The musculoskeletal system (mod 2, mod 10 (wk6), mod 11 (wk2)

Annotations:

• Originates predominantly from the mesoderm with some components from the ectoderm (neural crest cells) that become nervous and blood tissue incorporated into the skeletal system The ectodermal components form the bones of the face 

1. Mesoderm
   1. Paraxial
      1. Somites

         Annotations:

         • 38 pairs form cranially and caudally bilaterally along the neural tube ad notochord 
         1. Sclerotomes
            1. Vertebral columns and ribs
         2. Dermomyotomes
            1. Muscle cells and dermatomes
   2. Lateral

      Annotations:

      • Forms the lining of the primitive body cavity and organs, peritoneal, pleural and pericardial cavities
      1. Somatic

         Annotations:

         • Forms into the Bone, skeletal muscle, connective tissue of limbs, pelvis and sternum Dermis of skin in body wall and limbs
      2. Splanchnic

         Annotations:

         • Forms into the Smooth muscle and cardiac
2. Ectoderm
3. Ossification / osteogenesis

   Annotations:

   • Occurs in-utero in the foetus and continues into childhood
   1. Intra-membranous ossification

      Annotations:

      • Produces flat bones of the skull and clavicle
   2. Endochondral ossification

      Annotations:

      • This process of bone development utilises a template of hyaline cartilage that gradually becomes replaced by osseous tissue  Occurs in week 6 of foetal life and continues into the 20s Mode of development of most bones of the body 
4. The skull in utero and in childhood

   Annotations:

   • In utero, the cranial part of the skull is not a whole bone, but divided into separate bones by fontanelles, which fuse later in life to become sutures This is to allow molding through the vaginal and pelvic cavity during child birth, as the flat bones slide over each other during birth
   • The fontanelles: The anterior  The posterior The sphenod The mastoid 

1. Anatomy of bone
   1. Diaphysis
   2. Epiphysis

      Annotations:

      • The site of attachment for tendons and ligaments 
   3. Articular cartilage

      Annotations:

      • Covers the ephiphyseal parts of the bone Site of joint formation Made of hyaline cartilage Produces synovial fluid to lubricate the joint surfaces during movement to prevent wear and tear 
   4. Periosteum

      Annotations:

      • Provides a strong attachment and continuation for muscles to tendon to bone Plays a vital role in bone growth and fracture healing 
   5. Epiphyseal plate

      Annotations:

      • Found in children and adolescents A plate of hyaline cartilage that separates the epiphysis from the diaphysis The zone of bone growth in length Seen as a translucent line on X-Ray
   6. Metaphysis

      Annotations:

      • The metaphysis is the area connecting the epiphyseal head to the diaphysis, with the epiphyseal plate (in under 20s) or line (over 20s) runnng through it This is the site of bone growth (transitional zone) where cartilage turns into bone 
2. Function of the skeleton
   1. Support
   2. Protection
   3. Storage and balance of electrolytes
   4. Acid-Base balance
   5. Haematopoeisis
   6. Locomotion
3. Types of bone
   1. Irregular

      Annotations:

      • Vertebral bodies Ethmoid, sphenoid bones of the skull, etc. 
   2. Flat bones

      Annotations:

      • Cranial bones the sternum Scapula Ribs Hip bones
   3. Long bones

      Annotations:

      • Arm: Humerus, Radius, Ulna Legs: Tibia, Fibula, Femur Hands and feet: metacarpals, metatarsals, phalanges of the hands and feet
   4. Short bone

      Annotations:

      • Carpals and tarsals of the wrists and ankles Patella of the knee
4. Structure of the skeleton

   Annotations:

   • The skeleton is 75% compact bone and 25% spongy bone 
   1. Axial skeleton
      1. Skull
         1. Facial bones
            1. The maxillae
               1. intraorbital foramen

                  Annotations:

                  • infraorbital erves and bessels 
               2. Incisive foramen

                  Annotations:

                  • Naso-palantine nerves
            2. The palantine bones
               1. Greater palantine foramen

                  Annotations:

                  • Palantine nerves
            3. The zygomatic bones
               1. Zygomaticofacial foramen

                  Annotations:

                  • Zygomaticofacial nerve 
               2. Zygomaticotemporal foramen

                  Annotations:

                  • Zygomaticotemporal nerve
            4. The lacrimal bones
               1. Lacrimal foramen

                  Annotations:

                  • Tear duct leading to the nasal cavity
            5. The nasal bones
            6. Inferior nasal conchae
            7. The vomer
            8. The mandible
               1. Mental foramen

                  Annotations:

                  • mental nerve and vessels
               2. Mandibula foramen

                  Annotations:

                  • inferoior alveolar nerves and vessels to lower teeth
            9. Maxilla sphenoid region
               1. Infraorbital fissure

                  Annotations:

                  • Infraorbital nerve Zygomatic nerve Infraorbital nerve 
         2. Cranial bones

            Annotations:

            • Made up of 2 pairs of cranial fossa, divided into 3
            1. Cranial floor

               Annotations:

               • The anterior cranial fossa: frontal lobe Medial cranial fossa: temporal lobe Posterior cranial fossa: cerebellum
            2. Frontal bone
               1. Supraorbital foramen
            3. parietal bones

               Annotations:

               •  Made up of the sagittal surture, corononal suture, lambdoid suture ad squamous suture 
            4. Sphenoid bones
               1. foramen ovale

                  Annotations:

                  • Mandibular branch of the trigeminal nerve (CN V) Accessory meningeal artery
               2. Foramen rotundum

                  Annotations:

                  • Maxillary division of CN V (trigeminal nerve)
               3. Foramen spinosum

                  Annotations:

                  • Middle meningeal artery  Spinosal nerve Some branch of the trigeminal nerve 
               4. optic canal

                  Annotations:

                  • Optic nerve Ophthalmic artery 
               5. Superior orbital fissure

                  Annotations:

                  • Oculomotor nerve (CN III) trochlear (CN IV) abducens nerve (CN VI) Ophthalmic division of trigeminal nerve (CN V)
            5. Occipital bone
               1. Foramen magnum

                  Annotations:

                  • Spinal cord Accessory nerve (CN XI) Vertebral arteries 
               2. Hypoglossal canal
               3. Condylar canal

                  Annotations:

                  • Vein from transverse sinus
            6. Temporal bones
               1. Styloid process

                  Annotations:

                  • Attachment point for muscles of the tongue, pharynx and hyoid bone 
               2. Carotid canal

                  Annotations:

                  • internal carotid artery
               3. External acoustic meatus
               4. Internal acoustic meatus

                  Annotations:

                  • vestibulocochlear nerve (CN VIII)
               5. Stylomastoid foramena

                  Annotations:

                  • Facial nerve (CN VII) 
               6. Mastoid foramen

                  Annotations:

                  • Meningeal artery, sigmoid sinus vein branch
            7. Ethmoid bone
               1. Cribriform foramen

                  Annotations:

                  • Olfactory nerve (CN I)
         3. Cavities of the brain
            1. Nasal cavity

               Annotations:

               • The bones are designed to create air turbulence to allow contact with the membrane to warm, moisturise and humidify the air before reaching the lungs
               • Also involved carrying the sensory cells of smell 
            2. Oral cavity
            3. Auditory cavities
            4. Para-nasal sinuses

               Annotations:

               • Connected by the nasal cavity, and are filled with air making the skull light-weight, help in producing vocal sounds 
               1. Ethmoid sinus
               2. Maxillary sinus
               3. Sphenoid sinus
               4. Frontal sinus
            5. Orbital cavity
         4. Auditory ossicles

            Annotations:

            • Malleus Incus Stapes
         5. Hyoid bone
      2. The spinal column

         Annotations:

         • The vertebral column: Protects the spinal cord Absorbs the stresses from locomotion and external forces Attachment for the ribs, skull, pelvic and shoulder girdle 33 vertebral bones
         • Basic structure The spinal cord runs through the vertebral foramen The space between 2 pedicles of 2 vertebrae: intervertebral foramen--> the passage of pinal nerves 
         1. Vertebrae
            1. Cervical

               Annotations:

               • C1 - C7  C1: the atlas --> flexion and extension  C2: the axis --> rotation
            2. Thoracic

               Annotations:

               • T1-T12 The site of attachment of the 12 pairs of ribs to enclose the lungs, heart, and hepatobiliary and gastroenterological structures
            3. Lumbar

               Annotations:

               • L1-5
            4. Sacral

               Annotations:

               • Forms the posterior wall of the pelvic gurdle Begin as 5 separate bones  They contain foramena, passages for nerves and blood vessels to the pelvis  Forms the sacroiliac joint
            5. Coccygeal

               Annotations:

               • The coccyx is the attachment point for muscles of the pelvic floor  Consists of 4 fused bones
         2. Intervertebral discs

            Annotations:

            • Between each vertebrae is cushioning tissue: intervertebral discs  They bind adjacent vertebrae together Support the weight of the body bsorb shock
            1. Herniated disc
      3. The thoracic cage

         Annotations:

         • Formed by the thoracic verebrae, sternum and ribs  The enclosure of the heart and the lungs, the abdominal organs (spleen, liver, pancreas, kidneys) Also involved in breathing by helping to create the intra-thoracic pressures needed for exhalation ad inhalationThe attachment point for the pectoral girdle and upper limb
         1. The ribs

            Annotations:

            • Attach to the sternum anteriorly distally and the thoracic vertebrae posteriorly proximally,  Anteriorly, they have the costal cartilage 
         2. The sternum

            Annotations:

            • The body of the sternum extends from T5 to T9 The xiphoid process is the point of attachment of some of the abdominal muscles The landmark for CPR (2 fingers away from it)
   2. Appendicular skeleton
      1. Shoulder gurdle

         Annotations:

         • Also known as the pectoral gurdle acts as the attachmet of the upper limbs to the axial skeleton
         • It is formed by the  Sternoclavicular joint Acromioclavicular joint  Glenohumeral joint
         1. The clavicles
         2. The scapula
            1. The coracoid process

               Annotations:

               • The attachment of the tendons of the biceps brachii 
            2. The glenoid cavity
      2. Pelvic gurdle
      3. Upper Limbs
         1. The brachium
         2. Antebrachium
         3. The carpus
      4. Lower limb
5. Histology of bone
   1. Bone cells
      1. Osteoblasts

         Annotations:

         • Bone-forming cells: lay down the mineral deposits of bone to reinforce and rebuild bone Formed from osteogenic cells  Stress and fractures stimulate increased osteogenic cells mitosis and differentiation into osteoblasts  Also secrete osteocalcin that stimulates insulin secretion, and increases insulin sensitivity of adipocytes and limits their growth 
      2. Osteoclasts

         Annotations:

         • Bone-dissolving cells Different cell lineage from the other bone cells  Large cells, formed from multiple stem cells (3-50!) Bone resorption 
      3. Osteocytes

         Annotations:

         • Old osteoblasts  Resorb bone matrix, deposit bone matrix Play a role in bone density and blood concentrations of calcium and phosphate  Strain sensors --> stress induces bone remodelling of shape and density
      4. Osteogenic cells

         Annotations:

         • Stem cells from embryonic mesenchymal cells  Continuously undergo mitosis, some differentiate into osteoblasts 
   2. Histological structure
      1. Compact bone

         Annotations:

         • Layers of matrix: lamellae Arranged around central canals: Haversian canal Connected by canaliculi to make Haversian systems 
      2. Spongy bone
      3. Bone marrow
         1. Red marrow

            Annotations:

            • In children, all their bone contains red marrow  Red marrow is haemapoietic, containing myeloid tissue In adults, the red marrow is only found in the axial skeleton, part of the pelvic gurdle and the proximal heads of the humerus and femur 
         2. Yellow marrow

            Annotations:

            • Replaces most of the red marrow in adults Consists of adipose tissue  In severe chronic anaemia, it can revert back to red marrow!
   3. Bone matrix

      Annotations:

      • 85% hydroxyapatite (crystallized calcium  phosphate salt)  10% CaCO3 Mg, Na, K+,Fl, SO4(2-), HCO3-, OH- ions
6. Bone physiology
   1. Bone growth and remodelling
      1. Fractures and repair
      2. Bone elongation

         Annotations:

         • Occurs at the epiphyseal plate, the growth zone of bones, resulting in increase in height  The epiphyseal plate contains hyaline cartilage in the middle with transitional zones at each end Starts from the cartilage cells (zone 1), which are derived from the reserve zone Zone 5  is nearer to the bone marrow and the epiphyseal head. Growth starts in zone 1, 2 and 3 leading to interstitial growthFailure of growth from the cartilage results in dwarfism 
      3. Bone widening and thickening

         Annotations:

         • Occurs in appositional growth, growth of new tissue on the surface 
         1. paget's disease of the bone
      4. Bone remodelling

         Annotations:

         • Continues throughout life  Occurs by absorption of old bone and deposition of new bone Annually, we replace 10% of our bone to repair micro-fractures, release minerals into the blood and reshape bones in response to use and disuse. Increased stress in a bone over time increases its density Occurs via interaction of the osteoclasts and osteoblasts  Disuse: increased osteoclasts activity to decrease mass  Increased use: thickened bone 
         1. Osteoporosis
      5. Puberty

         Annotations:

         • Oestrogen, testosterone and GH are secreted at the start of puberty and are what initiate bone ossification of the epiphysial plates Thus it is the last thing that occurs in children (GnRH secretion by the hypothalamus) to allow the child to attain their potential height
         • The sex steroids have an influence on osteogenic cells, chondrocytes and osteoblasts
         1. Oestrogen

            Annotations:

            • Has a more significant effect on bone mineralization on girls than testosterone 
         2. Testosterone
         3. Precocious puberty

            Annotations:

            • Leads to rapid growth, but causes early fusion of the epiphyseal plates leading to stunted growth
         4. Delayed puberty

            Annotations:

            • Leads to prolonged bone growth, slow attainment of their adult height, and bone age less than their chronological age 
   2. Mineral deposition and resorption
      1. Mineral deposition

         Annotations:

         • Performed by osteoblasts by absorbing PO4(3-), Ca2+, etc. from the blood and layering them into the bone Involved in ossification  Can occur abnormally in organs and tissue such as the brain, kidneys, ureters, bladder, joints, arteries (arteriosclerosis), tendons, etc.
      2. Mineral resorption

         Annotations:

         • Performed by osteoclasts releasing minerals into the blood They have receptors to detect calcium levels in the blood and dissolve bone in response to low levels (using HCl- and acid phosphatase)
   3. Calcium homeostasis

      Annotations:

      • Calcium plays a role in action potential in neurones, activation of enzymes and intracellular metabolic processes, blood clotting, muscle contraction and exocytosis 
      • The skeleton acts a storage for calcium (~1kg) 1% flows in blood, 99% in bones 18% is exchanged with the blood per year Blood serum levels: 9.2-10.4mg/dl (2.25-2.6 mmol/L) 45% is ionised and can pass through membranes, the rest is bound to albumin and other plasma proteins
      1. Hypocalcaemia
         1. Signs

            Annotations:

            • Tetany (prolonged held contraction) Muscle tremors and spasms Trousseau's sign: strong spasmodic flexion of the wrist and thumb and extension of the fingers on compression of the brachial nerve by a blood pressure cuff Rarely, laryngospasm 
         2. Causes

            Annotations:

            • Vitamin D deficiency Diarrhoea, Thyroid tumours (suppress parathyroid glands) Hypoparathyroidism Pregnancy and lactation due to increased demand of calcium from the foetus Iatrogenic: accidental parathyroidectomy secondary to a thyroidectomy in hyperthyroidism or in a head & neck surgery (vascular damage)
            1. Osteomalacia
            2. Rickets
      2. Hypercalcaemia
         1. SIgns

            Annotations:

            • Depression of the nervous system Emotional disturbances Muscle weakness Sluggish reflexes Cardiac arrest 
      3. Skin

         Annotations:

         • The skin utilises UV B light to turn cholesterol into cholecalciferol (VD3)
         1. Liver

            Annotations:

            • The liver turns the VD3 into calcidiol
            1. Kidneys

               Annotations:

               • The kidneys turn VD2 into VD1 (calcitriol)
               1. Bowel

                  Annotations:

                  • The bowel uses vitamin D1 to absorb calcium into the blood system 
                  1. Bone

                     Annotations:

                     • The bone absorbs calcium in high levels with stimulation  In low levels, the PTH stimulates osteoclasts to resorb calcium and release it into the blood In high levels, calcitonin is released by the thyroid glands to inhibit osteoclast actitivity and increase osteoblast actitvity 
               2. Parathyroid gland
                  1. Thyroid
                     1. Calcitonin

                        Annotations:

                        • Secreted by c cells of the thyroid gland when serum calcium is too high
                        • Acts by inhibiting osteoclast activity and stimulating osteoblast activity  Essential in pregnant and lactating women 
                  2. Parathyroid hormone

                     Annotations:

                     • PTH is secreted in low calcium levels It acts on the bones, kidneys and gut
                     • Bones: binds to osteoblasts to stimulate RANKL secretion to bind to RANKR on osteoclasts to activate their differentiation and activity --> bone resorption Also inhibits bone deposition by osteoblasts 
                     • Increases calcium resorption by the kidneys from urine and increases phosphate excretion in the urine 
                     • Promotes vitamin D activation by the kidneys to increase calcium absorption by the gut
               3. Calcitriol

                  Annotations:

                  • Calcitriol on the gut: increases absorption of calcium and phosphate 
                  • On the bones: increases resorption by triggering osteoblasts to secrete RANKL which bind to RANK receptors on the osteoclasts to activate them to resorb bone and release calcium and phosphate into the blood 
                  • Kidneys: acts to increase reabsorption of Ca2+ from the urine
            2. Calcidiol
         2. Cholecalfiferol
   4. Phosphate homeostasis

      Annotations:

      • Phosphate is vital for enzyme activation, cell receptors, DNA, RNA, ATP and many other proteins in the body Phosphate ions are used to buffer in acidic conditions

1. Structure of muscles
   1. Macroscopic
      1. Fascia

         Annotations:

         • Compartmentalises muscles 
         1. Epimysium
            1. Perimysium

               Annotations:

               • Bundles muscle fibres together to form fascicles: the parallel strands of muscles  Carries the larger nerves and blood vessels and stretch receptors (muscle spindles)
               1. Endomysium

                  Annotations:

                  • Surrounds each muscle fibre, and creates room for capillaries and nerve fibres to each fibre, space for extra-cellular chemical environment and nerve endings 
   2. Microscopic
2. Anatomy of the muscular system
   1. Pelvic muscles
   2. Abdominal muscles
   3. Abdominal muscles
   4. Upper limb muscles
   5. Lower limb muscles
   6. Head and neck muscles
   7. Thoracic muscles
3. Physiology of muscles
4. Functions of muscles
   1. Movement

      Annotations:

      • Locomotion Movement of body contents: air, fluid, blood, foetus, food, faeces, urine Communication
   2. Stability
   3. Control of body openings and passages between the body and environment
   4. Heat production
   5. Glycaemic control