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PowerPoint® Lecture Slides prepared by Leslie Hendon University of Alabama, Birmingham

C H A P T E R

Copyright © 2011 Pearson Education, Inc.

Part 1

10 Muscle Tissue


Muscle

•  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


Overview of Muscle Tissue •  Functions of muscle tissue

•  Movement •  Skeletal muscle—attached to skeleton

•  Moves body by moving the bones •  Smooth muscle—squeezes fluids and other

substances through hollow organs •  Maintenance of posture—enables the body to

remain sitting or standing •  Joint stabilization •  Heat generation

•  Muscle contractions produce heat •  Helps maintain normal body temperature


Functional Features of Muscles •  Functional features

•  Contractility •  Long cells shorten and generate pulling force

•  Excitability •  Electrical nerve impulse stimulates the muscle cell

to contract •  Extensibility

•  Can be stretched back to its original length by contraction of an opposing muscle

•  Elasticity •  Can recoil after being stretched


Types of Muscle Tissue •  Skeletal muscle tissue •  Packaged into skeletal muscles •  Makes up 40% of body weight •  Cells are striated

•  Cardiac muscle tissue—occurs only in the walls of the heart

•  Smooth muscle tissue—occupies the walls of hollow organs •  Cells lack striations


Similarities of Muscle Tissue

•  Cells of smooth, cardiac & skeletal muscle are known as fibers

•  Muscle contraction •  Depends on two types of myofilaments (contractile

proteins) •  One type contains actin •  Another type contains myosin

•  These two proteins generate contractile force •  Plasma membrane is called a sarcolemma •  Cytoplasm is called sarcoplasm

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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

•  Sheaths of connective tissue 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

•  Connective tissue sheaths are continuous with tendons •  When muscle fibers contract, pull is exerted on all layers of

connective tissue and transmitted to the tendon •  Sheaths provide elasticity and allow blood vessels and nerves to

penetrate deep into the muscle to get to all fibers


Bone

Perimysium

Endomysium (between individual muscle fibers)

Muscle fiber

Fascicle (wrapped by perimysium)

Epimysium

Tendon

Epimysium

Muscle fiber in middle of a fascicle

Blood vessel

Perimysium

Endomysium

(a) Fascicle

(b)

Connective Tissue Sheaths in Skeletal Muscle

Figure 10.1 Copyright © 2011 Pearson Education, Inc.

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

•  Nerves and vessels branch repeatedly •  Smallest nerve branches serve:

•  Individual muscle fibers •  Neuromuscular junction— where the signals pass

from the nerve to the muscle to trigger contraction



•  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


Origin by direct attachment

Muscle contracting

Insertion by indirect attachment

Brachialis

Tendon

Muscle Attachments

Figure 10.3

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•  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 are long and cylindrical • Are huge cells—diameter is 10–100µm • Length—several centimeters to dozens of

centimeters •  Each cell formed by fusion of embryonic cells •  Cells are multinucleate •  Nuclei are peripherally located


Diagram of Part of a Muscle Fiber

Figure 10.4b

Nucleus Light I band

Dark A band

Sarcolemma

Mitochondrion

(b) Diagram of part of a muscle fiber showing the myofibrils. One myofibril is extended from the cut end of the fiber.

Myofibril


Myofibrils and Sarcomeres

•  Striations result from internal structure of myofibrils

•  Myofibrils •  Are long rods within cytoplasm •  Make up 80% of the cytoplasm •  Are a specialized contractile organelle found

in muscle tissue •  Are a long row of repeating segments called

sarcomeres (functional unit of Skeletal MT)


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

•  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 •  A bands and I bands refract polarized light differently

•  A bands—anisotropic •  I bands—isotropic


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

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I band

Z disc Z disc

I band A band

H zone

Thin (actin) filament

Thick (myosin) filament

Z disc Z disc

M line Sarcomere

(c) Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomere extends from one Z disc to the next.

Sarcomere Structure (continued)

I band

Z disc Z disc

I band

M line

Sarcomere



Elastic (titin) filaments

(d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments.

Myosin heads

Figure 10.4c, d Copyright © 2011 Pearson Education, Inc.

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 •  Contains calcium ions—released when muscle is stimulated to

contract •  Calcium ions diffuse through cytoplasm

•  Trigger the sliding filament mechanism •  T tubules—deep invaginations of sarcolemma

•  Triad—T tubule flanked by two terminal cisterns

Copyright © 2011 Pearson Education, Inc. Figure 10.6

Sarcoplasmic Reticulum and T Tubules in the Skeletal Muscle Fiber

Myofibril

Myofibrils

Triad

Tubules of the sarcoplasmic reticulum

Sarcolemma

Sarcolemma

Mitochondria

I band I band A band

H zone Z disc Z disc

Part of a skeletal muscle fiber (cell)

T tubule Terminal cistern of the sarcoplasmic reticulum (2)

M line


Mechanism of Contraction

•  Two major types of contraction •  Concentric contraction—muscle shortens to

do work •  Eccentric contraction—muscle generates

force as it lengthens • Muscle acts as a “brake” to resist gravity •  “Down” portion of a pushup is an example


Mechanism of Contraction

•  Sliding filament mechanism •  Explains concentric contraction

•  Myosin head attach to thin filaments at both ends of a sarcomere •  Then pull thin filaments toward the center of the

sarcomere •  Thin and thick filaments do not shorten

•  Initiated by release of calcium ions from the SR •  Powered by ATP


Sliding Filament Mechanism

Figure 10.7

Movement Thin (actin)

filament


Myosin head



(a) Myosin heads attach to actin in the thin filaments, then pivot to pull the thin filaments inward.

(b) Transmission electron micrograph of part of a sarcomere, showing myosin heads attached to the thin filaments



Myosin heads

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•  Contraction changes the striation pattern •  Fully relaxed—thin filaments partially overlap

thin filaments •  Contraction—Z discs move closer together • Sarcomere shortens •  I bands shorten, H zone disappears • A band remains the same length



I I A Z Z H

Fully relaxed sarcomere of a muscle fiber I I A Z Z

Fully contracted sarcomere of a muscle fiber 1 2

Figure 10.8


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 then 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


Innervation of Skeletal Muscle


Innervation of Skeletal Muscle

•  Motor neurons innervate skeletal muscle tissue •  Neuromuscular junction is the point where

nerve ending and muscle fiber meet •  Axon terminals—at ends of axons • Store neurotransmitters (acetylcholine for

skeletal muscle) •  Synaptic cleft—space between axon terminal

and sarcolemma

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Nerve impulse stimulates the release of the neurotransmitter acetylcholine (ACh) into the synaptic cleft.

Axon terminal of motor neuron Synaptic vesicle containing ACh

Muscle fiber

(a)

(b)

Triad

Synaptic cleft

Sarcolemma

Terminal cisterna of SR

Ca2+

Nucleus

Nerve impulse

Myelinated axon of motor neuron

Axon terminal of neuromuscular junction

Sarcolemma of the muscle fiber

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ACh stimulates changes in the sarcolemma that excite the muscle fiber. This stimulus is carried down the T tubules to initiate fiber contraction.

Enzymes in the synaptic cleft break down ACh and thus limit its action to a single muscle twitch.

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2

3

The Neuromuscular Junction

Figure 10.9 Copyright © 2011 Pearson Education, Inc.

Motor Units

Figure 10.10

Spinal cord

Motor neuron cell body

Muscle

Branching axon to motor unit

Nerve

Motor unit 1

Motor unit 2

Muscle fibers

Motor neuron axon

Axon terminals at neuromuscular junctions

(a) Axons of motor neurons extend from the spinal cord to the muscle. There each axon divides into a number of axon terminals that form neuromuscular junctions with muscle fibers scattered throughout the muscle.

(b) Branching axon terminals form neuromuscular junctions, one per muscle fiber (photomicrograph 110×).


Types of Skeletal Muscle Fibers

•  Skeletal muscle fibers are categorized according to two characteristics •  How they manufacture energy (ATP) •  How quickly they contract

•  Oxidative fibers—produce ATP aerobically •  Glycolytic fibers—produce ATP

anaerobically by glycolysis



•  Skeletal muscle fibers •  Are divided into three classes • Slow oxidative fibers • Red slow oxidative fibers

• Fast glycolytic fibers • White fast glycolytic fibers

• Fast oxidative fibers •  Intermediate fibers



•  Slow oxidative fibers •  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



•  Fast glycolytic fibers •  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

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•  Fast oxidative fibers •  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

Copyright © 2011 Pearson Education, Inc. Table 10.2 (1 of 3)

Copyright © 2011 Pearson Education, Inc. Table 10.2 (2 of 3) Copyright © 2011 Pearson Education, Inc. 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

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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

Embryonic mesoderm cells undergo cell division (to increase number) and enlarge.

Embryonic mesoderm cells Myoblasts

Myotube (immature multinucleate muscle fiber)

Satellite cell

Mature skeletal muscle fiber

Several myoblasts fuse together to form a myotube.

Myotube matures into skeletal muscle fiber.

1 2 3



•  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



•  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 is 50% by age 80 •  Sarcopenia—muscle wasting

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