Human Musculoskeletal Anatomy

• Cartilage


  Smooth, elastic connective tissue which provides structural support to the body. Cartilage consists of cells called chondrocytes, which produce and are surrounded by extracellular matrix. The spaces between cells are called lacunae.
• Types of cartilage


  • Yellow/elastic cartilage (highest density of chondrocytes)
  • Hyaline cartilage (middle density of chondrocytes)
  • White/fibrous cartilage (lowest density of chondrocytes)
• Compact bone


  Dense bone which forms the hard external layer of all bones to provide protection and strength to bones.
• Organic component of compact bone

  Mostly the protein collagen
• Inorganic component of compact bone

  Mostly hydroxy-apatite, containing calcium and phosphate
• Collagen


  Provides tensile strength (resistance to being pulled apart) to the bone
• Hydroxy-apatite


  Provides compressive strength (resistance to being compressed)
• Osteoblasts


  Cells, embedded in the matrix of the bone, which form, repair and reform the inorganic component of the bone
• Osteoclasts


  Cells which break down the inorganic component of the bone when the bone is broken down and reformed
• Haversian System


  A unit/osteon of compact bone. Haversian systems consist of a central canal containing the bone's blood vessels and nerve fibres, called the Haversian canal, surrounded by lamellae, which are layers of compact matrix containing organic and inorganic tissues. The function of Haversian systems is to help the bone resist bending and fracturing.
• Rickets


  A disorder, only found in children, caused by a deficiency of calcium, Vitamin D or phosphorus. Causes weak or soft bones, stunted growth and skeletal deformities.
• Osteomalacia


  The same disorder as rickets, except when found in adults. Also causes weak or softened bones. Also caused by a deficiency of Vitamin D, calcium or phosphate.
• Osteoporosis/brittle bone disease


  Caused by loss of bone density due to a fall in oestrogen levels due to menopause, or fall in testosterone levels due to alcohol consumption, hypogonadism or use of certain medications. Symptoms include back pain, loss of height and stooped posture, and bone fractures which occur much more easily than might be expected. Treated by use of bisphosphonates, selective oestrogen receptor modulators, parathyroid hormones, supplements of calcium or Vitamin D and HRT/testosterone treatment. Fractures would also be treated using plaster etc.
• Skeletal muscle


  Muscle, which is connected to the skeleton, which moves the limbs and other parts of the body.
• Myofibrils


  Smaller fibres that make up muscle fibres
• Actin


  A thin filament that is one of the two major filaments in myofibrils
• Myosin


  A thick filament that is one of the two major filaments in myofibrils
• Tropomyosin


  An accessory protein in actin that regulates muscle contraction
• Troponin


  An accessory protein in actin that regulates muscle contraction
• Sarcomere


  The smallest units of muscle fibres which can contract independently
• Muscle contraction


  1. An impulse stimulates the release of the neurotransmitter acetylcholine.

  2. Acetylcholine stimulates the release of calcium ions.

  3. Calcium ions bind to the accessory protein troponin. This causes tropomyosin (another accessory protein) to move away from the active site of actin.

  4. ATP is hydrolysed, which releases energy.

  5. The head of the myosin filament attaches to actin. This is called a cross-bridge.

  6. Myosin pulls the actin filament into the middle of the sarcomere. This shortens the muscle slightly.

  7. ATP attaches to the head of the myosin filament. Myosin detaches from the actin. The cross-bridge is broken.

  8. This repeats until either calcium ions or ATP run out.
• Sliding filament theory


  The mechanism of muscle contraction, where the proteins of muscles slide past/over one another, and this results in movement.
• Slow-twitch muscle fibres


  Responsible for endurance activities. They contract more slowly, and release large amounts of energy more slowly. They respire mostly aerobically, and therefore have high capillary density and a high concentration of mitochondria. They have a high concentration of myoglobin, and therefore can store more oxygen.
• Fast-twitch muscle fibres


  Used for rapid movements. They release small amounts of energy and contract very quickly. They respire mostly anaerobically and therefore have a lower density of mitochondria. They have a low concentration of myoglobin. They have large glycogen stores which are used for glycolysis (the first stage in aerobic or anaerobic respiration which produces pyruvate).
• Anaerobic respiration


  Occurs when there is insufficient oxygen for aerobic respiration. After glycolysis, the pyruvate is reduced to lactic acid using reduced coenzymes. The buildup of lactic acid in muscles decreases pH of muscles, which affects the Central Nervous System. Reduced stimulation from the CNS reduces muscle contraction. Anaerobic respiration is also much less efficient than aerobic respiration and produces many fewer molecules of ATP per molecule of glucose that enters into glycolysis.
• Creatine phosphate


  Donates a phosphate group to ADP molecules to regenerate ATP during a short burst of activity.
• Appendicular skeleton


  The bones of the limbs/that support the limbs.
• Bones of the appendicular skeleton

  • Pectoral girdle (clavicle and scapula)
  • Forelimb (humerus, radius, ulna)
  • Hand (carpals, metacarpals, phalanges)
  • Pelvic girdle (hip bone)
  • Hindlimb (femur, patella, tibia, fibula)
  • Foot (tarsals, metatarsals, phalanges)
• Axial skeleton


  Bones of the head and torso.
• Bones of the axial skeleton

  • Skull (cranium and facial bones)
  • Middle ear ossicles
  • Hyoid bone
  • Rib cage (ribs, sternum)
  • Vertebral column
• Types of fractures


  • Closed/simple (bone doesn't break the skin)
  • Open/compound (bone breaks the skin)
  • Stress (hairline crack)
  • Transverse (horizontal fracture)
  • Oblique (angled)
  • Segmental (two locations, same bone)
  • Comminuted (three or more locations, same bone)
  • Compression (bone is crushed)
• Causes of fractures


  • Trauma
  • Osteoporosis/some types of cancer (weakens bones)
  • Repeated stress
• Vertebral structure


  A series of 33 vertebrae, separated by intervertebral discs. There are also ligaments spanning the length of spine and in-between the vertebrae. The function of the vertebral column is protection of the spinal cord, support of the weight of the body above the pelvis, posture, and movement.
• Parts of a vertebra

  • Vertebral body (towards the back of the body, supports the weight of the body, lined with hyaline cartilage)
  • Vertebral arch (towards the sides and front of the body, muscles and ligaments are attached)
  • Vertebral foramen (all vertebral foramen together forms vertebral canal for the spinal cord)
• Types of vertebrae


  • Cervical (smaller vertebral body, wider vertebral canal, transverse foramen for vertebral arteries and veins)
  • Thoracic (attached to the ribs, have more limited motility)
  • Lumbar (larger vertebral body, as it bears more weight)
• Scoliosis


  Sideways curvature of the spine, most causes largely unknown, can be caused by neuromuscular conditions, or by injury/infection of the spine. Treated by a brace, surgery, or medication.
• Functions of the skeleton

  • Support
  • Muscle attachment
  • Protection
  • Production of red blood cells
  • Storage of calcium
• Types of joints


  • Movable
  • Slightly moveable
  • Fused/fixed/immovable
• Types of movable joints

  • Hinge
  • Ball and socket
  • Pivot
  • Gliding
  • Saddle
  • Planar
• Osteoarthritis


  A joint disease resulting from the breakdown of joint cartilage. Causes stiff and painful joints. Caused by joint injury, secondary arthritis, age, and obesity. Treated by lifestyle changes (weight loss, regular exercise, suitable footwear), medication, physiotherapy, and surgery.