anatomy

Musculoskeletal System Overview

Introduction to Weight-Bearing Structures

  • Weight Bearing While Standing

    • When standing, body weight is primarily borne by the heels (calcaneus), also known as the heel bone.

  • Weight Bearing While Sitting

    • While seated, the weight of the torso, arms, and head is supported by the ischial tuberosity, often referred to as the "sits bone."
    • The ischial tuberosity is a part of the os coxa, which comprises the hip bones.

Forearm and Shin Anatomy

  • Parallel Bones in the Forearm and Shin
    • The forearm consists of the radius and ulna, while the shin consists of the tibia and fibula.
  • Interosseous Membrane
    • The interosseous membrane is a fibrous membrane that connects these pairs of bones in the forearm and shin through a structure that is aptly named.

Joints and Any Relevant Structures

  • Types of Joints

    • The interosseous membrane represents a fibrous joint as it consists of fibrous connective tissue.
    • Structural joint types: fibrous, cartilaginous, and synovial.

  • Pectoral Girdle

    • The pectoral girdle has a single attachment to the axial skeleton via the clavicle, which connects to the sternal end at the manubrium of the sternum.

  • Pelvic Girdle

    • The pelvic girdle attaches to the sacrum at the sacroiliac joint (SI joint), forming the connection between the axial skeleton and the pelvic structure.

Nerve Pathways in the Pelvis

  • Sciatic Nerve

    • The sciatic nerve exits the sacrum and travels down the posterior side of the leg, passing through the greater sciatic notch.

  • Obturator Nerve

    • The obturator nerve exits the pelvis via the obturator foramen, which consists of two large holes located in the front of the pelvis.

  • Femoral Nerve

    • The femoral nerve exits the pelvis from the anterior aspect, originating from the lumbar plexus.

Muscular Actions and Joint Movements

  • Pectoralis Major

    • Functions include shoulder flexion (raising the arm) and adduction (bringing the arm closer to the body).

  • Pectoralis Minor

    • Primarily pulls the scapula forward, does not act on the shoulder joint, and is not considered a synergist of pectoralis major.
    • Synergist muscles for arm adduction include the latissimus dorsi, coracobrachialis, and biceps brachii.

  • Rotator Cuff Muscles

    • Comprise four muscles:
    • Supraspinatus
    • Infraspinatus
    • Teres Minor
    • Subscapularis
    • Functions mainly in stabilizing the head of the humerus within the glenoid cavity.

Carpal Tunnel Structure

  • The flexor retinaculum is a connective tissue structure that forms the carpal tunnel, holding tendons and nerves in place.

Innervation of Forearm Muscles

  • Median Nerve: Runs down the anterior side of the forearm, innervating flexor muscles.
  • Ulnar Nerve: PasSses around the medial epicondyle, innervating muscle in that region.
  • Radial Nerve: Innervates extensor muscles positioned on the posterior side of the forearm.

Adduction Muscles

  • Innervated by the obturator nerve as that nerve travels through the obturator foramen and supplies the adductor muscles located in the medial thigh.

Joints Overview

  • Functional Classification of Joints

    • Discussed classifications involve understanding how much movement is allowed.
    • Example classifications:
    • Diarthrosis: Freely moving joints such as the shoulder and knee.
    • Non-moveable or slightly movable joints are classified differently based on structural and functional capabilities.

  • Knee Anatomy

    • Composed of femur, tibia, and fibula, surrounded by various connecting tissues.
    • Key components include:
    • Collateral Ligaments:
      • Lateral Collateral Ligament (LCL)
      • Medial Collateral Ligament (MCL)
    • Cruciate Ligaments:
      • Anterior Cruciate Ligament (ACL)
      • Posterior Cruciate Ligament (PCL)
      • Possible movements upon injury include:
      • Lateral displacement with MCL damage
      • Anterior displacement with ACL damage
      • Posterior displacement with PCL damage

  • Meniscus Damage:

    • Tearing of the menisci leads to increased grinding of the femur on the tibia, resulting in pain and instability.

Muscle Contraction Types and Mechanics

  • Isotonic Contractions: Flexibility in muscle contraction types.
    • Concentric: Muscle shortens while contracting (e.g., lifting a weight).
    • Eccentric: Muscle lengthens while under tension (e.g., lowering a weight).
    • Isometric: Muscle length remains constant while contracting (e.g., holding a steady position).
    • Study the agonist-antagonist muscle relationship, where if the quadriceps (agonist) are contracted, the hamstrings (antagonist) are lengthening.