Skeletal System

• Skeletal system


  Performs vital functions - support, movement, protection, blood cell production, calcium storage and endocrine regulation
• Adult human skeletal system

  • Consists of 206 bones, as well as a network of tendons, ligaments and cartilage that connects them
• Animals with internal skeletons made of bone, called vertebrates, are actually the minority on Earth. As much as 98 percent of all animals are invertebrates, meaning they do not have internal skeletons or backbones
• Bones


  • Very much alive inside the body, being fed by a network of blood vessels from the circulatory system and nerves from the nervous system
  • Have a dense and tough outer layer, with a layer of spongy bone underneath which is lighter and slightly flexible
• Axial skeleton


  Consists of the vertebral column, the rib cage and the skull. Transmits the weight from the head, the trunk and the upper extremities down to the lower extremities at the hip joints, which help humans maintain our upright posture
• Appendicular skeleton


  Formed by the pectoral girdles, the upper limbs, the pelvic girdle and the lower limbs. Functions are to make walking, running and other movement possible and to protect the major organs responsible for digestion, excretion and reproduction
• The skeletal system is also susceptible to breaks, strains and fractures. While bones are meant to protect the body's vital organs, it takes about 10 to 16 pounds of pressure to break an average bone. Bones such as the skull and femur are much tougher to break
• Agnathans


  An ancient group of animals similar to fish but lacking jaws and paired fins. Instead of jaws, they have a cyclostomic (circular) toothed mouth with which they bore into the side of a fish and suck the blood of their victim. Lack an internal skeleton made of true bone
• Hagfish


  • Do not have a skeleton, except they do have a skull, which is made of cartilage. Many researchers think hagfish should not be in the subphylum Vertebrata, but they are called fish because of their fins and gills
• Recent DNA evidence supports the original scheme placing both hagfish and lampreys as the oldest ancestors of the vertebrates
• Chondrichthyes


  Fishes that lack bone. Instead, the skeleton is composed of cartilage that is partly calcified. Includes a skull, jaws with teeth, and a vertebral column (backbone), but unlike the bony fishes, they lack ribs
• Chondrichthyans


  • The upper jaw is only loosely attached to the underside of the skull by ligaments and connective tissue in living sharks and rays, but is fused to the underside of the skull in the holocephalans
  • The notochord of these species, which is present in the young, is gradually replaced by cartilage
  • Lack ribs, so if they leave water, the larger species' own body weight would crush their internal organs long before they would suffocate
  • Do not have bone marrow, so red blood cells are produced in the spleen and the epigonal organ
• Osteichthyes


  The skeletal system of fishes is either composed of thin and flexible cartilage or hard calcified bones or both. Consists of the vertebral column, jaw, ribs, cranium and intramuscular bones. Provides protection and control and also they produce red blood cells in addition to kidneys and spleen

  
• Osteichthyes


  • Have hinged jaws which aid them in feeding. Otoliths are unique characteristics of ear plates which help in steadiness. Gills are breathing organ, with three pairs of bones called gill arches that aid the gills. Fins are a vital part, with paired fins for steering and caudal/dorsal fins for propulsion and stability
• Amphibians


  Have a skeletal system that is structurally homologous to other tetrapods, though with a number of variations. All have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight, with the musculoskeletal system being strong to enable it to support the head and body

  
• Amphibian skeletal system


  • The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes. The pectoral girdle is supported by muscle, and the well-developed pelvic girdle is attached to the backbone by a pair of sacral ribs. Most have four digits on the fore foot and five on the hind foot, but no claws
• Frog skeletal system


  • The hind legs are larger than the fore legs, especially so in those species that principally move by jumping or swimming. The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinized tubercles on the hind feet for digging
• Salamander skeletal system


  • The limbs are short and more or less the same length and project at right angles from the body. Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing. Some species can regenerate lost tails and limbs
• Reptilian skeletal system


  Lizards have a fossilized skull, with ribs connected ventrally to a cartilaginous sternum. Snakes have a flexible backbone and lack limbs, while crocodilians have a heavy, bony skeleton with a strong tail

  
• Locomotion on land


  • Walking
  • Tail swings from side to side or used as a prop, particularly when climbing
  • Only one leg advanced at a time in the manner adopted by their ancestors, the lobe-finned fish
• Salamanders


  • Some climb trees and have long limbs, large toepads and prehensile tails
  • Use their tails in defense and some are prepared to jettison them to save their lives in a process known as autotomy
  • Certain species have a weak zone at the base of the tail and use this strategy readily
  • Tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape
  • Both tails and limbs can be regenerated
• Frogs


  • Adult frogs are unable to regrow limbs but tadpoles can do so
• Lizard skeletal system

  • Fossilized skull
  • Ribs connected ventrally to a cartilaginous sternum, which is never found in other reptiles such as the snake
  • Teeth are either acrodont or pleurodont and irreplaceable
  • Most are four legged and five toed
  • Regeneration of tail is not uncommon
  • Upper skeletal system consists of skull, scapula, humerus, ulna and radius
  • Lower part comprises of femur, fibula, pelvis and tibia
  • Blue tongue lizard has 70 bones overall, very delicate especially in the tail
  • Teeth are small but very sharp and could even harm considerably
  • Ribs are considered very vital for movement and overall fitness

  
• Snake skeletal system


  • Lower jaw has two bones connected at the chin by an elastic tissue, can be stretched widely apart
  • Lower jaw is loosely attached to the upper jaw, several bones of the upper jaw and roof of the mouth also loosely joined
  • Jaws have pointed teeth that curve back toward the throat, not suitable for chewing
  • Two sides of jaw can be moved separately, enabling wide mouth opening to swallow animals larger than their own head
  • 150 to over 400 vertebrae, strong flexible joints connect them enabling wide range of movements
  • More bones in backbone, more agile the snake
• Bird skeleton


  • Highly adapted for flight, extremely lightweight but strong
  • Bones fused into single ossifications, fewer bones than other terrestrial vertebrates
  • Lack teeth or true jaw, have a beak
  • Many bones are hollow (pneumatized) with criss-crossing struts for structural strength
  • Diving birds have less hollow bones than non-diving species, flightless birds like ostriches and emus have pneumatized femurs and cervical vertebrae
  • More cervical (neck) vertebrae than many other animals, 13-25
  • Fused clavicles (collarbone) and keeled sternum
  • Uncinated processes on ribs to strengthen rib cage
  • Vertebral column divided into 4 sections: cervical, trunk, synsacrum, pygostyle
  • Shoulder consists of scapula, coracoid, humerus
  • Innominate bones allow egg laying
  • Femur, tibiotarsus, tarsometatarsus form the leg, leg bones heaviest contributing to low center of gravity for flight
  • Skeleton accounts for only about 5% of total body weight

  
• Vertebrate skeletal system


  • Main component is bone, cartilage found mainly in joint areas
  • Segmental pattern with basic units repeated, particularly evident in vertebral column and ribcage
  • Bones support body and serve as calcium and phosphate storage at cellular level