Download Chapter 17 Autonomic Nervous System

Chapter 9 Muscle Tissue
Lab exam next Thurs. 2/12
CPR practice, essay entry complete this
morning, remainder due next Tuesday
Knee dissection Tuesday2/5
Objectives
 Discuss organization and functions of muscle as an organ
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including all tissue types
Describe the structural modifications of muscle cells and their
functional significance
Describe the neuromuscular junction and events
Discuss the sliding filament theory
Describe a motor unit and neural control of muscle
Explain the link between anatomy & physiology exemplified in
the length/tension curve
Compare and contrast the three types of skeletal muscle
cells and relate these to muscular performance
Compare and contrast the three types of muscle tissue
Discuss developmental Human
changes
of muscle
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Apply knowledge of levers to human skeletal muscles(if time)
Muscle Function
1. Movement – including moving substances
within body
•
Contract against resistance
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Skeletal move against bone
Cardiac move against fluid – blood
Smooth move against other contents
2. Muscles also maintain posture & stabilize joints
3. Regulate organ volume
4. Generate heat
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Functional Characteristics of Muscle
Tissue
 Contractility – the ability to shorten forcibly is the
unique feature of muscle
 Excitability, or irritability – the ability to receive
and respond to stimuli, have action potentials like
neurons
 Extensibility – the ability to be stretched or
extended
 Elasticity – the ability to recoil and resume the
original resting length
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Nerve
Epimysium
Muscle fascicle
Endomysium
Perimysium
Muscle fibers
Blood vessels
SKELETAL MUSCLE
(organ)
Perimysium
Muscle fiber
Endomysium
Epimysium
Blood vessels
and nerves
MUSCLE FASCICLE
(bundle of cells)
Capillary
Endomysium
Mitochondria
Endomysium Sarcolemma
Myosatellite
cell
Tendon
Myofibril
Perimysium
Axon
Sarcoplasm
Nucleus
MUSCLE FIBER
(cell)
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Human Anatomy
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Skeletal Muscle Organs
 Organs include muscle tissue,
blood vessels, nerve fibers, and
connective tissue
 The three connective tissue
wrappings are:
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Epimysium – an overcoat of
dense regular CT that
surrounds the entire muscle
Perimysium – fibrous CT that
surrounds groups of muscle
fibers called fascicles
Endomysium – fine sheath of
CT composed of reticular fibers
surrounding each muscle fiber
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Skeletal Muscle: Nerve and Blood
Supply
 Each muscle is served by at least one nerve,
artery, and vein
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Each skeletal muscle fiber is supplied with a
nerve ending that controls contraction – a
neuromuscular junction
Contracting fibers require continuous delivery of
oxygen and nutrients via arteries
Wastes must be removed via veins
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Skeletal Muscle: Attachments
 Muscles span joints and are attached in at least
two places
 When muscles contract the movable bone, the
muscle’s insertion moves toward the immovable
bone – the muscle’s origin (i.e., origin is
stationary— flawed concept, but customary)
 Muscles attach:
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Directly – epimysium of the muscle is fused to the
periosteum of a bone
Indirectly (more common) – CT wrappings extend
beyond the muscle as ropelike tendon or sheetlike
aponeurosis
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Microscopic Anatomy of a Skeletal
Muscle Fiber
 Each fiber is a long, cylindrical cell with multiple
nuclei just beneath the sarcolemma
 Fibers are 10 to 100 m in diameter, and up to
hundreds of centimeters long
 Each cell is a syncytium produced by fusion of
myoblasts (embryonic cells)
 Sarcoplasm has a unique oxygen-binding protein
called myoglobin
 Fibers contain the usual organelles plus
myofibrils, sarcoplasmic reticulum, and T tubules
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Myoblasts
Syncytium
Note
satellite
cells
Muscle Cell
Formation
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Sarcoplasmic Reticulum (SR)
 SR is an elaborate smooth endoplasmic reticulum that mostly runs
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longitudinally and surrounds each myofibril
Paired terminal cisternae form perpendicular cross channels
Functions in the regulation of intracellular calcium levels
Elongated tubes called T tubules penetrate into the cell’s interior at
each A band–I band junction
T tubules associate with the paired terminal cisternae to form triads
Mitochondria
Terminal cisterna
Sarcolemma
Sarcolemma
Sarcoplasm
Myofibril
Myofibrils
Thin filament
Thick filament
Internal organization of a muscle fiber.
Note the relationships among myofibrils,
sarcoplasmic reticulum, mitochondria,
triads, and thick and thin filaments.
Triad Sarcoplasmic T tubules
reticulum
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T Tubules
 T tubules are continuous with the sarcolemma
 They conduct impulses to the deepest regions
of the muscle
 These impulses signal for the release of Ca2+
from adjacent terminal cisternae
Mitochondria
Terminal cisterna
Sarcolemma
Sarcolemma
Sarcoplasm
Myofibril
Myofibrils
Thin filament
Thick filament
Internal organization of a muscle fiber.
Note the relationships among myofibrils,
sarcoplasmic reticulum, mitochondria,
triads, and thick and thin filaments.
Triad Sarcoplasmic T tubules
reticulum
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Myofibrils
 Myofibrils are densely packed, rodlike contractile
elements
 They make up most of the muscle volume
 The arrangement of myofibrils within a fiber is
such that a perfectly aligned repeating series of
dark A bands and light I bands is evident
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Figure 9.2b
Sarcomeres
 The smallest contractile unit of a muscle
 The region of a myofibril between two successive
Z discs
 Composed of myofilaments made up of contractile
proteins
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Myofilaments are of two major types – thick and
thin
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Myofilaments: Banding Pattern
 Thick filaments – extend the entire length of
an A band
 Thin filaments – extend across the I band and
partway into the A band
 Z-disc – coin-shaped sheet of proteins
(connectins) that anchors the thin filaments
and connects myofibrils to one another
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Myofilaments: Banding Pattern
 Thin filaments do not overlap thick filaments in
the lighter H zone
 M lines appear darker due to the presence of the
protein desmin
 Elastic filaments of protein titin
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Ultrastructure of Myofilaments:Thick
Filaments
 Each myosin molecule
has a rodlike tail and
two globular heads
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Sarcomere
H band
Myofibril
Z line
M line
Titin
The structure of
M line
thick filaments
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Myosin
head
Myosin tail
Hinge
Tails – two
interwoven, heavy
polypeptide chains
Heads – two smaller,
light polypeptide
chains called cross
bridges
A single myosin molecule detailing the structure and
movement of the myosin head after cross-bridge
binding occurs
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Figure 9.3a, b
Ultrastructure of Myofilaments:Thick
Filaments
 Thick filaments are
composed of the protein
myosin
 Myosin heads contain:
 2 smaller, light
polypeptide chains
that act as cross
bridges during
contraction
 Binding sites for actin
of thin filaments
 Binding sites for ATP
 ATPase enzymes
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Ultrastructure of Myofilaments: Thin
Filaments
 Thin filaments are chiefly composed of protein actin
 Each actin molecule is a helical polymer of globular
subunits called G actin
 The subunits contain the active sites to which myosin
heads attach during contraction
 Tropomyosin (filamentous protein) and troponin are
regulatory subunits bound to actin
Actinin
Sarcomere
H band
The attachment
of thin filaments
to the Active
Z line
Troponin
site
Nebulin
Z line Titin
G actin
Tropomyosin molecules
F actin
strand
Myofibril
Human Anatomy Spring 2012 The detailed structure of a thin filament showing
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M line
the organization of G actin, troponin, and
tropomyosin
Arrangement of Filaments in a
Sarcomere
 Longitudinal section within one sarcomere
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Figure 9.3d
Sliding Filament Mechanism of Contraction
 Thin filaments slide past the thick ones so that the
actin and myosin filaments overlap to a greater
degree
 In the relaxed state, thin and thick filaments
overlap only slightly
 Upon stimulation, myosin heads bind to actin and
sliding begins (interactive physiology page 17)
 Each myosin head binds and detaches several
times during contraction, acting like a ratchet to
generate tension and propel the thin filaments to
the center of the sarcomere
 As this event occurs throughout the sarcomeres,
the muscle shortens
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The Sliding Filament Theory
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Figure 9.7 Changes in a Sarcomere
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Sarcomere Structure
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Figure 9.4b Sarcomere Structure
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Regulation of Contraction
 In order to contract, a skeletal muscle must:
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Be stimulated by a nerve ending (NMJ)
Propagate an electrical current, or action potential,
along its sarcolemma (T-tubules)
Have a rise in intracellular Ca2+ levels, the final
trigger for contraction (SR)
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Nerve Stimulus of Skeletal Muscle
 Skeletal muscles are stimulated by motor
neurons of the somatic nervous system
 Axons of these neurons travel in nerves to
muscle cells
 Axons of motor neurons branch profusely as they
enter muscles
 Each axonal branch forms a neuromuscular
junction with a single muscle fiber
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Neuromuscular Junction
 The neuromuscular junction is:
Motor
neuron
Axonal endings, which have small
Path of action
potential
membranous sacs (synaptic vesicles)
Axon
Neuromuscular
that contain the neurotransmitter
synapse
acetylcholine (ACh)
 The motor end plate of a muscle, which
is a specific part of the sarcolemma
Motor
Myofibril
that contains ACh receptors that helps
end plate
form the neuromuscular junction
 Though exceedingly close, axonal ends
and muscle fibers are always separated
by a space called the synaptic cleft
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Neuromuscular Junction
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Figure 9.8a, b
Neuromuscular Junction
 When a nerve impulse reaches the end of an
axon at the neuromuscular junction:
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Voltage-regulated calcium channels open and
allow Ca2+ to enter the axon
Ca2+ inside the axon terminal causes axonal
vesicles to fuse with the axonal membrane
This fusion releases ACh into the synaptic cleft via
exocytosis
ACh diffuses across the synaptic cleft to ACh
receptors on the sarcolemma
Binding of ACh to its receptors initiates an action
potential in the muscle
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Neuromuscular Junction
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Figure 9.8c
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Summary
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Excitation-Contraction Coupling
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Motor Unit: The Nerve-Muscle
Functional Unit
 A motor unit is a motor
neuron and all the
muscle fibers it supplies
 The number of muscle
fibers per motor unit
can vary from four to
several hundred
 Muscles that control
fine movements
(fingers, eyes) have
small motor units
Spinal cord
Axon terminals at
neuromuscular junctions
Motor Motor
unit 1 unit 2
Nerve
Motor neuron
cell body
Motor
neuron
axon
Muscle
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Muscle
fibers
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Motor Unit: The Nerve-Muscle
Functional Unit
 Large weight-bearing
Axon terminals at
neuromuscular junctions
Spinal cord
Motor Motor
muscles (thighs, hips)
unit 1 unit 2
have large motor units
Nerve
 Muscle fibers from a
Motor neuron
cell body
Motor
motor unit are spread
neuron
axon
throughout the muscle; Muscle
therefore, contraction of
a single motor unit
causes weak contraction
of the entire muscle
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Muscle
fibers
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Neuromuscular Junction
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Muscle Tone
 Muscle tone:
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The constant, slightly contracted state of all
muscles, which does not produce active
movements
Keeps the muscles firm, healthy, and ready to
respond to stimulus
 Spinal reflexes account for muscle tone by:
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Activating one motor unit and then another
Responding to activation of stretch receptors in
muscles and tendons
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Force of Contraction
 The force of contraction is affected by:
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The number of
muscle fibers
contracting –
the more motor
fibers in a muscle,
the stronger the
contraction
The relative size
of the muscle –
the bulkier the
muscle, the
greater its strength
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Figure 9.19a
Force of Contraction
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Frequency of stimulation
Length-tension
relationships
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Series-elastic elements –
the noncontractile
structures in a muscle
Degree of muscle stretch –
muscles contract strongest
when muscle fibers are 80120% of their normal
resting length
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Figure 9.19a
Length/Tension Relationship
Sarcomeres
greatly
shortened
75%
Sarcomeres at
resting length
Sarcomeres excessively
stretched
100%
170%
Optimal sarcomere
operating length
(80%–120% of
resting length)
Maximum force generated between 80-120% of
resting length, interactive physiology page 16
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Think of cross-bridge mechanism for explanation
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Muscle Fiber Type: Functional
Characteristics
 Speed of contraction – determined by speed in
which ATPases split ATP
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The three types of fibers are slow and fast and
intermediate
 ATP-forming pathways
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Oxidative fibers – use aerobic pathways
Glycolytic fibers – use anaerobic glycolysis
 These two criteria define three categories – slow
oxidative fibers, fast oxidative fibers, and fast
glycolytic fibers
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Training
 Slow, oxidative respond to endurance
training. Diameter changes little.
 Fast, oxidative respond to strength and power
training. Diameter increases.
 Intermediate can take on characteristics of
fast or slow, depending on type of training.
In what birds do you expect to find FT? And ST?
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Muscle Hypertrophy
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Exercise causes:
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An increase in the number of mitochondria
An increase in the activity of muscle spindles
An increase in the concentration of glycolytic enzymes
An increase in the glycogen reserves
An increase in the number of myofibrils
The net effect is an enlargement of the muscle
(hypertrophy)
Disuse causes atrophy:
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A decrease in muscle size
A decrease in muscle tone
Developmental Aspects
 Muscle tissue develops from embryonic
mesoderm called myoblasts
 Multinucleated skeletal muscles form by fusion of
myoblasts forming a syncytium
 The growth factor agrin stimulates the clustering
of ACh receptors at newly forming motor end
plates
 As muscles are brought under the control of the
somatic nervous system, the numbers of fast and
slow fibers are also determined
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Developmental Aspects
 Cardiac myoblasts do not fuse but develop
gap junctions at an early embryonic stage
 Most smooth muscle follows the same
pattern of gap junctions rather than fusion
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Developmental Aspects:
After Birth
 Muscular development reflects
neuromuscular coordination
 Development occurs head-to-toe, and
proximal-to-distal
 Peak natural neural control of muscles is
achieved by midadolescence
 Athletics and training can improve
neuromuscular control
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Developmental Aspects:
Male and Female
 There is a biological basis for greater strength in
men than in women
 Women’s skeletal muscle makes up 36% of their
body mass
 Men’s skeletal muscle makes up 42% of their
body mass
 These differences are due primarily to the male
sex hormone testosterone
 With more muscle mass, men are generally
stronger than women
 Body strength per unit muscle mass, however, is
the same
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Homeostatic Imbalance:
Age Related
 With age, connective tissue increases and
myofibrils, glycogen and myoglobin decrease
 Muscles become stringier and more sinewy
 By age 80, 50% of muscle mass is lost
(sarcopenia), and myosatellite cells decrease
 Regular exercise reverses sarcopenia
 Aging of the cardiovascular system affects every
organ in the body
 Atherosclerosis may block distal arteries, leading
to intermittent claudication and causing severe
pain in leg muscles
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Developmental Aspects:
Regeneration
 Cardiac and skeletal muscle become
amitotic, but can lengthen and thicken
(hypertrophy)
 Myoblastlike satellite cells of skeletal
muscle show very limited regenerative
ability (Cardiac tissue lacks satellite cells)
 Smooth muscle has good regenerative
ability (hyperplasia)
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Levers
 F1L1 = F2L2
 Mass=Force L=length
 There are several ways to increase the force
efficiency of a lever:
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increasing the length of the in-lever arm
decreasing the length of the out-lever
or doing both of the above
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See-saw
Wheelbarrow
Less distance
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Hotdog tongs
most common, least
mechanical
advantage, more
force, more
speed/distance
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The Arm is a Lever and Fulcrum
System
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Figure 12-21b
The Lever-Fulcrum System Amplifies
the Load Distance Traveled and the
Speed of Movement
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Figure 12-22
Smooth Muscle
 Composed of
spindle-shaped
fibers diameter of
2-10 m and
lengths of several
hundred m
 Lack the coarse
CT sheaths of
skeletal muscle,
but have fine
endomysium
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Figure 9.23
Smooth Muscle
 Are generally
organized into two
layers (longitudinal
and circular) of
closely apposed
fibers
 Found in walls of
hollow organs
(except the heart)
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Figure 9.23
Innervation of Smooth Muscle
 Most smooth muscle lacks neuromuscular
junctions
 Innervating nerves have bulbous swellings
called varicosities
 Varicosities release neurotransmitters into
wide synaptic clefts called diffuse junctions
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Microscopic Anatomy
of Smooth Muscle
 SR is less developed than in skeletal muscle and
lacks a specific pattern (no cisterns)
 T tubules are absent
 Plasma membranes have pouchlike infoldings
called caveoli
 Ca2+ is sequestered in the extracellular space
near the caveoli, allowing rapid influx when
channels are opened
 There are no visible striations and no sarcomeres
 Thin and thick filaments are present
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Proportion and Organization of
Myofilaments in Smooth Muscle
 Ratio of thick to
thin filaments
(1:2) is much
lower than in
skeletal (1:6) or
cardiac (1:4)
 Thick filaments
have heads along
their entire length
 There is no
troponin complex
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Figure 9.25
Proportion and Organization of
Myofilaments in Smooth Muscle
 Thick and thin
filaments are
arranged
diagonally,
causing smooth
muscle to contract
in a corkscrew
manner
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Figure 9.25
Proportion and Organization of
Myofilaments in Smooth Muscle
 Noncontractile
intermediate
filament bundles
attach to dense
bodies
(analogous to Z
discs) at regular
intervals
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Figure 9.25
Contraction of Smooth Muscle
 Whole sheets of smooth muscle exhibit slow,
synchronized contraction
 They contract in unison, reflecting their electrical
coupling with gap junctions
 Action potentials are transmitted from cell to cell
 Some smooth muscle cells:
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Act as pacemakers and set the contractile pace for
whole sheets of muscle
Are self-excitatory and depolarize without external
stimuli
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Contractile Mechanism
 Actin and myosin interact according to the sliding
filament mechanism
 The final trigger for contractions is a rise in
intracellular Ca2+
 Ca2+ is released from the SR and from the
extracellular space
 Ca2+ interacts with calmodulin and myosin light
chain kinase to activate myosin
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Special Features of Smooth
Muscle Contraction
 Unique characteristics of smooth muscle
include:
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Smooth muscle tone
Slow, prolonged contractile activity
Low energy requirements
Response to stretch
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Response to Stretch
 Smooth muscles exhibits a phenomenon called
stress-relaxation response in which:
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Smooth muscle responds to stretch only briefly,
and then adapts to its new length
The new length, however, retains its ability to
contract
This enables organs such as the stomach and
bladder to temporarily store
contents
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Types of Smooth Muscle: Single Unit
 The cells of single unit smooth muscle, commonly
called visceral muscle:
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Contract rhythmically as a unit
Are electrically coupled to one another via gap
junctions
Often exhibit spontaneous action potentials
Are arranged in opposing sheets and exhibit
stress-relaxation response
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Types of Smooth Muscle: Multiunit
 Multiunit smooth muscles are found:
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In large airways to the lungs
In large arteries
In arrector pili muscles
In the internal eye muscles
 Characteristics include:

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Rare gap junctions
Infrequent spontaneous depolarizations
Structurally independent muscle fibers
A rich nerve supply, which, with a number of muscle
fibers, forms motor units
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Graded contractions in response to neural stimuli
Muscle Comparison Summary
Table 12-3