Axial System Complete PDF

AXIAL SKELETON Axial Skeleton→ bones along the central axis of the body 1. Consists of the a. Skull b. Hyoid bone c. Spinal column d. Ribs e. Sternum SKULL 1. Most complex part of the skeleton a. Often looks like one big bone...

AXIAL SKELETON Axial Skeleton→ bones along the central axis of the body 1. Consists of the a. Skull b. Hyoid bone c. Spinal column d. Ribs e. Sternum SKULL 1. Most complex part of the skeleton a. Often looks like one big bone b. Actually, consists of 37-38 separate bones 2. All of these bones are united by jagged, immovable, fibrous joints called sutures a. Only the mandible (lower jaw) is connected to the skull by a freely movable synovial joint Bones of Cranium 1. External bones noted are a. Occipital bone b. Interparietal bones c. Parietal bones d. Temporal bones e. Frontal bones 2. Internal bones a. Sphenoid bone b. Ethmoid bone Bones of Face 1. External (landmark bones) a. Incisive bones b. Nasal bones c. Maxillary bones d. Lacrimal bones e. Zygomatic bones f. Mandible 2. Internal (Hidden) a. Palatine bones b. Pterygoid bones c. Vomer bone d. Turbinates Bones of Ear 1. Three tiny, but important bones a. Hidden in the middle ear known as the ossicles i. Malleus (hammer) ii. Incus (anvil) iii. Stapes (stirrup) b. Their function is to transmit vibrations from the tympanic membrane (ear drum) across the middle ear to the inner ear structure called the cochlea c. In the cochlea, receptor cells convert vibrations to nerve impulses that are interpreted by the brain as sound.  CRANIUM Occipital Bone 1. A single bone that forms the caudoventral portion (base) of the skull 2. Important b/c it is where the spinal cord exits the skull and is the skull bone that articulates with the first cervical neck vertebrae 3. Foramen magnum center of the occipital bone: where the spinal cord exits the skull 4. On the lateral sides of the foramen magnum are the occipital condyles; the articular surfaces that join with the first cervical vertebrae (atlas) forming the atlantooccipital joint. [connects the head to the neck] Interparietal 1. Two small bones located on the dorsal midline btwn the occipital bone and the parietal bones a. Clearly visible in young animals b. May fuse in older animals i. Fuse together ii. Fuse to the parietal bone Parietal Bones 1. Form the dorsolateral walls of the cranium a. Large and well developed in dogs, cats, and humans b. Relatively small in horses and cattle Temporal Bone 1. Two temporal bones located ventral to the parietal bones 2. Important because they form the lateral walls of the cranium 3. Contain the middle and inner ear structures 4. Are the bones that form the temporomandibular junction (TMJ) with the mandible 5. Ear structures are contained within the temporal bones and aren’t visible from the outside  6. Only ear structure seen from outside is the external acoustic meatus (bony canal that leads into the middle and inner ear cavities Frontal Bone 1. Form the forehead region of the skull 2. Rostral to the parietal bones a. Form the rostrolateral portion of the cranium b. Form a portion of the orbit 3. Contained within the bone is a large paranasal sinus (frontal sinus) a. In horned cattle breeds i. Cornual process of the frontal bone is the core around the developing horn ii. This is what is removed when you dehorn an adult cow 1. When removed you can see into the frontal sinus iii. Why you want to dehorn when young 1. Before horn buds have united with frontal bones Sphenoid Bone 1. Ventral portion of the cranium 2. Located rostral to the occipital bone 3. If removed from the skull it looks like a flying bat 4. There is a fossa present a. Pituitary fossa i. This houses the pituitary gland 5. In most animals it contains a sinus called sphenoidal sinus Ethmoid Bone 1. Single bone located rostral to the sphenoid bone 2. Contains a sievelike structure a. Cribiform plate i. Many olfactory nerves pass form the upper portion of the nasal cavity to the olfactory bulbs of the brain 3. Horses and humans have small paranasal sinus a. Ethmoid sinus in the ethmoid bone  BONES OF THE FACE Incisive bones 1. Two of them AKA premaxillary bones 2. Are the most rostral bones 3. In all common domestic animals 4. Except ruminants Nasal Bone 1. Two form the bridge of the nose a. Which is the dorsal portion of the nasal cavity 2. Large variety in size a. Dolichocephalic i. Long thin nasal bones 1. Collies and greyhounds b. Brachycephalic i. Short and more triangular 1. Pugs, boston terriers Maxillary Bone 1. Two make up most of the upper jaw (incisive bones make up the rest) 2. House the upper canine teeth, all cheek teeth and maxillary sinus 3. Maxillary bones and palatine bones form the hard palate a. Bony separation btwn mouth and the nasal cavity i. AKA roof of the mouth b. Maxillary bones form the rostral portion of the hard palate c. Palatine bones form the caudal portion of the hard palate  Lacrimal Bones 1. Two small bones that form part of the medial portion of the orbit 2. A space in the bone houses the lacrimal sac Zygomatic Bone 1. AKA malar bones 2. Form a portion of the orbit and join with a process of the temporal bone to form the zygomatic arch on each side of the skull 3. The caudal-facing temporal process of the zygomatic bone joins with the rostral-facing zygomatic process of the temporal bone to make the arch Mandible 1. Is the lower jaw 2. Houses all the lower teeth 3. Is the only movable skull bone a. Forms the TMJ with the temporal bone 4. In some species (dogs, cats, and cattle) a. The sides of the mandible are joined by a cartilaginous joint, mandibular symphysis. i. Is the weakest portion of the mandible 5. Two main regions a. Shaft of the mandible i. Horizontal portion that houses all the teeth b. Ramus of the mandible i. Vertical portion ii. Is where jaw muscles attach to the articular condyles that form the TMJ Internal bones of the face Palatine 1. Two bones make up the caudal portion of the hard palate Vomer 2. Located on the midline of the skull and forms part of the nasal septum a. Acts as the central wall btwn the right and left nasal passages Turbinates/ Nasal Conchae 1. Four thin, scroll-like bones that fill most of the space in the nasal cavity 2. Each side has a dorsal and ventral turbinate a. Covered by the moist, very vascular soft tissue lining of the nasal passages b. Turbinates force inhaled air through the nose around them i. This warms and humidifies air ii. Helps trap any tiny particles in the air Pterygoid bone 1. Two small bones that support the lateral walls of the pharynx HYOID BONE 1. AKA hyoid apparatus 2. Supports the base of the tongue, the pharynx, and larynx a. Helps animal swallow 3. Is actually composed of several individual portions of bone united by cartilage 4. Attached to the temporal bone by two small cartilage rods SPINAL COLUMN 1. AKA vertebral column a. Made up of a series of irregular vertebrae 2. Divided into 5 regions a. Cervical b. Thoracic c. Lumbar d. Sacral e. Coccygeal 3. Most individuals aren’t named, just numbered Vertebral Characteristics 1. Typically consists of a body, an arch, and a group of processes 2. The body of a vertebra a. Is the main, ventral portion of the bone b. Is the strongest, most massive portion c. Bodies of adjacent vertebrae are separated by intervertebral discs i. Made of fibrocartilage and act as shock absorbers 3. Dorsal to the body is the hollow arch (vertebral foramen) a. Arches line up and form a long flexible tunnel, spinal canal i. Houses the spinal cord 4. Three types of processes a. Spinous process i. Dorsally projecting  b. Transverse process i. Two laterally projecting processes ii. Act as muscle attachment sites iii. Provide leverage to move the spine and trunk c. Articular processes i. Cranial and caudal ends of each vertebrae ii. Help form the joints btwn vertebrae Vertebral Formulas Cervical Vertebrae 1. In the neck region 2. Nearly all animals have seven cervical vertebrae a. First two have unusual shape and have specific names i. C1 is called the atlas 1. Is easily palpated due to the wings 2. Is special because it has no vertebral body ii. C2 is called the axis 1. Has large, blade like spinous process 2. Has the peg like dens that fits into the caudal end of the atlas to make the atlantoaxial joint Thoracic Vertebrae 1. Dorsal to the thorax a. Can identify these b/c they have tall spinous processes. b. Have lateral articular facets i. Make joints with the head of the ribs Lumbar Vertebrae 1. Dorsal to the abdominal region 2. Largest looking bones of the spinal column a. Have to support the weight of the abdominal cavity without support of the ribs 3. Have large transverse processes Sacral Vertebrae 1. Fuse to form a single, solid structure a. Sacrum 2. Dorsal to the pelvic region and forms the sacroiliac joint with the pelvis Coccygeal Vertebra 1. Bones of the tail 2. The cranial portion look like normal vertebrae a. The more caudal you move they are reduced to simple rods of bone Ribs 1. Flat bones that form the lateral walls of the thorax a. Number of rib pairs usually equals the number of thoracic vertebrae the animal has 2. Dorsal ends a. Heads of the ribs b. Form joints with the thoracic vertebrae 3. Ventral ends a. Are move variable b. Costal cartilage attaches to it at the costochondral junction  i. Costal cartilage either joins the sternum directly or joins to the costal cartilage to those ahead of them 4. Ribs that join the sternum are called sternal ribs a. Make up the cranial portion of the thorax 5. Ones that join costal cartilage are called asternal ribs 6. Some may not be attached to any thing and are called floating ribs Sternum 1. AKA the breastbone 2. Forms the floor of the thorax 3. Made of a series of rodlike bones called a. Sternebrae b. Only the first and last are named and used as landmarks i. Manubrium ii. Xiphoid 1. A piece of cartilage, known as the xiphoid cartilage extends caudally from the process and is easily felt in most animals.