chapter 12a
DESCRIPTION
Chapter 12a. Muscles. About this Chapter. Skeletal muscle Mechanics of body movement Smooth muscle Cardiac muscle. Three Types of Muscle. Nucleus. Muscle fiber (cell). Striations. (a) Skeletal muscle . Figure 12-1a. Three Types of Muscle. Striations. Muscle fiber. Intercalated disk. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 12a
Muscles
About this Chapter
• Skeletal muscle• Mechanics of body movement• Smooth muscle• Cardiac muscle
Three Types of Muscle
Figure 12-1a
NucleusMuscle fiber
(cell)Striations
(a) Skeletal muscle
Three Types of Muscle
Figure 12-1b
Muscle fiber
Nucleus
Striations
(b) Cardiac muscle
Intercalated disk
Three Types of Muscle
Figure 12-1c
Muscle fiber
Nucleus
(c) Smooth muscle
Skeletal Muscle
• Usually attached to bones by tendons• Origin: closest to the trunk• Insertion: more distal• Flexor: brings bones together• Extensor: moves bones away• Antagonistic muscle groups: flexor-extensor
pairs
Antagonistic Muscle Groups
Figure 12-2a
(a) Flexion
Biceps musclecontracts (flexor)
Tricepsmusclerelaxes
Antagonistic Muscle Groups
Figure 12-2b
(b) Extension
Triceps musclecontracts (extensor)
Bicepsmusclerelaxes
Organization of Skeletal Muscle
Figure 12-3a (1 of 2)
Skeletal muscle
Muscle fascicle:bundle of fibers
Muscle fiber
Connective tissue
Connectivetissue
Tendon Nerve andblood vessels
Nucleus
(a)
Organization of Skeletal Muscle
Figure 12-3a (2 of 2)
Ultrastructure of Muscle
Figure 12-3b-f
T-tubules
(c)
(d)
(b)
Sarcoplasmicreticulum
Sarcolemma
Mitochondria
Myofibril
Myofibril
Thickfilament
Thinfilament
A band
Z disk
Z disk
(f)
Z disk
I bandM line H zone
Z diskSarcomere
Thin filaments
Tropomyosin
Troponin
Actin chainG-actin molecule
Myosin tail
Myosin heads
Myosin molecule
Thick filaments
Nucleus
Hingeregion
(e)Titin
Nebulin
Titin
M line Myosincrossbridges
M line
ULTRASTRUCTURE OF MUSCLE
ANATOMY SUMMARY
Figure 12-3b
Ultrastructure of Muscle
T-tubules
Sarcoplasmicreticulum
Sarcolemma
Mitochondria
Myofibril
Thickfilament
ThinfilamentNucleus
ULTRASTRUCTURE OF MUSCLE
(b)
Figure 12-3c
Ultrastructure of Muscle
(c)
Myofibril
A bandZ disk
I bandM line H zone
Z diskSarcomere
Figure 12-3d
Ultrastructure of Muscle
(d)Z disk Z disk
Titin
M line Myosincrossbridges
Figure 12-3e
Ultrastructure of Muscle
(e)
Myosin tail
Myosin heads
Myosin molecule
Thick filaments
Hingeregion
M line
Figure 12-3f
Ultrastructure of Muscle
(f)
Thin filaments
Tropomyosin
Troponin
Actin chain G-actin molecule
TitinNebulin
Ultrastructure of Muscle
Figure 12-3c-f
(c)
(d)
Myofibril
A bandZ disk
Z disk
(f)
Z disk
I bandM line H zone
Z diskSarcomere
Thin filaments
Tropomyosin
Troponin
Actin chain G-actin molecule
Myosin tail
Myosin heads
Myosin molecule
Thick filaments
Hingeregion
(e) TitinNebulin
Titin
M line Myosincrossbridges
M line
T-Tubules and the Sarcoplasmic Reticulum
Figure 12-4
Sarcolemma
Thin filament
Thick filament
Triad Terminalcisterna
T-tubule brings actionpotentials into interiorof muscle fiber.
Sarcoplasmic reticulumstores Ca2+
The Two- and Three-Dimensional Organization of a Sarcomere
Figure 12-5
Sarcomere
(a)
(b)
A band I band H zone I band
Z diskZ disk M line
Thick filament
Thin filament
Z disk Z disk
(c)
I bandthin filaments
only
H zonethick filaments
only
Outer edgeof A band
thick and thinfilaments overlap
M linethick filaments
linked withaccessory proteins
Anatomy Review Animation
PLAY Interactive Physiology® Animation: Muscular System: Anatomy Review: Skeletal Muscle Tissue
Muscle Contraction
• Muscle tension: force created by muscle• Load: weight that opposes contraction• Contraction: creation of tension in muscle• Relaxation: release of tension• Steps leading up to muscle contraction:
1. Events at the neuromuscular junction2. Excitation-contraction coupling3. Contraction-relaxation cycle
Summary of Muscle Contraction
Figure 12-7
Events at the Neuromuscular Junction
PLAY Events at the Neuromuscular Junction
PLAY Interactive Physiology® Animation: Muscular System: Events at the Neuromuscular Junction
Changes in a Sarcomere During Contraction
Figure 12-8
Z
Z
Zline
Zline
Mline
Musclerelaxed
Musclecontracted
Sarcomere shortenswith contraction
I band
A bandActinZ
M
Z
Z
Myosin
Half ofI band
Half ofI band
H zone
H
H
I
A band constant
IH zone and I band both shorten
Z
A band
Half ofI band
Sliding Filament Theory
PLAY Interactive Physiology® Animation: Muscular System: Sliding Filament Theory
The Molecular Basis of Contraction
Figure 12-9a
ADP
Troponin G-Actin
Tropomyosinblocks binding
site on actin
Myosin headTN
(a) Relaxed state. Myosin head cocked.
Pi
The Molecular Basis of Contraction
Figure 12-9b
Actinmoves
Cytosolic Ca2+
Tropomyosin shifts,exposing bindingsite on actin
TN
Power stroke
(b) Initiation of contraction
Ca2+ levels increasein cytosol.
Ca2+ binds to troponin (TN).
Troponin-Ca2+
complex pulls tropomyosin away from actin’smyosin-binding site.
Myosin binds to actin and completes power stroke.
Actin filament moves.
Pi
1
2 3
4
5
5
4
3
2
1
ADP
The Molecular Basis of Contraction
Figure 12-10
G-actin molecule
Tight binding in the rigor state
ATP binds to myosin.Myosin releases actin.
Myosinbinding sites Myosin
filament
Myosin hydrolyses ATP. Myosinhead rotates and binds to actin.
ATP
Actin filament movestoward M line.
Myosin releases ADP.Contraction-relaxation
Sliding filament
ADP
Power strokeRelaxed state with myosin heads cocked
Ca2+
signal
ADPPiPi
1
2
3
4
The Molecular Basis of Contraction
Figure 12-10, step 0
G-actin molecule
Tight binding in the rigor state
Myosinbinding sites Myosin
filament
The Molecular Basis of Contraction
Figure 12-10, steps 0–1
G-actin molecule
Tight binding in the rigor state
ATP binds to myosin.Myosin releases actin.
Myosinbinding sites Myosin
filament
ATP
1
The Molecular Basis of Contraction
Figure 12-10, steps 1–2
1 ATP binds to myosin.Myosin releases actin.
Myosin hydrolyses ATP. Myosin head rotates and binds to actin.
ATP
Relaxed state with myosin heads cocked
ADPPi
2
The Molecular Basis of Contraction
Figure 12-10, steps 2–3
2 Myosin hydrolyses ATP. Myosin head rotates and binds to actin.
Actin filament movestoward M line.
Power stroke
Relaxed state withmyosin heads cocked
Ca2+
signalADP
Pi
Pi
3
The Molecular Basis of Contraction
Figure 12-10, steps 3–4
Actin filament movestoward M line.
Myosin releases ADP.
ADP
Power stroke
Pi
43
Excitation-Contraction Coupling
Figure 12-11a
Myosin head
Myosin thick filament
M line
Axon terminal ofsomatic motor neuron
Motor end plate
Sarcoplasmic reticulum
ACh
DHP
DHP = dihydropyridine L-type calcium channel
RyR
RyR = ryanodine receptor-channel
T-tubule
Muscle fiber
(a) Initiation of muscle action potential
Somatic motor neuron releases ACh at neuromuscular junction.
Net entry of Na+ through ACh receptor-channel initiates a muscle action potential
TroponinTropomyosin
KEY
ActinZ disk
Na+
Ca2+
1
2
1
2
Excitation-Contraction Coupling
Figure 12-11a, step 1
Myosin head
Myosin thick filament
M line
Axon terminal ofsomatic motor neuron
Motor end plate
Sarcoplasmic reticulum
ACh
DHP
DHP = dihydropyridine L-type calcium channel
RyR
RyR = ryanodine receptor-channel
T-tubule
Muscle fiber
(a) Initiation of muscle action potential
Somatic motor neuron releases ACh at neuromuscular junction.
TroponinTropomyosin
KEY
ActinZ disk
Ca2+
1 1
Excitation-Contraction Coupling
Figure 12-11a, steps 1–2
Myosin head
Myosin thick filament
M line
Axon terminal ofsomatic motor neuron
Motor end plate
Sarcoplasmic reticulum
ACh
DHP
DHP = dihydropyridine L-type calcium channel
RyR
RyR = ryanodine receptor-channel
T-tubule
Muscle fiber
(a) Initiation of muscle action potential
Somatic motor neuron releases ACh at neuromuscular junction.
Net entry of Na+ through ACh receptor-channel initiates a muscle action potential
TroponinTropomyosin
KEY
ActinZ disk
Na+
Ca2+
1
2
1
2
Excitation-Contraction Coupling
Figure 12-11b
DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel
Ca2+ released
(b) Excitation-contraction couplingDistance actin moves
Myosin thick filament
Action potential in t-tubule altersconformation of DHP receptor.
DHP receptor opens RyR Ca2+
release channels in sarcoplasmic reticulum and Ca2+ enters cytoplasm.
Ca2+ binds to troponin, allowing actin-myosin binding.
Myosin heads execute powerstroke.
Actin filament slides toward center of sarcomere.
KEY
3
4
5
6
7
3 4
5
6
7
Electrical and Mechanical Events in Muscle Contraction
• A twitch is a single contraction-relaxation cycle
Figure 12-12
Muscle fibermembrane
potentialin mV
Developmentof tension
during onemuscle twitch
+30
-70 2msec
Latentperiod
Contractionphase
Motorend plateAxonterminal
Muscle actionpotential
Time10–100 msec
Relaxationphase
Time
Neuronmembrane
potentialin mV
+30Muscle fiber
Action potentialfrom CNS
Recordingelectrodes
-70
Time
Tens
ion
Phosphocreatine
Figure 12-13
1. Creatine phosphate2. Glycolysis3. Krebs cycle
Locations and Possible Causes of Muscle Fatigue
Figure 12-14
Causes of Muscle Fatigue During Exercise
• Extended submaximal exercise • Depletion of glycogen stores
• Short-duration maximal exertion • Increased levels of inorganic phosphate• May slow Pi release from myosin• Decrease calcium release
• Maximal exercise• Potassium (K+) leaves muscle fiber, leading to
increased concentration that is believed to decrease Ca2+
Skeletal Muscle Metabolism During Fatiguing Submaximal Exercise
Question 12-1
Fast-Twitch Glycolytic and Slow-Twitch Oxidative Muscle Fibers
Figure 12-15
Fast-Twitch Glycolytic and Slow-Twitch Oxidative Muscle Fibers
Table 12-2
Length-Tension Relationships in Contracting Skeletal Muscle
Figure 12-16