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Understanding Muscle Tissue Structure and Function
Nov 19, 2024
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Anatomy and Physiology Chapter 10: Muscle Tissue
Introduction
Focus on muscle tissue details
Repetition of content for better understanding
Three main types of muscle:
Skeletal Muscle
: Voluntary, focus of this chapter
Cardiac Muscle
: Involuntary, found in the heart
Smooth Muscle
: Involuntary, lines hollow organs
Skeletal Muscle Overview
Specialized for contraction
Moves body by pulling on bones
Supports posture, body position, and soft tissues
Guards body entrances/exits, maintains temperature
Stores nutrients
Anatomy of Skeletal Muscle
Connective Tissue Layers
:
Epimysium
: Outermost layer, surrounds muscle
Perimysium
: Surrounds muscle fiber bundles (fascicles)
Endomysium
: Surrounds individual muscle cells/fibers
Rich blood supply and nerves
Collagen fibers from all layers converge to form:
Tendon
: Attaches muscles to bone
Aponeurosis
: Tendinous sheet
Muscle Fiber Structure
Skeletal Muscle Fibers
:
Large, multinucleate, and striated
Contain sarcolemma (cell membrane) and sarcoplasm (cytoplasm)
T-tubules transmit action potentials
Sarcoplasmic Reticulum (SR) stores/releases calcium
Myofibrils
: Subdivisions within muscle cells responsible for contraction
Myofilaments
: Thin (actin) and thick (myosin) filaments
Sarcomere Structure
Smallest functional unit of muscle fiber
Arrangement of thin and thick filaments creates striations
A Bands
: Include M line, H band, and zone of overlap
I Bands
: Contain Z lines and titan proteins
Muscle Contraction: Sliding Filament Theory
During contraction:
H and I bands narrow
Zones of overlap widen
Z lines move closer
Thin filaments slide toward sarcomere center
Action potentials trigger contractions
Neuromuscular Junction and Action Potentials
Neuromuscular Junction (NMJ)
:
Synapse between neuron and muscle fiber
Release of acetylcholine (ACh) causes sodium influx & depolarization
Action potential spreads via T-tubules, releasing calcium
Calcium binds to troponin, shifting tropomyosin, exposing active sites
Cross-Bridge Cycle
Myosin heads bind to actin's active sites forming cross-bridges
Power stroke pulls thin filaments towards center
ATP binds to myosin, re-cocks the head for repeated cycles
Types of Muscle Contractions
Isotonic Contractions
: Muscle changes length
Concentric: Muscle shortens
Eccentric: Muscle elongates
Isometric Contractions
: Muscle length remains unchanged
Muscle Relaxation
Elastic forces, opposing muscle groups, and gravity aid in relaxation
Muscle tone maintains posture without movement
ATP and Muscle Metabolism
ATP is primary energy source for contraction
Muscle fibers store ATP and regenerate more during activity
Oxygen debt occurs post-exercise
Muscle Performance
Fast Fibers
: Quick to contract, fatigue quickly
Slow Fibers
: Slow to contract, resist fatigue
Intermediate Fibers
: Have properties of both
Muscle hypertrophy vs. atrophy
Aging and Muscle Tissue
Muscle fibers shrink, become less elastic
Fibrosis increases, recovery slows
Types of Muscle Fibers
White Muscle (Fast Fibers)
: Quick contraction, low endurance
Red Muscle (Slow Fibers)
: High endurance, more myoglobin
Summary and Review
Understanding muscle fiber anatomy is crucial for grasping muscle function
Repetition and visualization key to mastering this complex subject
Looking Ahead
Chapter 12 will focus on the nervous system and its role in muscle control
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