Comparative Anatomy Topic 7: Skull and Jaws Skull and Jaws Protects brain, eyes, smell, hearing, taste Amplifies sound Eating ? muscles, bones, teeth Warms air ? turbinate bones Otherwise, pretty simple Cartilage and Bone Unique craniate characteristics Provide muscle attachment sites Protect nerves, brain, blood vessels Protects body (armor) Bone produces blood Calcium storage for body Cartilage vs. Bone Cartilage Bone Blood Supply No Yes Nerves No Yes Heal quickly No Yes Cartilage Firm, flexible material Chondroitin sulfate and collagen Cells = chondrocytes Cells in lacunae (spaces) Elastic cartilage Cartilage Types Hyaline Glassy appearance Long bones Mostly replaced by bone in adult Synovial capsules Cartilage Types Fibrocartilage Reinforced liberally with collagen Intervertebral disks, pubic symphysis Relaxin loosens pelvic symphysis before birth Cartilage Types Elastic cartilage Extra elastic fibers Epiglottis, ear Cartilage Structure Perichondrium - outer connective tissue layer Supplied with blood vessels Inner matrix - food diffuses in and waste out Slow to heal Bone Structure Calcium phosphate and other mineral salts in regular order in matrix Osteon (Haversion system) canal ? haversion canal, blood vessels, lymph, and nerves Calcium phosphate in concentric rings, lamellae (layers near surface) Volkmann?s canals ? diagonally between haversion canals, connects blood vessels Bone Structure Osteoblasts ? produce new bone (osteogenesis), mononucleate Osteocyte ? osteoblast encased in bone Osteoclasts ? remove existing bone, multinucleate Cancellous (spongy) vs. compact bone Spongy bone ? hard, but spongy-looking ? typically inside long bones function ? increase strength (lie along stress lines) ability to change (alter depending on load) Compact bone ? hard ? most bones Cortical vs. Medullary Cortical - outside Medullary ? inside Roughly equivalent to compact vs. spongy bone most of the time Endochondral vs. Intramembranous Endochondral - cartilage model (blue, and most red below neck) Intramembranous - no cartilaginous precursor (most red of skull) Endochondral Bone Long bones, vertebrae, some skull bones Diaphysis - shaft Epiphysis - tips Metaphysis - sometimes recognized as between the two Endochondral Bone Development a. Mesenchymal cells condense b. Cells of condensations become chondrocytes c. Chondrocytes at the centre of condensation stop proliferating and become hypertrophic (h, become larger). Endochondral Bone Development d. Perichondrial cells adjacent to hypertrophic chondrocytes become osteoblasts, forming bone collar (bc). Hypertrophic chondrocytes direct the formation of mineralized matrix, attract blood vessels, and undergo apoptosis. Endochondral Bone Development e. Osteoblasts of primary spongiosa accompany vascular invasion, forming the primary spongiosa (ps). f. Chondrocytes continue to proliferate, lengthening the bone. Osteoblasts of primary spongiosa are precursors of eventual trabecular bone; osteoblasts of bone collar become cortical bone. Endochondral Bone Development g. Secondary ossification centre (soc) forms at epiphyses through same process. The growth plate below the secondary centre of ossification forms orderly columns of proliferating chondrocytes (col). Haematopoietic marrow (hm) expands in marrow space along with stromal cells (connective tissue). Endochondral Bone Development Epiphyseal Plate Broken into Zones: Zone of resting (hyaline) cartilage ? just normal cartilage Zone of Proliferation - cartilage cells being produced Zone of Hypertrophy - Cartilage elongating Zone of Ossification - new bone forming Endochondral Bone Development When epiphyseal (growth) plate reaches epiphysis, growth stops Mammals with secondary center of ossification at epiphysis Birds and Mammals with determinate growth (growth stops at maturity) Other craniates with indeterminate growth - growth slows but never stops Intramembranous Bone Development Mesenchyme compacted into sheets (membranes) Process: Mesenchyme cells condense, supplied with blood vessels, gel-like ground substance formed Bone matrix deposited in bars as osteoblasts form (deeper red) Bars take up whole of bone Growth by adding layers Intramembranous bone types Dermal ? formed in dermis (most of skull, clavicle) Sesamoid ? because of mechanical stress in tendon (patella, pisiform) Perichondral and periosteal ? formed from connective tissue around cartilage and bone (adds thickness to structures) The Panda?s Thumb Giant Pandas have an opposable digit medially on manus It is actually a sesamoid ? radial bone of some Carnivora (RS) Pisiform is other weird bone Drawing, 1. Giant Panda, 2. extinct relative of red panda Used to hold bamboo Joints Synovial (diarthrosis) ? where bones move Synovial capsule ? fluid-filled, connective tissue cap at end of bone Next articular cartilage Joints ? Immovable or slightly moveable Amphiarhthrosis ? slightly moveable Synarthrosis ? no movement Cartilaginous joints ? Symphysis (at midline) - amphiarthrosis Synchondrosis ? synarthrosis Fibrous joint Suture - synarthrosis Syndesmosis ? amphiarthrosis Gomphosis ? teeth in socket, synarthrosis Synostosis ? fused bones (ankylosed), synarthrosis Skull and Jaws Complex origin Chondrocranium ? bones from original cartilaginous shelf Splanchnocranium (also visceral cranium) ? bones from gill arches Dermatocranium ? dermal bones (all except blue) Neurocranium ? parts of each, bones that surround the brain Chondrocranium primitive ? shelf or bowl that supports brain and covers sensor structures (nasal, optic, and otic capsules) Chondrichthyes ? arches up laterally and seals off at top Most Vertebrata ? ossifies at least somewhat A. Hagfish ? brain mostly supported by fibrous sheath (yellow) and notochord (green), blue is cartilage, B. Lamprey, C. Shark Shark Human Splanchnocranium origin ? gill arch skeleton of hemichordates becoming bony or cartilaginous Parts ? gill or branchial arches (green) Mandibular arch (jaws primitively, Pink) Hyoid arch (blue) Splanchnocranium Parts of gill arches ? pharyngobranchial, epibranchial, ceratobranchial, hypobranchial, basibranchial Splanchnocranium Mandibular arch ? Palatoquadrate Meckel?s cartilage Articulation of mandibular arch ? just like Ceratobranchial ? Hypobranchial (not on skull) Hyoid arch ? Hyomandibula Hyoid bones Splanchnocranium Action in sharks ? hyoid pushes forward to open and pulls back to shut Spiracle ? remnants of slit between hyoid arch and mandibular arch Draws in water in rays Gives oxygen to eye and brain Lost or reduced in fast swimmers Most Elasmobranchii, some Chondrostei, Cladistia, Actinistia Splanchnocranium in Sharks (colored parts) and humans (also includes some minor skull bones like the alisphenoid Jaw Evolution Serial hypothesis ? first or second gill arch formed jaws Next formed hyoid, Nothing else contributed Serial Hypothesis Composite Hypothesis Jaw Evolution Composite hypothesis (Erik Jarvik) ?second and third (maybe also first) arch formed mandibular arch Next hyoid Parts of all incorporated into skull (otic shelf, parts of neurocranium) Serial Hypothesis Composite Hypothesis Hyoid Fishes (excluding hyomandibula) ? changes size of mouth chamber (lie in floor of mouth) Tetrapods ? operates tongue, other arches form laryngeal cartilages Splanchnocranium Loses importance Jaws shift from Splanchnocranium To Dermatocranium Dermatocranium Roof of skull Shell around chondrocranium Maxilla, premaxilla, most bones of lower jaw (except articular), temporals, parietals, bones of palate Evolution of Mammalian Jaw/ear Ossicles Joint is dentary-Squamosal vs. Articular-Quadrate Embryology Meckel?s cartilage formed mesial to dentary End of Meckel?s cartilage malleus-like Articulation of malleus (articular) to incus (quadrate) to squamosal Tympanic in area angular normally forms Pelycosaur Jaw Reptilian Jaw joint Articular (lower jaw) - Quadrate (skull) Mammal Jaw Dentary Tympanic Malleus Incus Squamosal Stapes D T M I Sq St D An Ar Q Sq Probainognathus and Diarthrognathus Old Joint New Joint Double Joint Functional - Dentary-Squamosal Hearing - Articular-Quadrate D An Ar Q Sq Probainognathus and Diarthrognathus Auditory Chain Articular - Quadrate - Stapes already auditory chain - Reptile ear Lots of interference when feeding Therapsids chewed Develop new functional joint Old focused on hearing Probainognathus Skull Probainognathus Skull http://digimorph.org/specimens/Probainognathus_sp/ Mammal Jaw Evolution Nice progression in fossil record Also shows up in shape of lower jaw Particular dev. of angular and coronoid processes And relative sizes of bones White = Dentary and other bones Red = Articular/Malleus Green = Quadrate + Quadratojugal/Incus Blue = Angular/Tympanic Left, Mesial Right, Lateral But did it happen only once? Some think that monotremes are therapsids When you map the ear bones onto an independent phylogeny The malleus and incus evolve at least three different times Thus, monotremes may indeed represent a separate evolution towards the mammalian condition Jaw Bone Homologies Cranial Kinesis Definition 1: Joints in skull other than jaw joint Definition 2: Ability to move upper jaw up Who has it? Under #1, just about everything Who doesn?t? Amphibians, turtles, tuataras, non-avian archosaurs, mammals (except rabbits) Buccal Force Pump All fishes Retained in amphibians Used under stress in squamates Feeding and breathing in fishes Buccal Force Pump Hyoid lowers - throat floor drops Mouth opens Size of buccal cavity increases Water sucked in Hyoid raises, mouth closes Water forced out opercle or gill slits Buccal Force Pump Modified in Teleosts Pendulous maxilla and often premaxilla Rotate when mouth opens Squares off mouth opening Meanwhile, dermatocranium flares to sides Lots of hinges - most complex skulls among craniates Greater suction Fishes rarely bite, they suck things in Hyoid region Bowfin Teleost Osteolepimorphs and early Tetrapods Elements separate Easy to see joint when dermatocranium removed Shared with early tetrapods like Ichthyostega Lost in later tetrapods Eusthenopteron Ichthyostega Internal Choanae Nostril=nare=choana Fishes with anterior and posterior nares Connected by tube Not connected to mouth Not used in breathing up to and including lungfishes Anterior nare Posterior nare External Nare Nasolacrimal Canal Nasal Passage Internal nare Internal Choanae Osteolepimorphs and tetrapods New internal nare and nasal passage External nare = ant. Duct between nares = nasolacrimal duct Opening of nasolacrimal duct = post. nare Allow to breathe without surfacing Anterior nare Posterior nare External Nare Nasolacrimal Duct Nasal Passage Internal nare Labyrinthodont Teeth Complexly folded tooth Found in osteolepimorphs and early tetrapods (labyrinthodonts) Reptilian Kinesis Ability to move upper jaw up Presence of intracranial joint Separates skull into parts Metakinesis Joint at back of skull Neurocranium (yellow) remains still Primitive in Lizards Reptilian Kinesis Mesokinesis Joint just behind orbit Rare by itself Possibly in amphisbaenians and some burrowing lizards Rest of lizards dikinetic: With Meso- and metakinetic joints Reptilian Kinesis Prokinesis Intracranial joint in front of eye Snakes and birds (convergence) Reptilian Kinesis Streptostyly In order for meta-, meso-, and prokinetic joints to work Quadrate must move Streptostyly - pemdulous quadrate Black - rest Red - swing forward Blue - swing backwards Why Kinetic Skulls? Good for small, struggling or slippery prey Square-off jaws for vise-like grip Not good for large prey Or chewing This is due to loss of overall strength Lizards and Snakes Lizards lose lower temporal bar Snakes also lose upper temporal bar Increases flexibility Tuatara Lizard Snake UTB LTB UTB Snakes Lose lower jaw symphysis - operate each jaw independently Vipers - Pendulous maxilla - rotates forward to inject venom Birds Derived Diapsid skull Middle temporal bar lost No teeth Keratin sheeth on jaw bones (beak) Prokinetic Rhynchokinesis - ability to flex tip of upper jaw up - some shorebirds and starlings Mammals - Secondary Palate Separates nasal and buccal (mouth) cavities Soft palate (fibrocartilage) completes it to trachea Eat and breathe at same time Cynodonts had the hard palate partially developed Only other animals with secondary palates are crocodiles Primary palate AMPHIBIAN THERAPSID Secondary palate Primary palate MAMMAL Heterodonty First in early therapsids Incisors for clipping Canines for piercing Molars and premolars for chewing and ripping Chewing - break food into smaller particles More energy extracted Heterodonty rare outside of mammals and other therapsids In some fishes, a duckbill dinosaur Evolutionary Medicine Phenotypic Integration of Neurocranium and Brain by JOAN T. RICHTSMEIER et al. http://www3.interscience.wiley.com/cgi-bin/abstract/112475564/ABSTRACT?CRETRY=1&SRETRY=0 Brain and skull once thought of as different units Now found to be integrated - development of one effects the other Coronal Synostosis - when the coronal suture along the back of the skull closes prematurely Leads to brain and skull malformations if not treated Treatment is to break suture and allow skull to grow normally Right unilateral coronal synostosis in 21-week-old child CT scan - skull, MRI - brain Approach Used CT scans and MRI scans taken on same day Digitized landmarks on skull and brain Determined that growth of brain and skull correlated This includes parts that are anatomically distant from one another What does it mean? Synapsid evolution is defined by loss of bones and sutures in the skull and jaws These differences have in turn caused changes in brain structure These diseases may be part of the synapsid evolutionary process to fuse elements of the skull There is a complex interplay in the development of the brain, skull bones, muscles, and meninges in the skull that result in the human brain, but few genes that regulate this
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