Upon completion of this chapter, the reader should be able to:
24.1 Name the basic structures that make up the musculoskeletal system.
24.2 State the functions of the musculoskeletal system.
24.3 Discuss the structure of bone.
24.4 Discuss bone development and growth.
24.5 Detail muscle and bone groups and their relationship to movement.
24.6 Identify types of joints and where they are found in the body.
24.7 Describe common diseases and conditions of the musculoskeletal system.
Introduction to the Musculoskeletal System
The musculoskeletal system consists of:
Bones
Muscles
Tendons
Ligaments
Functions of the Musculoskeletal System:
Provides shape, support, and protection for vital organs.
Allows for movement, adaptability for bending and growth.
Composed largely of connective and muscle tissue.
Bones
Definition: Bone is a hard, active tissue consisting mostly of calcium, forming the animal's skeleton.
Functions of Bones:
Provide support and structure.
Protect internal organs.
Serve as a mineral reserve (calcium and phosphorus).
Aid in red blood cell formation.
Nutritional Needs: Young animals require calcium and essential minerals in their diets for bone formation and growth.
Blood Cell Production: Occurs within the medullary cavity of bones, where bone marrow is located.
Types of Bones
Classification by Shape:
Long Bones:
Definition: Straight and long with a shaft at either end (diaphysis).
Example: Femur, humerus.
Flat Bones:
Definition: Expand in two directions, serving as areas for muscle attachment.
Example: Skull, scapula.
Small Bones:
Definition: Cube-shaped, equal in all directions, often located at joints.
Example: Carpal and tarsal bones.
Irregular Bones:
Definition: Odd or irregular in shape.
Example: Vertebrae.
Sesamoid Bones:
Definition: Small bones found along tendons to reduce friction and stress.
Example: Patella.
Bone Structure
Types: Bones are classified as:
Compact Bone:
Definition: Thick tissue forming the outer layer, capable of repair; provides elasticity and rigidity.
Cancellous Bone:
Definition: Softer, spongelike bone located inside the ends of bones.
Ossification: The process through which bones are formed, producing a medullary cavity.
Additional Structures:
Osteoblast: Particles that initiate the ossification process in developing bones.
Osteocyte: A mature bone cell that develops from osteoblasts and maintains bone.
Osteoclast: Large cells that release minerals into the bone and resorb bony tissue.
Bone Development
Bone is living tissue continually repairing and remodeling in response to the body's calcium needs.
Processes Involved in Bone Health:
Involves complex interaction among osteoblasts, osteocytes, and osteoclasts.
Joints
Definition: The area where two bones meet, allowing for movement.
Types of Joints:
Fibrous Joint:
Description: Fixed joint with little to no movement.
Example: Sutures of the skull.
Cartilage Joint:
Description: Joints that protect and cushion the bones; growth plate in young animals turns to bone as they mature.
Synovial Joint:
Description: Movable joint with layers including cartilage and a joint capsule containing synovial fluid for lubrication.
Examples of movement: Hinge joints allow for one-way movement; pivot joints allow rotation; ball-and-socket joints allow for wide-range motion.
Examples: Elbow (hinge), vertebrae (pivot), hip (ball and socket).
Joint Movements
Two main types:
Flexion: Closing motion causing shortening of the joint.
Extension: Opening motion causing lengthening of the joint.
Abduction: Movement away from the body's midline.
Adduction: Movement toward the body's midline.
Rotation: A spinning motion around the joint's axis.
Muscles and Connective Tissues
Definition and Function: Muscles allow movement; they attach to different body locations and provide strength.
Ligaments: Attach bones to bones, providing support and strength.
Tendons: Attach muscles to bones and assist in limb movement.
Meniscus: A cartilage pad at some joints, providing cushioning (e.g., in the knee joint).
Terminology Tip
Root Words:
Cartilage: chondr/o
Joint: arthr/o
Ligament: ligament/o
Tendon: ten/o or tend/o
Axial Skeleton
Composed of skeleton parts that lie perpendicular to the body:
Includes::
Skull - consisting of multiple bones, maxilla, and mandible.
Spinal column: vertebrae surround and protect spinal cord.
Vertebral Sectioning:
Cervical (C): 7 vertebrae, includes atlas (C1) and axis (C2).
Thoracic (T): 13 vertebrae, each rib connects to a thoracic vertebra.
Lumbar (L): 5 vertebrae, lower back.
Sacral (S): Fused vertebra completing the pelvis.
Coccygeal (Ca): Tail vertebrae (number may vary by species).
Clinical Concepts
Intervertebral Disc Disease (IVDD):
Common in long-back breeds; caused by inflammation and pressure between discs, leading to pain and potential paralysis.
General Bone Structure:
Varies across species (e.g., cats 244 bones; dogs 320 bones).
Appendicular Skeleton
Structure includes upper and lower extremities or limbs.
Forelimbs:
-Components: Scapula, humerus, radius, and ulna.
Hind Limbs:
Components: Pelvis (ilium, ischium, pubis), femur, tibia, fibula, and their respective joints (hock).
Common Diseases and Conditions
Hip Dysplasia: Common in large breeds; the ball and socket of the femur isn't properly aligned, leading to degenerative joint disease.
Arthritis: Often seen in older animals with signs such as lameness and pain; managed with pain relief medications.
Cruciate Ligament Tears: Common in active dogs, often surgery required for large breeds.
Bone Fractures: Various types including simple, compound, and comminuted; treatment varies from splints to surgical interventions.
Navicular Syndrome: Common in horses, resulting in front limb lameness due to degeneration of the navicular bone.
Summary
The musculoskeletal system includes bones, muscles, joints, and tendons, providing structure, support, and enabling animal mobility while being susceptible to various diseases.