Download muscle fibers

Chapter
10
Muscle Tissue
PowerPoint® Lecture Slides
prepared by Jason LaPres
Lone Star College - North Harris
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Copyright © 2009 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
An Introduction to Muscle Tissue
 Muscle Tissue
 A primary tissue type, divided into
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
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An Introduction to Muscle Tissue
 Skeletal Muscles
 Are attached to the skeletal system
 Allow us to move
 Each skeletal muscle cell is a single muscle fiber
 The muscular system
 Includes only skeletal muscle
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Functions of Skeletal Muscles
 Produce skeletal movement
 Maintain body position
 Support soft tissues
 Guard openings
 Maintain body temperature
 Store nutrient reserves
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Skeletal Muscle Structures
 Organization of Connective Tissues
 Muscles have three layers of connective tissues
 Epimysium:
– exterior collagen layer
– connected to deep fascia
– separates muscle from surrounding tissues
 Perimysium:
– surrounds muscle fiber bundles (fascicles)
– contains blood vessel and nerve supply to fascicles
 Endomysium:
– surrounds individual muscle cells (muscle fibers)
– contains capillaries and nerve fibers contacting muscle cells
– contains myosatellite cells (stem cells) that repair damage
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Skeletal Muscle Structures
Figure 10–1 The Organization of Skeletal Muscles.
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Skeletal Muscle Structures
 Organization of Connective Tissues
 Muscle attachments
 Endomysium, perimysium, and epimysium come
together:
– at ends of muscles
– to form connective tissue attachment to bone matrix
– i.e., tendon (bundle) or aponeurosis (sheet)
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Skeletal Muscle Structures
 Blood Vessels
 Muscles have extensive vascular systems that
 Supply large amounts of oxygen
 Supply nutrients
 Carry away wastes
 Nerves
 Skeletal muscles are voluntary muscles, controlled
by nerves of the central nervous system (brain and
spinal cord)
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Skeletal Muscle Fibers
 Are very long
 Develop through fusion of mesodermal cells
(myoblasts)
 Become very large
 Contain hundreds of nuclei
 Possess myosatellite cells that help with repair
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Skeletal Muscle Fibers
Figure 10–2 The Formation of a Multinucleate Skeletal Muscle Fiber.
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Skeletal Muscle Fibers
Figure 10–2a The Formation of a Multinucleate Skeletal Muscle Fiber.
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Skeletal Muscle Fibers
Figure 10–2b The Formation of a Multinucleate Skeletal Muscle Fiber.
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 The sarcolemma
 The cell membrane of a muscle fiber (cell)
 Surrounds the sarcoplasm (cytoplasm of muscle
fiber)
 A change in transmembrane potential begins
contractions
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Transverse tubules (T tubules)
 Narrow tubes filled with extracellular fluid that are continuous
with the sarcolemma and extend into the sarcoplasm at right
angles.
 Transmit action potential through cell
 Allow entire muscle fiber to contract simultaneously
 Have same properties as sarcolemma
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Myofibrils
 Lengthwise subdivisions within muscle fiber and encircled by
transverse tubules
 Each skeletal muscle fiber contains hundreds to thousands of
myofibrils
 Made up of bundles of protein filaments (myofilaments)
 Myofilaments
 responsible for muscle contraction
 Types of myofilaments:
– thin filaments:
» made of the protein actin
– thick filaments:
» made of the protein myosin
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcoplasmic reticulum (SR)
 A membrane complex similar to the smooth
endoplasmic reticulum
 Forms a tubular network around each individual
myofibril
 On either side of a T tubule, the tubules of the SR
enlarge, fuse, and form expanded chambers called
terminal cisternae.
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcoplasmic reticulum (SR)
 The combination of a pair of terminal cisternae
plus a transverse tubule is called a triad.
 Calcium ions are stored in the terminal cisternae of
the sarcoplasmic reticulum. A muscle contraction
begins when stored calcium ions are released into
the sarcoplasm. These ions then diffuse into
individual contractile units called sarcomeres.
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Skeletal Muscle Fibers
Figure 10–3 The Structure of a Skeletal Muscle Fiber.
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcomeres
 The contractile units of muscle
 Structural units of myofibrils
 Form visible patterns within myofibrils
 Muscle striations
 A striped or striated pattern within myofibrils:
– alternating dark, thick filaments (A bands) and light, thin
filaments (I bands)
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcomeres
 A Bands
 Contains the thick filaments and portions of the thin filaments
 Contain three subdivisions:
– M line
» Central portion of each thick filament, is connected to its
neighbor by proteins of the M line.
» They help stabilize the positions of the thick filaments
– H zone
» Found in a resting sarcomere (not contracting)
» Lighter region on either side of the M line
» Contains thick filaments but no thin filaments
– Zone of Overlap
» Thin filaments are situated between the thick filaments
» Where triads are found
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcomeres
 I Bands
 Contains thin filaments but no thick filaments
 Extends from the A band of one sarcomere to the A band
of the next sarcomere
 Contains the Z line
– which interconnect thin filaments of adjacent sarcomeres.
– Z line to Z line = sarcomere
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Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcomeres
 Titin:
– are strands of protein
– reach from tips of thick filaments to the Z line
– stabilize the filaments
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Skeletal Muscle Fibers
Figure 10–4a Sarcomere Structure.
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Skeletal Muscle Fibers
Figure 10–4b Sarcomere Structure.
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Skeletal Muscle Fibers
Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.
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Skeletal Muscle Fibers
Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.
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Skeletal Muscle Fibers
 Four Thin Filament Proteins
1. F actin
 A twisted strand composed of two rows of 300-400
individual globular molecules of G actin.
 2. Nebulin
 Found in the cleft between the rows of G actin
molecules
 Holds the F actin strand together
 Each G actin contains an active site that can bind to
myosin
 Under resting conditions, myosin binding is
prevented by the troponin-tropomyosin complex
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Skeletal Muscle Fibers
 Four Thin Filament Proteins
3. Tropomyosin
 Cover the active sites on the G actin and prevent actin-myosin
interaction
 Double stranded protein
 It is bound to one molecule of troponin midway along its length
4. Troponin
 Consists of three globular subunits
 One subunit binds to tropomyosin, locking them together in the
troponin-tropomyosin complex
 A second subunit binds to one G actin, holding the complex in
place
 The third subunit has a receptor that binds a calcium ion. This site
is empty in a resting muscle.
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Skeletal Muscle Fibers
Figure 10–7a, b Thick and Thin Filaments.
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Skeletal Muscle Fibers
 Initiating Contraction
 Ca2+ binds to receptor on troponin molecule
 Troponin–tropomyosin complex changes
 Exposes active site of F-actin
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Skeletal Muscle Fibers
 Thick Filaments
 Contain twisted myosin subunits
 Contain titin strands that recoil after
stretching
 The mysosin molecule
 Tail:
– binds to other myosin molecules
 Head:
– made of two globular protein subunits
– reaches the nearest thin filament
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Skeletal Muscle Fibers
Figure 10–7c, d Thick and Thin Filaments.
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Skeletal Muscle Fibers
 Myosin Action
 During contraction, myosin heads
 Interact with actin filaments, forming crossbridges
 Pivot, producing motion
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Skeletal Muscle Fibers
 Skeletal Muscle Contraction
 Sliding filament theory
 Thin filaments of sarcomere slide toward M line,
alongside thick filaments
 The width of A zone stays the same
 Z lines move closer together
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Skeletal Muscle Fibers
Figure 10–8a Changes in the Appearance of a Sarcomere during the
Contraction of a Skeletal Muscle Fiber.
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Skeletal Muscle Fibers
Figure 10–8b Changes in the Appearance of a Sarcomere during the
Contraction of a Skeletal Muscle Fiber.
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Skeletal Muscle Fibers
 When a skeletal muscle fiber contracts the
following happens:




the H zones and I bands get smaller
the zones of overlap get larger
the Z lines move closer together
the width of the A bands remains constant
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The Neuromuscular Junction
 Is the location of neural stimulation
 Action potential (electrical signal)
 Travels along nerve axon
 Ends at synaptic terminal
 Synaptic terminal:
– releases neurotransmitter (acetylcholine or
ACh)
– into the synaptic cleft (gap between synaptic
terminal and motor end plate)
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The Neuromuscular Junction
Figure 10–10a, b Skeletal Muscle Innervation.
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The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.
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The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.
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The Neuromuscular Junction
 The Neurotransmitter
 Acetylcholine or ACh
 Travels across the synaptic cleft
 Binds to membrane receptors on sarcolemma
(motor end plate)
 Causes sodium–ion rush into sarcoplasm
 Is quickly broken down by enzyme
(acetylcholinesterase or AChE)
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The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.
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The Neuromuscular Junction
 Action Potential
 Generated by increase in sodium ions in
sarcolemma
 Travels along the T tubules
 Leads to excitation–contraction coupling
 Excitation–contraction coupling:
– action potential reaches a triad:
» releasing Ca2+
» triggering contraction
– requires myosin heads to be in “cocked” position:
» loaded by ATP energy
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The Contraction Cycle
 Five Steps of the Contraction Cycle
 Exposure of active sites
 Formation of cross-bridges
 Pivoting of myosin heads
 Detachment of cross-bridges
 Reactivation of myosin
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The Contraction Cycle
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The Contraction Cycle
Step One: Once the action
potential reaches the triad
Calcium is released from
the cisternae of the
sarcoplasmic reticulum
and binds to the troponin.
The troponin molecule
changes position, pulling
the tropomyosin molecule
away from the active sites
on actin and allowing
interaction with the
energized myosin heads.
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The Contraction Cycle
Step Two: When
the active sites
are exposed,
the energized
myosin heads
bind to them,
forming crossbridges.
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The Contraction Cycle
Step Three: At rest, the
myosin head points
away from the M line.
When the cross-bridge
forms the myosin
head pivots toward the
M line. This is called
the power stroke.
Once the head pivots,
the ADP + P are
released.
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The Contraction Cycle
 Step Four: When another
ATP binds to the myosin
head, the link between the
active site on the actin
molecule and the myosin
head is broken. The active
site is now exposed and able
to form another cross-bridge.
 Cocking the myosin head
requires energy, which is
obtained by breaking down
ATP into ADP + P.
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The Contraction Cycle
Step Five: Myosin
reactivation occurs
when the free myosin
head splits the ATP
into ADP and a
phosphate group.
The energy released
in this process is
used to recock the
myosin head.
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The Contraction Cycle
 Fiber Shortening
 As sarcomeres shorten, muscle pulls together,
producing tension
 Contraction Duration
 Depends on
 Duration of neural stimulus
 Number of free calcium ions in sarcoplasm
 Availability of ATP
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The Contraction Cycle
Figure 10–13 Shortening during a Contraction.
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The Contraction Cycle
 Relaxation – Steps to end a contraction
 Step One: Action potential generation ceases as ACh is
broken down by AChE.
 Step Two: The sarcoplasmic reticulum reabsorbs calcium
ions
 Step Three: When calcium concentrations approach
normal resting levels
 calcium ions detach from the troponin
 troponin-tropomyosin complex returns to its normal position.
 tropomyosin re-covers the active sites and prevents further crossbridge interaction.
 Step Four: Without cross-bridge interactions, further
sliding cannot take place, and the contraction ends.
 Step Five: Muscle relaxation occurs, and the muscle
returns passively to its resting length.
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The Contraction Cycle
 Rigor Mortis
 A fixed muscular contraction after death
 Caused when
 Ion pumps cease to function; ran out of ATP
 Calcium builds up in the sarcoplasm
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Tension Production
 The all–or–none principle
 As a whole, a muscle fiber is either contracted or
relaxed
 Tension of a Single Muscle Fiber
 Depends on
 The number of pivoting cross-bridges
 The fiber’s resting length at the time of stimulation
 The frequency of stimulation
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Tension Production
 Tension of a Single Muscle Fiber
 Length–tension relationship
 Number of pivoting cross-bridges depends on:
– amount of overlap between thick and thin fibers
 Optimum overlap produces greatest amount of tension:
– too much or too little reduces efficiency
 Normal resting sarcomere length:
– is 75% to 130% of optimal length
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Tension Production
Figure 10–14 The Effect of Sarcomere Length on Active Tension.
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Tension Production
 Tension of a Single Muscle Fiber
 Frequency of stimulation
 A single neural stimulation produces:
– a single contraction or twitch
– which lasts about 7–100 msec.
 Sustained muscular contractions:
– require many repeated stimuli
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Tension Production
 Three Phases of Twitch
 Latent period before contraction
 Begins at stimulation and lasts about 2msec
 Action potential sweeps across the sarcolemma, and
sarcoplasmic reticulum releases calcium ions
 No tension produced because the contraction cycle has not begun
 Contraction phase
 Tension rises to a peak
 As tension rises, calcium ions are binding to troponin, active sites
are exposed, and cross-bridge interactions are occurring.
 Relaxation phase
 Calcium levels fall
 Active sites are covered by tropomyosin, and the number of active
cross-bridges declines
 Tension levels fall to resting levels
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Tension Production
Figure 10–15 The Development of Tension in a Twitch.
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Tension Production
 Treppe
 A stair-step increase in twitch tension
 Repeated stimulations immediately after relaxation
phase
 Stimulus frequency <50/second
 Causes a series of contractions with increasing
tension
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Tension Production
 Tension of a Single Muscle Fiber
 Wave summation
 Increasing tension or summation of twitches
 Repeated stimulations before the end of relaxation
phase:
– stimulus frequency >50/second
 Causes increasing tension or summation of
twitches
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Tension Production
 Tension of a Single Muscle Fiber
 Incomplete tetanus
 Twitches reach maximum tension
 If rapid stimulation continues and muscle is not
allowed to relax completely, twitches reach
maximum level of tension
 Complete Tetanus
 If stimulation frequency is high enough, muscle
never begins to relax, and is in continuous
contraction
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Tension Production
Figure 10–16 Effects of Repeated Stimulations.
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Tension Production
Figure 10–16 Effects of Repeated Stimulations.
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Tension Production
 Tension Produced by Whole Skeletal
Muscles
 Depends on
 Internal tension produced by muscle fibers
 External tension exerted by muscle fibers on
elastic extracellular fibers
 Total number of muscle fibers stimulated
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Tension Production
 Tension Produced by Whole Skeletal Muscles
 Motor units in a skeletal muscle
 Contain hundreds of muscle fibers
 That contract at the same time
 Controlled by a single motor neuron
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Tension Production
Motor Unit
 All the muscle fibers controlled by a single
motor neuron
 The size of the motor unit is an indication of
how fine the control of movement can be.
– The less motor fibers controlled by a neuron the
more precise movement is. (ex. Eye)
– The more motor fibers controlled by a neuron the
less precise movement is. (ex. Leg muscles)
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Tension Production
 Recruitment
 The smooth, but steady, increase in muscular
tension produced by increasing the number of
active motor units
 Movement begins by activating muscle fibers that
contract relatively slowly. As the movement
continues, larger motor units containing faster and
more powerful muscle fibers are activated, and
tension rises steeply.
 This results in smooth motion
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Tension Production
 Tension Produced by Whole Skeletal Muscles
 Sustained tension
 Less than maximum tension
 Allows motor units rest in rotation
 Muscle tone
 The normal tension and firmness of a muscle at rest
 Muscle units actively maintain body position, without motion
 Increasing muscle tone increases metabolic energy used,
even at rest
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Tension Production
 Two Types of Skeletal Muscle Contraction
 Isotonic Contraction
 Skeletal muscle changes length:
– resulting in motion (walking, lifting, etc)
 If muscle tension > load (resistance):
– muscle shortens (concentric contraction)
 If muscle tension < load (resistance):
– muscle lengthens (eccentric contraction)
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Tension Production
 Two Types of Skeletal Muscle Tension
 Isometric contraction
 Skeletal muscle develops tension, but is prevented
from changing length
Note: iso- = same, metric = measure
 Carrying groceries, holding a baby, holding our
heads up
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Tension Production
 Opposing Muscle Contractions
 Reverse the direction of the original motion
 Are the work of opposing skeletal muscle pairs
 Gravity
 Can take the place of opposing muscle contraction to
return a muscle to its resting state
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ATP and Muscle Contraction
 Sustained muscle contraction uses a lot of
ATP energy
 Muscles store enough energy to start
contraction
 Muscle fibers must manufacture more ATP
as needed
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ATP and Muscle Contraction
 ATP and CP Reserves
 Adenosine triphosphate (ATP)
 The active energy molecule
 Creatine phosphate (CP)
 The storage molecule for excess ATP energy in resting
muscle
 Energy recharges ADP to ATP
 Using the enzyme creatine phosphokinase (CPK or
CK)
 When CP is used up, other mechanisms generate
ATP
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ATP and Muscle Contraction
 ATP Generation
 Cells produce ATP in two ways
 Aerobic metabolism of fatty acids in the
mitochondria
 Anaerobic glycolysis in the cytoplasm
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ATP and Muscle Contraction
 ATP Generation
 Aerobic metabolism
 Is the primary energy source of resting muscles
 Breaks down fatty acids to make ATP
 Produces 34 ATP molecules per glucose molecule
 Anaerobic glycolysis
 Is the primary energy source for peak muscular activity
 Produces two ATP molecules per molecule of glucose
 Breaks down glucose from glycogen stored in skeletal
muscles
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ATP and Muscle Contraction
 Energy Use and Muscle Activity
 At peak exertion
 Muscles lack oxygen to support mitochondria
 Muscles rely on glycolysis for ATP
 Pyruvic acid builds up, is converted to lactic acid
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ATP and Muscle Contraction
 Muscle Fatigue
 When muscles can no longer perform a required
activity, they are fatigued
 Results of Muscle Fatigue
 Depletion of metabolic reserves
 Damage to sarcolemma and sarcoplasmic reticulum
 Low pH (lactic acid)
 Muscle exhaustion and pain
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ATP and Muscle Contraction
 The Recovery Period
 The time required after exertion for muscles to
return to normal
 Oxygen becomes available
 Mitochondrial activity resumes
 Lactic acid converted back into pyruvic acid
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ATP and Muscle Contraction
 The Cori Cycle
 The removal and recycling of lactic acid by the liver
 Liver converts lactic acid to pyruvic acid
 Glucose is released to recharge muscle glycogen
reserves
 Oxygen Debt
 After exercise or other exertion
 The body needs more oxygen than usual to normalize
metabolic activities
 Resulting in heavy breathing
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Muscle Fiber Types
 Three Types of Skeletal Muscle Fibers
 Fast fibers
 Slow fibers
 Intermediate fibers
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Muscle Fiber Types
 Three Types of Skeletal Muscle Fibers
 Fast fibers
 Contract very quickly
 Have large diameter, large glycogen reserves, few
mitochondria
 Have strong contractions, fatigue quickly
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Muscle Fiber Types
 Three Types of Skeletal Muscle Fibers
 Slow fibers
 Are slow to contract, slow to fatigue
 Have small diameter, more mitochondria
 Have high oxygen supply
 Contain myoglobin (red pigment, binds oxygen)
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Muscle Fiber Types
 Three Types of Skeletal Muscle Fibers
 Intermediate fibers
 Are mid-sized
 Have low myoglobin
 Have more capillaries than fast fibers, slower to
fatigue
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Muscle Fiber Types
 Muscles and Fiber Types
 White muscle
 Mostly fast fibers
 Pale (e.g., chicken breast)
 Red muscle
 Mostly slow fibers
 Dark (e.g., chicken legs)
 Most human muscles
 Mixed fibers
 Pink
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Muscle Fiber Types
 Muscle Hypertrophy
 Muscle growth from heavy training
 Increases diameter of muscle fibers
 Increases number of myofibrils
 Increases mitochondria, glycogen reserves
 Muscle Atrophy
 Lack of muscle activity
 Reduces muscle size, tone, and power
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Muscle Fiber Types
 Physical Conditioning
 Improves both power and endurance
 Anaerobic activities (e.g., 50-meter dash,
weightlifting):
– use fast fibers
– fatigue quickly with strenuous activity
 Improved by:
– frequent, brief, intensive workouts
– hypertrophy
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Muscle Fiber Types
 Physical Conditioning
 Improves both power and endurance
 Aerobic activities (prolonged activity):
– supported by mitochondria
– require oxygen and nutrients
 Improved by:
– repetitive training (neural responses)
– cardiovascular training
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Muscle Fiber Types
 What you don’t use, you lose
 Muscle tone indicates base activity in motor
units of skeletal muscles
 Muscles become flaccid when inactive for days
or weeks
 Muscle fibers break down proteins, become
smaller and weaker
 With prolonged inactivity, fibrous tissue may
replace muscle fibers
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Cardiac Muscle Tissue
 Structure of Cardiac Tissue
 Cardiac muscle is striated, found only in
the heart
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Cardiac Muscle Tissue
 Seven Characteristics of Cardiocytes
 Unlike skeletal muscle, cardiac muscle cells
(cardiocytes)
 Are small
 Have a single nucleus
 Have short, wide T tubules
 Have no triads
 Have SR with no terminal cisternae
 Are aerobic (high in myoglobin, mitochondria)
 Have intercalated discs
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Cardiac Muscle Tissue
 Intercalated Discs
 Are specialized contact points between
cardiocytes
 Join cell membranes of adjacent cardiocytes
(gap junctions, desmosomes)
 Functions of intercalated discs
 Maintain structure
 Enhance molecular and electrical connections
 Conduct action potentials
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Cardiac Muscle Tissue
Figure 10–22 Cardiac Muscle Tissue.
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Cardiac Muscle Tissue
Figure 10–22a Cardiac Muscle Tissue.
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Cardiac Muscle Tissue
Figure 10–22c Cardiac Muscle Tissue.
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Cardiac Muscle Tissue
 Intercalated Discs
 Coordination of cardiocytes
 Because intercalated discs link heart cells
mechanically, chemically, and electrically, the heart
functions like a single, fused mass of cells
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Cardiac Muscle Tissue
 Four Functions of Cardiac Tissue
 Automaticity
 Contraction without neural stimulation
 Controlled by pacemaker cells
 Variable contraction tension
 Controlled by nervous system
 Extended contraction time
 Ten times as long as skeletal muscle
 Prevention of wave summation and tetanic
contractions by cell membranes
 Long refractory period
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Smooth Muscle Tissue
 Smooth Muscle in Body Systems
 Forms around other tissues
 In blood vessels
 Regulates blood pressure and flow
 In reproductive and glandular systems
 Produces movements
 In digestive and urinary systems
 Forms sphincters
 Produces contractions
 In integumentary system
 Arrector pili muscles cause “goose bumps”
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Smooth Muscle Tissue
 Structure of Smooth Muscle
 Nonstriated tissue
 Different internal organization of actin and
myosin
 Different functional characteristics
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Smooth Muscle Tissue
Figure 10–23a Smooth Muscle Tissue.
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Smooth Muscle Tissue
Figure 10–23b Smooth Muscle Tissue.
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Smooth Muscle Tissue
 Eight Characteristics of Smooth Muscle Cells
 Long, slender, and spindle shaped
 Have a single, central nucleus
 Have no T tubules, myofibrils, or sarcomeres
 Have no tendons or aponeuroses
 Have scattered myosin fibers
 Myosin fibers have more heads per thick filament
 Have thin filaments attached to dense bodies
 Dense bodies transmit contractions from cell to cell
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Smooth Muscle Tissue
 Functional Characteristics of Smooth
Muscle
 Excitation–contraction coupling
 Length–tension relationships
 Control of contractions
 Smooth muscle tone
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Smooth Muscle Tissue
 Functional Characteristics of Smooth Muscle
 Excitation–contraction coupling
 Free Ca2+ in cytoplasm triggers contraction
 Ca2+ binds with calmodulin (a calcium binding protein):
– in the sarcoplasm
– activates myosin light–chain kinase
» enables the attachment of myosin heads to actin
 Enzyme breaks down ATP, initiates contraction
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Smooth Muscle Tissue
 Functional Characteristics of Smooth
Muscle
 Length–Tension Relationships
 Thick and thin filaments are scattered
 Resting length not related to tension development
 Functions over a wide range of lengths (plasticity)
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Smooth Muscle Tissue
 Functional Characteristics of Smooth Muscle
 Control of contractions
 Multiunit smooth muscle cells:
– connected to motor neurons
 Visceral smooth muscle cells:
– not connected to motor neurons
– rhythmic cycles of activity controlled by pacesetter cells
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Smooth Muscle Tissue
 Functional Characteristics of Smooth
Muscle
 Smooth muscle tone
 Maintains normal levels of activity
 Modified by neural, hormonal, or chemical factors
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