE

  • supports pectoral limbs or fins
    • In humans: clavicle, collarbone, shoulder, some bones in upper back etc
  • Articulates w skull (in fish)
  • GLENOID FOSSA (attachment point for forelimbs): socket in pectoral girdle

PELVIC GIRDLE

  • Supports pelvic limbs or fin
  • ACETABULUM (socket in pelvic girdle)
  • presence of public symphysis in some animals (jointed cartilaginous area that aids in childbirth/movement

FINS

  • Fin rays- lepidotrichia (in actinopterygians) & ceratotrichia (in cartilaginous fish)
  • Phylogenetically, source of limbs of tetrapods

LIMBS

  • jointed, bears digits
  • components:
    • STYLOPODIUM (bone directly attached to girdle)
      • humerus for pectoral girdle, femur for pelvic girdle
    • ZEUGOPODIUM (attached to lower limb)
      • radius & ulna - forelimbs, tibia & fibula - hind limbs),
    • AUTOPODIUM
      • manus- forelimbs, pes- hind limbs
      • made up of the:
        • carpals, metacarpals, and phalanges - hands
        • tarsals, metatarsals, phalanges - feet
    • Autopodium can be further divided into the ff:
      • BASIPODIUM (carpals & tarsals)
      • METAPODIUM (metacarsals & metatarsals)
      • ACROPODIUM (phalanges)