Download Chapter 10 Muscle Tissue Lecture Outline

Chapter 10 Muscle Tissue Lecture Outline
Muscle tissue types
1. Skeletal muscle = voluntary striated
2. Cardiac muscle = involuntary striated
3. Smooth muscle = involuntary nonstriated
Characteristics
1. cells
2. excitability
3. contractility
4. extensibility
5. elasticity
Skeletal Muscle Tissue
Functions
1. movement
2. posture
3. stability
4. support
5. guard
6. heat
Anatomy
Connective tissue sheaths
1. Epimysium
Collagen
2. Perimysium
Fascicles
Collagen & Elastin
3. Endomysium
Reticular fibers
Satellite cells
Tendon
Aponeurosis
Muscle fiber (cell)
Myoblasts
Satellite cells
Sarcolemma
Transmembrane potential
Resting potential = -85mV
Transverse tubules
Sarcoplasm
Glycosomes
Myoglobin
Myofibrils
Myofilaments
Actin = thin filaments
Myosin = thick filaments
Sarcoplasmic reticulum: Ca2+
Terminal cisternae
Triad
Sarcomere
Compostion
1. thick filaments
2. thin filaments
3. stabilizing proteins
4. regulatory proteins
Regions
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1. A-band
2. M-line
3. H-zone
4. Zone of overlap
5. I-band
6. Z-disc/line
Actinins
Titin
Thin filaments
1. Actin
F actin
Active site
G actin
2. Nebulin
3. Tropomyosin
4. Troponin
Cross bridge = contraction
Thick filaments
1. Myosin
a. tail
b. hinge
c. head
2. Titin
Sliding Filament Theory
1. H-zones and I-bands ↓ width
2. Zones of overlap ↑ width
3. Z-lines closer
4. A-band constant
Events of Muscle Contraction
Neuromuscular junction
Synaptic terminal
Acetylcholine (Ach)
Synaptic cleft
Motor end plate
Ach receptors
Acetylcholinesterase (AchE)
A. Excitation
1. action potential at terminal
2. Ach released
3. Ach binds receptors
Na+ channels open
4. action potential down transverse tubules
5. AchE breaks down Ach
B. Excitation-Contraction coupling
1. action potential at triad = Ca2+ release
2. Ca2+ binds troponin
3. troponin frees active sites
C. Contraction
1. actin binds myosin
2. cross bridges
3. power stroke
4. ATP resets myosin
5. repeat
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SCCC BIO130 Chapter 10 Handout
D. Relaxation
1. Ca2+ absorbed
2. Ca2+ detaches from troponin
3. tropomyosin covers active sites
4. sarcomeres stretch out
Rigor Mortis
Necrosis
Diseases
Botulism
Flaccid paralysis
Tetanus
Spastic paralysis
Myasthenia gravis
Tension Production
Muscle tension
Load
Cell tension
1. Resting length
2. Frequency of stimulation
Twitch
a. Latent period
b. Contraction phase
c. Relaxation phase
Treppe
Wave summation
Incomplete tetanus
Complete tetanus
Muscle tension
1. Internal tension vs. External tension
2. Number of fibers
Motor unit
Recruitment
Muscle tone
Isotonic contractions
Isometric contractions
Muscle Metabolism
Creatine phosphate
Creatine phosphokinase
Activity
1. Rest
Aerobic respiration
2. Moderate activity
Aerobic respiration
3. High activity
Anaerobic fermentation
Glycolysis
Lactic acid
Muscle fatigue
1. depletion of reserves
2. acid pH
Lactic acid disposal
Liver
Glucose
Muscle performance
Fiber types
1. Fast glycolytic fibers
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Fast Myosin ATPase
Fermentation: glucose
Glycogen
2. Slow oxidative fibers
Slow Myosin ATPase
Aerobic respiration: glucose, lipid, aa’s
Mitochondria
Myoglobin
3. Intermediate fibers / Fast oxidative fibers
Physical conditioning
1. Aerobic exercise
2. Resistance exercise
Hypertrophy
Growth Hormone
Epinephrine
Atrophy
Cardiac Muscle Tissue
Heart
Cardiocytes
Few nuclei
Amitotic
Aerobic respiration
Mitochondria
Myoglobin
Glycogen & lipid reserves
Intercalated discs
Features
1. automaticity
2. nervous adjustment
3. longer contraction
4. twitch only
Smooth Muscle Tissue
Hollow organs & Arrector pili
Circular layer
Longitudinal layer
Cell
Uninuclear
Dense bodies
Desmin
Excitation-Contraction:
1. Ca2+ released
2. Ca2+ binds calmodulin
3. Calmodulin activates MLC kinase
4. ATP→ ADP: cock myosin head
5. Cross bridges → contraction
Aging
↓ myofibrils ↓ reserves
↓ cardiovascular performance
↑ fibrosis
↓ satellite cells
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SCCC BIO130 Chapter 10 Handout
Amy Warenda Czura, Ph.D.
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SCCC BIO130 Chapter 10 Handout
Sarcomere
-resting length 1.6-2.6 µm
-composed of:
1. thick filaments - myosin
2. thin filaments - actin
3. stabilizing proteins: hold thick and thin filaments in place
4. regulatory proteins: control interactions of thick and thin filaments
-organization of the proteins in sarcomere causes striated appearance of the muscle fiber
Regions of the sarcomere:
1. A-band = whole width of thick filaments, looks dark microscopically
2. M-line = center of each thick filament, middle of A-band: attaches neighboring thick filaments
3. H-zone = light region either side of M line, contains thick filaments only
4. Zone of overlap = ends of A-bands, place where thin filaments intercalate between thick filaments
(triads encircle zones of overlap)
5. I-band = area that contains thin filaments outside zone of overlap (not whole width of thin filaments)
6. Z-line/disc = center of I band, constructed of actinins, function to anchor thin filaments and bind
neighboring sarcomeres, titin proteins bind thick filaments to Z-line,
Z-lines mark ends of each sarcomere
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SCCC BIO130 Chapter 10 Handout
Thin filaments (5-6nm diameter)
made of four proteins:
1. actin 2. nebulin
F-actin (filamentous) consists of rows of G-actin (globular), held together with nebulin. Each Gactin has an active site that can bind to myosin
3. tropomyosin: covers the active sites on G actin to prevent myosin binding
4. troponin: holds tropomyosin on the actin.
Also has receptor for Ca2+: when Ca2+ binds the troponin-tropomyosin complex it releases actin
allowing it to bind to myosin
Actin + Myosin binding = crossbridge → crossbridge formation = contraction
The end of each thin filament is bound to thin filaments in neighboring sarcomeres by actinin in the Z-line
Thick Filaments (10-12nm diameter)
-composed of bundled myosin molecules
each myosin has three parts:
1. tail: tails bundled together to make length of thick filament, all point toward M-line
2. hinge: flexible region, allows movement for contraction
3. head: hangs off tail by hinge, will bind actin at active site. No heads in H-zone
-also contains core of titin: elastic protein that attaches thick filament to Z-line
-titin holds thick filament in place and aid elastic recoil of muscle after stretching
-each thick filament is surrounded by a hexagonal arrangement of thin filaments with which it will interact
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SCCC BIO130 Chapter 10 Handout
The Neuromuscular Junction
Neuromuscular junction = where a nerve terminal interfaces with a muscle fiber at the motor end plate, one
junction per fiber (control of fiber from one neuron)
Synaptic terminal = expanded end of axon, contains vesicles of neurotransmitter → Acetylcholine (Ach)
Motor end plate = specialized sarcolemma that contains Ach receptors and the enzyme
acetylcholinesterase (AchE)
Synaptic cleft = space between synaptic terminal and motor end plate where neurotransmitter is released
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SCCC BIO130 Chapter 10 Handout
Excitation
resting transmembrane potential restored
Vesicles containing Ach fuse with the
neuronal membrane and exocytose
their contents into the synaptic cleft
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through sodium channels triggering
channels close.
a change in the transmembrane potential
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and the sodium
SCCC BIO130 Chapter 10 Handout
Excitation-Contraction Coupling
Action potential on the sarcolemma is coupled to contraction events via the triads
1. The action potential on the transverse tubules reaches a triad and causes release of calcium ions from
the cisternae of the sarcoplasmic reticulum into the sarcoplasm around the zones of overlap of the
sarcomeres.
2. Calcium binds to troponin on the thin filaments.
3. Troponin pulls tropomyosin off the active sites of the actin so that cross bridges can form.
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SCCC BIO130 Chapter 10 Handout
Contraction
1. Actin, free of
tropomyosin, binds to
myosin via its active sites.
2. Cross bridges are formed (actin active
sites bound to myosin heads)
3. Myosin heads have been pre-primed for movement via ATP
energy prior to cross bridge formation and are pointed away
from the M line. Upon actin binding, the myosin heads pivot
toward the M line in an event called the power stroke, which
pulls the thick filament along the thin filament
5. The myosin head is now primed to interact with a
new active site on actin. Myosin can carry out 5
power strokes per second while calcium and ATP
are available. Each power stroke shortens the
sarcomere by 1%
4. Myosin ATPase uses ATP to break the cross
bridges releasing the myosin head from the actin
active site, and resets the myosin head pointed away
from the M-line
Amy Warenda Czura, Ph.D.
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SCCC BIO130 Chapter 10 Handout