Muscle Time with Hans and Franz
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Muscle Time with Hans and Franz Today’s goal: learn types, characteristics, functions, attachments, organization of muscles http://www.hulu.com/watch/4184/satu rday-night-live-pumping-up-with-han s-and-franz
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Muscle Time with Hans and Franz . Today’s goal: learn types, characteristics, functions, attachments, organization of muscles . http://www.hulu.com/watch/4184/saturday-night-live-pumping-up-with-hans-and-franz. Post it Time. First muscle test will be general: Focus on Types - PowerPoint PPT Presentation
Transcript of Muscle Time with Hans and Franz
Muscle Time with Hans and Franz
Today’s goal: learn types, characteristics, functions,
attachments, organization of muscles
http://www.hulu.com/watch/4184/saturday-night-live-pumping-up-with-hans-and-franz
Post it Time
• First muscle test will be general:• Focus on • Types• Characteristics• Functions• The Tough stuff is organization!
2.0 test questions
• What are the characteristics of muscle?• What are the types of muscle?• What are the characteristics of cardiac
muscle?• What are the functions of muscles?
3 Muscle Types
• Skeletal (our major focus over the next ~2 weeks)
• Smooth – surrounds hollow organ • Cardiac – Bachelor Rejects have broken these
Three Types of Muscle Tissue
1. Skeletal muscle tissue:– Attached to bones and skin– Striated – Voluntary– Powerful
Three Types of Muscle Tissue
2. Cardiac muscle tissue:– Only in the heart – Striated – Involuntary
Three Types of Muscle Tissue
3. Smooth muscle tissue:– In the walls of hollow organs, e.g., stomach,
urinary bladder, and airways– Not striated– Involuntary
Special Characteristics of Muscle Tissue
• Excitability (responsiveness or “irritability”): receive and respond to stimuli
• Contractility: ability to shorten when stimulated
• Stretchable• Elasticity: recoils to resting length
Muscle Functions
1. Movement of bones or fluids (e.g., blood)2. Maintaining posture and body position 3. Stabilizing joints4. Heat generation
Skeletal Muscle: Attachments
• Muscles attach:– Directly—epimysium of muscle fuses to outer
membrane of bone– tendon or sheetlike aponeurosis
Skeletal Muscle• Each muscle is served by one artery, one
nerve, and one or more veins• But just what is a muscle???
Muscle organization• Muscles made up of tons (100s to 1000s)
muscle fibers– Muscle fiber is a sophisticated way of saying
muscle cell!– Muscle cell is bourgeois to say muscle fiber
• Blood vessels and nerve fibers also found throughout muscle
Fibers are wrapped by CT
Russian Dolls
• Muscle• Fascicle • Fiber• Myofibrils • Myofilaments – Above: Your next week, somewhat simplified
though not a perfect analogy
Connective tissue sheaths of skeletal muscle
1. Epimysium: dense regular CT surrounding entire muscle
2. Perimysium: fibrous CT surrounding fascicles (groups of muscle fibers)
3. Endomysium: fine areolar CT surrounding each muscle fiber
Figure 9.1
Bone
Perimysium
Endomysium(between individualmuscle fibers)
Muscle fiber
Fascicle(wrapped by perimysium)
Epimysium
Tendon
Epimysium
Muscle fiberin middle ofa fascicle
Blood vessel
PerimysiumEndomysium
Fascicle(a)
(b)
• Fiber is an individual cells • Fibers are bundled into fascicles • Fascicles bundled into muscle
Today:
• Review yesterday • Muscle “cells”• Organelles of the muscle fiber
What is a muscle cel… you mean fiber like?
• Cylindrical up to 1 foot long!• Multiple nuclei • Many mitochondria
1 muscle cell
Muscle fibers
• Glycosomes for glycogen storage, myoglobin for O2 storage
• Modified organelles: myofibrils, sarcoplasmic reticulum, sarcolemma and T tubules
Myofibrils
• Densely packed, rodlike elements • ~80% of cell volume • These are where we will see striations– A and I bands alternate
Myofibrils are made of myofilaments!
• Forest is a fiber• Tree is a myofibril• 1 branch is myofilament
NucleusLight I bandDark A band
Sarcolemma
Mitochondrion
(b) Diagram of part of a muscle fiber showing the myofibrils. Onemyofibril is extended afrom the cut end of the fiber.
Myofibril
Sarcomere
• Smallest contractile unit (functional unit) of a muscle fiber
• region of a myofibril – between two successive Z discs
• Composed of thick and thin myofilaments made of contractile proteins
Poorly comparble to an osteonAnd bone
Features of a Sarcomere
• Thick filaments: run the entire length of an A band• Thin filaments: run the length of the I
band and partway into the A band
• Z disc: sheet of proteins that anchors the thin filaments – connects myofibrils to one another
• H zone: lighter midregion where filaments do not overlap
• M line: line of protein myomesin that holds adjacent thick filaments together
Figure 9.2c, d
I band I bandA bandSarcomere
H zoneThin (actin)filament
Thick (myosin)filament
Z disc Z disc
M line
(c) Small part of one myofibril enlarged to show the myofilamentsresponsible for the banding pattern. Each sarcomere extends fromone Z disc to the next.
Z disc Z discM lineSarcomere
Thin (actin)filament
Thick(myosin)filament
Elastic (titin)filaments
(d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments.
Structure of Thick Filament• Composed of the protein myosin (tail and head)– Myosin tails contain: • 2 interwoven, protein chains
– Myosin heads contain: • 2 smaller, light chains that act as cross bridges during
contraction 1. Binding sites for actin (thin filaments)2. Binding sites for ATP3. ATPase enzymes
Structure of Thin Filament
• Twisted double strand of fibrous protein F actin
• F actin consists of G (globular) actin subunits • G actin bears active sites for myosin head
attachment during contraction• Tropomyosin and troponin: regulatory
proteins bound to actin
Figure 9.3
Flexible hinge region
Tail
Tropomyosin Troponin ActinMyosin head
ATP-bindingsite
Heads Active sitesfor myosinattachment
Actinsubunits
Actin-binding sites
Thick filamentEach thick filament consists of manymyosin molecules whose heads protrude at opposite ends of the filament.
Thin filamentA thin filament consists of two strandsof actin subunits twisted into a helix plus two types of regulatory proteins(troponin and tropomyosin).
Thin filamentThick filament
In the center of the sarcomere, the thickfilaments lack myosin heads. Myosin heads are present only in areas of myosin-actin overlap.
Longitudinal section of filamentswithin one sarcomere of a myofibril
Portion of a thick filamentPortion of a thin filament
Myosin molecule Actin subunits
Sarcoplasmic Reticulum (SR)
• Network of smooth endoplasmic reticulum surrounding each myofibril
• Pairs of terminal cisternae form perpendicular cross channels
• Regulates intracellular Ca2+ levels
T Tubules
• Continuous with the sarcolemma – Sarcolemma = cell membrane of muscle fiber
• Penetrate the cell’s interior at each A band–I band junction
• Associate with the paired terminal cisternae to form triads that encircle each sarcomere
Organelles
Figure 9.5
Myofibril
Myofibrils
Triad:
Tubules ofthe SR
Sarcolemma
Sarcolemma
Mitochondria
I band I bandA bandH zone Z discZ disc
Part of a skeletalmuscle fiber (cell)
• T tubule• Terminal
cisternaeof the SR (2)
M line
Triad Relationships
• T tubules conduct impulses deep into muscle fiber
• Integral proteins protrude from T tubule and SR cisternae membranes
• T tubule proteins: voltage sensors• SR has gated channels that regulate Ca2+
release from the SR cisternae
Contraction
• The generation of force • Does not necessarily cause shortening of the
fiber• Shortening occurs when tension generated by
cross bridges on the thin filaments exceeds forces opposing shortening
Sliding Filament Model of Contraction
• In the relaxed state, thin and thick filaments overlap only slightly
• During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line
• As H zones shorten and disappear, sarcomeres shorten, muscle cells shorten, and the whole muscle shortens
Role of Calcium (Ca2+) in Contraction
• At low intracellular Ca2+ concentration:– Tropomyosin blocks the active sites on actin– Myosin heads cannot attach to actin– Muscle fiber relaxes
Role of Calcium (Ca2+) in Contraction
• At higher intracellular Ca2+ concentrations:– Ca2+ binds to troponin – Troponin changes shape and moves tropomyosin
away from active sites– Events of the cross bridge cycle occur – When nervous stimulation ceases, Ca2+ is pumped
back into the SR and contraction ends
Cross Bridge Cycle
• Continues as long as the Ca2+ signal and adequate ATP are present
• Cross bridge formation—high-energy myosin head attaches to thin filament
• Working (power) stroke—myosin head pivots and pulls thin filament toward M line
Cross Bridge Cycle
• Cross bridge detachment—ATP attaches to myosin head and the cross bridge detaches
• “Cocking” of the myosin head—energy from hydrolysis of ATP cocks the myosin head into the high-energy state
Figure 9.12
1
Actin
Cross bridge formation.
Cocking of myosin head. The power (working) stroke.
Cross bridge detachment.
Ca2+
Myosincross bridge
Thick filament
Thin filament
ADP
Myosin
Pi
ATPhydrolysis
ATP
ATP
24
3
ADPPi
ADPPi
Figure 9.12, step 1
Actin
Cross bridge formation.
Ca2+
Myosincross bridge
Thick filament
Thin filament
ADP
Myosin
Pi
1
Figure 9.12, step 3
The power (working) stroke.
ADPPi
2
Figure 9.12, step 4
Cross bridge detachment.
ATP
3
Figure 9.12, step 5
Cocking of myosin head.
ATPhydrolysis
ADPPi
4
Figure 9.12, step 1
Actin
Cross bridge formation.
Ca2+
Myosincross bridge
Thick filament
Thin filament
ADP
Myosin
Pi
1
Figure 9.12, step 3
The power (working) stroke.
ADPPi
2
Figure 9.12, step 4
Cross bridge detachment.
ATP
3
Figure 9.12, step 5
Cocking of myosin head.
ATPhydrolysis
ADPPi
4
Figure 9.12, step 1
Actin
Cross bridge formation.
Ca2+
Myosincross bridge
Thick filament
Thin filament
ADP
Myosin
Pi
1
Figure 9.12, step 3
The power (working) stroke.
ADPPi
2
Figure 9.12, step 4
Cross bridge detachment.
ATP
3
Figure 9.12, step 5
Cocking of myosin head.
ATPhydrolysis
ADPPi
4
Figure 9.12
1
Actin
Cross bridge formation.
Cocking of myosin head. The power (working) stroke.
Cross bridge detachment.
Ca2+
Myosincross bridge
Thick filament
Thin filament
ADP
Myosin
Pi
ATPhydrolysis
ATP
ATP
24
3
ADPPi
ADPPi
Figure 9.6
I
Fully relaxed sarcomere of a muscle fiber
Fully contracted sarcomere of a muscle fiber
IAZ ZH
I IAZ Z
1
2
Requirements for Skeletal Muscle Contraction
1. Activation: neural stimulation at aneuromuscular junction
2. Excitation-contraction coupling: – Generation and propagation of an action
potential along the sarcolemma– Final trigger: a brief rise in intracellular Ca2+ levels
Events at the Neuromuscular Junction
• Skeletal muscles are stimulated by somatic motor neurons
• Axons of motor neurons travel from the central nervous system via nerves to skeletal muscles
• Each axon forms several branches as it enters a muscle
• Each axon ending forms a neuromuscular junction with a single muscle fiber
Nucleus
Actionpotential (AP)
Myelinated axonof motor neuron
Axon terminal ofneuromuscular junction
Sarcolemma ofthe muscle fiber
Ca2+ Ca2+
Axon terminalof motor neuron
Synaptic vesiclecontaining AChMitochondrionSynapticcleft
Fusing synaptic vesicles
1 Action potential arrives ataxon terminal of motor neuron.
2 Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal.
Figure 9.8
Neuromuscular Junction
• Situated midway along the length of a muscle fiber
• Axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft
• Synaptic vesicles of axon terminal contain the neurotransmitter acetylcholine (ACh)
• Junctional folds of the sarcolemma contain ACh receptors
Events at the Neuromuscular Junction
• Nerve impulse arrives at axon terminal• ACh is released and binds with receptors on
the sarcolemma• Electrical events lead to the generation of an
action potential
PLAY A&P Flix™: Events at the Neuromuscular Junction
Figure 9.8
Nucleus
Actionpotential (AP)
Myelinated axonof motor neuron
Axon terminal ofneuromuscular junction
Sarcolemma ofthe muscle fiber
Ca2+ Ca2+
Axon terminalof motor neuron
Synaptic vesiclecontaining AChMitochondrionSynapticcleft
Junctionalfolds ofsarcolemma
Fusing synaptic vesicles
ACh
Sarcoplasm ofmuscle fiber
Postsynaptic membraneion channel opens;ions pass.
Na+ K+
Ach–
Na+
K+
Degraded ACh
Acetyl-cholinesterase
Postsynaptic membraneion channel closed;ions cannot pass.
1 Action potential arrives ataxon terminal of motor neuron.
2 Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal.
3 Ca2+ entry causes some synaptic vesicles to release their contents (acetylcholine)by exocytosis.
4 Acetylcholine, aneurotransmitter, diffuses across the synaptic cleft and binds to receptors in the sarcolemma.
5 ACh binding opens ionchannels that allow simultaneous passage of Na+ into the musclefiber and K+ out of the muscle fiber.
6 ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinesterase.
Destruction of Acetylcholine
• ACh effects are quickly terminated by the enzyme acetylcholinesterase
• Prevents continued muscle fiber contraction in the absence of additional stimulation
Events in Generation of an Action Potential
1. Local depolarization (end plate potential):– ACh binding opens chemically (ligand) gated ion
channels– Simultaneous diffusion of Na+ (inward) and K+
(outward)– More Na+ diffuses, so the interior of the
sarcolemma becomes less negative– Local depolarization – end plate potential
Events in Generation of an Action Potential
2. Generation and propagation of an action potential:– End plate potential spreads to adjacent
membrane areas– Voltage-gated Na+ channels open– Na+ influx decreases the membrane voltage
toward a critical threshold– If threshold is reached, an action potential is
generated
Events in Generation of an Action Potential
• Local depolarization wave continues to spread, changing the permeability of the sarcolemma
• Voltage-regulated Na+ channels open in the adjacent patch, causing it to depolarize to threshold
Events in Generation of an Action Potential
3. Repolarization:• Na+ channels close and voltage-gated K+
channels open• K+ efflux rapidly restores the resting polarity• Fiber cannot be stimulated and is in a
refractory period until repolarization is complete
• Ionic conditions of the resting state are restored by the Na+-K+ pump
Figure 9.9
Na+
Na+
Open Na+
Channel
Closed Na+
Channel
Closed K+
Channel
Open K+
Channel
Action potential++++++
++++++
Axon terminal
Synapticcleft
ACh
ACh
Sarcoplasm of muscle fiber
K+
2 Generation and propagation ofthe action potential (AP)
3 Repolarization
1 Local depolarization: generation of the end plate potential on the sarcolemma
K+
K+Na+
K+Na+
Wave of dep
olar
izat
io n
Figure 9.9, step 1
Na+
Na+
Open Na+
ChannelClosed K+
Channel
K+
Na+ K+Action potential
+++++++++++
+
Axon terminal
Synapticcleft
ACh
ACh
Sarcoplasm of muscle fiber
K+
1 Local depolarization: generation of the end plate potential on the sarcolemma
1Wave of
depo
lariz
atio
n
Figure 9.9, step 2
Na+
Na+
Open Na+
ChannelClosed K+
Channel
K+
Na+ K+Action potential
+++++++++++
+
Axon terminal
Synapticcleft
ACh
ACh
Sarcoplasm of muscle fiber
K+
Generation and propagation of the action potential (AP)
1 Local depolarization: generation of the end plate potential on the sarcolemma
2
1Wave of
depo
lariz
atio
n
Figure 9.9, step 3
Na+
Closed Na+
ChannelOpen K+
Channel
K+
Repolarization3
Figure 9.9
Na+
Na+
Open Na+
ChannelClosed K+
Channel
Action potential++++++
++++++
Axon terminal
Synapticcleft
ACh
ACh
Sarcoplasm of muscle fiber
K+
2 Generation and propagation ofthe action potential (AP)
3 Repolarization
1 Local depolarization: generation of the end plate potential on the sarcolemma
K+
K+Na+
K+Na+
Wave of dep
olar
izat
io n
Closed Na+
ChannelOpen K+
Channel
Figure 9.10
Na+ channelsclose, K+ channelsopen
K+ channelsclose
Repolarizationdue to K+ exit
Threshold
Na+
channelsopen
Depolarizationdue to Na+ entry
Excitation-Contraction (E-C) Coupling
• Sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments
• Latent period:– Time when E-C coupling events occur– Time between AP initiation and the beginning of
contraction
Events of Excitation-Contraction (E-C) Coupling
• AP is propagated along sarcomere to T tubules• Voltage-sensitive proteins stimulate Ca2+
release from SR – Ca2+ is necessary for contraction
Figure 9.11, step 1
Axon terminalof motor neuron
Muscle fiber Triad
One sarcomere
Synaptic cleft
Setting the stage
Sarcolemma
Action potentialis generated
Terminal cisterna of SR ACh
Ca2+
Figure 9.11, step 2
Action potential is propagated alongthe sarcolemma and down the T tubules.
Steps in E-C Coupling:
Troponin Tropomyosinblocking active sites
Myosin
Actin
Active sites exposed and ready for myosin binding
Ca2+
Terminal cisterna of SR
Voltage-sensitivetubule protein
T tubule
Ca2+
releasechannel
Myosincross bridge
Ca2+
Sarcolemma
Calcium ions are released.
Calcium binds to troponin andremoves the blocking action oftropomyosin.
Contraction begins
The aftermath
1
2
3
4
Figure 9.11, step 3
Steps inE-C Coupling:
Terminal cisterna of SR
Voltage-sensitivetubule protein
T tubule
Ca2+
releasechannel
Ca2+
Sarcolemma
Action potential ispropagated along thesarcolemma and downthe T tubules.
1
Figure 9.11, step 4
Steps inE-C Coupling:
Terminal cisterna of SR
Voltage-sensitivetubule protein
T tubule
Ca2+
releasechannel
Ca2+
Sarcolemma
Action potential ispropagated along thesarcolemma and downthe T tubules.
Calciumions arereleased.
1
2
Figure 9.11, step 5
Troponin Tropomyosinblocking active sitesMyosin
Actin
Ca2+
The aftermath
Figure 9.11, step 6
Troponin Tropomyosinblocking active sitesMyosin
Actin
Active sites exposed and ready for myosin binding
Ca2+
Calcium binds totroponin and removesthe blocking action oftropomyosin.
The aftermath
3
Figure 9.11, step 7
Troponin Tropomyosinblocking active sitesMyosin
Actin
Active sites exposed and ready for myosin binding
Ca2+
Myosincross bridge
Calcium binds totroponin and removesthe blocking action oftropomyosin.
Contraction begins
The aftermath
3
4
Figure 9.11, step 8
Action potential is propagated alongthe sarcolemma and down the T tubules.
Steps in E-C Coupling:
Troponin Tropomyosinblocking active sites
Myosin
Actin
Active sites exposed and ready for myosin binding
Ca2+
Terminal cisterna of SR
Voltage-sensitivetubule protein
T tubule
Ca2+
releasechannel
Myosincross bridge
Ca2+
Sarcolemma
Calcium ions are released.
Calcium binds to troponin andremoves the blocking action oftropomyosin.
Contraction begins
The aftermath
1
2
3
4
