Download Muscular System PPT

Muscles Part I
H. Biology II
Adapted 2014-2015
• Overview of Muscular Tissue
• Skeletal Muscle Tissue
• Contraction and Relaxation of Skeletal Muscle Fibers
• Muscle Metabolism
• Control of Muscle Tension
• Types of Skeletal Muscle Fibers
• Exercise and Skeletal Muscle Tissue
• Cardiac Muscle Tissue
• Smooth Muscle Tissue
• Regeneration of Muscle Tissue
• Development of Muscle
• Aging and Muscular Tissue
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Muscular System
Three Types of Muscle Tissues
Skeletal Muscle
Cardiac Muscle
• usually attached
to bones
• voluntary- under
conscious control
• striated
• wall of heart
• involuntary - not
under conscious
control
• striated
Smooth Muscle
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• walls of most viscera,
blood vessels, skin
• involuntary - not under
conscious control
• not striated
9-2
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Table 9.3
Special Characteristics of Muscle Tissue
• Excitability (responsiveness or
irritability): ability to receive and
respond to stimuli
• Contractility: ability to shorten
when stimulated
• Extensibility: ability to be
stretched or extended without
damage
• Elasticity: ability to recoil to
resting length (bounce back)
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Functions of a Muscle Tissue
• Movement:
• Skeletal- locomotion, vision, facial expression
• Cardiac- blood pumping
• Smooth- food digestion
• Posture: (skeletal)
• Joint Stability: (skeletal)
• Heat Generation:(skeletal)
• A. shivering to increase heat production
• B. contract muscle to provide heat
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Structure of a Skeletal Muscle
Skeletal Muscle
• organs of the muscular system
• skeletal muscle tissue
• nervous tissue
• blood
•Each muscle is served by one artery,
one nerve, and one or more veins
Connective tissues and muscle
tissue:
1.fascia – covers the muscle
2.tendon – attaches the
muscle
3.aponeuroses – muscle to
muscle
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Macroscopic Anatomy of skeletal muscles
epimysium
tendon
perimysium
Muscle Fascicle
Surrounded by
perimysium
Skeletal
muscle
Surrounded by
epimysium
endomysium
Skeletal
muscle fiber
(cell)
Surrounded by
endomysium
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Play IP Anatomy of Skeletal muscles (IP p. 4-6)
Epimysium
Bone Epimysium
Perimysium
Endomysium
Tendon
(b)
Perimysium Fascicle
(a)
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Muscle fiber
in middle of
a fascicle
Blood vessel
Fascicle
(wrapped by perimysium)
Endomysium
(between individual
muscle fibers)
Muscle fiber
Figure 9.1
Anatomy of a Skeletal Muscle
Coverings of a muscle
1. Epimysium - outer
2. Perimysium - middle
3. Endomysium - inner
Organization of Muscle
• muscle
• fascicles
• muscle fibers
• myofibrils
• thick and thin filaments
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Anatomy of a Skeletal Muscle
Coverings of a muscle
1. Epimysium – dense regular connective tissue surrounding the
entire muscle
2. Perimysium – fibrous connective tissue surrounding a fascicle
3. Endomysium – thin areolar connective tissue surrounding each
muscle cell
Organization of Muscle
• muscle
• fascicles – bundle of muscle cells
• muscle fibers – a muscle cell
• myofibrils – a long, filamentous organelle found within muscle cells that
has a banded appearance
• thick and thin filaments (myofilament)- actin &myosin filaments
• sarcomere – contractile unit of muscle
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9-4
Skeletal Muscle Tissue
• The number of skeletal muscle fibers is set before you
are born
• Most of these cells last a lifetime
• Muscle growth occurs by hypertrophy
• An enlargement of existing muscle fibers
• Testosterone and human growth hormone stimulate
hypertrophy
• Satellite cells retain the capacity to regenerate
damaged muscle fibers
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Microscopic Anatomy of Skeletal Muscle
Fiber
• sarcolemma
• sacroplasm
• sarcoplasmic reticulum
• transverse tubule
• triad
• cisterna of sarcoplasmic
reticulum
• transverse tubule
• myofibril
• actin filaments
• myosin filaments
• sarcomere
9-5
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Skeletal Muscle Tissue-Microscopic Anatomy
• Sarcolemma
• The plasma membrane of a muscle cell
• Transverse (T tubules)
• Tunnel in from the plasma membrane
• Muscle action potentials travel through the T tubules
• Sarcoplasm, the cytoplasm of a muscle fiber
• Sarcoplasm includes glycogen used for synthesis of ATP and a
red-colored protein called myoglobin which binds oxygen
molecules
• Myoglobin releases oxygen when it is needed for ATP production
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Skeletal Muscle Tissue- Microscopic Anatomy
• Myofibrils
• Thread like structures which have a contractile function
• Sarcoplasmic reticulum (SR)
• Membranous sacs which encircles each myofibril
• Stores calcium ions (Ca++)
• Release of Ca++ triggers muscle contraction
• Filaments
• Function in the contractile process
• Two types of filaments (Thick and Thin)
• There are two thin filaments for every thick filament
• Sarcomeres
• Compartments of arranged filaments
• Basic functional unit of a myofibril
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Triad Relationships
• T tubules conduct impulses deep into muscle
fiber
• Integral proteins protrude into the
intermembrane space from T tubule and SR
cisternae membranes
• T tubule proteins: voltage sensors
• SR foot proteins: gated channels that regulate
Ca2+ release from the SR cisternae
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Sarcomere
• Smallest contractile unit (functional unit) of a
muscle fiber
• The region of a myofibril between two
successive Z discs
• Composed of thick and thin myofilaments
made of contractile proteins
• Each myofibril contains 10,000 sarcomeres
end to end.
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Check for
Understanding 1:
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Check for Understanding 2:
16.
19.
20.
22.
24.
23.
21.
(inner covering)
17.
(outer covering)
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18.
(middle covering)
Microanatomy of a Muscle Fiber (Cell)
transverse
(T) tubules
sarcoplasmic
reticulum
sarcolemma
terminal
cisternae
mitochondria
myoglobin
thick myofilament
thin myofilament
myofibril
nuclei
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triad
Play IP Anatomy of Skeletal
muscles (IP p. 7)

Muscle fiber
sarcomere
Z-line
myofibril
Thin filaments
Thick filaments
Thin myofilament
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Myosin molecule of
thick myofilament
Sarcomere
• I band
• A band
• H zone
• Z line
• M line
9-6
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Skeletal Muscle Tissue
• Z discs
• Separate one sarcomere from the next
• Thick and thin filaments overlap one another
• A band
• Darker middle part of the sarcomere
• Thick and thin filaments overlap
• I band
• Lighter, contains thin filaments but no thick filaments
• Z discs passes through the center of each I band
• H zone
• Center of each A band which contains thick but no
thin filaments
• M line
• Supporting proteins that hold the thick filaments
together in the H zone
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Skeletal Muscle Tissue
• Muscle Proteins
• Myofibrils are built from
three kinds of proteins
• 1) Contractile proteins
• Generate force
during contraction
• 2) Regulatory proteins
• Switch the
contraction process
on and off
• 3) Structural proteins
• Align the thick and
thin filaments
properly
• Provide elasticity
and extensibility
• Link the myofibrils to
the sarcolemma
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Contractile Proteins
• Myosin
• Thick filaments
• Functions as a motor protein which can achieve motion
• Convert ATP to energy of motion
• Projections of each myosin molecule protrude outward (myosin head)
• Actin
• Thin filaments
• Actin molecules provide a site where a myosin head can attach
• Tropomyosin and troponin are also part of the thin filament
• In relaxed muscle
Myosin is blocked from binding to actin
Strands of tropomyosin cover the myosin-binding sites
• Calcium ion binding to troponin moves tropomyosin away from
myosin-binding sites
• Allows muscle contraction to begin as myosin binds to actin
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Structural Proteins
• Titin
• Stabilize the position of myosin
• accounts for much of the elasticity and extensibility of
myofibrils
• Dystrophin
• Links thin filaments to the sarcolemma
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The Sliding Filament Mechanism
• Myosin heads attach to and “walk” along the thin
filaments at both ends of a sarcomere
• Progressively pulling the thin filaments toward the
center of the sarcomere
• Z discs come closer together and the sarcomere
shortens
• Leading to shortening of the entire muscle
• In the relaxed state, thin and thick filaments overlap
only slightly
• During contraction, myosin heads bind to actin,
detach, and bind again, to propel the thin filaments
toward the M line
• As H zones shorten and disappear, sarcomeres
shorten, muscle cells shorten, and the whole muscle
shortens
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Sliding Filament Mechanism
When
sarcomeres
shorten, actin
and myosin
filaments slide
past one another
VIDEO#1
VIDEO #2
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Z
Z
H
A
I
I
1 Fully relaxed sarcomere of a muscle fiber
Z
I
Z
A
I
2 Fully contracted sarcomere of a muscle fiber
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Figure 9.6
Longitudinal section of filaments
within one sarcomere of a myofibril
Thick filament
Thin filament
In the center of the sarcomere, the thick
filaments lack myosin heads. Myosin heads
are present only in areas of myosin-actin overlap.
Thick filament
Thin filament
Each thick filament consists of many
A thin filament consists of two strands
myosin molecules whose heads protrude of actin subunits twisted into a helix
at opposite ends of the filament.
plus two types of regulatory proteins
(troponin and tropomyosin).
Portion of a thick filament
Portion of a thin filament
Myosin head
Tropomyosin
Troponin
Actin
Actin-binding sites
ATPbinding
site
Heads
Tail
Flexible hinge region
Myosin molecule
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Active sites
for myosin
attachment
Actin
subunits
Actin subunits
Figure 9.3
Contraction & Relaxation of Skeletal Muscle
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Microscopic Contraction Events
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Contraction & Relaxation of Skeletal Muscle
• The Contraction Cycle
• The onset of contraction begins with the SR releasing
calcium ions into the muscle cell
• Where they bind to actin opening the myosin binding
sites
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Contraction & Relaxation of Skeletal Muscle
• The contraction cycle consists of 4 steps
• 1) ATP hydrolysis
• Hydrolysis of ATP reorients and energizes the myosin head
• 2) Formation of cross-bridges
• Myosin head attaches to the myosin-binding site on actin
• 3) Power stroke
• During the power stroke the crossbridge rotates, sliding the filaments
• 4) Detachment of myosin from actin
• As the next ATP binds to the myosin head, the myosin head detaches
from actin
• The contraction cycle repeats as long as ATP is available and the
Ca++ level is sufficiently high
• Continuing cycles applies the force that shortens the sarcomere
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Cross Bridge Cycle
• Continues as long as the Ca2+ signal and adequate ATP
are present
• Cross bridge formation—high-energy myosin head
attaches to thin filament
• Working (power) stroke—myosin head pivots and pulls
thin filament toward M line
• Cross bridge detachment—ATP attaches to myosin head
and the cross bridge detaches
• “Cocking” of the myosin head—energy from hydrolysis of
ATP cocks the myosin head into the high-energy state
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Contraction & Relaxation of Skeletal Muscle
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Key:
= Ca2+
1 Myosin heads
hydrolyze ATP and
become reoriented
and energized
ADP
P
P
ATP
ATP
4 As myosin heads
bind ATP, the
crossbridges detach
from actin
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Contraction cycle continues if
ATP is available and Ca2+ level in
the sarcoplasm is high
2 Myosin heads
bind to actin,
forming
crossbridges
ADP
ADP
3 Myosin crossbridges
rotate toward center of the
sarcomere (power stroke)
Thin filament
Actin
Ca2+
Myosin
cross bridge
ADP
Pi
Thick
filament
Myosin
Cross
bridge
formation.
1
ADP
ADP
Pi
Pi
ATP
hydrolysis
2 The power (working)
stroke.
4 Cocking of myosin head.
ATP
ATP
3 Cross bridge
detachment.
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Figure 9.12
Contraction & Relaxation of Skeletal Muscle
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Role of Calcium (Ca2+) in Contraction
• At low intracellular Ca2+ concentration:
• Tropomyosin blocks the active sites on actin
• Myosin heads cannot attach to actin
• Muscle fiber relaxes
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Role of Calcium (Ca2+) in Contraction
• At higher intracellular Ca2+ concentrations:
• Ca2+ binds to troponin
• Troponin changes shape and moves
tropomyosin away from active sites
• Events of the cross bridge cycle occur
• When nervous stimulation ceases, Ca2+ is
pumped back into the SR and contraction ends
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Contraction & Relaxation of Skeletal Muscle
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Muscle Contraction
• The generation of force
• Does not necessarily cause shortening of the
fiber
• Shortening occurs when tension generated by
cross bridges on the thin filaments exceeds
forces opposing shortening
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Requirements for Skeletal Muscle
Contraction
1. Activation: neural stimulation at a
neuromuscular junction
2. Excitation-contraction coupling: (
not heavily discussed 2015)
•
Generation and propagation of an action
potential along the sarcolemma
•
Final trigger: a brief rise in intracellular Ca2+
levels
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Skeletal Muscle Contraction
?
How does a muscle contract?
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Sequence of a Muscle Contraction (Summary)
Brain
Spinal Cord
Nerve
(Action potential)
Motor Unit
Neuromuscular Junction
(Calcium is released)
Acetylcholine
(Neurotransmitter)
Contraction
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Motor Unit
• single motor neuron (a single nerve)
• one motor neuron and many skeletal muscle fibers
9-9
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Contraction & Relaxation of Skeletal Muscle
• The Neuromuscular Junction
•
Motor neurons have a threadlike axon that extends from the brain or spinal cord to
a group of muscle fibers
• Neuromuscular junction (NMJ)
•
Action potentials arise at the interface of the motor neuron and muscle fiber
• Synapse
•
Where communication occurs between a somatic motor neuron and a muscle fiber
• Synaptic cleft
•
Gap that separates the two cells
• Neurotransmitter
•
Chemical released by the initial cell communicating with the second cell
• Synaptic vesicles
•
Sacs suspended within the synaptic end bulb containing molecules of the
neurotransmitter acetylcholine (Ach)
• Motor end plate
•
The region of the muscle cell membrane opposite the synaptic end bulbs
•
Contain acetylcholine receptors
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Neuromuscular Junction
• site where a motor
nerve fiber and a
skeletal muscle fiber
meet
9-8
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Muscle Contraction
• Action potential causes
the release of Ca++ at the
NMJ.
•a neurotransmitter
releases a chemical
substance from the motor
end fiber, causing
stimulation of the muscle
fiber
•That substance is called
acetylcholine (ACh)
•ACh causes the muscle
fibers to become
stimulated and contract
(shorten).
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9-10
Contraction & Relaxation of Skeletal Muscle
• Nerve impulses elicit a muscle action potential in the
following way
• 1) Release of acetylcholine
• Nerve impulse arriving at the synaptic end bulbs causes many synaptic
vesicles to release ACh into the synaptic cleft
• 2) Activation of ACh receptors
• Binding of ACh to the receptor on the motor end plate opens an ion channel
• Allows flow of Na+ to the inside of the muscle cell
• 3) Production of muscle action potential
• The inflow of Na+ makes the inside of the muscle fiber more positively charged
triggering a muscle action potential
• The muscle action potential then propagates to the SR to release its stored
Ca++
• 4) Termination of ACh activity (Relaxation)
• Ach effects last only briefly because it is rapidly broken down by
acetylcholinesterase (AChE)
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Axon collateral of
somatic motor neuron
Axon terminal
Nerve impulse
Synaptic vesicle
containing
acetylcholine
(ACh)
Synaptic
end bulb
Sarcolemma
Axon terminal
Synaptic
end bulb
Motor
end
plate
Neuromuscular
junction (NMJ)
Synaptic cleft
(space)
Sarcolemma
Myofibril
(b) Enlarged view of the
neuromuscular junction
(a) Neuromuscular junction
1 1ACh is released
from synaptic vesicle
Synaptic end bulb
Synaptic cleft
(space)
4 ACh is broken down
2
2 ACh binds to Ach
receptor
Junctional fold
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Motor end plate
Na+
3 Muscle action
potential is produced
(c) Binding of acetylcholine to ACh receptors in the motor end plate
• Pearson NMJ
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Relaxation of a Muscle- Review
• acetylcholinesterase – an enzyme that
breaks down acetylcholine. NMJ
• muscle impulse stops
• calcium moves back into sarcoplasmic
reticulum
• myosin and actin action prevented
• muscle fiber relaxes
• Cd
9-14
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Recruitment of Motor Units
Recruitment - increase in the number of motor units
activated
• whole muscle composed of many motor units
• as intensity of stimulation or contraction increases,
recruitment of motor units continues until all motor
units are activated = all or none principle
9-22
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Applications for M. Contraction/Relaxation
• Botulinum toxin
• Blocks release of ACh from synaptic vesicles
• May be found in improperly canned foods
• A tiny amount can cause death by paralyzing
respiratory muscles
• Used as a medicine (Botox®)
• Strabismus (crossed eyes)
• Blepharospasm (uncontrollable blinking)
• Spasms of the vocal cords that interfere with
speech
• Cosmetic treatment to relax muscles that
cause facial wrinkles
• Alleviate chronic back pain due to muscle
spasms in the lumbar region
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Applications for Muscle Contraction/Relaxation
• Curare
• A plant poison used by South American
Indians on arrows and blowgun darts
• Causes muscle paralysis by blocking
ACh receptors inhibiting Na+ ion
channels
• Derivatives of curare are used during
surgery to relax skeletal muscles
• Anticholinesterase
• Slow actions of acetylcholinesterase
and removal of ACh
• Can strengthen weak muscle
contractions
• Ex: Neostigmine
• Treatment for myasthenia gravis
• Antidote for curare poisoning
• Terminate the effects of curare
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after surgery
Myasthenia Gravis
Common symptoms can
include:
A drooping eyelid
Blurred or double vision
Slurred speech
Difficulty chewing and
swallowing
Weakness in the arms and
legs
Chronic muscle fatigue
Difficulty breathing
Question ????
We now know how a muscle contracts and
relaxes, so is energy needed for that to
happen?
NO
or
YES
?
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How is energy that is stored in food
released?
Cellular Respiration
Oxygen
Glucose
H2O + CO2
Energy ATP
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ENERGY
The energy used to power the interaction
between actin and myosin filaments comes
from ATP (useable chemical energy) produced
by cellular respiration.
ATP stored in skeletal muscle last only about
six seconds.
ATP must be regenerated continuously if
contraction is to continue
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Ways to Make Energy Sources for
Contraction
1) Creatine phosphate (ADP)
2) Cellular respiration
(Aerobic or Anaerobic)
• Creatine phosphate – stores energy that quickly converts
unusable energy (ADP) to usable energy (ATP) 6 Seconds!!
•Cellular respiration is the process by which the chemical
energy of "food" molecules is released and partially
captured in the form of ATP.
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Muscle Metabolism
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Muscle Metabolism
• Creatine Phosphate
• Excess ATP is used to
synthesize creatine
phosphate
• Energy-rich molecule
• Creatine phosphate
transfers its high energy
phosphate group to ADP
regenerating new ATP
• Creatine phosphate and
ATP provide enough
energy for contraction for
about 15 seconds
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Ways to Make Energy Sources for
Contraction
1) Creatine phosphate (ADP)
2) Cellular respiration
(Aerobic or Anaerobic)
• Creatine phosphate – stores energy that quickly converts
unusable energy (ADP) to usable energy (ATP) 6 Seconds!!
•Cellular respiration is the process by which the chemical
energy of "food" molecules is released and partially
captured in the form of ATP.
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Cellular Respiration (CR)
THREE SERIES OF REACTIONS in CR
1. Glycolysis
2. Citric acid cycle
3. Electron transport chain
Produces
• carbon dioxide
• water
• ATP (chemical energy)
• heat
Two Types of Reactions
• Anaerobic Respiration (without O2) - produce little ATP
• Aerobic Respiration (requires O2) - produce most ATP
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4-11
Anaerobic Reaction (Glycolysis)
• Recall that glycolysis results in pyruvate acid.
If O2 is not present, pyruvate can be
fermented into LACTIC ACID.
• Lactic Acid
• It is a waste product of pyruvate acid.
• Occurs in many muscle cells.
• Accumulation causes muscle soreness
and fatigue.
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Muscle Metabolism
• Anaerobic Respiration
• Series of ATP producing reactions that do
not require oxygen
• Glucose is used to generate ATP when the
supply of creatine phosphate is depleted
• Glucose is derived from the blood and
from glycogen stored in muscle fibers
• Glycolysis breaks down glucose into
molecules of pyruvic acid and produces
two molecules of ATP
• If sufficient oxygen is present, pyruvic acid
formed by glycolysis enters aerobic
respiration pathways producing a large
amount of ATP
• If oxygen levels are low, anaerobic
reactions convert pyruvic acid to lactic acid
which is carried away by the blood
• Anaerobic respiration can provide enough
energy for about 30 to 40 seconds of
muscle activity
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Ways to Make Energy Sources for
Contraction
1) Creatine phosphate (ADP)
2) Cellular respiration
(Aerobic or Anaerobic)
• Creatine phosphate – stores energy that quickly converts
unusable energy (ADP) to usable energy (ATP) 6 Seconds!!
•Cellular respiration is the process by which the chemical
energy of "food" molecules is released and partially
captured in the form of ATP.
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Oxygen Supply & Cellular Respiration
• Anaerobic Phase
•Steps are called glycolysis.
•occur in the cytoplasm
• no oxygen
• produces pyruvic acid
and produces lactic acid
• little ATP
• Aerobic Phase
•Steps are called citric acid
cycle and electron transport
chain.
• occur in the mitochondrion
•oxygen
•produces most ATP / CO2/
H2O
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Muscle Metabolism
• Aerobic Respiration
•
Activity that lasts longer than half a minute depends on
aerobic respiration
•
Pyruvic acid entering the mitochondria is completely
oxidized generating
• ATP
• carbon dioxide
• Water
• Heat
•
Each molecule of glucose yields about 36 molecules
of ATP
•
Muscle tissue has two sources of oxygen
• 1) Oxygen from hemoglobin in the blood
• 2) Oxygen released by myoglobin in the muscle
cell
•
Myoglobin and hemoglobin are oxygen-binding
proteins
•
Aerobic respiration supplies ATP for prolonged activity
•
Aerobic respiration provides more than 90% of the
needed ATP in activities lasting more than 10 minutes
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Ways to Make Energy Sources for
Contraction
1) Creatine phosphate (ADP)
2) Cellular respiration
(Aerobic or Anaerobic)
• Creatine phosphate – stores energy that quickly converts
unusable energy (ADP) to usable energy (ATP) 6 Seconds!!
•Cellular respiration is the process by which the chemical
energy of "food" molecules is released and partially
captured in the form of ATP.
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Summary of Cellular Respiration
Total ATP Production
2 ATP – Glycolysis
2 ATP – Citrus Acid Cycle
34 ATP – Electron Transport Chain
38 ATP – Total energy released from one
molecule of glucose.
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Oxygen Debt
Oxygen debt – amount of oxygen needed by liver to convert
lactic acid to glucose
• oxygen not available
• glycolysis continues
• pyruvic acid converted
to lactic acid
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Muscle Metabolism
• Oxygen Consumption After Exercise
• After exercise, heavy breathing continues and oxygen
consumption remains above the resting level
• Oxygen debt
• The added oxygen that is taken into the body after exercise
• This added oxygen is used to restore muscle cells to
the resting level in three ways
• 1) to convert lactic acid into glycogen
• 2) to synthesize creatine phosphate and ATP
• 3) to replace the oxygen removed from myoglobin
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What happens to the lactic acid once it has
accumulated?
• The liver filters the blood and rids the
body of toxins. Lactic acid is a toxin.
• liver converts lactic acid to glucose
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Muscle Fatigue
• Muscle fatigue- is a state of physiological
inability to contract
• commonly caused from
– decreased blood flow
– ion imbalances
– accumulation of lactic acid
• cramp – sustained, involuntary
contraction
9-18
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Muscle Metabolism
• Muscle Fatigue
• Inability of muscle to maintain force of
contraction after prolonged activity
Factors that contribute to muscle fatigue:
• Inadequate release of calcium ions from the SR
• Depletion of creatine phosphate
• Insufficient oxygen
• Depletion of glycogen and other nutrients
• Buildup of lactic acid and ADP
• Failure of the motor neuron to release enough acetylcholine
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Control of Muscle Tension
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Contraction and Relaxation of Skeletal
Muscle
• Length–Tension Relationship
• The forcefulness of muscle contraction depends on the length of
the sarcomeres
• When a muscle fiber is stretched there is less overlap between
the thick and thin filaments and tension (forcefulness) is
diminished
• When a muscle fiber is shortened the filaments are compressed
and fewer myosin heads make contact with thin filaments and
tension is diminished
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Types of Contractions
Two Types
1. Isometric – muscle
2. Isotonic – muscle
contracts but does not change contracts and changes
length
length
Two Types of Isotonic Contractions
1. Eccentric – lengthening
contraction
2. Concentric – shortening contraction
9-24
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Muscle Tone
Muscle tone – continuous state of partial contraction
-Even when a muscle appears to be at rest, a certain
amount of sustained contraction is occurring in its
fibers.
Atrophy – a wasting away or decrease in size of an
organ or tissue.
Hypertrophy – Enlargement of an organ or tissue.
9-23
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Types of Contractions
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Smooth and Cardiac Muscle
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Smooth Muscle Fibers
Compared to skeletal muscle fibers
• shorter
• single nucleus
• elongated with tapering ends
• myofilaments randomly organized
• no striations
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Two Types of Smooth Muscle
SEM: Arteriole
Multiunit Smooth Muscle
• irises of eye
• walls of blood vessels
• contractions are rapid and vigorous
• similar to skeletal muscle tissue
Visceral Smooth Muscle
Location - walls of most hollow organs (intestine)
• contractions are slow and sustained
•exhibit rhythmicity – pattern of repeated
contractions
• exhibit peristalsis – wave-like motion that helps
SEM: Stomach
substances through passageways.
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Smooth Muscle Tissue
• Microscopic Anatomy of Smooth Muscle
• Contains both thick filaments and thin filaments
• Not arranged in orderly sarcomeres
• No regular pattern of overlap thus not striated
• Contain only a small amount of stored Ca++
• Filaments attach to dense bodies and stretch from one
dense body to another
• Dense bodies
• Function in the same way as Z discs
• During contraction the filaments pull on the dense bodies
causing a shortening of the muscle fiber
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Smooth Muscle Tissue
• Physiology of Smooth Muscle
• Most smooth muscle fibers contract or relax in
response to:
• Action potentials from the autonomic nervous
system
• Pupil constriction due to
increased light energy
• In response to stretching
• Food in digestive tract stretches
intestinal walls initiating peristalsis
• Hormones
• Epinephrine causes relaxation of
smooth muscle in the air-ways
and in some blood vessel walls
• Changes in pH, oxygen and carbon dioxide
levels
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Smooth Muscle Contraction
• Resembles skeletal muscle contraction
• interaction between actin and myosin
• both use calcium and ATP
• both depend on impulses
• Different from skeletal muscle contraction
• hormones affect smooth muscle
• stretching can trigger smooth muscle contraction
• smooth muscle slower to contract and relax
• smooth muscle more resistant to fatigue
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9-28
Cardiac Muscle
Anatomy
• only in the heart
• striated uninuclear cells join end-to-end forming a
network
• arrangement of actin and myosin are not as organized
as skeletal muscle
Physiology
• self-exciting tissue (Pacemaker)
• rhythmic contractions
• involuntary, all or nothing contractions
Pumps blood to:
• 1. lungs for oxygenation
• 2. body for distribution of O2 and nutrients
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Cardiac Muscle Tissue
• Principal tissue in the heart wall
• Intercalated discs
• Allow muscle action potentials to spread from
one cardiac muscle fiber to another
• autorhythmic muscle fibers
• Continuous, rhythmic activity
• Have the same arrangement of actin and
myosin as skeletal muscle fibers
• Mitochondria are large and numerous
• Depends on aerobic respiration to generate
ATP
• Requires a constant supply of oxygen
• Able to use lactic acid produced by skeletal
muscle fibers to make ATP
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Aging and Muscular Tissue
• Aging
• Brings a progressive loss of
skeletal muscle mass
• A decrease in maximal strength
• A slowing of muscle reflexes
• A loss of flexibility
• With aging, the relative number of
slow oxidative fibers appears to
increase
• Aerobic activities and strength training
can slow the decline in muscular
performance
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Of Note: Types of Skeletal Muscle Fibers
• Muscle fibers vary in their content of
myoglobin
• Red muscle fibers
• Have a high myoglobin content
• Appear darker (dark meat in chicken legs and
thighs)
• Contain more mitochondria
• Supplied by more blood capillaries
• White muscle fibers
• Have a low content of myoglobin
• Appear lighter (white meat in chicken breasts)
Copyright © 2010 Pearson Education, Inc.