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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
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
DiagramCross
ofsection
Partof one
ofcell
a Muscle Fiber
Figure 10.4b
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
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
***
*
*
*
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
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
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
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)
• a) aerobic fibers.
• b) half the diameter of fast twitch muscle fibers. Thin = doesn’t generate
as much power.
• c) Takes 3 times as long to contract than fast twitch but has a steadier
tug & more endurance
than fast
twitch. Resistant to fatigue as long as oxygen is present.
• d) Have many mitochondria
• e) rich in blood: a lot of capillary beds for more oxygen
• f) have a lot of myoglobin : protein pigment that binds to O2 for O2
reserves
• e) These muscles are used in endurance sports: running, biking,
swimming.
• f) No slow fibers in eye or hand.
Fast glycolytic fibers (Type IIx)
White fast-twitch
• a) Tend to be anaerobic
• b) large in diameter, generate much more power.
• c) Fibers are light in color because of little or no myoglobin
• d) have fewer mitochondria compared to red fibers.
• e) Have fewer blood vessels.
• f) Their dependence on anaerobic activity leaves them
vulnerable to accumulation of lactic
acid that can
cause fatigue quickly.
• g) Have a lot of glycogen reserve
• h) Provide explosions of energy & helpful in sports like sprinting
& weight lifting.
• i) eye and hand have only fast twitch muscles
Fast oxidative fibers (Type IIa)
Intermediate fibers
• a) intermediate characteristics of other types. Size of fiber
is in between fast & slow twitch
• b) contract quickly but dependent on oxygen, so has more
mitochondria & capillaries &
myoglobin
• c) fatigue resistant , but not as resistant as slow twitch
fibers
• * possible to transform muscle types through training, but
revert back to original type after training.
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
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)
Terminology
• Origin: Insertion pulled toward the origin. Usually the more proximal
•
•
•
•
•
•
•
•
•
attachment
Insertion: bone (or CT or skin) which moves. Usually the more distal
attachment
* the terms origin and insertion are being phased out. They are now
using “proximal attachment & distal attachment”
Action: the main movement that occurs when the muscle contracts.
Prime mover (agonist): a muscle that does most of the work in an action
Synergists :
a) add extra force eg) biceps brachii & brachialis muscles have
same action
b) fixator: A fixator holds the bone still that the agonist is attached
to.
For example, during elbow flexion and extension the shoulder
muscles hold the scapula (shoulder blade) still (both the biceps and
triceps attach to the scapula).The
fixators hold the
scapula still by increasing tension, but keeping the same length.
Antagonist: works opposite the synergists.
Agonists vs antagonist
Synergists
Fixator
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
• 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