Chapter 10
Muscular Tissue
Your objectives today!
• 40-50% of body
weight
Chemical E to
Mechanical E
• Learn the functions and properties of
muscle
• Master the anatomy of muscles
• Understand the “sliding filament model”
• Learn a few other tidbits
10-1
10-2
Muscle organization
Development of Muscle Fibers (cells)
Muscle = many fascicles
Fascicles = many muscles fibers (cells)
Muscle fibers (cells) = many myofibrils
Myofibrils = many myofilaments
Mature cells develop from fused myoblasts!!!!
• Mature muscle cells can not divide
• Growth is a result of cellular enlargement
(hypertrophy)
• Satellite cells can regenerate new cells.
• Fibrosis
10-3
Muscle = many fascicles
Fascicles = many muscles fibers (cells)
Muscle fibers (cells) = many myofibrils
Myofibrils = many myofilaments
Fig 10.1
10-4
Skeletal Muscle -- Connective Tissue
Fascicle
Fig 10.1
10-5
• Superficial fascia: separates muscle from skin
• Deep fascia = connective tissue around muscle
• Connective tissue components of the muscle
include
– epimysium = surrounds the whole muscle
– perimysium = surrounds fascicles of 10-100
muscle cells
– endomysium = separates individual muscle
cells
• All these connective tissue layers extend
beyond muscle to form tendons!!!!!!!!!!!
10-6
1
Connective Tissue Components
Muscle = many fasciles
Fascicles = many muscles fibers (cells)
Muscle fibers (cells) = many myofibrils
Myofibrils = many myofilaments
10-7
10-8
Myofibrils & Myofilaments
Muscle Fiber (Cell)
• Sarcolemma = muscle cell membrane
• Sarcoplasm = cytoplasm
• Myofibrils
Myofibrils are made up of myofilaments
•
Myofilaments are contractile proteins
1. Thin myofilaments = actin
2. Thick myofilaments = myosin
10-9
10-10
Other components of Muscle cell
Sarcoplasmic Reticulum (SR)
Sarcoplasmic
reticulum
• T-tubules are tubes from surface into the center
of the cell (interstitial fluid)
10-11
•
•
•
•
System of tubular sacs
Stores Ca+ in a relaxed muscle
Release Ca+ - - contraction
Let’s return to the Myofibril
10-12
2
Thick & Thin Myofilaments
Myosin
Structural Proteins
Actin
• The M line (myomesin) connects to titin and
adjacent thick filaments.
• Titin filaments
• Z-discs (Z-lines)
• The contracting proteins of muscle
10-13
10-14
Myofilaments and the Sarcomere!!!!
• Thick and thin filaments overlap each other
in a pattern that creates striations
• They are arranged in compartments called
sarcomeres!!!!!!!
10-15
Overlap of Thick & Thin Myofilaments within
a Myofibril
10-17
10-16
Myosin myofilaments
• Thick filaments =
Myosin
• myosin heads
Actin myofilaments = thin filaments
10-18
3
Actin
• Associated with actin: troponin, & tropomyosin
AKA = T-T Complex
Motor Unit: a motor neuron AND all the mm
fibers it supplies
10-19
10-20 9.13a
Figure
Structures of NMJ Region
Neuromuscular Junction (NMJ) or Synapse
• Motor neurons
• End bulbs of motor
neurons release
acetylcholine (ACh)
(neurotransmitter)
• NMJ = myoneural junction
10-21
10-22
The Big Picture
Neuromuscular Junction
Axon terminal of
somatic motor neuron
Motor nerve fiber
Myelin
Synaptic knob
Schwann cell
1
Muscle fiber
Synaptic vesicles
(containing ACh)
Basal lamina
Sarcolemma
Synaptic cleft
2
Motor end plate
RyR
Nucleus
T-tubule
ACh receptor
DHP
Z disk
Actin
Sarcoplasm
Myofilaments
Troponin
Tropomyosin
M line
Myosin head
Mitochondria
Nucleus
Sarcoplasmic
reticulum
Ca2+
Junctional folds
Figure 11.7b
11-23
(b)
ACh
Na+
Myosin thick filament
(a) Initiation of muscle action potential
KEY
DHP = dihydropyridine L-type calcium channel
RyR = ryanodine receptor-channel
Figure 12-11a
4
1. Chemical step
Muscle contraction:
“Sliding filament model”
• motor nerve stimulates muscle
(acetyocholine)
- this causes an electrical change in the
sarcolema (depolarization)
- electrical impulse moves along
sarcolema
T-tubules
Sarcoplasmic reticulum
• Functional unit of muscle contraction is
the sarcomere
• Two steps to muscle contraction:
1. Chemical
2. Mechanical
10-25
10-26
Figure 38-8
• In response to electrical impulse
sarcoplasmic reticulum releases Ca+
- Released Ca+ causes Actin and Myosin
filaments to slide past each other
Impulse
• (causes the sarcomere to shorten)
Ca+
Ca+
Ca+
10-27
2. Mechanical step
10-28
Fig. 38-9
2. Mechanical step (cross bridges)
- Myosin filaments have little heads
Myosin
Actin
= binding sites
How does this happen?
10-29
10-30
5
At rest binding sites on Actin are covered by
•Active sites are exposed
Troponin
Tropomyosin
Tropomyosintroponin complex
Ca+ released from sarcoplasmic reticulum
- Myosin heads reach down and bind
“Cross bridges”
- Requires ATP
- binds to troponin
- causes TT complex to change shape
and move off of the binding site
10-31
10-32
10-33
10-34
Binding
sites
Muscle Contraction & Relaxation
• four major phases of contraction and relaxation
1. excitation
• firing nerve leads to muscle excitation
2. excitation-contraction coupling
• Wave of depolarization of sarcolemma to
activation of myofilaments
3. contraction
• step in which the muscle fiber develops tension
and may shorten
4. Relaxation
• work is done, muscle fiber relaxes and returns to
its resting length
Cross bridge
11-36
10-35
6
Excitation-Contraction Coupling
Axon terminal of
somatic motor neuron
Terminal
cisterna
of SR
1
Muscle fiber
2
T tubule
T tubule
ACh
Sarcoplasmic
reticulum
Na+
Ca2+
Motor end plate
RyR
Ca2+
T-tubule
Sarcoplasmic
reticulum
Ca2+
DHP
Z disk
6 Action potentials propagated
down T tubules
Troponin
Actin
Tropomyosin
Myosin thick filament
(a) Initiation of muscle action potential
7 Calcium released from
terminal cisternae
Voltage-gated Ca+ channels on
Transverse Tubules –change shape
and cause Ca+ release channels on
S.R. to release Ca+
M line
Myosin head
KEY
DHP = dihydropyridine L-type calcium channel
11-38
RyR = ryanodine receptor-channel
Figure 12-11a
Contraction
Excitation-Contraction Coupling
Process in which APs initiate Ca+ signals that activate a contraction-rleaxation cycle
Troponin
Ca2+
Tropomyosin
Active sites
Troponin
Tropomyosin
Actin
Thin filament
ADP
Pi
Myosin
10
Myosin
Ca2+
8
Binding of calcium
to troponin
9
Hydrolysis of ATP to ADP + Pi;
activation and cocking of myosin head
Shifting of tropomyosin;
exposure of active sites
on actin
Cross-bridge:
Actin
Myosin
11
Formation of myosin–actin cross-bridge
11-39
Contraction
ATP
13
Binding of new ATP;
breaking of cross-bridge
ADP
ADP
PPi i
12
Power stroke; sliding of thin
filament over thick filament
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42
10-42
7
Relaxation
• Nerve Impulse stops
•No electrical charge (depolorization) over
sarcolemma – t-tubules – sarcoplasmic ret.
•Ca+ moves back into sarcoplasmic reticulum
•Myosin and actin binding prevented
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operating systems, some animations
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Also Acetylcholinesterase – breaks down Ach
remaining in synapse
• Muscle fiber relaxes
43
10-43
•Rigor Mortis!!!!!!!!!!!!
44
10-44
8