Download Skeletal muscle tissue

Muscle Tissue / Muscles of the
Body
3 Types of Muscle Tissue
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Skeletal muscle tissue
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Cardiac muscle tissue – occurs only in the walls
of the heart
Smooth muscle tissue – occupies the walls of
hollow organs, cells lack striations
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• Packaged into skeletal muscles
• Makes up 40% of body weight
• Cells are striated
Functions Of Muscle Tissue
• Produce movement - movement of the body as a whole,
propels blood, food, wastes, and babies, eye movement
• Maintain posture and body position - muscles continuously
contract to help you maintain your body posture
• Support soft tissues - soft tissues such as the organs in your
abdominal and pelvic cavity are supported by skeletal
muscle
• Control entrances and exits - openings to the urinary and
digestive tracts have muscles that allow you to control
swallowing, defecation, and urination
• Maintain body temperature - contractions produce heat
through shivering
Functional Features of Muscles
• 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
Similarities of Muscle Tissue
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Cells of muscles are known as fibers
Plasma membrane is called a sarcolemma
Cytoplasm is called sarcoplasm
Muscle contraction
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Depends on two types of myofilaments (contractile
proteins) called actin and myosin
These two proteins generate contractile force
Skeletal Muscle
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Each muscle is an organ
• Consists mostly of muscle tissue
• Skeletal muscle also contains
• Connective tissue
• Blood vessels
• Nerves
• Each skeletal muscle supplied by branches of
• One nerve
• One artery
• One or more veins
Muscle Attachments
• Most skeletal
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muscles run from one
bone to another
One bone will move –
other bone remains
fixed
• Origin – less
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movable attachment
Insertion – more
movable attachment
Muscle Attachments
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Muscles attach to origins and
insertions by CT
• Tendon - a cordlike attachment of
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muscles to bone (usually), or
sometimes to skin, cartilage, or sheets
of fascia. Most muscles attach by
tendons.
Aponeuroses - flat sheet that attaches
muscles to bones (usually) or
sometimes to skin, cartilage, or sheets
of fascia.
• Bone markings present where tendons
meet bones: Tubercles, trochanters,
and crests
Connective Tissue And Fascicles
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Connective tissue sheaths
bind a skeletal muscle and its
fibers together
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Epimysium – dense
irregular 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
Histology of Skeletal Muscle Tissue
• The skeletal muscle fiber
• Fibers are long and cylindrical
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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
• 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)
Sarcomere
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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
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Overlap inner ends of the
thin filaments
Contain ATPase enzymes
Sarcomere Structure
• A bands – full length of the thick filament, includes inner end of
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thin filaments
H zone – center part of A band where no thin filaments occur
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
• A specialized smooth ER
• Interconnecting tubules
surround each myofibril
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Some tubules form crosschannels called terminal
cisternae
Cisternae occur in pairs on
either side of a t-tubule
SR Contains calcium ions
– released when muscle is
stimulated to contract
The Contraction Process
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Muscle contraction is controlled by nerve-generated impulse (action potentials)
The nerve impulsel is propagated along (across) the sarcolemma and travels
down through the T tubules causing calcium channels in the SR to open and
releasing calcium into the sarcoplasm (where the myofilaments are)
Calcium ions diffuse through cytoplasm, Triggering the sliding filament
mechanism
T tubule
Terminal button
Surface membrane of muscle cell
Acetylcholine
Acetylcholinegated cation
channel
Tropomyosin
Actin
Troponin
Cross-bridge binding
Myosin cross bridge
Sliding Filament Model of Contraction
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Contraction refers to the
activation of myosin’s cross
bridges – the sites that generate
the force
In the relaxed state, actin and
myosin filaments do not fully
overlap
With the presence of calcium
form the SR, the myosin heads
bind to actin and pull the thin
filaments
Actin filaments slide past the
myosin filaments so that the
actin and myosin filaments
overlap to a greater degree (the
actin filaments are moved
toward the center of the
sarcomere, Z lines become
closer)
Changes in Striation During Contraction
Figure 10.8a–c
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Innervation of Skeletal Muscle
Motor neurons innervate skeletal muscle
tissue
Neuromuscular junction is the point where
nerve ending and muscle fiber meet
Motor Units
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Motor Unit —A motor neuron and all the muscle cells it controls
Recruitment—To increase muscle tension by activating more motor
units
Small motor units provide finer control
Muscles performing powerful, coarsely controlled movement have
larger number of fibers per motor unit
Types of Skeletal Muscle Fibers
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Skeletal muscle fibers are categorized according to
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How they manufacture energy (ATP)
How quickly they contract
Divided into 3 classes
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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
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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
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mitochondria
About twice the diameter of slowoxidative 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
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supply of capillaries
Somewhat fatigue-resistant
More powerful than slow oxidative fibers
Smooth Muscle
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Occurs within most organs
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Walls of hollow visceral organs, such
as the stomach
Urinary bladder
Respiratory passages
Arteries and veins
Helps substances move through
internal body channels via
peristalsis
No striations
• Filaments do not form myofibrils
• Not arranged in sarcomere pattern
found in skeletal muscle
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Is Involuntary
Single Nucleus
Smooth Muscle
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Composed of spindle-shaped fibers with a diameter of
2-10 m and lengths of several hundred m
Cells usually arranged in sheets within muscle
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Organized into two layers (longitudinal and circular) of
closely apposed fibers
Have essentially the same contractile mechanisms as
skeletal muscle
Smooth Muscle
• Cell has three types of filaments
• Thick myosin filaments
• Longer than those in skeletal
muscle
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Thin actin filaments
• Contain tropomyosin but lack
troponin
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Filaments of intermediate size
• Do not directly participate in
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contraction
• Form part of cytoskeletal
framework that supports cell
shape
Have dense bodies containing same
protein found in Z lines
Cardiac Muscle Tissue
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Occurs only in the heart
Is striated like skeletal muscle but
but has a branching pattern with
intercalated Discs
Usually one nucleus, but may
have more
Is not voluntary
Contracts at a fairly steady rate
set by the heart’s pacemaker
Neural controls allow the heart to
respond to changes in bodily
needs
Comparison of Muscle Tissues
Table 10.2 (2 of 3)
Muscles of the Body
• Skeletal muscles
• Produce movements
• Blinking of eye, standing on tiptoe,
swallowing food, etc.
• General principles of leverage
• Muscles act with or against each other
• Criteria used in naming muscles
Lever Systems: Bone-Muscle Relationships
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Movement of skeletal muscles involves leverage
• Lever – a rigid bar that moves
• Fulcrum – a fixed point
• Effort – applied force
• Load – resistance
Lever Systems: Bone-Muscle Relationships
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Bones – act as levers
Joints – act as fulcrums
Muscle contraction – provides effort, applies
force where muscle attaches to bone
Load – bone, overlying tissue, and anything
lifted
Lever Systems: Bone-Muscle Relationships
• Levers allow a given effort to
• Move a heavier load, moves a large
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load over small distances
Move a load farther, allows a load to be
moved over a large distance
Lever Systems: Bone-Muscle Relationships
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First-class lever
• Effort applied at one end
• Load is at the opposite end
• Fulcrum is located between load and effort
Lever Systems: Bone-Muscle Relationships
• Second-class lever
• Effort applied at one end
• Fulcrum is at the opposite end
• Load is between the effort and fulcrum
Lever Systems: Bone-Muscle Relationships
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Third-class lever
• Effort is applied between the load and the fulcrum
• Work speedily
• Always at a mechanical disadvantage
Figure 11.2c
Lever Systems: Bone-Muscle Relationships
• Most skeletal muscles are third-class
levers
• Example – biceps brachii
• Fulcrum – the elbow joint
• Force – exerted on the proximal region
of the radius
• Load – the distal part of the forearm
Interactions of Skeletal Muscles in the Body
• A muscle cannot reverse the movement
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it produces
Another muscle must undo the action
Muscles with opposite actions lie on
opposite sides of a joint
Muscles Classified into Several Functional Groups
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Prime mover (agonist)
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Has major responsibility for a certain movement
Antagonist
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Opposes or reverses a movement
Synergist – helps the prime mover
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By adding extra force
By reducing undesirable movements
Fixator - a type of synergist that holds a bone firmly in
place
Arrangement of Fascicles in Muscles
• Skeletal muscles – consist of fascicles
• Fascicles – arranged in different
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patterns
Fascicle arrangement – tells about
action of a muscle
Types of Fascicle Arrangement
• Parallel – fascicles run
parallel to the long axis of
the muscle
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Strap-like –
sternocleidomastoid
Fusiform – biceps brachii
• Convergent
• Origin of the muscle is
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broad
Fascicles converge toward
the tendon of insertion
Example – pectoralis
major
Types Of Fascicle Arrangement
• Pennate
• Unipennate – fascicles
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insert into one side of the
tendon
• Bipennate – fascicles
insert into the tendon
from both sides
• Multipennate – fascicles
insert into one large
tendon from all sides
Circular -fascicles are
arranged in concentric rings
• Surround external body
openings
• Sphincter – general
name for a circular
muscle
Naming the Skeletal Muscles
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Number of origins
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Flexor, extensor, adductor, or abductor
Relative size
Maximus, minimus, and longus indicate size
Example – gluteus maximus and gluteus minimus
Direction of fascicles and muscle fibers
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Indicates type of muscle movement
Location - ex. the brachialis is located on the arm
Shape – ex. the deltoid is triangular
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Indicated by the words biceps, triceps, and quadriceps
Action - The action is part of the muscle’s name
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Two, three, or four origins
Name tells direction in which fibers run
Example – rectus abdominis and transversus abdominis
Location of attachments – name reveals point of origin and insertion,
ex. brachioradialis
Muscle Movements
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Flexion
Extension
Hyperextension
Abduction
Adduction
Circumduction
Rotation
• Pronation, supination
Angular Movements
Figure 6-32(a)
Angular Movements
Figure 6-32(b)
Angular Movements
Figure 6-32(c)
Angular Movements
Figure 6-32(d)
Rotational Movements
Figure 6-33(a)
Rotational Movements
Figure 6-33(b)
Special Movements
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Foot and ankle
• Inversion, eversion
• Dorsiflexion, plantar flexion
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Hand - opposition of thumb, palm
Head
• Protraction, retraction
• Depression, elevation (jaw)