Biological Foundations of Kinesiology

KIN 202: 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: Bone provides structure and support to the body.

  • Protection of Internal Organs: Bone encases and safeguards vital organs.

  • Linkages & Sites for Muscle Attachment: Bones form joints and provide surfaces for muscles to attach, enabling movement.
     

Physiological Functions of Bone

  • Storage of Minerals: Bones store essential minerals such as calcium and phosphorus.

  • Production of Blood Cells: Bones contain marrow, where blood cells are produced.

  • Immune Function: Bone also plays a role in the immune response, particularly in its marrow.
     

Composition of Bone

  • Water: 25% of bone

  • Remaining dry bone components:

    • 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%

  • Significance of mineral content:

    • 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: Resist bending and twisting; material positioned away from the center is stronger per unit weight.

    • Expanded Ends: Provide a large surface area which results in less pressure per unit area.

    • Areas of Compact Bone & Spongy Bone: Balance rigidity and shock absorption.
       

Mechanical Components of Bone

  • Toughness & Flexibility: Provided by collagen and other organic compounds.

  • Rigidity: Resulting from the presence of calcium and other minerals.

  • Hypothetical scenarios:

    • (a) If calcium/mineral is removed, bones would become brittle and unable to support weight.

    • (b) If collagen/organic materials are removed, bones would become too rigid and susceptible to breaking.
       

Bone Shape & Function

  • Protection: Flat bones protect vital organs (e.g., skull protecting the brain).

  • Cushion Reaction Forces: Short bones (e.g., carpals) absorb shock and reduce impact forces.

  • Leverage for Soft Tissues: Long bones (e.g., femur) provide leverage for muscular movements, enhancing motion.

  • Dominant function determined by shape: An irregular shape often reflects a balance of functions (e.g., vertebrae).
     

Joint Structure & Function

  • Definition of Joint: A union of two or more bones.

    • Types of Joints:

    • Fibrous (Immovable)

    • Cartilaginous (Semi-movable)

    • Synovial (Freely movable) - Focus of KIN 202
       

Features of Synovial Joints

  • Synovial Fluid: Provides lubrication, nutrition, and protection. Viscosity can change during movement.

  • Ligaments:

    • Mostly made of collagen; provide stability.

    • Resists forces that separate bones.

    • Forms the inner layer of the joint capsule, produced fluid, and removes cell debris from wear and tear.

  • Collagen Fibers:

    • In liquid matrix consisting of 80% water, they form a smooth bearing, cushion forces, and contribute to joint boundary.

  • Dense Connective Tissue: Made of collagen, providing joint stability with some restriction on motion.
     

Musculotendinous Unit

  • Components:

    • Bone:

    • Tendon: Binds muscle to bone.

    • Ligament: Binds bone to bone.

    • Skeletal Muscle:

    • Muscle may attach directly or indirectly to bone.
       

Role of Musculoskeletal Joints

  • Functional Unit of the Musculoskeletal System: Joints are instrumental for the function of the skeletal system.

  • Skeletal Muscles: Cross joints, facilitating movement while also serving as secondary stabilizers for joints through contractions and reflexes.
     

Types of Muscle

  • Cardiac Muscle: Found in the heart, involuntary control.

  • Skeletal Muscle: Voluntary muscle used for movement; intriguing when referring to joints.

  • Smooth Muscle: Involuntary muscle found in internal organs.
     

Organization of Skeletal Muscle

  • Components of Skeletal Muscle:

    • Tendons connecting muscles to bones.

    • Blood vessels providing nutrients.

    • Endomysium: Connective tissue surrounding individual muscle fibers.

    • Fascicle: Bundles of muscle fibers surrounded by perimysium.

    • Epimysium: Surrounds entire muscle, also known as deep fascia.

    • Example: Biceps brachii with attachments to ulna and radius bones.
       

Organization of a Muscle Fiber

  • Key Components:

    • Sarcolemma: Cell membrane of muscle fiber.

    • Myofibrils: Individual contractile units containing myofilaments.

    • Z Disc: Boundary lines of sarcomeres.

    • Sarcoplasmic Reticulum (SR): Storage site for calcium ions.

    • Thick/Thin Filaments:

    • Thick Filament: Composed of myosin.

    • Thin Filament: Composed of actin, troponin, and tropomyosin.
       

Organization of a Sarcomere

  • Key Features:

    • Z Disc: Defines the boundaries of each sarcomere.

    • Thick and Thin Filament Structures: Crucial in muscle contraction mechanics.
       

The Cross-Bridge Cycle

  • Components Involved:

    • Nerve signal triggers the release of calcium ions from the SR.

    • ACh (Acetylcholine): Neurotransmitter binding to receptors initiates the contraction process.

    • Troponin and Tropomyosin: Regulatory proteins on thin filaments that control access to myosin binding sites on actin.

  • Mechanism of Muscle Contraction:

    • Calcium binds to troponin, which shifts tropomyosin to expose binding sites; myosin heads then attach to actin, forming cross-bridges.

    • Power stroke occurs as ADP and Pi are released from myosin, resulting in sarcomere shortening.

    • New ATP molecule binds to myosin, allowing detachment from actin and preparation for next contraction cycle.
       

Muscle Contraction & Motor Units

  • Chemical Changes Preceding Contraction: Initiated by electrical stimuli from motor units.

  • Motor Unit Defined: A single motor nerve and all muscle fibers it innervates, affecting control precision.

    • Fine Control: Hand muscles (less fibers per motor unit).

    • Powerful Control: Larger muscles (more fibers per motor unit).
       

Characteristics of Motor Units

  • Number of Motor Units: Multiple units can innervate a single muscle, promoting coordination.

  • Activity Level: Motor units can fire asynchronously, allowing smooth muscle contractions.

  • EMG Activation: Electrical activity tracked through electromyography (EMG) for assessing muscle activation levels.
     

Types of Muscle Contraction

  • Concentric: Muscle shortens as it contracts (e.g., lifting a weight).

  • Isometric: Muscle length remains constant as tension develops (e.g., pushing against an immovable object).

  • Eccentric: Muscle lengthens while contracting (e.g., lowering a weight).

Lecture 1: Basic Concepts of the Musculoskeletal System
Structure & Function of the Skeletal System

  • Types/Components of Bone: There are two primary types of bone: cortical (compact) bone, which is dense and forms the outer layer of bone, and trabecular (spongy) bone, which is less dense and found inside bones, providing structural support and flexibility. Key components of bone include osteocytes (mature bone cells), osteoblasts (bone-forming cells), and osteoclasts (bone-resorbing cells).

  • Mechanical Properties: Bones are strong and capable of withstanding weight and tension, largely due to their mineral composition, which includes calcium phosphate. The mechanical properties of bone can be affected by factors such as age, diet, and physical activity.

  • Cell Structure: Bone cells are embedded in a matrix that is rich in minerals, giving bones their rigid characteristics. The microstructure of bone includes lamellae, which are thin layers of bone, and Haversian canals, which contain blood vessels and nerves.

  • Function/Structure of Bone and Joints: Bones play an essential role in the overall framework of the body. Joints, where two or more bones meet, serve as pivotal points for movement and are crucial for maintaining posture and stability.

Mechanical Functions of Bone

  • Weight Bearing/Support: The skeletal system must support the body’s weight in various positions while maintaining balance and postural alignment. Bone density and strength are critical for effective weight support.

  • Protection of Internal Organs: The skeleton provides a protective encasement for vital organs like the heart, lungs, and brain. Features such as the rib cage and the skull are specifically adapted to safeguard these organs.

  • Linkages & Sites for Muscle Attachment: Bones serve as levers for muscles to act upon, and their various shapes contribute to the types of movements achievable. The arrangement of bones and joints allows for a wide range of motion throughout the body.

Physiological Functions of Bone

  • Storage of Minerals: Beyond calcium and phosphorus, bones store other vital minerals, including magnesium and fluoride, which play roles in bone density and health.

  • Production of Blood Cells: The process of hematopoiesis occurs in the bone marrow, where red blood cells, white blood cells, and platelets are generated. This function is especially important for maintaining oxygen transport and immune response.

  • Immune Function: Bone marrow is a key component of the immune system, housing various immune cells that commence the body’s defense mechanisms against pathogens.

Composition of Bone

  • Water: Comprises approximately 25% of bone tissue, essential for metabolic processes within the bone.

  • Remaining dry bone components: Organic compounds (including collagen), account for about 33% of bone structure, providing flexibility and tensile strength. Mineral content comprises:

    • Calcium - 39%

    • Potassium - 0.2%

    • Sodium - 0.7%

    • Magnesium - 0.5%

    • Carbonate - 9.8%

    • Phosphate - 17%

    • Total inorganic components: Total mineral content of about 67%.

  • Significance of mineral content: Bones are a significant reservoir for several minerals, influencing various physiological functions beyond structural support, such as muscle function and nerve signaling.

Bone Architecture

  • Key Elements: The hollow shafts of long bones reduce weight while maintaining strength, and the expanded ends of bone help disperse pressure and enhance leverage during movement. The architecture balances strength and flexibility, critical for preventing fractures during high-impact activities.

Mechanical Components of Bone

  • Toughness & Flexibility: The organic matrix, primarily made of collagen fibers, lends bones the ability to absorb shock and resist stress.

  • Rigidity: Minerals, particularly calcium, impart rigidity to bone, allowing it to withstand compressive forces.

  • Hypothetical scenarios: If calcium content were decreased, bone integrity would be compromised, leading to conditions such as osteoporosis. Conversely, removing collagen would make bones prong-like and brittle, prone to fractures under stress.

Bone Shape & Function

  • Protection: Various bone shapes, such as flat bones like the ribs and skull, serve specific protective roles while contributing to overall body architecture.

  • Cushion Reaction Forces: Short bones like those in the wrist serve to disperse forces and absorb shock, whereas long bones help with leverage during movement.

  • Dominant function determined by shape: Each bone type is specialized based on its function, such as the vertebrae, which support the spinal cord while allowing for flexibility and movement.

Joint Structure & Function

  • Definition of Joint: Joints represent the point of intersection of two or more bones, enabling diverse ranges of movement.

  • Types of Joints:

    • Fibrous (Immovable) – bones connected by dense connective tissue, allowing for no movement (e.g., sutures in the skull).

    • Cartilaginous (Semi-movable) – joints that allow limited movement, connected by cartilage (e.g., intervertebral discs).

    • Synovial (Freely movable) – characterized by a fluid-filled joint cavity offering a wide range of motion; the focus of KIN 202 studies.

Features of Synovial Joints

  • Synovial Fluid: This viscous fluid not only lubricates joints to reduce friction but also delivers nutrients to cartilage and acts as a shock absorber during activities.

  • Ligaments: Provide both stability and support, maintaining joint integrity under stress and resisting dislocation.

  • Collagen Fibers: These fibers, embedded in a gel-like matrix, minimize wear and tear by cushioning and distributing mechanical loads across the joint.

  • Dense Connective Tissue: Composed of collagen, this tissue helps maintain joint stability while allowing some movement, facilitating agility without compromising structural integrity.

Musculotendinous Unit

  • Components: The functional unit comprised of bone, tendon (which attaches muscle to bone), ligament (attaching bone to bone), and skeletal muscle plays an essential role in movement and stability. Muscle attachments may be direct or indirect through a tendon.

Role of Musculoskeletal Joints

  • Functional Unit of the Musculoskeletal System: Joints are vital to the movement, enabling the skeletal system to perform various functions effectively.

  • Skeletal Muscles: They cross joints and facilitate movement but also act as dynamic stabilizers, using contraction and reflexive actions to support joint stability and function.

Types of Muscle

  • Cardiac Muscle: Found exclusively in the heart, this involuntary muscle type is responsible for pumping blood throughout the body and is characterized by intercalated discs that allow synchronized contractions.

  • Skeletal Muscle: This voluntary muscle group enables movement and is intricately related to joint function; contractions can be controlled consciously and allow for precise movements.

  • Smooth Muscle: Involuntary muscle found in the walls of internal organs, facilitating processes like digestion and blood vessel regulation without conscious control.

Organization of Skeletal Muscle

  • Components of Skeletal Muscle: Include tendons that anchor muscles to bones, blood vessels, and connective tissues that provide support and structure, such as:

    • Endomysium: Envelops individual muscle fibers, providing an internal environment conducive to electrical impulses and nutrients.

    • Fascicle: Groups of muscle fibers, encapsulated by perimysium that facilitates coordination within the muscle.

    • Epimysium: The outermost layer that encases the entire muscle.

    • Example: The biceps brachii, which attaches to the ulna and radius, allows for the flexion of the elbow joint.

Organization of a Muscle Fiber

  • Key Components:

    • Sarcolemma: The cell membrane that contains receptors for neurotransmitters.

    • Myofibrils: Dense structures containing the contractile elements of muscle, consisting of myofilaments for contraction.

    • Z Disc: Defines the boundaries of each sarcomere, crucial for muscle contraction.

    • Sarcoplasmic Reticulum (SR): Key organizer of calcium ions, which are essential for muscle contraction initiation.

    • Thick and Thin Filaments:

      • Thick Filament: Composed primarily of myosin, essential for interaction with actin.

      • Thin Filament: Comprised of actin, tropomyosin, and troponin, facilitating contraction response.

Organization of a Sarcomere

  • Key Features: Each sarcomere showcases a precise arrangement of thick and thin filaments, enabling myofilaments to interact during muscle contractions, key in the overall efficiency of muscle function.

The Cross-Bridge Cycle

  • Components Involved: Nerve signals trigger calcium ion release, initiating the contraction sequence. Acetylcholine (ACh) binding to receptors catalyzes muscle contraction processes, with troponin and tropomyosin facilitating muscle fiber engagement.

  • Mechanism of Muscle Contraction: The calcium-troponin complex shifts tropomyosin to reveal myosin-binding sites on actin, allowing for the attachment of myosin heads leading to sarcomere shortening; ATP is vital for muscle fiber detachment and re-cycling, ensuring readiness for subsequent contraction cycles.

Muscle Contraction & Motor Units

  • Chemical Changes Preceding Contraction: Involves a cascade of electrical impulses from motor neurons stimulating muscle fibers for contraction.

  • Motor Unit Defined: A collective unit, comprising a singular motor neuron and the muscle fibers it innervates, defining the precision and control achievable within voluntary movements.

  • Fine Control vs. Powerful Control: Fine movements (e.g., in hand muscles) require fewer fibers per motor unit, while larger muscle groups tend to have more motor unit fibers for greater force generation.

Characteristics of Motor Units

  • Number of Motor Units: Coordination of movements is enhanced by multiple motor units innervating a single muscle, allowing dynamic adjustments during activities.

  • Activity Level: Often firing asynchronously, motor units contribute to smooth movements of muscle fibers, maintaining muscle tone and efficiency during various levels of activity.

  • EMG Activation: Through electromyography (EMG), electrical activity is monitored, providing insights into muscle activation patterns and assisting with diagnostic assessments and performance evaluations.

Types of Muscle Contraction

  • Concentric: This contraction type denotes muscle shortening while generating force, as seen in weight-lifting exercises.

  • Isometric: During isometric contractions, the muscle maintains its length while developing tension, crucial for stabilizing positions (e.g., holding a weight without moving).

  • Eccentric: Muscle lengthening while under tension, such as during the controlled lowering of weights, plays vital roles in muscle development and joint resilience, crucial during deceleration movements and rehabilitation practices.