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PowerPoint® Lecture Presentations prepared byLeslie Hendon

University of Alabama, Birmingham

10Skeletal Muscle Tissue

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I. Muscle

A. Muscle = a Latin word for “little mouse”

1. skeletal muscle

2. cardiac muscle tissue

3. smooth muscle tissue

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Properties of Muscle Tissue

Contractility

► Myofilaments are responsible for shortening of muscles cells

► Actin and myosin are two type of myofilaments

Excitability

► Nerve signals excite muscle cells

Extensibility► Contraction of a skeletal muscle stretches the opposing muscle

► Smooth muscle is stretched by substances within that hollow organ

► Food in stomach; urine in urinary bladder

Elasticity

► Recoils after being stretched

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II. Terminology Specific to Muscle Tissue

A. Myo- and mys- - prefixes meaning “muscle”

B. Sarco—prefix meaning “flesh”

1. Sarcolemma - plasma membrane of muscle cells

2. sarcoplasm—cytoplasm of muscle cells

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III. Functions of Muscle Tissue

A. Produce movement

1. skeletal muscle - attached to skeleton (movement)

e.g. biceps, triceps

2. smooth muscle - squeezes fluids through hollow organs

e.g. walls of intestines and arteries

B. Maintain posture and stabilize joints

1. enables the body to remain sitting or standing

2. muscle tone helps stabilize many synovial joints

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C. Heat generation

1. muscle contractions produce heat

2. helps maintain normal body temperature

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IV. Types of Muscle Tissue

A. Skeletal muscle tissue

1. packaged into skeletal muscles

2. makes up 40% of body weight

3. cells are striated

4. innervated by voluntary division of the nervous system

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C. Cardiac muscle tissue

1. occurs only in the walls of the heart

2. cells are striated

3. contraction is involuntary

D. Smooth muscle tissue

1. occupies the walls of hollow organs

2. cells lack striations

3. innervated by involuntary division of the nervous system

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V. Gross Anatomy of a Skeletal Muscle

A. Sheaths of connective tissue

1. epimysium - surrounding entire muscle

2. perimysium - surrounds each fascicle (bundle of fibers)

3. endomysium - wrapping each muscle cell

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EpimysiumBone

Tendon

Epimysium Perimysium Fascicle

Endomysium Muscle fiber

Blood vessel

Fascicle(wrapped by perimysium)

Endomysium(between individualmuscle fibers)

Epimysium

Perimysium

Endomysium

Muscle fiberin middle ofa fascicle

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B. Each skeletal muscle supplied by branches of

► one nerve

► one artery

► one or more veins

C. Nerves and vessels branch repeatedly

D. Smallest branches serve individual muscle fibers

E. Muscle attachments

► origin - less movable attachment

► insertion - more movable attachment

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Muscle contracting

OriginStable

Insertionmoving

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F. Muscles attach by connective tissue (CT)

1. fleshy attachments - CT fibers are short

2. indirect attachments - CT forms a tendon or aponeurosis

G. Bone markings present where tendons meet bones

► tubercles

► trochanters

► crests

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H. skeletal muscle cell (fiber)

1. fibers are long and cylindrical

► Are huge cells—diameter is 10–100 µm

► Length—several centimeters to dozens of centimeters

2. cells are multinucleate

3. nuclei are peripherally located

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Muscle >>> Fascicle >>> Muscle Cell >>> Myofibril

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

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Sarcolemma

Mitochondrion

Dark A band Light I band Nucleus

Myofibril

Muscle cell

Muscle Cell >>> Myofibril

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Thin (actin)filament

Thick (myosin)filament

I band I bandA band M line

Z disc Z discH zone

Sarcomere

Myofibril >>> Sarcomeres

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VI. Sarcomeres

A. Basic unit of contraction of skeletal muscle

Z line - boundaries of each sarcomere ► Thin (actin) filaments—from Z disc to center of the sarcomere

► Thick (myosin) filaments—located in the center of the sarcomere

A bands - full length of the thick filament

H zone - center part of A band where no thin filaments occur

M line - in center of H zone

I band - region with only thin filaments

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Sarcolemma

Mitochondrion

Dark A band Light I band Nucleus

Myofibril

muscle cell

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Thin (actin)filament

Thick (myosin)filament

I band I bandA band M line

Z disc Z discH zone

Sarcomere

myofibril

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Thin (actin)filament

Elastic (titin)filaments

Thick (myosin)filament

Myosin heads

Z disc Z discM line

sarcomere

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VII. Sarcoplasmic Reticulum and T Tubules

A. Sarcoplasmic reticulum

1. specialized smooth ER

2. contains calcium ions - released when muscle is stimulated

3. calcium ions diffuse through cytoplasm

► Trigger the sliding filament mechanism

B. T tubules - deep invaginations of sarcolemma

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Part of a skeletalmuscle fiber (cell)

Sarcolemma

Myofibril

I band I bandA band

Z disc Z discH zone

Mline

Sarcolemma

Myofibrils

T Tubules ofthe sarcoplasmicreticulum

Sarcoplasmic Reticulum and T Tubules

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VIII. Mechanism of Contraction

A. Two major types of contraction

1. Concentric contraction – force as muscle shortens

2. Eccentric contraction - force as muscle lengthens

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Thin (actin) filament Movement

Myosinhead

Thick (myosin) filament

Thin (actin)filament

Thick (myosin)filament

Thick (myosin)filament

Thin (actin)filament

Myosinheads

Sliding Filament Mechanism of Contraction

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Fully relaxed sarcomere of a muscle fiber1 2 Fully contracted sarcomere of a muscle fiber

Z Z Z ZH

I I I IA A

Sliding Filament Mechanism of Contraction

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Muscle >>> muscle fiber

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muscle fiber >>> myofibril >>> sarcomere

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sarcomere

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IX. Innervation of Skeletal Muscle

A. Motor neurons innervate skeletal muscle tissue

1. neuromuscular junction - nerve ending meets muscle fiber

2. Terminal boutons (axon terminals)

► Located at ends of axons

► Store neurotransmitters

3. Synaptic cleft - between axon terminal and sarcolemma

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neuromuscular junction

Terminal bouton of nerve

Synapticcleft

Terminalcistern of SR

Triad

Muscle fiber

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Spinal cord

Muscle

Nere

Branching axonto motor unit

Motor neuroncell body

Motorunit 1

Motorunit 2

Motorneuronaxon

Musclefibers

neuromuscularjunctions

Motor unit = motor neuron and muscle cells innervated

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X. Types of Skeletal Muscle Fibers

A. Skeletal muscle fibers categorized according to two characteristics

1. how they manufacture energy (ATP)

2. how quickly they contract

B. Oxidative fibers - produce ATP aerobically

C. Glycolytic fibers - produce ATP anaerobically by glycolysis

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D. Slow oxidative fibers

► Red slow oxidative fibers

E. Fast glycolytic fibers

► White fast glycolytic fibers

F. Fast oxidative fibers

► Intermediate fibers

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G. Slow oxidative fibers

► Contract slowly and resistant to fatigue

► Red color due to abundant myoglobin

► Obtain energy from aerobic metabolic reactions

► Contain a large number of mitochondria

► Richly supplied with capillaries

► Fibers are small in diameter

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H. Fast glycolytic fibers

► Contract rapidly and tire quickly

► 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

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I. Fast oxidative fibers

► Contract quickly like fast glycolytic fibers

► Somewhat fatigue resistant

► Have an intermediate diameter

► Are oxygen dependent

► Have high myoglobin content and rich supply of capillaries

► More powerful than slow oxidative fibers

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Skeletal vs. Cardiac vs. Smooth Muscle

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Skeletal vs. Cardiac vs. Smooth Muscle

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Skeletal vs. Cardiac vs. Smooth Muscle

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Skeletal vs. Cardiac vs. Smooth Muscle

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XI. Disorders of Muscle Tissue

A. Muscular dystrophy

1. a group of inherited muscle destroying disease

► Affected muscles enlarge with fat and connective tissue

► Muscles degenerate

► Types of muscular dystrophy

a. Duchenne muscular dystrophy

b. Myotonic dystrophy

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B. Fibromyalgia

► A mysterious chronic-pain syndrome

► Affects mostly women

Symptoms

fatigue

sleep abnormalities

severe musculoskeletal pain

headache

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Embryonicmesoderm cells

MyoblastsMyotube(immaturemultinucleatemuscle fiber)

Satellite cell

Matureskeletalmusclefiber

3

XII. Formation of Skeletal Muscle Cell

21