Anatomy of the Musculoskeletal System

Musculoskeletal System

• Muscular systems terminology: "my", "myo", "musc"
• Skeletal systems terminology: "os", "osteo", "oss"

Skeletal System

• Functions: support, protection, movement, storage, haemopoiesis
• Classification: long, flat, irregular, short, sesamoid
• Bone structure:
  • Epiphysis: end of each long bone
  • Metaphysis: attached to the epiphysis
  • Diaphysis: long bone (body of bone)
  • Periosteum: outer layer of the diaphysis
  • Compact bone: within the diaphysis with marrow/medulla cavity
  • Spongy bone: within the epiphysis and metaphysis
• Articular Cartilage:
  • Smooth, slippery surface (20x more slippery than ice)
  • Transmission of loads with little friction
  • Devoid of blood vessels, lymphatics, and nerves

Bone Structure

• Cavity of bone: filled with compact cortical (less dense) and cancellous spongy trabecular (denser)
• Compact cortical: within the cavity of the metaphysis and epiphysis
• Compact cortical: located at the diaphysis

Axial and Appendicular Skeleton

• Axial skeleton: skull/cranium, vertebral column, bony thorax
• Appendicular skeleton: limbs (appendages), pectoral girdle, pelvic girdle

Skull

• Made up of many bones
• Divided into 2 regions:
  • Face (viscerocranium)
  • Head (neurocranium)

Vertebral Column Regions

• Cervical: lower head/neck
• Thoracic: ribcage
• Lumbar: stomach
• Sacral: hips
• Coccygeal (Caudals): below hips

Limbs

• Upper limbs (humans) / Forelimb (quadrupeds):
  • 1 bone for proximal part
  • Humerus in arms
  • Femur in legs
• Lower limb (human) / Hindlimb (quadrupeds):
  • 2 bones
  • Radius and Ulna in forearms
  • Fibula and Tibia in lower legs
• Hands and Feet contain short bones
  • Hands: Carpals, Metacarpals, and Phalanges
  • Feet: Tarsals, Metatarsals, and Phalanges

Muscles

• Muscle structure:
  • 1. Muscle
  • 2. Fascicle
  • 3. Muscle fibre cell
  • 4. Myofibril
  • 5. Myofilaments
• Muscle mass: usually proximal to limb and tendon
• Muscles contract by shortening, always pull, never push
• Muscles always span joints or multiple joints to move
• Muscle contractions:
  • Isotonic:
    • Concentric: muscle shortens
    • Eccentric: muscle lengthens, used against force
  • Isometric: change in tension, no change in length

Joints

• Cavitated: Synovial (freely moving)
• Solid:
  • Fibrous:
    • Gomphosis (teeth)
    • Syndesmosis (Tibiofibular)
    • Suture (Skull)
  • Cartilages:
    • Primary (Synchondrosis, growth plates)
    • Secondary (Symphysis, pelvis)

Bone Growth

• Hypertrophy: increased cell size, not number
• Hyperplasia: increased cell number, not size
• Types of bone growth:
  • Interstitial: division of chondroblast from within cartilage
  • Appositional: differentiation of cells from surface or perichondrium
  • Longitudinal: indirect growth via interstitial cartilage at growth plate and ossification
  • Circumferential: occurs directly via oppositional growth at bone surface

Hormones

• Gigantism: excess GH before closure of epiphysis, tall stature, long bones, delayed puberty
• Acromegaly: excess GH after epiphysis closure, unaffected height and gonads, facial characteristics changed
• Parathyroid Hormone (PTH):
  • Regulates Calcium and Phosphate in body
  • Released from parathyroid glands
  • Effects of too much/too little PTH on calcium levels and bone health
• Vitamin D: works with PTH to help absorb Calcium and Phosphate in GI tract
• Calcitonin: opposes PTH, reduces blood plasma Calcium from thyroid glands
• Vitamin C: involved in collagen synthesis
• Oestrogen: reduces bone resorption, stimulates bone development
• Testosterone: reduces bone resorption, stimulates bone development, increases muscle mass

PEDs and Hormone Modulators

• Erythropoietin (EPO): affects erythropoiesis
• Anabolic androgen steroid (AAS): testosterone
• Peptide hormones + releasing factors: GH
• Growth factors and modulators: IGF-1, VEGF
• Hormone and metabolic modulator: anti-oestrogen

Wolff's Law

• Optimisation of bone strength with respect to bone mass
• Alignment of trabeculae with principle of stress direction
• Self-regulation of bone cells responding to mechanical stimulus
• Increased mechanical loading = Increased bone strength (Greater mineralisation and bone mass and decreased porosity)

Osteoarthritis and Sarcopenia

• Osteoarthritis: joint degeneration of articular cartilage and bone, progressive, joint pain only present when bone is damaged
• Sarcopenia: age-related loss of skeletal muscle mass and decline in strength, decrease in size and quality of muscle, presence of 50% in 80-year-olds

Bone Development

• Cartilage is retained between the epiphysis and the shaft
• Endochondral ossification: bone formation within cartilage
• Intramembranous ossification: bone formation within a membrane

Hormones

• Gigantism: excess GH before epiphysis closure, resulting in tall stature and long bones
• Acromegaly: excess GH after epiphysis closure, resulting in facial characteristic changes, but unaffected height and gonads
• Parathyroid Hormone (PTH):
  • Regulates calcium and phosphate in the body
  • Released from parathyroid glands
  • Excess PTH: increases calcium in blood plasma, decreases bone calcium, and increases risk of kidney stones and osteoporosis
  • Insufficient PTH: decreases calcium in blood plasma, causes muscle rigidity and spasms
• Vitamin D: works with PTH to help absorb calcium and phosphate in the GI tract
• Calcitonin: opposes PTH, reduces blood plasma calcium, and is released from thyroid glands
• Vitamin C: involved in collagen synthesis, and deficiency can cause scurvy or barlow's disease
• Oestrogen: reduces bone resorption, stimulates bone development, and plays a big part in bone maintenance
• Testosterone: reduces bone resorption, stimulates bone development, and increases muscle mass

PEDs

• Erythropoietin (EPO): affects erythropoiesis
• Anabolic androgen steroid (AAS): testosterone
• Peptide hormones + releasing factors: GH
• Growth factors and modulators: IGF-1, VEGF
• Hormone and metabolic modulator: anti-oestrogen

Wolff's Law

• Bones adapt to mechanical loading by increasing strength, mineralization, and bone mass, and decreasing porosity
• Trabeculae align with the principle of stress direction

Bone Disorders

• Osteoarthritis: joint degeneration of articular cartilage and bone, progressive, and joint pain only present when bone is damaged
• Sarcopenia: age-related loss of skeletal muscle mass and decline in strength, decrease in size and quality of muscle

Muscle

• Muscle types: fast twitch (chicken breasts) or slow twitch (duck breasts)
• Muscle arrangement: into compartments, typically with the same nerve and blood supply
• Isometric: change in tension, no change in length
• Muscle contraction: always pulls, never pushes, and muscles always span joints or multiple to move

Bone Growth

• Hypertrophy: increased cell size, not number
• Hyperplasia: increased cell number, not size
• Types of bone growth:
  • Interstitial: division of chondroblast from within cartilage
  • Appositional: differentiation of cells from the surface or perichondrium
  • Longitudinal: indirect growth via interstitial cartilage at growth plate and ossification
  • Circumferential: occurs directly via oppositional growth at bone surface

Bone Structure

• Epiphysis: end of each long bone
• Metaphysis: attached to the epiphysis
• Diaphysis: long bone (body of bone)
• Outer layer of Epiphysis: has an articular surface/cartilage
• Spongy bone: located within the epiphysis and metaphysis
• Compact bone: within the diaphysis with marrow/medulla cavity
• Periosteum: outer layer of the diaphysis
• Articular cartilage: smooth, slippery surface, transmits loads with little friction, devoid of blood vessels, lymphatics, and nerves

Musculoskeletal System

• Terminology: muscular systems = "my", "myo", "musc", skeletal systems = "os", "osteo", "oss"
• Function: support, protection, movement, storage, and haemopoiesis
• Classification: long, flat, irregular, short, and sesamoid

Bone Section Summary

• Axial: skull/cranium, vertebral column, bony thorax
• Appendicular: limbs (appendages), pectoral girdle, pelvic girdle

The Skull

• Made up of many bones
• Split into 2 regions: face (viscerocranium) and head (neurocranium)

Vertebral Column Regions

• Cervical: lower head/neck
• Thoracis: ribcage
• Lumbar: stomach
• Sacral: hips
• Coccygeal (Caudals): below hips

Limbs

• Upper limbs (humans) Forelimb (quadrupeds): 1 bone for proximal part
• Lower limb (human) Hindlimb (quadrupeds): 2 bones
• Hands and feet: full of short bones