Overview
This lecture provides a comprehensive overview of upper limb anatomy, focusing on nerves, muscles, joints, and movement mechanics essential for midterm preparation.
Nerve Innervation of the Upper Limb
- Radial nerve innervates the wrist and elbow extensors.
- Median nerve innervates the wrist and elbow flexors, and first two lumbricals.
- Ulnar nerve supplies hypothenar muscles, medial two lumbricals, and interossei muscles.
- Median nerve sensation covers palmar thumb, index, middle, and half-ring finger.
Muscle Actions & Anatomy
- Lumbrical grip: MCP flexion, PIP and DIP extension.
- Lumbrical muscles originate from FDP tendons and insert into extensor expansion.
- Flexor digitorum superficialis flexes PIP joints only; profundus flexes both DIP and PIP.
- Flexor carpi ulnaris causes wrist flexion, ulnar deviation; innervated by ulnar nerve.
- Thenar muscles (thumb): flexor, abductor, opponens pollicis; Hypothenar (pinky): flexor, abductor, opponens digiti minimi.
Joints & Movements
- MCP joint: flexion, extension, abduction (dorsal interossei), adduction (palmar interossei).
- Wrist: radiocarpal and midcarpal joints allow flexion, extension, radial and ulnar deviation.
- Elbow: uniaxial hinge; radioulnar: biaxial pivot (radius pivots over ulna in pronation).
Biomechanics & Levers
- Longer lever arms increase muscular effort.
- Placing load farther from joint (wrist vs elbow) increases demand on muscle (e.g., deltoid).
- Muscle contraction types: isometric (no length change), concentric (shortens), eccentric (lengthens).
Key Upper Limb Muscles O/I/A/N
- Deltoid: O—clavicle/acromion/spine; I—deltoid tuberosity; A—abduction, flexion, extension, rotation; N—axillary.
- Brachialis: O—anterior humerus; I—ulnar tuberosity/coronoid; A—elbow flexion; N—musculocutaneous.
- Pronator teres: O—medial epicondyle/coronoid; I—mid-radius; A—pronation/elbow flexion; N—median.
- Pronator quadratus: O—distal ulna; I—distal radius; A—pronation, stabilizes joint; N—median.
Shoulder & Scapular Mechanics
- Rotator cuff (SITS): supraspinatus, infraspinatus, teres minor, subscapularis.
- Impingement syndrome affects supraspinatus.
- Upward rotation: upper/lower trapezius, serratus anterior.
- Downward rotation: levator scapulae, rhomboids, pectoralis minor.
- Scapulohumeral rhythm: 2:1 ratio GH to ST movement in shoulder elevation.
Spine & Ligaments
- Vertebral arch formed by pedicle and lamina.
- Nucleus pulposus moves posteriorly with spinal flexion, anteriorly with extension.
- Transverse ligament stabilizes atlantoaxial joint by keeping dens from spinal cord.
- Ligaments connect bone to bone; tendons connect muscle to bone; bursa reduce friction.
Additional Concepts
- Tenodesis: finger movement occurs due to passive tendon action, not muscle contraction.
- Arthrokinematics: joint surface motion; osteokinematics: bone movement around joint axis.
- Flexor retinaculum forms carpal tunnel roof.
Key Terms & Definitions
- Passive insufficiency — Muscle cannot stretch enough to allow full motion at all joints.
- Tenodesis — Passive finger flexion/extension with wrist movement due to tendon tension.
- Isometric contraction — Muscle generates force without changing length.
- Concentric contraction — Muscle shortens during contraction.
- Eccentric contraction — Muscle lengthens while contracting.
- Scapulohumeral rhythm — Ratio of shoulder to scapula movement in elevation.
Action Items / Next Steps
- Review labelled diagrams of nerve distributions and muscle attachments.
- Practice identifying actions, origins, insertions, and nerves for major upper limb muscles.
- Study movement types and lever mechanics with relevant upper extremity examples.