Transcript Presentation

9.1: Introduction
Three (3) Types of Muscle Tissues
• Skeletal Muscle
• Cardiac Muscle
• Usually attached to bones
• Under conscious control
• Somatic nervous control
• Striated
• Wall of heart
• Not under conscious control
• Autonomic nervous control
• Striated
• Smooth Muscle
• Walls of most viscera, blood vessels
and skin
• Not under conscious control
• Autonomic
• Not striated
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9.2: Structure of Skeletal Muscle
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• Skeletal Muscle
• Organ of the muscular system
• Skeletal muscle tissue
• Nervous tissue
• Blood
• Connective tissues
• Fascia
• Tendons
•
Aponeuroses
Skeletal muscles
Tendons
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Skeletal Muscle Fibers
• Sarcolemma
• Sarcoplasm
• Sarcoplasmic reticulum (SR)
• Transverse (‘T’) tubule
• Triad
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Myofibrils
Cisternae of
sarcoplasmic reticulum
Transverse tubule
Nucleus
• Cisternae of SR
• T tubule
• Myofibril
• Actin myofilaments
• Myosin myofilaments
• Sarcomere
Sarcoplasmic
reticulum
Openings into
transverse tubules
Mitochondria
Thick and thin
filaments
Sarcoplasm
Nucleus
Sarcolemma
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Triad
9.3: Skeletal Muscle Contraction
• Movement within
the myofilaments
• I band (thin)
• A band (thick and
thin)
• H zone (thick)
• Z line (or disc)
• M line
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Skeletal muscle fiber
Sarcoplasmic
reticulum
Thick (myosin) Thin (actin)
filaments
filaments
Myofibril
Sarcomere
Z line
I band
(a)
H zone
Z line
M line
A band
I band
A band
(b)
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Myofilaments
• Thick myofilaments
• Composed of myosin protein
• Form the cross-bridges
• Thin myofilaments
• Composed of actin protein
• Associated with troponin and
tropomyosin proteins
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Cross-bridges
Troponin
Tropomyosin
Myosin
molecule
Thick
filament
Thin filament
Actin molecule
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Neuromuscular Junction
• Also known as NMJ or
myoneural junction
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Synaptic
vesicles
Mitochondria
• Site where an axon and
muscle fiber meet
• Parts to know:
• Motor neuron
• Motor end plate
• Synapse
Motor
neuron axon
Acetylcholine
Synaptic
cleft
Folded
sarcolemma
Axon branches
Muscle fiber
nucleus
Motor
end plate
Myofibril of
muscle fiber
• Synaptic cleft
• Synaptic vesicles
• Neurotransmitters
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(a)
Motor Unit
• Single motor neuron
• All muscle fibers controlled
by motor neuron
Motor neuron
• As few as four fibers
of motor unit 1
• As many as 1000’s of
muscle fibers
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Motor neuron
of motor unit 2
Branches of
motor neuron
axon
Skeletal muscle
fibers
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Stimulus for Contraction
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• Acetylcholine (ACh)
• Nerve impulse causes release of
ACh from synaptic vesicles
• ACh binds to ACh receptors on
motor end plate
• Generates a muscle impulse
• Muscle impulse eventually
reaches the SR and the cisternae
Synaptic
vesicles
Mitochondria
Motor
neuron axon
Acetylcholine
Synaptic
cleft
Folded
sarcolemma
Axon branches
Muscle fiber
nucleus
Motor
end plate
Myofibril of
muscle fiber
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(a)
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Cross Bridge Cycling
• Myosin cross-bridge attaches
to actin binding site
• Myosin cross-bridge pulls
thin filament
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Tropomyosin
Troponin
ADP + P
Thick filament
Ca+2
Muscle relaxation
Active transport of Ca+2 into sarcoplasmic
reticulum, which requires ATP, makes
myosin binding sites unavailable.
Ca+2
Muscle contraction
Release of Ca+2 from sarcoplasmic
reticulum exposes binding sites on
actin:
Ca+2 binds to troponin
ATP
Tropomyosin pulled aside
Binding sites on
actin exposed
Ca+2
ADP + P
Ca+2
ADP + P
Ca+2
2 Exposed binding sites on actin molecules
allow the muscle contraction cycle to occur
ADP + P
ADP + P
Contraction cycle
6 ATP splits, which
provides power to
“cock” the myosin
cross-bridges
ADP + P
ADP + P
3 Cross-bridges
bind actin to
myosin
ADP
ATP
ATP
ATP
P
ATP
• Myosin cross-bridge goes back
to original position
ADP + P
1 Relaxed muscle
• ADP and phosphate
released from myosin
• New ATP binds to
myosin
• Linkage between actin
and myosin cross-bridge
break
• ATP splits
Thin filament
Actin monomers
5 New ATP binds to myosin, releasing linkages
ADP
P
ADP + P
4 Cross-bridges pull thin filament (power stroke),
ADP and P released from myosin
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The Sliding Filament Model
of Muscle Contraction
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• When sarcromeres
shorten, thick and thin
filaments slide past one
another
• H zones and I bands
narrow
• Z lines move closer
together
Sarcomere
Z line
Thin
filaments
A band
1 Relaxed
Z line
Thick
filaments
2 Contracting
3 Fully contracted
(a)
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Animation:
Breakdown of ATP
and Cross-Bridge Movement
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Oxygen Supply and
Cellular Respiration
• Aerobic Phase
• Citric acid cycle
• Electron transport system
• Occurs in the mitochondria
• Produces most ATP
• Myoglobin stores extra oxygen
Glucose
2 In the absence of
sufficient oxygen,
glycolysis leads to
lactic acid
accumulation.
1 Oxygen carried from
the lungs by
hemoglobin in red
blood cells is stored
in muscle cells by
myoglobin and is
available to support
aerobic respiration.
Energy
Pyruvic acid
2
ATP
Cytosol
• Glycolysis
• Occurs in cytoplasm
• Produces little ATP
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Lactic acid
Mitochondria
• Cellular respiration:
• Anaerobic Phase
Citric acid
cycle
Electron
transport
chain
Synthesis of 34 ATP
CO2 + H2O + Energy
Heat
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Oxygen Debt
• Oxygen debt – amount of oxygen needed by liver cells to use
the accumulated lactic acid to produce glucose
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• Oxygen not available
• Glycolysis continues
• Pyruvic acid converted to
lactic acid
• Liver converts lactic acid to
glucose
Glycogen
Energy to
synthesize
Glucose
Energy
from
ATP
ATP
Pyruvic acid
Lactic acid
Glycolysis and
lactic acid formation
(in muscle)
Synthesis of glucose
from lactic acid
(in liver)
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Muscle Fatigue
• Inability to contract muscle
• Commonly caused from:
• Decreased blood flow
• Ion imbalances across the sarcolemma
• Accumulation of lactic acid
• Cramp – sustained, involuntary muscle contraction
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Heat Production
• By-product of cellular respiration
• Muscle cells are major source of body heat
• Blood transports heat throughout body core
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9.4: Muscular Responses
• Muscle contraction can be observed by removing a
single skeletal muscle fiber and connecting it to a device
that senses and records changes in the overall length of
the muscle fiber.
•Threshold Stimulus
• Minimal strength required to cause contraction
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Recruitment of Motor Units
• Recruitment - increase in the number of motor units
activated
• Whole muscle composed of many motor units
• More precise movements are produced with fewer muscle
fibers within a motor unit
• As intensity of stimulation increases, recruitment of motor
units continues until all motor units are activated
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Sustained Contractions
• Smaller motor units (smaller diameter axons) - recruited first
• Larger motor units (larger diameter axons) - recruited later
• Produce smooth movements
• Muscle tone – continuous state of partial contraction
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Types of Contractions
• Isotonic – muscle contracts and
changes length
• Eccentric – lengthening
contraction
• Concentric – shortening contraction
• Isometric – muscle contracts but does
not change length
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(a) Muscle contracts with
force greater than
resistance and
shortens (concentric
contraction)
(b) Muscle contracts
with force less than
resistance and
lengthens (eccentric
contraction)
(c) Muscle contracts but
does not change length
(isometric contraction)
No
movement
Movement
Movement
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9.5: Smooth Muscles
• Compared to skeletal muscle fibers, smooth muscle fibers
are:
• Shorter
• Single, centrally located nucleus
• Elongated with tapering ends
• Myofilaments randomly organized
• Lack striations
• Lack transverse tubules
• Sarcoplasmic reticula (SR) not well developed
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Smooth Muscle Fibers
• Visceral Smooth Muscle
• Single-unit smooth muscle
• Sheets of muscle fibers
• Fibers held together by gap
junctions
• Exhibit rhythmicity
• Exhibit peristalsis
• Walls of most hollow organs
• Multi-unit Smooth Muscle
• Less organized
• Function as separate units
• Fibers function separately
• Iris of eye
• Walls of blood vessels
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Smooth Muscle Contraction
• Resembles skeletal muscle contraction in that:
• Interaction between actin and myosin
• Both use calcium and ATP
• Both are triggered by membrane impulses
• Different from skeletal muscle contraction in that:
• Smooth muscle lacks troponin
• Smooth muscle uses calmodulin
• Two neurotransmitters affect smooth muscle
• Acetlycholine (Ach) and norepinephrine (NE)
• Hormones affect smooth muscle
• Stretching can trigger smooth muscle contraction
• Smooth muscle slower to contract and relax
• Smooth muscle more resistant to fatigue
• Smooth muscle can change length without changing tautness
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9.6: Cardiac Muscle
• Located only in the heart
• Muscle fibers joined together by intercalated discs
• Fibers branch
• Network of fibers contracts as a unit
• Self-exciting and rhythmic
• Longer refractory period than skeletal muscle
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Characteristics of Muscle Tissue
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9.7: Skeletal Muscle Actions
• Skeletal muscles generate a great variety of body
movements.
• The action of each muscle mostly depends upon the kind
of joint it is associated with and the way the muscle is
attached on either side of that joint.
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