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MUSCLE TISSUE
Muscle
• 3 muscle types: skeletal, smooth, cardiac
• Muscle – a Latin word for “little mouse”
• Muscle is the primary tissue in the
• Heart (cardiac MT)
• Walls of hollow organs (Smooth MT)
• Skeletal muscle
• Makes up nearly half the body’s mass
Muscle Tissue Function
• Functions of muscle tissue
• Movement
• Skeletal muscle - attached to skeleton
• Moves body by moving the bones
• Posture maintenance
• Joint stabilization
• Heat generation
• Supports soft tissues
• Smooth muscle – squeezes fluids and other substances through
hollow organs
• Regulates movement of substances from tubes to blood (food)
Characteristics
• Contractility – fibers get shorter
• Excitability – fibers can carry an electrochemical current
• Extensibility – ability to stretch
• Elasticity – after stretch, the fiber can recoil
Similarities of Muscle Tissue
• Cells of muscles
• Are known as fibers
• Plasma membrane is called a
sarcolemma
• Cytoplasm is called sarcoplasm
• Muscle contraction
• Depends on two types of myofilaments (contractile proteins)
• One type contains actin
• Another type contains myosin
• These two proteins generate contractile force
Skeletal Muscle
• Each muscle is an organ
• Consists mostly of muscle tissue
• Skeletal muscle also contains
• Connective tissue
• Blood vessels
• Nerves
Basic Features of a Skeletal Muscle
• Connective tissue and fascicles
• Connective tissue sheaths bind a skeletal muscle and its fibers
together
• Epimysium – dense regular connective tissue surrounding entire
muscle
• Perimysium – surrounds each fascicle
(group of muscle fibers)
• Endomysium – a fine sheath of connective tissue wrapping each
muscle cell
Terminology
• Terminology:
• “sarco- flesh” “lemma”= sheath
• Sarcoplasm: cytoplasm of muscle cells
• Sarcolemma: the plasma membrane
• sarcoplasmic reticulum : the endoplasmic reticulum of
muscle cells
- Continuous with the epimysium, endomysium and perimysium
Surrounds whole muscle
Surrounds each muscle cell
A muscle cell fascicle
Surrounds each fasicle -
Contains
myofibrils – rows
of sarcomeres
Figure 10.1a
Basic Features of a Skeletal Muscle
• Nerves and blood vessels
• Each skeletal muscle supplied by branches of
• One nerve
• One artery
• One or more veins
• http://www.viddler.com/embed/d2b8a8b3
Basic Features of a Skeletal Muscle
• Nerves and blood vessels
• Nerves and vessels branch repeatedly
• Smallest nerve branches serve
• Individual muscle fibers
• Neuromuscular junction – signals the muscle to contract
• Draw a picture of neuromuscular junction
Basic Features of a Skeletal Muscle
• Muscle attachments
• Most skeletal muscles run from one bone to another
• One bone will move – other bone remains fixed
• Origin – less movable attachment
• Insertion – more movable attachment
Muscle Attachments
Figure 10.3
Basic Features of a Skeletal Muscle
• Muscle attachments (continued)
• Muscles attach to origins and insertions by CT
• Fleshy attachments – CT fibers are short
• Indirect attachments – CT forms a tendon or aponeurosis
• Bone markings present where tendons meet bones
• Tubercles, trochanters, and crests
Microscopic and Functional Anatomy
of Skeletal Muscle Tissue
• The skeletal muscle fiber
• Fibers (cells) are long and cylindrical
• Are huge cells – diameter is 10–100µm
• Length – several centimeters to dozens of centimeters
• Cells are multinucleate
• Nuclei are peripherally located
DiagramCross
ofsection
Partof one
ofcell
a Muscle Fiber
Figure 10.4b
Myofibrils and Sarcomeres
• Striations result from internal structure of myofibrils
• Myofibrils (many per cell and run parallel)
• Long rods within cytoplasm
• Make up 80% of the cytoplasm
• Are a specialized contractile organelle found in muscle tissue
• A long row of repeating segments called sarcomeres (functional
unit of Skeletal MT)
• Organization of a sarcomere
H
Sarcomere
• Basic unit of contraction of skeletal muscle
• Z disc (Z line) – boundaries of each sarcomere
• Thin (actin) filaments – extend from Z disc toward the center of
the sarcomere
• Thick (myosin) filaments – located in the center of the sarcomere
• Overlap inner ends of the thin filaments
• Contain ATPase enzymes
During contraction, the I band shortens and the H zone disappears completely
Sarcomere Structure
• A bands – full length of the thick filament
• Includes inner end of thin filaments
• H zone – center part of A band where no thin filaments
occur
Sarcomere Structure (continued)
• M line – in center of H zone
• Contains tiny rods that hold thick filaments together
• I band – region with only thin filaments
• Lies within two adjacent sarcomeres
Sarcoplasmic Reticulum and T Tubules
• Sarcoplasmic reticulum
• A specialized smooth ER
• Interconnecting tubules surround each myofibril
• Some tubules form cross-channels called terminal cisternae
• Cisternae occur in pairs on either side of a
t-tubule
Sarcoplasmic Reticulum and T Tubules
• Sarcoplasmic reticulum
• Contains calcium ions – released when muscle is stimulated to
contract
• Calcium ions diffuse through cytoplasm
• Trigger the sliding filament mechanism (this is the mechanism for
muscle contraction)
Sarcoplasmic Reticulum and T Tubules
in the Skeletal Muscle Fiber
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Figure 10.6
Sarcomere and Myofibrils
Figure 10.4c
Mechanism of Contraction
• Sliding filament theory
• Myosin heads attach to
actin in the thin
filaments
• Then pivot to pull thin
filaments inward toward
the center of the
sarcomere
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin
Cummings
Sliding Filament Mechanism
Figure 10.7a
Changes in Striation During Contraction
Titin lends elasticity to
muscles
The A band does not
change length during
contraction
Figure 10.8a–c
Microscopic and Functional Anatomy
of Skeletal Muscle Tissue
• Muscle extension
• Muscle is stretched by a movement opposite that which contracts it
• Muscle fiber length and force of contraction
• Greatest force produced when a fiber starts out slightly stretched
• Myosin heads can pull along the entire length of the thin filaments
The Role of Titin
• Titin – a spring-like molecule in sarcomeres
• Resists overstretching
• Holds thick filaments in place
• Unfolds when muscle is stretched
Figure 10.4d
Sarcoplasmic Reticulum and T Tubules
• Muscle contraction
• Ultimately controlled by nerve-generated impulse
• Impulse travels along the sarcolemma of the muscle cell
• Impulses further conducted by T tubules
• T tubule – a deep invagination of the sarcolemma
Innervation of Skeletal Muscle
• Motor neurons innervate skeletal muscle tissue
• Neuromuscular junction is the point where nerve ending and
muscle fiber meet
• Typically, each skeletal muscle is supplied by one artery and one
nerve (with branches)
Innervation of Skeletal Muscle
Figure 10.9
Innervation of Skeletal Muscle
Figure 10.10
Types of Skeletal Muscle Fibers
• Skeletal muscle fibers are categorized according to
• How they manufacture energy (ATP)
• How quickly they contract
Types of Skeletal Muscle Fibers
• Skeletal muscle fibers
• Are divided into 3 classes
• Slow oxidative fibers (Type I)
• Red Slow twitch
• Fast glycolytic fibers (Type IIx)
• White fast-twitch
• Fast oxidative fibers (Type IIa)
• Intermediate fibers
Types of Skeletal Muscle Fibers
• Slow oxidative fibers (Type I)
• Red color due to abundant myoglobin
• Obtain energy from aerobic metabolic reactions
• Contain a large number of mitochondria
• Richly supplied with capillaries
• Contract slowly and resistant to fatigue
• Fibers are small in diameter
Types of Skeletal Muscle Fibers
• Fast glycolytic fibers (Type IIx)
• Contain little myoglobin and few mitochondria
• About twice the diameter of slow-oxidative fibers
• Contain more myofilaments and generate more power
• Depend on anaerobic pathways
• Contract rapidly and tire quickly
Types of Skeletal Muscle Fibers
• Fast oxidative fibers (Type IIa)
• Have an intermediate diameter
• Contract quickly like fast glycolytic fibers
• Are oxygen-dependent
• Have high myoglobin content and rich supply of capillaries
• Somewhat fatigue-resistant
• More powerful than slow oxidative fibers
Overview
What do the fibers look like?
Table 10.2 (1 of 3)
Table 10.2 (2 of 3)
Table 10.2 (3 of 3)
Disorders of Muscle Tissue
• Muscle tissues experience few disorders
• Heart muscle is the exception
• Skeletal muscle
• Remarkably resistant to infection
• Smooth muscle
• Problems stem from external irritants
Disorders of Muscle Tissue
• Muscular dystrophy
• A group of inherited muscle destroying disease
• Affected muscles enlarge with fat and connective tissue
• Muscles degenerate
• Types of muscular dystrophy
• Duchenne muscular dystrophy
• Myotonic dystrophy
Disorders of Muscle Tissue
• Myofascial pain syndrome
• Pain is caused by tightened bands of muscle fibers
• Fibromyalgia
• A mysterious chronic-pain syndrome
• Affects mostly women
• Symptoms – fatigue, sleep abnormalities, severe musculoskeletal
pain, and headache
Muscle Tissue Throughout Life
• Muscle tissue develops from myoblasts
• Myoblasts fuse to form skeletal muscle fibers
• Skeletal muscles contract by the seventh week of development
Muscle Tissue Throughout Life
• Cardiac muscle
• Pumps blood three weeks after fertilization
• Satellite cells
• Surround skeletal muscle fibers
• Resemble undifferentiated myoblasts
• Fuse into existing muscle fibers to help them grow
Muscle Tissue Throughout Life
• With increased age
• Amount of connective tissue increases in muscles
• Number of muscle fibers decreases
• Loss of muscle mass with aging
• Decrease in muscular strength by 50% by age 80
• Sarcopenia – muscle wasting