Introduction to the MSK System

The skeleton

  • Axial skeleton: bones of the skull, neck and trunk
  • Appendicular skeleton: bones of the pectoral and pelvic girdles, bones of the lower limbs
notion image

Upper limbs

  • 1 long bone in arm - humerus
  • 2 long bones in forearm - radius and ulna
  • Hand: carpal bones → metacarpals → phalanges

Lower limbs

  • 1 long bone in thigh - femur
  • 2 long bones in leg - tibia and fibula
  • Foot: tarsal bones → metatarsals → phalanges

Features of bone

  • Bony feature: functional hole, bump or groove found on bone which develops during bone growth
    • Adjacent structure applies force to bone, moulding its shape OR
    • Adjacent structure develops at the same time as bone and the bone has to grow around the other structure - forms a foramen
  • Tuberosity: rough area of bone where muscles attach e.g. ischial tuberosity

Bone

  • Hard, connective tissue

Cartilage

  • Less rigid than bone
  • Located where mobility is required - articulations

Joints

  • Three types - synovial, cartilaginous and fibrous
  • Each is a compromise between mobility and stability - the more mobile a joint, the more easily it is dislocated
  • Joins have an excellent sensory nerve supply

Skeletal muscle

  • Usually found deep to deep fascia
  • Usually two points of attachment to bone - ‘origin’ (usually most proximal part) and ‘insertion’ on the other side
  • During contraction, the origin and insertion are moved closer together
    • Muscle fibres shorten along the long axis

Tendon

  • Attach muscle (usually) to bone

Aponeurosis

  • Flattened tendon
  • Most commonly associated with flat muscles
  • Attach muscle to soft tissue

Biceps brachii

  • Attachments:
    • Long head originates from the supraglenoid tubercle of the scapula
    • Short head originates from the coracoid process of the scapula
    • Both heads insert distally into the radial tuberosity and the fascia of the forearm via the bicipital aponeurosis
  • Innervation: musculocutaneous nerve
  • Actions: supination of the forearm (spans proximal radioulnar joint anteriorly) and flexion of the shoulder and elbow joint (spans shoulder and elbow joint anteriorly)

Deltoid muscle

  • Attachments: originates from the lateral third of the clavicle, the acromion and the spine of the scapula, attaches to the deltoid tuberosity on the lateral aspect of the humerus
  • Innervation: axillary nerve
  • Actions:
    • Anterior fibres: flexion and medial rotation of the shoulder
    • Posterior fibres: extension and lateral rotation of the shoulder
    • Middle fibres: the major abductor of the arm

Clinical examination of skeletal muscle - reflexes

  • Reflexes are protective and automatic
  • Testing reflexes tests the ability to move and power of movement - testing muscle and nerve(s) supplying it
  • 2 main skeletal muscle reflexes - stretch and flexion withdrawal

Stretch reflex - reflex arc

  1. Sensory nerve (muscle) detects stretch and tells spinal cord
  1. Motor nerve from spinal cord passes message to contract
  1. Neuromuscular junction - synapse where motor nerve communicates with skeletal muscle

Deep tendon relaxes

  • Biceps jerk, triceps jerk, knee jerk and ankle jerk reflexes
  • Hammer applies stretch → stretch reflex (if normal)

Flexion withdrawal reflex

  • Touch something potentially damaging
  • Sudden flexion to withdraw from the danger

Muscle damage

  • Muscle strain: overstretched, torn or twisted muscle
  • Paralysis: a muscle without a functioning motor nerve supply - can’t contract
    • Muscle would have reduced tone
  • Spasticity: muscle has intact and functioning motor nerve but the descending controls from the brain aren’t working
  • Atrophy: 'wasting’ of the muscles through inactivity, myocytes become smaller
  • Hypertrophy: individual myocytes enlarge