Musculoskeletal System Notes

Musculoskeletal System

Learning Outcomes

• Identify and describe the basic anatomical structure of equine organ systems, using correct anatomical terminology.
• Identify and describe the basic functions of equine organ systems with regard to underlying physiological processes.
• Outline and explain how equine body systems communicate to achieve homeostasis.

Importance

• Important for further subjects.
• Focus on ONE species (equine).
• Knowledge of bones is crucial.

Axial Skeleton

• Skull – Consider whether it is one bone or many.
• Vertebrae – Understanding the divisions.
• Ribs – Differentiating between true and false ribs.

Appendicular Skeleton

• Essential to know bones and joints.
• Vastly different comparative anatomy of:
  • Distal limb
  • Thoracic attachment

The Role of the Skeleton

• Cancellous (spongey) bone
• Medullary cavity
• Cortical (compact) bone
• Bone Marrow
• Functions:
  • Structure and protection
  • Mineral reservoir (Calcium and Phosphorus)
  • Blood cell production

Bone Type

• Long bones – Cylindrical with diaphysis and epiphysis.
• Short bones – Length = Width; provide stability and resistance to compression.
• Flat Bones – Protection.
• Irregular bones – Specific roles without fitting into other categories.
• Sesamoids – Pulley-like action for tendon over joint or prominence.

Bone Cells

• Osteocyte – maintenance.
• Osteoblasts – produce matrix.
• Osteoclasts – break down matrix.
• Different segments important for growth (the –physis).
• Blood vessels enter via foramen and run in vertical canals.

Periosteum

• Thin membranous layer on the outside of the bone.
• Vascular and well innervated.
• Attachment for all muscle tendons.
• Rich in osteoblasts/clasts.

Cartilage

• Produced and maintained by chondrocytes.
• 3 types:
  • Hyaline cartilage
  • Fibrocartilage
  • Elastic cartilage
• Serves as a suspension system for the skeleton or scaffold for soft structures.

Endochondral Ossification

• Bone growth (and repair).
• Physis = growth plate.
• Cartilage continues to be produced at the physis and then ossified.
• Limb ossification @ 3 years.
• Vertebrae ossification @ 5 years.

Wolff’s Law

• “Bone tissue will adapt according to the stresses placed upon it”.
• Example: Stress fractures of the metacarpal in paddock vs stable environments.

The Role of Muscle

• Contractile tissue responsible for movement.
• Origin (attachment that does not move) and insertion (attachment that moves).
• Actions:
  • Flex – decrease angle between bones.
  • Extend – increase angle between bones.
  • Abduct – away from midline.
  • Adduct – toward midline.
  • Sphincter – circular, control openings.

Muscle Type

• Skeletal – Striated and voluntary.
• Cardiac – Striated and non-voluntary (with intercalated discs).
• Smooth – Non-striated and non-voluntary.
• Striations = repeating organised sarcomeres.

Muscle

• Specialised functional cell = myocyte.
• Myocyte is multinucleate, packed full of microfilaments and mitochondria, and contains myoglobin.
• Myocyte contains multiple myofibrils which are made up of multiple repeating sarcomeres.
• Myocytes bundled upon themselves to create a muscle.

Muscle Contraction

• High energy usage.
• Starts with an action potential.
• Action potential causes calcium release from specialized endoplasmic reticulum called sarcoplasmic reticulum.
• Calcium and ATP then allow the microfilaments actin and myosin to slide along each other.

Sliding Filament Theory

• Involves:
  • Troponin
  • Actin
  • Myosin
• Occurring in multiple repeating sarcomeres along a myofibril.

Tendons

• Attach muscle to bone.
• High tensile strength from parallel collagen fibers.
• Elastic recoil.
• Small force at the level of the muscle = large force in the distal limb.

Ligaments

• Attach bone to bone.
• Similar composition to tendons but with more elastin.
• Provide joint stability.

Tendons and Ligaments of the Distal Limb

• (Further details and examples would be included here, based on the specific content covered.)