Skeletal System Study Notes

General Composition: Bone is a dynamic specialized connective tissue. It is covered by the periosteum, a fibrous membrane on the outer surface.
Bone Cells: - Osteoclast: Functions to remove bone. - Osteoblast: Responsible for producing bone. - Osteocyte: A mature bone cell (an osteoblast surrounded by hard tissue).
Types of Ossification: - Intramembranous Ossification: Occurs in flat bones of the skull; involves no cartilage template. - Endochondral Ossification: Occurs in long bones of limbs; hyaline cartilage is replaced by bone. Processes involve a primary center in the diaphysis (shaft) and secondary centers in the epiphyses (ends), with growth continuing at the epiphyseal plate.
Functions: Provides support (internal scaffold), locomotion (muscle attachment), protection of soft tissues, storage for $Calcium$ and $Phosphate$ , and hematopoiesis (blood cell production in marrow).

Bone Tissue Types: - Compact Bone: Solid outer cortex. - Cancellous Bone: Spongy texture composed of trabeculae filled with red bone marrow.
Microscopic Arrangement: Haversian system consists of Haversian canals (containing nerves and blood vessels) surrounded by lamellae (concentric cylinders) containing osteocytes trapped in lacunae.
Bone Shapes: - Long Bones: Contain a shaft and marrow cavity (e.g., femur, humerus). - Flat Bones: Outer compact and inner cancellous layers with no medullary cavity (e.g., skull, scapula). - Short Bones: Irregular core of cancellous bone (e.g., carpal, tarsal). - Irregular Bones: Unpaired bones in the midline (e.g., vertebrae). - Sesamoid Bones: Located within tendons to change angles (e.g., patella). - Pneumatic Bones: Contain sinuses to decrease weight (e.g., maxillary). - Splanchnic Bone: Bone within an organ, specifically the Os penis in dogs and cats.

The Skull: Divided into the Cranium (brain case: Parietal, Temporal, Frontal, Occipital, Sphenoid), Nasal Chambers (Maxilla, Ethmoid bone, Hard palate), and Mandible (two halves joined at the mandibular symphysis).
Skull Shapes: - Brachycephalic. - Mesaticephalic. - Dolichocephalic.
Hyoid apparatus: Suspends the larynx and tongue from the skull.
Vertebral Column: Standard dog and cat formula: $C7, T13, L7, S3, Cd$ ( $20-23$ ). - C1: Atlas. - C2: Axis (contains the dens).
Ribs and Sternum: Dogs and cats have $13$ pairs of ribs. The sternum consists of $8$ sternebrae, beginning with the Manubrim and ending with the Xiphoid.

Forelimb Bones: Scapula (shoulder blade), Humerus (upper arm), Radius, Ulna (forearm containing the olecranon), Carpus ( $7$ short bones), Metacarpus ( $5$ bones), and Digits (phalanges $P1, P2, P3$ ).
Clavicle: Vestigial and frequently absent in dogs; present but non-articulating in cats.
Hind Limb Bones: - Pelvis: Composed of the Ilium, Ischium, and Pubis; features the Acetabulum (hip socket) and Obturator Foramen. - Femur: Thigh bone; articulates with the patella (large sesamoid) and fabellae. - Tibia and Fibula: Lower leg bones. - Tarsus: $7$ short bones, including the talus and calcaneus (point of hock).

Joint Types: - Fibrous: Immovable sutures (e.g., skull). - Cartilaginous: Limited movement (e.g., pubic symphysis, intervertebral discs). - Synovial: Wide range of motion; contains synovial fluid within a joint capsule.
Synovial Joint Varieties: Plane/gliding, Hinge (elbow), Pivot (Atlantoaxial joint), Condylar (hock), and Ball & Socket (hip, shoulder).
Movements: - Flexion/Extension: Decr./Incr. joint angle. - Abduction/Adduction: Moving away from/toward the median plane. - Protraction/Retraction: Moving limb cranially/caudally. - Rotation, Circumduction, and Gliding.

Visual Analysis: Can you see $3$ abnormalities? (Reference to pelvic/hind limb radiographic image).