Chapter 9 Biol3210

Chapter 9: Muscle

  • Ho-Jin Koh, PhD

  • Harned Hall Rm312

  • hkoh@tnstate.edu

I. Overview

A. Importance of Muscle Physiology

  • Sarcopenia: Loss of muscle mass, strength, and function as a natural part of aging.

  • Diabetes: Muscle plays a crucial role in glucose metabolism and insulin sensitivity.

  • Cardiovascular Disease:

    • a. Cardiac Hypertrophy: Thickening of the heart muscle, affecting heart function.

    • b. Coronary Artery Disease: Affects smooth muscle in arterial walls.

B. Basic Muscle Function

  • Converts chemical energy into mechanical force.

    • ATP → ADP + Pi + Heat + Work

II. Functional Characteristics of Muscle Tissue

  • Excitability: Ability to respond to stimuli by changing membrane potential.

  • Contractility: Capacity to shorten forcefully to generate movement.

  • Extensibility: Ability to be stretched or extended.

  • Elasticity: Ability to recoil and return to the original resting length.

III. Types of Muscle Tissue

A. Comparison of Muscle Types

Characteristic

Skeletal Muscle

Cardiac Muscle

Smooth Muscle

Body Location

Attached to bones or skin

Walls of the heart

Walls of hollow visceral organs

Cell Shape

Long, cylindrical, multinucleate with striations

Branching, uni- or binucleate with striations

Fusiform, uninucleate, no striations

B. Types of Muscle

  1. Skeletal Muscle (Voluntary)

    • Functions: movement, posture maintenance, joint stabilization, heat production, metabolism.

  2. Cardiac Muscle (Involuntary)

    • Function: cardiac output.

  3. Smooth Muscle (Involuntary)

    • Functions: controls vascular tone and gastrointestinal motility.

IV. Skeletal Muscle Development

  • Myoblast: Mesoderm cells that fuse to form multinucleated myotubes.

  • Myotube: Immature muscle fiber that matures into myofiber.

  • Cells have mitotic potential and can alter size by adding or subtracting nuclei.

A. Skeletal Muscle Structure

  • Sarcomere: functional unit of muscle, composed of myofibrils.

  • Striated muscles characterized by dark and light bands (A band, I band).

V. Sliding Filament Theory

  • Fundamental mechanism of muscle contraction involving overlapping thick (myosin) and thin (actin) filaments.

  • During contraction:

    • Thin filaments slide over thick filaments, increasing overlap of actin and myosin.

A. Stages of Contraction

  1. Cross Bridge Formation: Myosin heads attach to actin filaments.

  2. Power Stroke: Myosin head pivots, pulling actin toward the M line.

  3. Cross Bridge Detachment: Myosin heads detach from actin when ATP binds.

  4. Cocking of Myosin Head: Requires ATP hydrolysis to return to the high-energy position.

B. Role of Calcium (Ca²+) in Contraction

  • Ca²+ Binding: Binds to troponin, which shifts tropomyosin to expose binding sites on actin, initiating contraction.

VI. Smooth Muscle Characteristics

  • Location: Found in walls of hollow organs except the heart.

  • Cellular Structure: Spindle-shaped fibers, single nucleus, no striations.

A. Types of Smooth Muscle

  1. Single-Unit: Contracts rhythmically as a unit, electrically coupled via gap junctions.

  2. Multiunit: Independent fibers, graded contractions, rich nerve supply.

B. Smooth Muscle Functions

  • Peristalsis: Alternating contractions that mix and move substances through organs.

  • Stress-Relaxation Response: Adapts to stretch, allowing organs to maintain function under changing volumes.

VII. muscle Fiber Types Comparison

  • Oxidative Fibers: Use aerobic pathways.

  • Glycolytic Fibers: Utilize anaerobic glycolysis.

A. Fiber Types Based on Metabolism

  • Slow Oxidative Fibers: Endurance activities, fatigue-resistant.

  • Fast Oxidative Fibers: Medium intensity, moderately fatigue-resistant.

  • Fast Glycolytic Fibers: Short bursts of intense activity, fatigue easily.

VIII. Rigor Mortis

  • Occurs 3-4 hours post-mortem when ATP synthesis ceases, causing muscle to contract and remain rigid until proteins break down.