review and levers

Convex-Concave Concepts

• Definition of Convex Shape:
  • Curves outward and is rounded.
• Definition of Concave Shape:
  • Encloses or makes a cave-like structure.

Convex-Concave Rule

• Overview:
  • Addresses joint surfaces and the body part that is moving.
• Two Distinct Rules:
  1. When the concave surface is moving.
  2. When the convex surface is moving.

Movement Dynamics

• Concave Joint Surface Movement:
  • Moves on a fixed convex surface in the same direction as motion at the joint.
  • Example: When the concave surface slides up, the bony segment (forearm) moves upwards.
• Convex Joint Surface Movement:
  • When the convex surface is fixed, and the concave surface moves, it results in opposite directional movement of the segment.
  • Example: If the convex surface rolls up, it must also slide down to maintain congruency.

Exam Strategies

• Body Movement During Board Exams:
  • Minor movements allowed, such as adjustments at the table, but no standing or large movements.
  • It is acceptable to use aids or notes discreetly.

Kinematic Principles

• Dynamic Mechanics:
  • Focus on forces associated with moving systems, contrasted with static mechanics, which deals with non-moving systems.
• Kinetics and Kinematics:
  • Kinetics: Forces producing stability or movement.
  • Kinematics: Refers to motions created by forces in terms of body movement (osteokinematics) and joint surface movement (arthrokinematics).

Scalar and Vector Quantities

• Scalar Quantities:
  • Describe an amount (e.g., speed, length, area, volume).
• Vector Quantities:
  • Describe both magnitude and direction (e.g., movement speed in a specific direction).
• Mass Definition:
  • Amount of matter in an object.
  • Example: A cotton object has low mass compared to a sand object of the same size, which has greater mass.

Forces Acting on the Body

• Muscular Contraction Force and Gravity:
  • Gravity exerts a constant downward force on the body at approximately 9.81 m/s².
• Weight Definition:
  • Weight = Mass × Gravitational Force.
• Ground Reaction Force:
  • The upward force opposing gravity when we move or apply weight.
• Friction:
  • Resistance between two surfaces, affecting smoothness of movement.

Types of Forces

• Linear Forces:
  • Forces acting on the same line in the same direction.
• Parallel Forces:
  • Forces acting in opposite directions.
• Force Couples:
  • When multiple forces act in opposite directions to create rotation (e.g., muscles acting on the scapula).
  • Example: Upper trapezius elevating the scapula, lower trapezius pulling it downward, resulting in upward rotation.

Concurrent Forces

• Definition:
  • Forces acting on a joint in slightly different, non-parallel directions.
• Resultant Force Diagrams:
  • Understanding resultant forces (not requiring diagramming in this class).

Traction and Compression Forces

• Traction (Distraction):
  • Moving two surfaces apart to create space in a joint, beneficial for improving movement.
• Compression (Approximation):
  • Forcing two surfaces together, promoting stability in the joint.
• Shear Forces:
  • Parallel forces that cause surfaces to move in opposite directions.
• Bending Forces:
  • Resulting from forces acting through a long limb, causing compression on one side and distraction on the other.

Understanding Velocity and Acceleration

• Velocity:
  • Rate at which an object changes its position (speed).
• Acceleration:
  • Rate of change in velocity over time (e.g., increasing speed).

Torque Definition

• Torque:
  • Rotary motion generated by muscle at a joint, dependent on muscle proximity to the joint axis and contraction force.
• Moment Arm:
  • Distance from the muscle's line of pull to the joint axis influences the amount of torque produced.
  • Longer moment arms increase rotational capability but require greater force from the muscle.

Length-Tension Relationship in Muscles

• Length-Tension Curve:
  • Shows muscle force production capabilities based on muscle length.
  • Optimal tension occurs within a mid-range position due to ideal overlap of myosin and actin filaments.

Newton's Laws of Motion

• First Law (Inertia):
  • An object at rest stays at rest, and an object in motion stays in motion unless acted upon by an external force.
• Second Law (Acceleration):
  • The acceleration of an object is directly proportional to the force acting on it and inversely proportional to its mass.
• Third Law (Action-Reaction):
  • For every action, there is an equal and opposite reaction (e.g., ground reaction force).

Levers in the Human Body

• Types of Levers:

  1. First Class Levers: Axis in the middle, force and resistance acting in opposite directions (e.g., seesaw).
  2. Second Class Levers: Resistance in the middle, with axis at one end and force at the other (e.g., wheelbarrow).
  3. Third Class Levers: Force in the middle, resistance at one end, and axis at the other (e.g., shovel).

• Key Considerations:

  • Identify the components (axis, force, resistance) correctly, taking care to place them relative to the center of mass.

• Function of Sesamoid Bones:

  • Increase moment arm for greater rotational capability while requiring higher muscle force for movement.

Practical Exam Preparation

• Exam Structure Overview:

  • Review focus on application rather than definition; understanding forces and directions is essential.

• Hands-on Practice:

  • Expect to apply concepts in laboratory settings for hands-on understanding.

• Classroom Dynamics:

  • Expect student-led discussions and clarifying practices leading up to exams.

• Material Review:

  • Utilize available resources (bone boxes, skeletal models) to practice concepts live.

• Final Notes for Success:

  • Leverage access to materials and engage in labs for comprehensive understanding prior to exams.
  • During practical applications, visualize lines of pull, origins, and insertions for improved outcomes.