Chapter 18 Heart Lecture 3 Marieb’s Human Anatomy and Physiology Ninth Edition Marieb Hoehn.
Muscular Histology and Physiology. Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn...
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Transcript of Muscular Histology and Physiology. Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn...
Muscular Histology and Physiology
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Photomicrograph of the capillary network surrounding skeletal muscle fibers
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Microscopic anatomy of a skeletal muscle fiber
Nuclei Fiber
NucleusLightI band
DarkA band
Sarcolemma
Mitochondrion
H zone(b)
Myofibril
(a)
(c)
Thin (actin) filament
Thick (myosin) filament
Z disc Z disc
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Composition of thick and thin filaments
(b)
(c)
(d)
(e)
(a)
Heads
Flexible hinge region
Tail
Myosin head
Troponin complex Tropomyosin Actin
Thin filamentThick filament
Thin filament (actin) Thick filament (myosin)Myosin heads
Myosin molecule
Portion of a thick filament
Portion of a thin filament
Longitudinal section of filaments within one sarcomere of a myofibril
Transmission electron micrograph of part of a sarcomere
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Microscopic anatomy of a skeletal muscle fiber
I band
Z disc Z disc
I bandA band
H zone
(c)
(d)
(e)
Thin (actin) filament
Thick (myosin) filament
Thin (actin) filament
Elastic (titin) filaments
Z disc Z disc
M line
M line
Sarcomere
Thick (myosin) filament
I bandthin filaments
only
H zonethick filaments
only
M linethick filaments linkedby accessory proteins
Outer edge of A band
thick and thinfilaments overlap
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle
MyofibrilMyofibrils
Triad
Tubules of sarcoplasmic reticulum
Sarcolemma
Sarcolemma
Mitochondrion
I band I bandA band
H zone Z discZ disc
Part of a skeletal muscle fiber (cell)
T tubule
Terminal cisternaof the sarcoplasmic reticulum
Mline
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Sliding filament model of contraction
A
Z Z
II A
Z Z
A
Z Z
H
1
2
3
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Connective tissue sheaths of skeletal muscle
(b)
(a)
Bone
PerimysiumEndomysiumBlood
vessel
Muscle fiber(cell)
Fascicle(wrapped byperimysium)
Endomysium(betweenfibers)
Epimysium
Tendon
Epimysium
Muscle fiberin middle of a fascicle
Perimysium
Blood vessel
Endomysium
Figure 4.30
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
The neuromuscular junction
(a)
(b) (c)
Axon terminal ofa motor neuron
Junctionalfolds of thesarcolemmaat motor endplate
Part of amyofibril
Mitochondrion
Synaptic cleft
T tubule
Binding of Achto receptor opensNa+/K+ channel
Acetylcholinesterase
Synapticcleft
ACh molecules
Fusing synapticvesicle
Synapticvesicle Acetic acid
Choline
Axon terminal
Actionpotential Axon terminal at
neuromuscular junction
Sarcolemmaof themuscle fiber
Nucleus
Na+K+
Myelinated axonof motor neuron
Ca2+
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
(a)
Actionpotential
Axon terminal atneuromuscular junction
Sarcolemmaof themuscle fiber
Nucleus
Myelinated axonof motor neuron
Figure 9.7a: The neuromuscular junction, p. 290.
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
The neuromuscular junction
(b)
Axon terminal ofa motor neuron
Junctionalfolds of thesarcolemmaat motor endplate
Part of amyofibril
Mitochondrion
Synaptic cleft
T tubule
Synapticvesicle
Ca2+
Muscle Contraction Physiology
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
(c)
Binding of Achto receptor opensNa+/K+ channel
Acetylcholinesterase
Synapticcleft
ACh molecules
Fusing synapticvesicle
Acetic acid
Choline
Axon terminal
Na+K+
The neuromuscular junction
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
An action potential in a skeletal muscle fiber
(b)
(c)
(d)
(a)
(b) Step 1: Depolarization and generation of the action potential.Production of an end plate potential at the motor end plate causes adjacent areas of the sarcolemma to become permeable to sodium (voltage-gated sodium channels open). As sodium ions diffuse rapidly into the cell, the resting potential is decreased (i.e., depolarization occurs). If the stimulus is strong enough, an action potential is initiated.
(c) Step 2: Propagation of the action potential.The positive charge inside the initial patch of sarcolemma changes the permeability of an adjacent patch, opening voltage-gated Na+ channels there. Consequently the membrane potential in that region decreases and depolarization occurs there as well. Thus, the action potential travels rapidly over the entire sarcolemma.
(d) Step 3: Repolarization.Immediately after the depolarization wave passes, the sarcolemma's permeability changes once again: Na+ channels close and K+ channels open, allowing K+ to diffuse from the cell. This restores the electrical conditions of the resting (polarized) state. Repolarization occurs in the same direction as depolarization, and must occur before the muscle fiber can be stimulated again. The ionic concentrations of the resting state are restored later by the sodium-potassium pump
(a) Electrical conditions of a resting (polarized) sarcolemma.The outside face is positive, while the inside face is negative. The predominant extracellular ion is sodium (Na+); the predominant intracellular ion is potassium (K+). The sarcolemma is relatively impermeable to both ions.
Na+
Stimulus
[Na+] [K+]
K+
[K+] [Na+]
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
0 1 2 3 4
–70
–55
0
+30
Time (ms)
Na+ channelsclose
Action potential
K+ channelsopen
Na+
channelsopen Threshold
Action potential scan showing changing sarcolemma permeability to Na+ and K+ ions
Mem
bra
ne
po
ten
tial
(m
V)
Rel
ativ
e m
emb
ran
e p
erm
eab
ilit
y
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Excitation-contraction coupling
ADP
Pi
Net entry of Na+ initiatesan action potential which is propagated along thesarcolemma and downthe T tubules.
T tubuleSarcolemma
SR tubules (cut)
SynapticcleftSynaptic
vesicle
Axon terminal
ACh ACh ACh
Neurotransmitter released diffuses across the synaptic cleft and attaches to ACh
Action potentialin T tubule activatesvoltage-sensitive receptors, which in turn trigger Ca2+
release from terminalcisternae of SRinto cytosol.
Calcium ions bind to troponin;troponin changes shape, removingthe blocking action of tropomyosin;actin active sites exposed.
Contraction; myosin heads alternately attach toactin and detach, pulling the actin filaments towardthe center of the sarcomere; release of energy byATP hydrolysis powers the cycling process.
Removal of Ca2+ by active transportinto the SR after the actionpotential ends.
SR
Tropomyosin blockagerestored, blocking myosinbinding sites onactin; contraction ends and muscle fiber relaxes.
Ca2+
Ca2+
Ca2+
Ca2+
Ca2+Ca2+
Ca2+
Ca2+
Ca2+
Ca2+
1
2
6
5
4
3
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Role of ionic calcium in the contraction mechanism
(a) (b) (c) (d)
Actin
Actin
Tnl
TnT
Tropomyosin
Myosinbindingsites
Troponincomplex
TnC
Myosinhead
Myosinbindingsite
Additionalcalciumionsbind
Additionalcalciumionsbindto TnC
Myosinhead
Actin
Overview
Troponin
TropomyosinMyosinhead
Plane of (a) Plane of (d)
+ Ca2+
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
The cross bridge cycle
ATP
ADP
ADPATPhydrolysis
ADP
ATP
Pi
Pi
Myosin head(high-energyconfiguration)
Myosin head attaches to the actinmyofilament, forming a cross bridge.
Thin filament
As ATP is split into ADP and Pi, the myosinhead is energized (cocked into the high-energyconformation).
Inorganic phosphate (Pi) generated in theprevious contraction cycle is released, initiatingthe power (working) stroke. The myosin headpivots and bends as it pulls on the actin filament,sliding it toward the M line. Then ADP is released.
Myosin head(low-energyconfiguration)
Thick filament
As new ATP attaches to the myosin head, the link betweenMyosin and actin weakens, and the cross bridge detaches.
1
2
3
4
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
, p. 296.
(b)(a)
Spinal cord
Motor neuroncell body
Muscle
Branching axonto motor unit
Muscle fibers
Nerve
Motorunit 1
Motorunit 2
Musclefibers
Motor neuronaxon
Axon terminals atneuromuscular junctions
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
The muscle twitch
Latentperiod
Period ofcontraction
Period ofrelaxation
Per
cen
tag
e o
fm
axim
um
ten
sio
n
Time (ms)
0 200
(a)
40 60 80 100 120 140Singlestimulus
Latent period
Extraocular muscle (lateral rectus)
GastrocnemiusSoleus
Per
cen
tag
e o
fm
axim
um
ten
sio
n
Time (ms)
0 400 80 120 160 200Singlestimulus(b)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Methods of regenerating ATP during muscle activity
Creatine
Energy source: CP
Oxygen use: NoneProducts: 1 ATP per CP, creatineDuration of energy provision: 15s
(a) Direct phosphorylation [coupled reaction of creatine phosphate (CP) and ADP]
(b) Anaerobic mechanism (glycolysis and lactic acid formation)
(c) Aerobic mechanism (aerobic cellular respiration)
Energy source: glucose
Oxygen use: NoneProducts: 2 ATP per glucose, lactic acidDuration of energy provision: 30–60 s.
Energy source: glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism
Oxygen use: RequiredProducts: 38 ATP per glucose, CO2, H2ODuration of energy provision: Hours
O2
O2
ATP ATP
net gain
Glucose (fromglycogen breakdown ordelivered from blood)
Pyruvic acid
Glycolysisin cytosol
Glucose (fromglycogen breakdown ordelivered from blood)
Pyruvic acid
2
ATP
net gain per glucose
38Lactic acidReleased
to blood
O2
H2O
O2
Fattyacids
Aminoacids
CP ADP
Aerobic respirationin mitochondria
CO2
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Factors influencing force, velocity, and duration of skeletal muscle contraction
(a) (b) (c)Increasedcontractileforce
Large numberof musclefibers activated
Largemusclefibers
Asynchronoustetaniccontractions
Muscle andsarcomerelength slightlyover 100% ofresting length
Predominanceof fast glycolytic(fatigable) fibers
Predominanceof slow oxidative(fatigue-resistant)fibers
Small load
Increasedcontractilevelocity
Increasedcontractileduration
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Influence of load on contraction velocity and duration
(a)
Time (ms)
60
Dis
tan
ce s
ho
rten
ed
0 20 40 80 100 120
Single actionpotential initiated (b)
Increasing load
0
Vel
oci
ty o
f sh
ort
enin
g
Intermediate load
Light load
Heavy load
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Innervation of smooth muscle
Smooth muscle cell
Mucosa
Varicosities
Autonomic nervefiber
Varicosity
Synaptic vesicles
Mitochondrion
Submucosa
Serosa
Muscularisexterna
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Sequence of events in excitation-contraction coupling of smooth muscle
ATP
Pi
Pi
Pi
Pi
ADP
Calcium ions (Ca2+) enterthe cytosol from the ECFor from the scant SR.
Ca2+ binds to andactivates calmodulin.
Ca2+
Ca2+
Ca2+Sarcoplasmic reticulum
Plasma membrane
Activated calmodulin activatesthe myosin light chain kinaseenzymes.
Inactivecalmodulin
Activatedcalmodulin
Inactivekinase
Activatedkinase
Extracellular fluid
Cytoplasm
The activated kinase enzyme catalyzes transfer of phosphate to myosin heads, activating themyosin head ATPases.
Phosphorylated myosin heads form cross bridges with actin of the thin filaments and shorteningoccurs.
Inactive myosinmolecule
Activated(phosphorylated)myosin molecule
Thin myofilament
Thick filament
Cross bridge activity ends when phosphate is removed from the myosin heads by phosphorylase enzymes and intracellular Ca2+ levels fall.
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