3426 Mod 01 Exercising Muscle

TEXAS A&M UNIVERSITY SAN ANTONIO

Structure and Function of Exercising Muscle

EDKN 3426 Module 1

Lecture Outline

  • 1. Introduction

    • 1.1 Anatomy of Skeletal Muscle

      • 1.1.1 Muscle Fibers

      • 1.1.2 Myofibrils

    • 1.2 Muscle Fiber Contraction

      • 1.2.1 Excitation-Contraction Coupling

      • 1.2.2 Role of Ca2+ in the Muscle Fiber

      • 1.2.3 Sliding Filament Theory: How Muscles Create Movement

      • 1.2.4 Energy for Muscle Contraction

      • 1.2.5 Muscle Relaxation

  • 1.3 Muscle Fiber Types

    • 1.3.1 Characteristics of Type I and Type II Fibers

    • 1.3.2 Distribution of Fiber Types

    • 1.3.3 Fiber Types and Exercise

    • 1.3.4 Determination of Fiber Type

  • 1.4 Skeletal Muscle and Exercise

    • 1.4.1 Muscle Fiber Recruitment

    • 1.4.2 Fiber Type and Athletic Success

    • 1.4.3 Muscle Contraction

Introduction

  • Similarities Between Exercise and Disease

    • Both exercise and disease act as stressors to bodily systems, leading to distinct physiological changes.

  • Definition of Physiology

    • Study of the function of organisms.

  • Definition of Homeostasis

    • Maintenance of a constant internal environment.

Acute vs Chronic Exercise

  • Acute Exercise

    • Refers to a single bout of exercise; immediate responses are observed.

  • Chronic Adaptation

    • Physiological changes post repeated exercise over weeks/months, improving bodily efficiency during rest and exercise.

Types of Muscle Tissue

  • Three Types of Muscle Tissue:

    1. Skeletal Muscle

    2. Cardiac Muscle

    3. Smooth Muscle

1.1 Anatomy of Skeletal Muscle

  • Muscle Structure

    • Entire muscle surrounded by epimysium; consists of bundles (fasciculi) surrounded by perimysium.

    • Individual muscle cells (muscle fibers) surrounded by endomysium, which contains myofibrils organized into sarcomeres.

1.1.1 Muscle Fibers

  • Fiber Structure

    • Plasmalemma (cell membrane) conducts action potentials, maintains pH, and transports nutrients, fuses with tendon.

    • Satellite Cells involved in muscle growth, development, and response to injury/training.

  • Sarcoplasm

    • Cytoplasm of muscle cell, specialized for glycogen storage and contains myoglobin.

  • T-tubules

    • Extensions of plasmalemma carrying action potentials into muscle fibers.

  • Sarcoplasmic Reticulum (SR)

    • Main site for calcium ion storage, essential for contraction.

1.1.2 Myofibrils

  • Structure

    • Myofibrils run the length of the muscle fiber; each fiber has hundreds to thousands of myofibrils.

  • Sarcomeres

    • Basic contractile unit in skeletal muscle; end-to-end linkages provide the entire myofibril length.

  • Striations

    • Visible under the microscope; distinct dark (A-bands) and light (I-bands) zones are important for muscle function.

1.2 Muscle Fiber Contraction

  • Motor Units

    • Single alpha-motor neuron and all muscle fibers it innervates; more operating motor units leads to more contractile force.

  • Excitation-Contraction Coupling

    • Process linking action potentials in nerve fibers to action potentials in muscle fibers, resulting in muscle contraction.

1.2.1 Excitation-Contraction Coupling

  • Process Overview

    • Involvement of action potentials propagating from nerves to muscle fibers, activating myofibrils.

1.2.2 Role of Ca2+ in Muscle Fiber

  • Mechanism

    • Action potential triggers calcium release from SR into sarcoplasm; calcium binds to troponin, allowing myosin to bind to actin.

1.2.3 Sliding Filament Theory

  • Mechanism of Muscle Movement

    • In relaxed state, actin-myosin interaction is absent;

    • During contraction, myosin heads pull actin filaments toward the center of the sarcomere, leading to muscle shortening.

1.2.4 Energy for Muscle Contraction

  • ATP Usage

    • ATP binds to myosin head, necessary for muscle contraction; broken down to ADP and Pi to release energy.

1.3 Muscle Fiber Types

1.3.1 Characteristics of Type I and II Fibers

  • Type I

    • ~50% of fibers; slow twitch; high fatigue resistance.

  • Type II

    • Fast twitch; quicker fatigue; further divided into IIa and IIx with varying force production characteristics.

1.3.2 Distribution of Fibers

  • Various ratios of fiber types exist across individuals, with endurance athletes favoring Type I and power athletes favoring Type II.

1.3.3 Fiber Types and Exercise

  • Type I Fibers

    • High aerobic capacity; suitable for prolonged, low-intensity activities.

  • Type II Fibers

    • Fatigue quickly; suitable for high-intensity activities like sprints.

1.3.4 Determination of Fiber Type

  • Factors Influencing Fiber Type

    • Genetic and training factors influence which motor neurons innervate muscle fibers, leading to differentiation.

1.4 Skeletal Muscle and Exercise

1.4.1 Muscle Fiber Recruitment

  • Higher force production utilizes larger or more motor units; Type I motor units are smaller than Type II.

1.4.2 Fiber Type and Athletic Success

  • Performance influenced by various factors including cardiovascular function, motivation, and training habits, not solely muscle fiber type.

1.4.3 Types of Muscle Contraction

  • Static (Isometric)

    • Produces force without changing length;

  • Dynamic

    • Produces force while changing length, categorized into concentric (shortening) and eccentric (lengthening).

1.4.3 Generation of Force

  • Force developed varies with motor unit recruitment, frequency of stimulation, and length-tension relationships.

  • Optimal Sarcomere Length

    • Required for maximal tension production; if muscles are stretched or overly shortened, force generation is diminished.

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