Introduction to the Locomotor Apparatus

Osteology

• The study of bones
• Primary functions of bones:
  • Support the weight of the body
  • Movement in concert with joints and muscles
  • Protection of internal organs
  • Growth
  • Storage of minerals (e.g., Ca2+ and P+)
  • Storage of fat → marrow
  • Blood cell formation (hematopoiesis) → marrow
• Forelimb region and bones:
  • Scapular region → Scapula
  • Brachium → Humerus
  • Antebrachium → Radius and Ulna
  • Manus = Front paw, includes:
    • Carpus → carpal bones
    • Metacarpus → metacarpal bones
    • Digits → Phalanges & sesamoids
• Types of bones according to shape:
  • Flat bone: scapula
  • Long bones: humerus, radius, ulna
  • Short bones: carpal bones
  • Sesamoids = special type of short bones within tendons
  • Irregular bones: vertebrae

Long Bones

• Gross anatomy:
  • At least 3 centers of ossification
  • Diaphysis = bone shaft → medullary cavity (contains yellow marrow)
  • Epiphysis = end regions of bone
  • Physeal growth plate: located between epiphyses and diaphysis in young animals; comprised of cartilage cells
• Growth plate relevance:
  • Primary site for fractures, infections, metastasis, and effects of endocrine bone disorders
• Bony prominences:
  • Non-articular prominences: attachment sites for muscles; passages of vessels and nerves, etc.
  • Articular prominences: make up joints (e.g., glenoid cavity)

Arthrology

• The study of joints
• A joint is the point of contact, or articulation, between two or more bones/cartilages
• Provides support and movement to the skeleton
• Not all joints are moveable!
• Structural classification of joints:
  • Fibrous joints: strong connective tissue unites articular surfaces of bones
  • Cartilaginous joints: cartilage unites articular surfaces of bones
  • Synovial joints: joint cavity between articular surfaces of bones filled with synovial fluid

Synovial Joints

• Articular surfaces: protected by articular cartilage enclosed within a fluid-filled joint cavity
• Joint capsule:
  • Produces synovial fluid
  • Highly vascularized and innervated
  • Provides strength and resistance
  • For lubrication and nutrition of the articular cartilages
• Accessory structures of synovial joints:
  • Ligaments (lig.): bands of tough fibrous connective tissue
  • Meniscus (pl.menisci): fibrocartilages located within a synovial cavity; allow articular surfaces to fit together

Myology

• The study of muscles
• Locomotor System (Apparatus) = bones + joints (PASSIVE components) + muscles (ACTIVE component)
• Importance: lameness can be caused by muscle/tendon damage, not just bone or joint pathology
• Skeletal muscles attach to bones via tendons
• PROXIMAL Tendon of origin (proximal attachment) – Usually fixed point
• Muscle head or belly – the part that contracts
• Tendon of insertion (distal attachment) – Usually point moved by muscle contraction
• Aponeurosis: a flat, sheet-like tendon; allows muscle to have a broader attachment
• Accessory structures of muscles:
  • Synovial bursa: synovial fluid-filled "balloon" protecting a tendon from a bony surface
  • Tendon Retinaculum: fibrous band holding down tendon(s) to a bone
  • Synovial tendon sheath: synovial fluid-filled "sleeve" completely surrounding a tendon (like a sock) easing its gliding between a retinaculum and bone

Basic Synovial Joint Movements

• Gliding / Sliding of two surfaces on each other
• Angular motions:
  • Flexion: decreasing angle between limb segments
  • Extension: increasing angle between limb segments
  • Abduction: moving away from median plane
  • Adduction: moving towards median plane
  • Circumduction: movement circumscribing a cone shape
  • Medial/Lateral Rotation: "rolling pin movement on the axis of limb
  • Pronation vs. supination of forearm (antebrachium)

Sesamoid Bones

• Found in the tendons of origin or insertion of certain muscles or in a muscle

• Can develop as a response to strain or as a normal occurrence

• Functions:

  • Provide a smooth surface for tendons to slide over, preventing friction of the associated tendon
  • Act as a fulcrum providing extra leverage to the muscle, enhancing the tendon's ability to transmit muscular forces
  • Displace the axis of force by altering the direction of tension in the muscle tendon### Osteology

• Osteology is the study of bones

• Primary functions of bones: • Support the weight of the body • Movement in concert with joints and muscles • Protection of internal organs • Growth • Storage of minerals (e.g., Ca2+ and P+) • Storage of fat → marrow • Blood cell formation (hematopoiesis) → marrow

Bones and Regions

• Forelimb region: • Scapular region → scapula • Brachium → humerus • Antebrachium → radius and ulna • Manus → front paw (carpus, metacarpus, digits, phalanges, and sesamoids)
• Types of bones according to shape: • Flat bones (e.g., scapula) • Long bones (e.g., humerus, radius, ulna) • Short bones (e.g., carpal bones) • Sesamoid bones (special type of short bones within tendons) • Irregular bones (e.g., vertebrae)

Long Bones

• Gross anatomy: • Diaphysis (bone shaft) → medullary cavity (contains yellow marrow) • Epiphysis (end regions of bone) • Physeal growth plate (located between epiphyses and diaphysis in young animals; comprised of cartilage cells)
• Bony prominences: • Non-articular prominences (attachment sites for muscles; passages of vessels and nerves, etc.) • Articular prominences (make up joints)

Arthrology

• Arthrology is the study of joints
• Joint classification: • By number of articulating bones:
  • Simple (between 2 bones)
  • Compound (more than 2 bones) • By how well the bones fit together:
  • Congruent (articular surfaces fit well together)
  • Incongruent (articular surfaces do not fit well together) • By shape & permitted motions around the joint:
  • Hinge (least versatile, flexion and extension only)
  • Spheroidal (ball & socket, most versatile, all range of movements)
  • Others (condylar, ellipsoidal, etc.)

Synovial Joints

• General characteristics: • Joint cavity between articular surfaces of bones filled with synovial fluid • Full movement
• Accessory structures of synovial joints: • Ligaments (bands of tough fibrous connective tissue) • Meniscus (fibrocartilages located within a synovial cavity)
• Anatomy of a synovial joint: • Articular surfaces protected by articular cartilage enclosed within a fluid-filled joint cavity • Joint capsule (produces synovial fluid, highly vascularized and innervated, provides strength and resistance)

Myology

• Myology is the study of muscles
• Importance: lameness can be caused by muscle/tendon damage, not just bone or joint pathology
• Skeletal muscles attach to bones via tendons
• Proximal tendon of origin (proximal attachment) – usually fixed point
• Muscle head or belly – the part that contracts
• Tendon of insertion (distal attachment) – usually point moved by muscle contraction