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Zoology, lecture 24
Vertebrates: Skeletal structure and development
| Question | Answer |
|---|---|
| Three parts of the skeleton | Skull/cranium, trunk וג and limbs םייפג |
| Parts of the skull/cranium | תלוגלוג: Includes the neurocranium (brain box) and viscerocranium (facial bones) |
| Parts of the trunk | וג Includes the spinal column (spinal axis with the neck, chest, trunk and tail) and the ribs and chest bones |
| Parts of the limbs | (Fins in fish) limb attachments like the shoulder blades, joints, pelvis in addition to the limb bones themselves |
| From what did the limbs develop? | From the fins in fish--the first organisms with limbs (tetrapoda) are the amphibia |
| What's the difference between the skeletal systems of fish and mammals? | Mammals went through reduction (not in water, need to support themselves) starting with reptiles there is a neck, fish have ribs all the way along, mammals don't. |
| What type of limbs are there in fish? | All kinds of fins (dorsal, anal etc) They don't exist in land animals. Pelvic fins became rear limbs, pectoral fins became frontal limbs. |
| Purpose of the skeleton | Carries/protects/supports soft tissues, functions in locomotion, protects internal organs, production of blood cells and storage of calcium and phosphorus |
| Why is our skeleton segmented? | Allows for flexibility and motion even though it weakens us a little. |
| What does the skeleton protect? | The brain in the cranium, the spinal cord by the vertebrae, the ribs protect the lungs heart etc. the pelvis protects the reproductive organs/bladder/etc. |
| Blood cell production in the bones | During embryonic development stem cells move into the bones and remain there during the life time producing blood cells. |
| Bone Marrow | Substance in the center of bones made of embryonic stem cells that replaces blood cells (which live 120 days) |
| Types of skeletons | Hydrostatic skeleton (invertebrates) based on water pressure, tough skeleton can be made of calcium carbonate or phosphocalcium like in vertebrates. Exoskeleton-invertebrates (though also exists in vertebrates) endoskeleton-characteristic of vertebrates. |
| Exoskeleton | More characteristic of invertebrates (calcium carbonate/chitin as in insects) |
| Chitin | A polysaccharide that makes up the exoskeleton of insects. |
| Vertebrate skeleton | Made of calcium phosphate. |
| Lower vertebrate skeleton | Had a full exoskeleton that was lost with evolution |
| Types of exoskeletons | Can be jointed, plates, one unit, shells, scales etc. |
| Agnathostoma skeleton | Cyclostoma (early vertebrates with a skull) have a skeleton along their entire bodies giving them protection but makes it difficult to move. |
| Gnathostoma skeleton | The later vertebrates produced a skeleton of three main layers: two compact layers sandwiching a spongy middle layer. Later the skeleton started to break down leaving just a few cells (protection AND flexibility) ex. scales on fish. |
| Dermal skeleton | Exoskeleton present in fish as remaining cells of the original exoskeleton. Called dermal cause it is made by the dermatome. |
| Ostracoderms | Any of several groups of extinct, primitive, jawless fishes that were covered in an armor of body plates |
| Ectodermal skeleton | Sometimes covered on top of the dermal skeleton that produced a tough enamel layer. |
| Remainders of the primitive exoskeleton in higher vertebrates | For example: human teeth that have a mesodermal "dermal" center with an ectodermal enamel covering. In fish the dermal layer forms the scales (they got segmented). |
| Placoid scales | Present in cartilaginous fishes--they form the teeth in sharks. |
| Exoskeletal remains in higher vertebrates | Turtle shells, alligators, armadillos (mammals!) all have remaining structures of the original exoskeleton. |
| Adaptations of the exoskeleton to allow locomotion | They segmented it into scales to allow for movement. Some parts adapted to protect certain areas (LOTS of bones around the skull in fish including a gill cover--all made of remainders of the exoskeleton). |
| Exoskeletal remains in higher vertebrates | Turtle shells, alligators, armadillos (mammals!) all have remaining structures of the original exoskeleton. |
| What were skeletal adaptations necessary for the move to dry land? | Lowering of the body weight through fusion and loss of certain bones, especially in the skull. |
| What are the main skeletal changes between cartilaginous fishes and amphibians? | Loss of lots and lots of skull bones that were no longer necessary as well as lowering in the weight by making holes in the bones. |
| What was the purpose of the cavities in the skull with the evolutionary changes from fish to amphibians? | Made the skull lighter, provided space for the muscles in the skull. |
| Endoskeleton | Characteristic of vertebrate animals. Even when invertebrates have an endoskeleton it's made of calcium carbonate whereas in vertebrates its made of calcium phosphate. |
| How does the skeletal system start? | In amphioxus the original notochord is made of a springy tough structure (not bone or cartilage) and thats what the skeleton develops from. |
| What are the stages in skeletal development? | Notochord, cartilage develops around it, sclerotome gives the bone structure around the cartilage and the bones are segmented. Ribs develop from the spine. From the fins the limbs develop. |
| What are the two types of skeletal bones | Those that develop from cartilage (like the vertebrae and limbs, most bones in the body) called enchondral bones and those that, like the exoskeleton developed from the dermatome. |
| Enchondral bones | Bones that developed from cartilage originally like the vertebrae and limbs--most bones in the body. (sclerotome) |
| Dermal bones | Bones that develop from the dermatome with no intermediate cartilage stage. Usually their origin is the primitive exoskeleton. |
| Neural crest bone origin | Certain neural crest cells form the cartilage in the skull and in the fins. In cartilaginous fish they stay cartilage, in bony fishes and higher vertebrates they become bone. |
| Sclerotome contribution to the skeleton | The part of the somite that sits right next to the notochord and produces a cartilaginous skeleton around the notochord that eventually produces bony vertebrae. |
| Lateral somatomesoderm contribution to the skeleton | Some of it grows out into the chest bones (giving ribs and chest bones) and it gives fins in lower vertebrates that are cartilaginous but when they become limbs in tetrapods they become bone. |
| Which parts of the somatomesoderm given skeleton remains cartilaginous? | In fish, the fins and in higher vertebrates one part of the front of the chest. The sternum starts cartilaginous and becomes bone. |
| Who has a sternum? | Fish don't, later animals close their chest cavity with it. |
| What is the origin of the limb bones? | They develop from the fins that develop from the somatomesoderm. |
| Dermal bones | They develop from the dermatome and do not originate from cartilage. Lots in the skull of fish and in their scales. Land animals, just the skull. |
| Most of the bones in the body are based on | Cartilage ---like the neurocranium, gill slit structures, most of the viscerocranium. |
| How does cartilage become bone? | In embryonic development they start as cartilaginous poles made of hyeline cartilage. In the center, blood vessels enter and bring chondroclasts that eat the cartilage out from the center. |
| Hyeline cartilage | One of three types of cartilage that is the original structure of the limbs, for example |
| Chondroblast | Cells that build cartilage and build the cartilaginous bones outwards and upwards |
| Chondroclasts | Cells that eat cartilage thereby emptying the center of the cartilaginous bones while the cartilage builds outwards. |
| Osteoblasts | Cells that enter the cavity of the cartilaginous structures that have been emptied by the chondroclasts--they build the bones from the inside out producing bone where there was cartilage. |
| Epiphysis building | Epiphysis is the end of the bone that become bony last--eventually it also gets blood vessels. It continues to build cartilage and the bones continue to eat it and grow (growth plate) |
| Diaphysis | The center of the bones that are built into bone first, before the epiphysis. Then blood vessels enter it. |
| What happens when the epiphysal plate disappears? | The organism stops growing. (around age 20 in humans) |
| Why is the structure of the bone hollow? | Muscles need big bones for surface area but the heavier the bone the more muscle you need so it hollowed the bones out. |
| Osteoclasts | Bone eating cells that hollow out the bones to make them lighter. |
| Bone Marrow | Light stem cells that produce blood cells throughout our life time. |
| Periost | Connective tissue around our bones--organic fibers of collagen that allow for attachment of muscles to the bones. |
| Perichondrium | Like the periost but exists during the carilaginous stage...disappears when the bone takes over. |
| Layers of mature bone | Periost on the outside, layer of compact bone, spongy bone, filled with bone marrow on the inside where there is a cavity. Spongy bone is also filled with marrow. |
| Havers osteon | Circular units of bone that make up the compact bone. During embryonic development the blood vessels go in and branch out, then around it the bone building cells build the bone around the blood vessel. |
| Havers canal | Canal in the center of each circular unit of compact bone that holds the original embryonic blood vessel. |
| Osteoblast secondary purpose | They build the bone structures in the outer circles of bone to allow for distribution of blood to those layers further from the Havers canal where the blood vessels are situated. |
| Osteocytes | the name for osteoblasts that distribute blood to external circles of bone after they have stopped producing bone. |
| Where will you find osteoblasts? | In the periphery of the bone where new bone is being built. Eventually they all become osteocytes. |
| How are nutrients brought to and waste removed from the bones? | Through the central havers canal. |
| At what point does the bone stop changing? | Never. We're in equilibrium. They are always being destroyed and rebuilt. |
| Spongy bone composition | As opposed to the compact made of havers, its made of plates sitting at angles with cavities between the plates. |
| Production of the skeletal axis | While lower chordates have a notochord w/no vertebrae but in cyclostoma it's cartilaginous from the sclerotome, and vertebra form for the first time in fish through segmentation. |
| How do the vertebrae form? | Somites are segmental so the sclerotome that closes forms a segmental structure, and they myotome produces the muscles next to it. |
| Why are segmented muscles problematic? | If they remained segmental along with the vertebrae they will not be able to move the entire spine, just individual vertebrae |
| How do you solve the problem of segmental muscles? | The final bone production of the vertebrae results in the splitting of each vertebra reconnecting them to their neighboring halves resulting in muscles that are each connected to two vertebrae. |
| Intersegmental muscles | Muscles connected to two different vertebrae allowing for complex and varied motion in the spinal collumn. |
| םיזיז | The part of the vertebra used as a joint between the vertebrae and as a point of holding on for the muscles. |
| Neural arch | Part of the vertebrae that protects the nerve cord. |
| Aorta dorsalis | Dorsal blood vessel that sits below the vertebrae. |
| Caudal vein | Dorsal blood vessel found in fish in addition to the aorta dorsalis. |
| Hemal arch | Ventral םיזיז in fish tails that protect the caudal vein. |
| Ribs | Produced by the somatomesoderm and connected to the vertebrae. They are long bones on a cartilaginous base. They don't ever become entirely bone. In humans the front part remains cartilage. |
| Sternum | The ventral "chest bone" produced by the somatomesoderm. It starts as cartilage and becomes bone. |
| Joints between the vertebrae and ribs | Double joints that limit motion or in snakes, single joints that are more flexible |
| Viscero cranium | develops from the gill arches. The first arch gives the jaws, the second gives the tongue bone and the 3-7th give the gills in fish or the tracheal cartilage in tetrapods. |
| What is the origin of the cartilage in the skull? | Neural crest cells. |
| Viscerocranium in land animals | The first arch becomes the upper jaw (maxilla=palatoquadrate) and the bottom one (mandibula=meckel) and the second arch becomes the tongue bone. |
Created by:
YaelNoa
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