Skeletal System – body’s framework of bones and their associated cartilage & ligaments Functions of skeletal system
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Comparative Anatomy and Physiology Skeletal System
Levers for movement – muscles attached Mineral homeostasis – stores and releases minerals as needed (eg. calcium and phosphorus) Blood cell production – in red marrow
1/3 fibers (organic matrix)– collagen 2/3 ground substance (inorganic matrix)– mineral salts (hydroxyapatite) mainly calcium salts calcification – deposition of mineral salt crystals in bone hardness depends on amount of mineral salts resistance to deformation depends on collagen fibers
contain enzymes and acids to digest bone matrix (resorption) involved in bone repair and remodelling remove Ca+2 from bone when it is needed in blood 2 Types of Bone – compact and spongy bone 1) Compact bone – bone arranged in cylindrical structures called osteons or Haversian systems very dense and strong
pathways for exchange of nutrients and wastes with blood vessels in the central canal osteons align along lines of stress to resist bending of bone compact bone forms the shafts of long bones and the outer shell of all bones
with spaces between arrangement gives strength but lightness
site of blood cell formation (hematopoiesis) spicules are composed of layers of matrix with lacunae containing osteocytes, connected by canaliculi nutrients and wastes are exchanged with the red marrow spongy bone is found in the ends of long bone and center of other bones
outer fibrous layer – dense irregular connective tissue site of tendon, ligament, and joint capsule attachment inner cellular layer – contains osteoblast cells for growth, remodeling and fracture repair some collagen fibers (Sharpey’s fibers) penetrate bone to anchor the periosteum Endosteum – thin cellular layer lining inner surfaces of bone contains osteoblasts for remodelling and repair Blood and Nerve Supply of Bone – has a rich blood supply bones are very metabolically active and usually heal rapidly Periosteal arteries – many small vessels that penetrate the periosteum and bone matrix through Volkman’s canals supply vessels in central canals of compact bone
(most bones of limbs and paws) Structure of Long Bones diaphysis – shaft; mainly compact bone epiphyses (sing. –sis) – proximal and distal ends mainly spongy bone with an outer shell of compact bone spaces filled with red marrow metaphyses (sing. –sis) – narrow zone between diaphysis and epiphysis epiphyseal plate (growth plate) – in immature bones plate of hyaline cartilage at metaphysis site where bones grow in length epiphyseal line – in mature bones line of bone where epiphyseal plate has ossified (closed)
reduces friction and absorbs shock at joints medullary cavity(marrow cavity) – space in central diaphysis which contains yellow (fatty) marrow Short bones – nearly equal length and width spongy bone except at surface (carpals and tarsals of paws) Flat bones – 2 thin, flat layers of compact bone enclosing spongy bone surround and protect organs provide large surface area for muscle attachment (most skull bones, rib cage, shoulder blades) Irregular bones – don’t fit other categories complex shapes and variable composition (vertebrae, some facial bones) Sesamoid bones (shaped like a sesame seed) – develop in tendons provide strength to areas of unusual mechanical stress (patella is the largest)
(remember all connective tissues come from embryonic mesoderm) 2 methods of ossification – intramembranous and endochondral Intramembranous ossification – bone forms within loose fibrous connective tissue membranes forms flat bones of skull ossification center develops in fibrous membrane embryonic mesenchyme cells differentiate into osteoblasts and secrete bone matrix around themselves osteocytes become trapped in lacunae matrix around adjacent osteocytes fuses to form spicules of spongy bone connective tissue between spicules differentiates into red marrow osteoblast cells and connective tissue around spongy bone condense to form periosteum and endosteum osteoblasts of periosteum form a thin layer of compact bone on surface of bone Endochondral ossification – bone forms within a hyaline cartilage model most bones form this way cartilage model develops embryonic mesenchyme cells cluster in shape of future bone differentiate into chondroblasts, which secrete hyaline cartilage matrix outer layer of chondroblasts and connective tissue condense to form perichondrium cartilage model grows interstitial growth – chondrocytes of model divide and secrete matrix between themselves model grows in length appositional growth – chondroblasts in perchondrium divide and secrete matrix beneath perichondrium model grows in thickness primary ossification center develops chondrocytes in center of diaphysis die and are replaced by osteoblasts
ossification center grows outwards towards metaphyses of bone osteoclasts hollow out medullary cavity remodeling replaces spongy bone of diaphysis with compact bone secondary ossification centers develop begin in center of each epiphysis and spread outwards, filling epiphyses with spongy bone
anabolic steroids – stimulate tissue growth, including bone high levels at maturity eventually close growth plates
injury to the plate can cause early closure Growth in Thickness – appositional growth osteoblasts in periosteum divide and secrete matrix beneath periosteum Bone remodeling – constant process in which osteoclasts remove bone tissue and osteoblasts replace it renews aging bone tissue, repairs damaged bone redistributes bone along lines of mechanical stress Features of Bones – develop in response to mechanical forces on bone surfaces articular surfaces – smooth, contoured ends of bones that form joints with other bones condyle – cylindrical to rounded end facet – flat surface head – spherical to rounded end depressions and openings – result from compressive forces or allow passage of soft tissues fissure – crack fossa – pocket or cup foramen – hole sulcus – groove meatus – tunnel fovea – small depression processes – prominences on bones resulting from tension (pulling)forces attachment points for tendons and ligaments line tubercle epicondyle crest tuberosity spine trochanter process Remodeling Processes bone resorption – breakdown of bone matrix by osteoclast secretions enzymes - digest collagen (organic matrix) acid – dissolves mineral salts (inorganic matrix) ossification (osteogenesis) – formation of new bone by osteoblasts calcification – deposition of mineral salts in bone by osteoblasts and osteocytes Bone Homeostasis resorption = ossification and calcification
osteogenesis and calcification exercise increases bone mass and strength osteoporosis – weak, porous bone resorption is greater than ossification and calcification may be due to lack of exercise, poor nutrition, hormonal imbalance Calcium Homeostasis – bone stores 99% of body’s calcium calcium aids in nerve and muscle function, blood clotting, and enzyme function blood calcium level is regulated within a narrow range Hormonal regulation of blood calcium Calcitonin negative feedback loop high blood calcium thyroid gland produces and secretes more calcitonin calcitonin inhibits osteoclasts less bone is resorbed more calcium remains in bone blood calcium decreases Parathyroid Hormone(PTH) negative feedback loop low blood calcium parathyroid gland produces and secretes more PTH PTH stimulates osteoclasts more bone is resorbed calcium released from bone matrix enters bloodstream blood calcium increases
the diet and excreted from the body in urine) Fracture Repair fracture hematoma – forms within hours injured bone tissue forms a clot and becomes inflamed phagocytic cells and osteoclasts remove damaged tissue cartilage callus – forms within weeks fibroblasts enter hematoma and differentiate into chondroblasts produce hyaline cartilage bony callus – forms within months beginning near healthy bone ends, osteoblasts replace cartilage callus with spongy bone bridges broken ends and stabilizes fracture bone remodeling – may take months to years bony callus replaced with “normal” bone Joint (arthrosis or articulation) – connection between 2 bones, bone and cartilage, or bone and teeth Naming Joints – usually named after the articulating structures (eg. intervertebral joints, radiocarpal joint, sacroiliac joint) some large, complex joints are given special names (eg. stifle, elbow, hip, shoulder, hock, carpal joint) skull joints can be named using directional terms (eg. sagittal suture) Classification of Joints Fibrous Joints – connected by fibrous connective tissue no movement (synarthroses) sutures – skull joints gomphoses – tooth joints Cartilaginous Joints – connected by cartilage slightly moveable as cartilage compresses (amphiarthroses) symphysis – connected by fibrocartilage Synovial Joints – freely moveable (diarthroses) 2 bone ends covered by articular cartilage joint cavity – small space between bone ends joint capsule – connective tissue enclosing joint cavity fibrous outer layer – dense irregular connective tissue attaches to periosteum; flexible yet strong synovial membrane – inner loose connective tissue layer synovial fluid – secreted by synovial membrane viscous fluid that lubricates the joint Structures Associated with Synovial Joints ligaments – dense fibrous connective tissue that attaches bone to bone
extracapsular – outside joint capsule (eg. collateral ligaments) intracapsular – inside joint capsule (eg. cruciate ligaments of stifle) menisci (sing. meniscus) – extra pads of fibrocartilage between articulating bones stabilize joint and provide extra cushioning bursae – sac-like synovial structures located at points of friction associated with a joint filled with viscous fluid to provide cushioning bursitis – inflammation of a bursa tendon sheath – tube-like bursa surrounding tendons at sites of friction Types of Synovial Joints – based on shape of articulating surfaces determines type of movement at the joint gliding(planar)joint – surfaces relatively flat glide over each other (eg. intercarpal joints) hinge joint – one rod-like and one groove-like surface allows monaxial flexion or extension (eg. elbow) pivot joint – one pointed and one ring-like surface one bone rotates around the other (eg. atlantoaxial joint, C1-C2 vertebrae)
allows biaxial movement (eg. metacarpophalangeal joints)
allows multiaxial movement (shoulder and hip) AXIAL SKELETON – bones arranged around the body’s longitudinal axis SKULL – most joints are immovable fibrous joint called sutures Cranium (braincase) – surrounds and protects brain frontal bones parietal bones interparietal bones temporal bones occipital bone sphenoid bone ethmoid bone Facial Bones – create cavities containing special senses (nasal cavity, orbits, mouth); assist in eating nasal bones incisive bones maxillary bones zygomatic bones lacrimal bones pterygoid bones palatine bones nasal turbinates (conchae) vomer bone mandible – only moveable skull bone (articulates with temporal) temporomandibular joint – synovial hinge joint
help moisturize and warm inhaled air act as resonating chambers frontal, sphenoid, ethmoid, and maxillary sinuses
formed by vomer and ethmoid bones and septal cartilage orbits – eye sockets hard palate – separates nasal cavity from mouth formed by incisive, maxillary and palatine bones horn processes – extensions of frontal bones VERTEBRAL COLUMN (spine) – flexible rod that surrounds and protects the spinal cord, and serves as an attachment site for the head, thoracic cage, and hind limbs
articulates with adjacent vertebral bodies intervertebral discs – fibrocartilage discs between vertebral bodies; have soft, pulpy center which acts as a cushion form cartilaginous joints which are slightly moveable intervertebral disc disease – can degenerate or be damaged by excessive stress inner pulp squeezes out (herniates) dorsally and compresses spinal cord or nerve roots vertebral arch – dorsal to the body vertebral foramen – hole in arch which contains spinal cord spinal canal – formed by all vertebral foramina lined up intervertebral foramina – openings in spinal canal between 2 adjoining vertebrae; allows passage of spinal nerves vertebral processes transverse processes (2) – lateral; muscle attachment sites spinous process (1) – dorsal; muscle and ligament attachment site nuchal ligament – thick, elastic ligament on dorsal spinous processses from thoracic vertebrae to head helps to support the head cranial and caudal articular processes (2 of each) – sites of intervertebral articulation; joint surfaces called facets intervertebral joints – synovial gliding joints
usually 7 atlas vertebra (C1) – holds up skull ring of bone with 2 large ala articulates with skull– synovial hinge joint (nodding) axis vertebra (C2) – dens (peg-like process) articulates with atlas atlantoaxial joint – synovial pivot joint (“no” joint)
usually 13-18 body and transverse processes have facets for articulation with ribs
usually 5-7 largest, thickest vertebrae
highly variable numbers between and within species Thoracic Cage – encloses and protects organs of thoracic cavity Ribs – usually 1 pair for each thoracic vertebra dorsal end articulates with vertebral body and transverse process synovial gliding joints that allow the thoracic cage to expand when breathing sternal ribs – attach to sternum via costal cartilages asternal ribs - don’t attach to sternum attach to costal cartilages of other ribs floating ribs – most caudal ribs with no ventral attachment intercostal space – space between adjacent ribs Sternum (breastbone) – ventral midline made up of rod-like bones called sternebra manubrium – cranial sternebra xiphoid – caudal sternebra xiphoid cartilage – hyaline cartilage attached to the caudal xiphoid
function as levers for movements of skeletal muscles THORACIC (PECTORAL) LIMB – forelimb Scapula (shoulder blade) – doesn’t articulate with the axial skeleton strongly attached to the thorax by muscles Humerus (brachium of forelimb) proximal end articulates with scapula (scapulohumeral joint) shoulder joint – synovial ball-and-socket joint distal end articulates with radius and ulna elbow joint – synovial hinge joint
proximal end articulates with medial humerus distal end connected lateral carpus (the ulna doesn’t reach the carpus in the horse) Radius (antebrachium of forelimb) main weight-bearing bone of antebrachium proximal end articulates with lateral humerus distal end articulates with medial carpus (radius and ulna also articulate with each other, allowing some rotational movement of the forepaw) Carpals (carpus) – carpal joint (“knee” of horse or cow) 2 rows of short bones forming 3 joint regions radiocarpal joint – proximal row articulates with radius synovial ellipsoid or hinge joint intercarpal joint – proximal row articulates with distal row synovial gliding joints carpometacarpal joint – distal row articulates with metacarpals mainly synovial gliding joints Metacarpals – bones of forepaw numbered 1-5 starting medially cats and dogs have all 5 ruminants – metacarpals 3 and 4 fused to bear weight metacarpals 2 and 5 are remnants horse – metacarpal 3 (cannon bone) bears all weight metacarpals 2 and 4 are remnants (splint bones) metacarpophalangeal joints (distal articulations with phalanges) cats and dogs – synovial ellipsoid joints horse – synovial hinge joint (fetlock) has 2 sesamoids caudally (proximal sesamoids)
digits numbered 1-5 starting medially most digits have 3 phalanges – proximal, middle, and distal cat and dog – 5 digits, most with 3 phalanges each digit 1 (dewclaw) has 2 phalanges ruminants – 4 digits digits 3 and 4 bear weight and have 3 phalanges each digits 2 and 5 bear no weight and are remnants with reduced phalanges
horse – 1 digit digit 3 bears weight and has 3 phalanges distal phalanx is the coffin bone navicular bone – sesamoid at caudal P2-P3 joint
slightly moveable cartilaginous joint sacroiliac joints – coxae articulate with sacrum synovial gliding joint the coxal bones form from 3 embryonic bone which fuse
forms sacroiliac joint ischium – caudal portion pubis – ventromedial portion forms pubic symphysis obturator foramen – large hole that makes pelvis lighter acetabulum – deep, rimmed socket which articulates with femur formed where ilium, ischium, and pubis join coxofemoral (hip) joint – synovial ball-and-socket joint hip dysplasia – poorly formed, loose hip joint leads to wear-and-tear at joint (osteoarthritis) Femur – hindquarter or thigh region proximal end articulates with coxal bone round ligament – anchors head of femur in acetabulum distal end articulates with tibia and patella stifle (knee) joint – synovial hinge joint medial and lateral menisci – fibrocartilage pads anchored to tibia; add stability to joint cruciate ligaments – crossed intracapsular ligaments that add stability to joint cranial cruciate lig.– prevents tibia sliding cranially and stifle hyperextension caudal cruciate lig.- prevent tibia sliding caudally fabellae – 2 sesamoids on caudal stifle in cat & dog Patella (kneecap) – sesamoid bone in quadriceps femoris tendon patellar ligament – connects patella to cranial tibia patella fits into a groove on the cranial femur stay apparatus – in horses, additional patellar ligaments and certain muscles lock the stifle and hock joints so the horse can stand with very little effort
the hock when the stifle flexes luxating patella – patella slips medially, causing pain
medial, weight-bearing bone of hind leg proximal end articulates with femur distal end articulates with tarsals Fibula – leg or gaskin region non-weight bearing bone; site of attachment for muscles proximal end articulates with tibia cats and dogs – distal end articulates with tibia and tarsus horse and cattle – fibula is a remnant
2 rows of short bones forming 3 joint regions tibiotarsal joint – proximal row articulates with tibia synovial hinge joint intertarsal joints – proximal row articulates with distal row synovial gliding joints tarsometatarsal joint – distal row articulates with metatarsals mainly synovial gliding joints Metatarsals – bones of hind paw numbered 1-5 starting medially cats and dogs usually have metatarsals 2-5 metatarsal 1 may be a small remnant ruminants – as with forefoot horse – as with forefoot metatarsophalangeal joints (distal articulations with phalanges) similar to forefeet Phalanges (singular phalanx) – digits of hind paw as with forefoot cat and dog – usually 4 digits (2-5) with 3 phalanges each remnant of digit 1 may be present with reduced phalanges ruminants and horse – as with forefoot
strong yet lightweight fewer bones, fused together for strength
upper and lower jaws covered by beaks lighter than teeth both jaws are moveable large orbits
nasal cavity usually very reduced 1 round occipital condyle (ball-and-socket type joint) allows greater rotation of the head vertebrae birds have more cervical vertebrae than mammals increased flexibility of the neck thoracic vertebrae are fewer and fused synsacrum – lumbar, sacral, and cranial coccygeal vertebrae fuse with the coxal bones forms a strong, light plate to articulate with the legs
attachment site for retrices (tail feathers) thoracic cage – rigid structure for attachment of flight muscles ribs – reduced numbers no costal cartilages (ossified except at a small, cartilaginous joint)
sternum
keel – large, bony ridge for attachment of flight muscles APPENDICULAR SKELETON pectoral limb – securely attached to axial skeleton by scapula and coracoid furcula (wishbone) – fused clavicles braces the shoulder during flight major and minor metacarpals digit I – anchors feathers of the alula (feathers for steering) digits II, III, metacarpals and ulna anchor remiges (flight feathers of wing)
ilium – fused to synsacrum pubis and ischium – not united caudally open pelvis for laying large eggs femur (drumstick)
digits – most birds have 4 digits have 2-5 phalanges (numbering corresponds to number of joints) digits II and III point anteriorly digit I points posteriorly digit IV may point posteriorly (parrots) anteriorly (chickens) either (owls) Download 73.43 Kb. Share with your friends:
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