Biological Foundations of Kinesiology

Biological Foundations of Kinesiology

Lecture 1: Basic Concepts of the Musculoskeletal System

Structure & Function of the Skeletal System

• Types/Components of Bone

• Mechanical Properties

• Cell Structure

• Function/Structure of Bone and Joints

Mechanical Functions of Bone

• Weight Bearing/Support

• Protection of Internal Organs

• Linkages & Sites for Muscle Attachment

Physiological Functions of Bone

• Storage of Essential Minerals

• Production of Blood Cells

• Immune Function

Composition of Bone

• Components:

  • 25% Water

  • Remaining weight (dry bone):

  • Organic compounds (mostly collagen) - 33%

  • Calcium - 39%

  • Potassium - 0.2%

  • Sodium - 0.7%

  • Magnesium - 0.5%

  • Carbonate - 9.8%

  • Phosphate - 17%

• Total Inorganic Components:

  • 67%

  • Contains 99% of the body's Calcium

  • 4% of the body's Potassium

  • 35% of the body's Sodium

  • 50% of the body's Magnesium

  • 80% of the body's Carbonate

  • 99% of the body's Phosphate

Bone Architecture

• Key Elements:

  • Hollow Shafts: Resists bending/twisting; material further from center enhances strength per unit weight

  • Expanded Ends: Provides large contact area; reduces pressure per unit area

  • Areas of Compact and Spongy Bone: Offers rigidity versus shock absorption

Mechanical Components of Bone

• Toughness & Flexibility: Provided by collagen/organic compounds

• Rigidity: Provided by calcium/mineral components

Bone Shape & Function

• Protection: Engaged by flat bones

• Cushioning Reaction Forces: Primarily enabled by short bones

• Leverage for Soft Tissues: Captured by long bones

• Dominant Function Classification:

  • Whether a bone's primary function is ascertained by its shape, it is usually irregular (e.g., vertebrae)

Bone Shapes & Functions

• Body: Functions like a short bone to support weight-bearing and cushion compressive forces

• Vertebral Arch: Resembles a flat bone (especially lamina) to protect the spinal cord

• Processes: Operates like a long bone to provide leverage for attached ligaments and muscles, resisting bending & twisting

Joint Structure & Function

• Joint Definition: A union of two or more bones

  • Types:

  • Fibrous Joints: Immoveable

  • Cartilagenous Joints: Semi-moveable

  • Synovial Joints: Freely moveable (focused on in KIN 202)

Features of Synovial Joints

• Synovial Fluid:

  • Functions include lubrication, protection, and nutrition

  • Viscosity may change; pressure movement causes fluid exit/entry from the cavity

• Ligaments:

  • Composed mostly of collagen, providing stability

  • Resists forces separating bones

  • Forms the inner layer of the joint capsule, producing fluid and removing debris from “wear & tear”

• Collagen Fibers in Liquid Matrix:

  • Composed of 80% water, forms a smooth bearing and cushions forces

  • Contributes to joint boundary stability with some restriction of motion

Musculotendinous Unit

• Components:

  • Bone

  • Tendon: Binds muscle to bone

  • Ligament: Binds bone to bone

  • Skeletal Muscle: May directly or indirectly attach to bones

Role of Musculoskeletal Joints

• Functional Unit of the Musculoskeletal System:

  • Skeletal muscles cross joints to initiate and control movements

  • Muscles act as secondary stabilizers for joints supporting ligaments

Types of Muscle

• Cardiac Muscle

• Skeletal Muscle

• Smooth Muscle

Organization of Skeletal Muscle

• Structures:

  • Tendons

  • Blood vessels

  • Endomysium: Surrounds individual muscle fibers

  • Muscle Fibers: Wrapped by endomysium

  • Fascicles: Wrapped by perimysium

  • Example: Biceps Brachii

  • Epimysium: Deep fascia surrounding muscle

Organization of a Muscle Fiber

• Components:

  • Sarcolemma: Muscle fiber membrane

  • Mitochondria: Energy production

  • Myofilaments: Contractile proteins

  • Z disc: Structural marking for sarcomeres

  • Myofibrils: Muscle fiber's functional units

  • A band: Dark band in muscle

  • I band: Light band in muscle

  • Sarcoplasmic Reticulum: Stores calcium

  • T Tubules: Transmit the action potential

  • Nuclei: Multiple per muscle fiber

  • Thick filament: Myosin

  • Thin filament: Actin, with associated proteins

  • Troponin complex

  • Tropomyosin

Organization of a Sarcomere

• Structure:

  • Head and Tail of myosin

  • Interactions between thick (myosin) and thin (actin) filaments

  • Z discs: Mark the boundaries of sarcomeres

The Cross-Bridge Cycle

• Process:

  • Cross-bridge forms when the myosin heads bind to actin

  • Components involved:

  • Calcium ions (released from sarcoplasmic reticulum)

  • Nerve signals (ACh and receptors)

  • ADP and Pi

• Steps:

  1. Signal from motor neuron reaches muscle fiber

  2. Calcium released from sarcoplasmic reticulum into the cytosol

  3. Calcium binds to troponin, shifting tropomyosin and exposing myosin binding sites

  4. Myosin head binds to actin

  5. Pi released from myosin head; power stroke occurs, shortening the sarcomere

  6. ADP is released; new ATP binds to myosin head

  7. ATP is hydrolyzed, allowing myosin head to return to its original position

Muscle Contraction & Motor Units

• Definition: The mechanical response of muscle (contraction) is preceded by chemical changes due to electrical stimuli

• Motor Unit: A single motor nerve and all muscle fibers it innervates, facilitating fine control (like in hands) versus power (like in quadriceps)

Characteristics of Motor Units

• Numerous motor units can innervate a single muscle

• On/Off Activation: Function based on asynchronous firing

• Electrical activity can be detected using an EMG

Assessing Motor Unit Activity - EMG

• Electromyograph (EMG): Instrument to assess muscle electrical activity

• Components:

  • Signals

  • Amplifier

  • A/D converter

Types of Muscle Contraction

• Concentric: Muscle shortens during contraction

• Isometric: No movement but muscle tension increases

• Eccentric: Muscle lengthens during contraction