Vertebrate Skeletal Vertebrate Skeletal SystemsSystems

Part IPart I

Presented by: Presented by:

Geonyzl Lepiten-AlviolaGeonyzl Lepiten-Alviola

BoneBone: :

inorganic components of bone comprise 60% of the dry weight (largely calcium hydroxy-appetite crystals) & provide  the compressive strength of bone.

The organic component is primarily collagen, which gives bone great tensile strength.

FunctionFunction

provides support and movement via attachments for soft tissue and muscle,

protects vital organs, is a major site for red marrow

for production of blood cells, and plays a role in the metabolism of

minerals such as calcium and phosphorus.

Two basic structural types of Two basic structural types of bonebone

compact and spongy. Compact bone forms the outer

shell of all bones and also the shafts in long bones.

Spongy bone is found at the expanded heads of long bones and fills most irregular bones. . bones. .

BoneBone formation formation begins with a blastemabegins with a blastema (any (any

aggregation of embryonic aggregation of embryonic mesenchymal cells which will mesenchymal cells which will differentiate into tissue such differentiate into tissue such as muscle, cartilage, or bone). as muscle, cartilage, or bone).

These cells then develop into These cells then develop into either :either :

1. FIBROBLASTS 1. FIBROBLASTS or or 2. OSTEOBLASTS2. OSTEOBLASTS. .

Fibroblasts form collagen;osteoblasts form bone cells. Together, these form

MEMBRANE BONE (bone deposited directed in a blastema).

Two Ossification Centers:Two Ossification Centers: IntramembranousIntramembranous ossification ossification is the is the

process of process of membrane bone formationmembrane bone formation. .

This process give rise to: This process give rise to:

a. bones of the lower jaw, skull, & a. bones of the lower jaw, skull, & pectoral girdle pectoral girdle

b. dentin & other bone that develops b. dentin & other bone that develops in the skin vertebrae in some in the skin vertebrae in some vertebrates (teleosts, urodeles, & vertebrates (teleosts, urodeles, & apodans) apodans)

Endochondral ossification is the process in which bone is deposited in pre-existing cartilage, & such bone is called REPLACEMENT BONE.

Skeletal Skeletal elements:elements:

Dermal skeleton skin of most living vertebrates has no hard skeletal parts but dermal bone elements are usually present in the head region

early vertebrates (ostracoderms) had so much dermal bone they were called 'armored fishes'

after ostracoderms, fish continued to develop much bone in skin but that bone has become 'thinner' over time

Endoskeleton Somatic - axial & appendicular skeletons Visceral - cartilage or bone associated

with gills & skeletal elements (such as jaw cartilages) derived from

them

Dermal bone of fishes: Dermal bone of fishes:

Basic structure includes 1. lamellar (compact) bone, 2. spongy bone, 3. dentin, , a surface with a layer of

enamel-like material

Evolutionary 'trend' = large bony plates giving way to smaller, thinner bony scales Ancient armor - not found on living fish Ganoid scales - found only on Latimeria

(coelocanth) & sturgeons Placoid scales - elasmobranchs (diagram

to the right; pulp cavity > dentin layer > enamel)

Ctenoid & Cycloid scales - modern bony fish

Tetrapods - retain dermal Tetrapods - retain dermal elements in the skull, jaws, & elements in the skull, jaws, & pectoral girdlepectoral girdle

Somatic skeleton = axial skeleton Somatic skeleton = axial skeleton (vertebral column, ribs, sternum, (vertebral column, ribs, sternum, & skull) + appendicular skeleton& skull) + appendicular skeleton

Vertebral column:Vertebral column:

Vertebrae - consist of a centrum (or body),

1 or 2 arches, plus various processes

Type of vertebra according to Type of vertebra according to Centrum or bodyCentrum or body

AmphicelousAmphicelous concave at both ends concave at both ends most fish, a few salamanders most fish, a few salamanders

((NecturusNecturus), & caecilians ), & caecilians   

OpisthocoelousOpisthocoelous convex in front & concave in back convex in front & concave in back most salamanders most salamanders

Type of vertebra according to Type of vertebra according to Centrum or bodyCentrum or body

ProcelousProcelous concave in front & convex in back concave in front & convex in back anurans & present-day reptiles anurans & present-day reptiles

AcelousAcelous flat-ended flat-ended mammals mammals

HeterocelousHeterocelous saddle-shaped centrum at both saddle-shaped centrum at both

ends ends birds birds

Vertebral Vertebral processes: processes:

projections from arches & centra projections from arches & centra some give rigidity to the column, some give rigidity to the column,

articulate with ribs, or serve as sites articulate with ribs, or serve as sites of muscle attachment of muscle attachment

Transverse processesTransverse processes - most common - most common type of process; extend laterally from type of process; extend laterally from the base of a neural arch or centrum & the base of a neural arch or centrum & separate the epaxial & hypaxial muscles separate the epaxial & hypaxial muscles

Diapophyses & parapophysesDiapophyses & parapophyses - - articulate with ribs articulate with ribs

Prezygapophyses Prezygapophyses (cranial (cranial zygapophyses) & zygapophyses) & postzygapophyses postzygapophyses (caudal zygapophyses)(caudal zygapophyses) - articulate - articulate with one another & limit flexion & torsion with one another & limit flexion & torsion of the vertebral column of the vertebral column

Vertebral Vertebral arches: arches:

  Neural archNeural arch - on top of centrum - on top of centrum   Hemal archHemal arch (also called chevrons) - (also called chevrons) -

beneath centrum in caudal vertebrae beneath centrum in caudal vertebrae of fish, salamanders, most reptiles, of fish, salamanders, most reptiles, some birds, & many long-tailed some birds, & many long-tailed mammals mammals

Vertebral Vertebral columns:columns:

Cartilaginous fishes Cartilaginous fishes do not have typical fish vertebral columns do not have typical fish vertebral columns vertebrae include neural arches (cartilaginous vertebrae include neural arches (cartilaginous

dorsal plates) & dorsal intercalary plates are dorsal plates) & dorsal intercalary plates are located between successive arches located between successive arches

  TeleostsTeleosts well-ossified amphicelous vertebrae well-ossified amphicelous vertebrae notochord persists within each centrum notochord persists within each centrum

(but constricted) (but constricted) neural arch associated with each neural arch associated with each

centrum & hemal arches in tail (caudal) centrum & hemal arches in tail (caudal) vertebrae vertebrae

Chondrosteans (sturgeons & paddlefish) & Chondrosteans (sturgeons & paddlefish) & modern lungfishes modern lungfishes

incomplete incomplete centracentra notochord is not constricted notochord is not constricted cartilage deposited in notochord sheath cartilage deposited in notochord sheath

provides structural supportprovides structural support

Diplospondyly = 2 centra and 2 sets of Diplospondyly = 2 centra and 2 sets of arches per body segment; occurs in some arches per body segment; occurs in some fish (including sharks) fish (including sharks)

Agnathans - only skeletal elements Agnathans - only skeletal elements associated with the notochord are paired, associated with the notochord are paired, lateral neural cartilages lateral neural cartilages

Vertebral columnsVertebral columns of tetrapods of tetrapods

Cervical regionCervical region AmphibiansAmphibians - single cervical vertebra; - single cervical vertebra;

allows little head movement allows little head movement Reptiles - increased numbers of cervical Reptiles - increased numbers of cervical

vertebrae (usually 7) & increased vertebrae (usually 7) & increased flexibility of head flexibility of head

BirdsBirds - variable number of cervical - variable number of cervical vertebrae (as many as 25 in swans) vertebrae (as many as 25 in swans)

Mammals - usually 7 cervical vertebrae Mammals - usually 7 cervical vertebrae

Reptiles, birds, & mammals - 1st two Reptiles, birds, & mammals - 1st two cervical vertebrae are modified & cervical vertebrae are modified & called the atlas & axis called the atlas & axis

atlas - 1st cervical vertebra; ring-like atlas - 1st cervical vertebra; ring-like (most of centrum gone); provides (most of centrum gone); provides 'cradle' in which skull can 'rock' (as 'cradle' in which skull can 'rock' (as when nodding 'yes') when nodding 'yes')

axis - 2nd cervical vertebra axis - 2nd cervical vertebra

Transverse foramen (#6 in above caudal view of a cervical vertebra)

- found in cervical vertebrae of birds & mammals - provides canal for vertebral artery & vein

Dorsal regionDorsal region Dorsals - name given to Dorsals - name given to

vertebrae between vertebrae between cervicals & sacrals when all cervicals & sacrals when all articulate with similar ribs articulate with similar ribs (e.g., fish, amphibians, & (e.g., fish, amphibians, & snakes) snakes)

  Crocodilians, lizards, birds, Crocodilians, lizards, birds, & mammals - ribs are & mammals - ribs are confined to anterior region confined to anterior region of trunk of trunk thoracic - vertebrae with ribs thoracic - vertebrae with ribs lumbar - vertebrae without lumbar - vertebrae without

ribsribs

Sacrum & SynsacrumSacrum & Synsacrum sacral vertebrae - have short sacral vertebrae - have short

transverse processes that brace the transverse processes that brace the pelvic girdle & hindlimbs against the pelvic girdle & hindlimbs against the vertebral column vertebral column Amphibians - 1 sacral vertebra Amphibians - 1 sacral vertebra Living reptiles & most birds - 2 sacral Living reptiles & most birds - 2 sacral

vertebrae vertebrae Most mammals - 3 to 5 sacral vertebrae Most mammals - 3 to 5 sacral vertebrae

Sacrum - single bony complex Sacrum - single bony complex consisting of fused sacral vertebrae; consisting of fused sacral vertebrae; found when there is more than 1 sacral found when there is more than 1 sacral vertebra (see examples below): vertebra (see examples below):

SynsacruSynsacrum m

found in birds found in birds produced by fusion of last thoracics, produced by fusion of last thoracics,

all lumbars, all sacrals, & first few all lumbars, all sacrals, & first few caudals caudals

fused with pelvic girdle fused with pelvic girdle provides rigid support for bipedal provides rigid support for bipedal

locomotionlocomotion

Caudal regionCaudal region

Primitive tetrapods - 50 or more Primitive tetrapods - 50 or more caudal vertebrae caudal vertebrae Present-day tetrapods Present-day tetrapods

number of caudal vertebrae is number of caudal vertebrae is reduced reduced

arches & processes get arches & processes get progressively shorter (the last progressively shorter (the last few caudals typically consist of few caudals typically consist of just cylindrical centra as shown just cylindrical centra as shown below)below)

Anurans - unique terminal segment Anurans - unique terminal segment called the urostyle (section of called the urostyle (section of unsegmented vertebral column unsegmented vertebral column probably derived from separate probably derived from separate caudals of early anurans) caudals of early anurans)

Birds - last 4 or 5 caudal vertebrae Birds - last 4 or 5 caudal vertebrae fused to form fused to form pygostyle pygostyle (see (see drawing above) drawing above)

Apes & humans - last 3 to 5 caudal Apes & humans - last 3 to 5 caudal vertebrae fused to form vertebrae fused to form coccygealcoccygeal (or tail bone) (or tail bone)