5.a&p i muscle2010
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Power Point I for Dr. Krasilovsky's Bio 110TRANSCRIPT
Muscle Structure and Physiology
Marieb: Chap. 9
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Muscles
I. Introduction
1. Types of muscles: a) Skeletal = Voluntary Striated b) Cardiac = Involuntary Striated c) Visceral = Involuntary Smooth/Nonstriated
2. Properties: a) respond to stimulus with contraction =
excitability b) passively stretched = extensible c) return to original shape or length = elasticity
3. Functions: a) motion b) posture c) heat production d) stabilize joints
3Fig. 9.1
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Figure 9.1 Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium.
Bone
Perimysium
Endomysium(between individualmuscle fibers)
Muscle fiber
Fascicle(wrapped by perimysium)
Epimysium
Tendon
Epimysium
Muscle fiberin middle ofa fascicle
Blood vessel
Perimysium
Endomysium
Fascicle(a)
(b)
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II. Skeletal MuscleA. Extramuscular Tissue
1. Fascia - sheets of fibrous CT wrapped around muscle
2. Epimysium - fibrous CT, extension of fascia
3. Perimysium - separates muscle into individual bundles or fascicles
4. Endomysium - separates into individual muscle cells or fibers
5. Tendon - a) cordlike CT connected to
epimysium & bone b) aponeurosis - broad, flat
band connected to muscle or bone
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II. Skeletal muscle = Voluntary Striated
6. Blood Vessels a) outside perimysium but below or under epimysium =
larger vessels b) capillaries and small branches associated with
endomysium layer 7. Nervous Tissue
a) Travel with larger blood vessels b) branches to individual muscles or groups of muscles
8. Motor Unit - single motor neuron plus all muscle fibers it stimulates
1 neuron can stimulate 10 separate muscle fibers 150 separate muscle fibers 500 separate muscle fibers (Behavior?)
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9. Neuromuscular Junction (NMJ) Point of contact or
communication between neuron and muscle
10. Motor End Plate Specialized portion
of muscle membrane at a NMJ
Fig. 9.13
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Figure 9.13 A motor unit consists of a motor neuron and all the muscle fibers it innervates.
Spinal cord
Motor neuroncell body
Muscle
Branching axonto motor unit
Nerve
Motorunit 1
Motorunit 2
Musclefibers
Motor neuronaxon
Axon terminals atneuromuscular junctions
Axons of motor neurons extend from the spinal cord to the muscle.There each axon divides into a number of axon terminals that formneuromuscular junctions with muscle fibers scattered throughoutthe muscle.
Branching axonterminals formneuromuscularjunctions, one permuscle fiber (photo-micrograph 330x).
(b)
(a)
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B. Ultrastructure of Skeletal Muscle
1. Sarcolemma - cell membrane 2. Sarcoplasm - cytoplasm 3. Multinucleated with many mitochondria 4. Sarcoplasmic Reticulum (SR)
Smooth ER SR usually in longitudinal direction If SR is perpendicular to surface, right angles,
known as Transverse SR or T-Tubules Triad = one T-Tubule plus 2 SR
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Fig. 9.5
5. Endomysium surrounding single muscle fiber
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5. Endomysium surrounds single muscle fiber/cell
Up to 30 cm long and 10-100um diameter Each muscle cell contains many myofibrils
Myofibril (1-2um) = bundles of myofilaments Myofilaments = individual muscle filaments
Thick = myosin Thin = actin or troponin or tropomyosin
Sarcomere = contractile unit, segment of a myofibril
6. Myofilament Information
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Fig. 9.2a/b
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Figure 9.2a Microscopic anatomy of a skeletal muscle fiber.
Nuclei
Fiber
(a) Photomicrograph of portions of two isolated musclefibers (700x). Notice the obvious striations (alternatingdark and light bands).
Dark A band
Light I band
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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
Figure 9.2b Microscopic anatomy of a skeletal muscle fiber.
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Figure 9.2c Microscopic anatomy of a skeletal muscle fiber.
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.
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Figure 9.2d Microscopic anatomy of a skeletal muscle fiber.
Z disc Z discM line
Sarcomere
Thin (actin)filament
Thick(myosin)filament
Elastic (titin)filaments
(d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments.
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Figure 9.2e Microscopic anatomy of a skeletal muscle fiber.
I bandthin
filamentsonly
Actinfilament
Myosinfilament
H zonethick
filamentsonly
M linethick filaments
linked byaccessoryproteins
Outer edgeof A band
thick and thinfilaments overlap
(e) Cross-sectional view of a sarcomere cut through in different locations.
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Fig. 9.3
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Fig. 9.3
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Fig. 9.4
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6. Myofilament Information a) Myosin - rod like tail terminating in two globular
heads (sites of cross bridges) Each thick filament = 200 myosin molecules with tails in
the center and heads facing outwards on each side (away from H zone)
b) Actin - thin filaments that contain active sites where myosin bridges attach
c) Regulatory proteins on actin Tropomyosin - spiral around actin and block actin sites to
bind myosin at rest Troponin - 3 sites: bind to actin, tropomyosin and calcium
d) Elastic (Titin) filaments - extend from Z disc to myosin to anchor myosin in place and help help muscle spring back after being stretched
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7. Anatomy of Relaxed muscle Sarcomere - region of a myofibril between two
successive Z discs/lines Z disc = anchors the thin actin filaments I band = extends from both sides of a Z disc,
contains only thin actin filaments A band = boundary of thicker myosin filaments
plus contain some thin actin from I band H zone of A band = less dense area where actin
ends but myosin continues M line of center of H zone = protein strands that
stabilize myosin together
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Fig. 9.2 c/d
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C. Sliding filament model of contraction Huxley 1954
1. Thin actin filaments slide past the thicker myosin due to activation of myosin cross bridges to sites on actin
2. Each cross bridge attaches and reattaches to move actin towards H zone
3. H zone disappears 4. I band shortens as Z discs move closer to each
other 5. A bands move closer to each other but do not
change length since length of myosin does not change, only actin sliding over myosin
19Fig. 9.6 - 1
M
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Figure 9.6 Sliding filament model of contraction (1 of 2).
I IA
Z ZH
1 Fully relaxed sarcomere of a muscle fiber
20Fig. 9.6
21Fig. 9.6
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Figure 9.6 Sliding filament model of contraction (2 of 2).
I IA
Z Z
2 Fully contracted sarcomere of a muscle fiber
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D. Physiology of Contraction 1. ATP = energy chemical for contraction
Hydrolysis of ATP ATP + H2O ADP + P + ENERGY Energy used by cell for active transport,
synthesis, and muscle contraction Dehydration Synthesis of ATP ADP + P + ENERGY ATP + H2O Energy supplied from cellular respiration
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D. Physiology of Contraction 2. At rest -
a) Calcium stored in the SR (not free in the sarcoplasm)
b) ATP attached to the myosin cross bridge heads in relaxed position (not power position)
c) troponin-tropomyosin attached to actin filament - blocking the actin site for the myosin head :. NO ACTIN-MYOSIN ATTACHMENTS AT THE CROSS BRIDGES - NO TENSION
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FIG. 9.11
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3. Nerve becomes active/excites a) conducts electrical charge down motor
neuron axon towards terminal branch endings at neuromuscular junction
b) in the ending of the neuron, vesicles are present that contain the neurotransmitter chemical - nerves that stimulate skeletal muscles contain acetylcholine (ACh)
c) electrical current dies out in nerve ending but vesicles move towards nerve membrane and release ACh contents into NMJ via exocytosis
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FIG. 9.9 modified
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Fig.9.11
modified
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4. ACh diffuses across the space towards muscle membrane of motor end plate (net diffusion) where there are receptors for ACh on the muscle membrane
ACh will change membrane permeability to sodium and muscle becomes electrically excited and active in this region
5. Excitation - Contraction coupling - the electrical changes on the muscle membrane lead to sliding of the myofilaments
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5. Excitation - Contraction Coupling a) electrical changes on surface of sarcolemma
spread down the T- tubules to the inner core of the muscle
b) remember - T-tubules meet the horizontal SR and form a triad
c) electrical changes of the SR cause Calcium (Ca2+) to be released into the sarcoplasm by opening Ca2+channels of the SR
Ca2+ is available to bind to the myofilaments 6. Calcium is free in the sacroplasm
a) Ca2+ activates the ATPase activity on the myosin head and powers the bending of the head
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Fig.9.11
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6b) Ca2+ also displaces the troponin - tropomyosin complex from the actin binding sites (see Figure 9.10 & 11)
c) actin-myosin cross bridge forms and flips backwards pulling the actin past the myosin towards the center of the sarcomere
d) TENSION develops e) one working stroke of head shortens
muscle 1% - usual muscle shortening 30 to 35% - therefore each myosin cross bridge attaches and reattaches several times during a contraction
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Figure 9.12 Cross Bridge Cycle
Actin
Cross bridge formation.
Cocking of myosin head. The power (working)stroke.
Cross bridgedetachment.
Ca2+
1
2
3
4
Myosinhead
Thickfilament
Thin filament
ADP
Myosin
P i
ADP
P iATPhydrolysis
ADP
P i
ATP
ATP
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7. Nerve stops firing and stops releasing ACh
As long as ACh is in gap - keeps stimulating muscle and Ca2+
ACh is destroyed in the space by an enzyme always present - acetylcholinesterase
Therefore - muscle membrane no longer electrically active and this cessation causes the free Ca2+ to be transported BACK into the SR spaces via an ATP-dependent active pump
NO FREE CALCIUM
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8. Without free Ca2+ - troponin-tropomyosin reoccupy the active site that binds myosin heads and cross bridges are broken and not reformed.
a) ATP is resynthesized and occupy the myosin binding sites
b) since cross bridges were broken - tension is lost and muscle returns to its original resting length
Myostenia gravis - problem with ACh receptor destruction
Rigor mortis - explain it????? 3-4 hours muscle stiffens, maximum by 12 hrs Dissipates over the next 2-3 days
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9. Creatine Phosphate Muscles cannot store adequate ATP for
continues muscle contractions At rest: ADP + P + Energy = ATP stored and on myosin ATP + creatine = creatine-phosphate + ADP
Exercise: ATP = ADP + P + Energy Creatine-phosphate + ADP =creatine + ATP
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E. Skeletal Muscle Physiology 1. Single Twitch Phenomenon (lab)
a) single stimulus - threshold Weakest stimulus that causes a muscle
contraction b) latent period (01. sec) - time between the
stimulation and actual mechanical contraction of muscle
chemical / electrical change / Calcium any tendon slack taken up first c) contraction phase - developing tension (.04s) d) relaxation phase (.05 sec) - calcium upt6ake
and breaking cross bridges
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e) fast muscle = 0.03 sec
(insect 0.003 sec) slow muscles =
seconds f) refractory period -
no response to second equal stimulus, but a response to a stronger stimulus
Fig. 9.14
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g) 1) slow oxidative muscle - posture, marathon red muscles (myoglobin) + mitochondria +
abundant capillaries = high aerobic activity but slow ATPase activity
2) fast glycolytic fibers - quick powerful movement - hitting baseball
White muscle low in myoglobin, more anaerobic and faster ATPase activity
Most muscle have a mixture of both Table 9.2 textbook
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2. All or None Phenomenon a) threshold - individual fibers respond maximally
when stimulated b) influenced by :
Temperature Products of metabolism Oxygen availability Fatigue
c) muscle contain many individual fibers Each fiber = all or none Entire muscle has graded response determined by the
number of fibers contracting Entire muscle has a maximum response (100% fibers)
40Copyright © 2010 Pearson Education, Inc.
Stimulus strength
Proportion of motor units excited
Strength of muscle contraction
Maximal contraction
Maximalstimulus
Thresholdstimulus
Figure 9.16 Relationship between stimulus intensity (graph at top) and muscle tension (tracing below).
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Fig. 9.16/17
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3. Summation - 2 consecutive stimuli with second response greater than the first
4. Staircase or Treppe - stimulate muscle second time after it relaxes and compare tension
Fig. 9.15b
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5. Tetanus - physiological response a) many rapid responses to prevent relaxation (2) b) fusion of twitches - continuous sustained
contraction (4) c) partial or incomplete tetanus - contractions do not
fuse (3) 6. Tonic Contraction
a) some cells contracted, others relaxed, interchange Posture Flaccid - less than normal tone to muscle
Fig. 9.15-9.16
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7. Isotonic a) same tone or tension b) change in length during contraction c) pick up a book
Fig. 9.18a
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8. Isometric a) same length b) develop or change tension c) try to left heavy object, push wall
Fig. 9.18b
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III. Cardiac muscle 1. Involuntary, striated muscle 2. Single nucleus, branched 3. Intercalated discs
Area of low resistance to electrical flow of current - network contraction response
4. Intrinsic rhythm - normal rate of pacemaker = 120+ per minute
Vagus nerve slows down intrinsic pacemaker to 60-80 beats per minute
5. Refractory period - rest No tetanus possible High rate = fibrillation
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Fig. 18.11
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6. Skeletal vs. cardac contraction Cardiac has longer tension due to calcium
involved from both SR and extracellular environment
Fig. 18.12
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IV. Smooth Muscle 1. Involuntary,
nonstriated muscle a) actin & myosin
poorer organization of fibers
b) fibers attached to membrane or lattice in sarcoplasm
c) SR less developed d) spindle shaped
Fig. 9.28a/b
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Figure 9.29 Sequence of events in excitation-contraction coupling of smooth muscle.
Activated myosin forms crossbridges with actin of the thinfilaments and shortening begins.
1
2
3
4
5
ATP
PiPi
Extracellular fluid (ECF)
ADP
Ca2+
Ca2+
Ca2+
Plasma membrane
Sarcoplasmicreticulum
Inactive calmodulin
Inactive kinase
Inactivemyosin molecule
Activated (phosphorylated)myosin molecule
Activated kinase
Activated calmodulin
Cytoplasm
Calcium ions (Ca2+)enter the cytosol fromthe ECF via voltage-dependent or voltage-independent Ca2+
channels, or fromthe scant SR.
Ca2+ binds to andactivates calmodulin.
Activated calmodulinactivates the myosinlight chain kinaseenzymes.
The activated kinase enzymescatalyze transfer of phosphateto myosin, activating the myosinATPases.
Thinfilament
Thickfilament
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2. Type of Contraction Slow contraction due to poor arrangement of
fibers Does not fatigue Tonic type of contraction Calcium involved from
SR Extracellular Movement is slower since there are no T-Tubules
See Fig. 9.29
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3. Visceral/single unit vs. Multiunit a) sheets lining blood vessels a) larger blood vessels
and walls of organs airways, eye muscles, arrector pili muscles
b) tight junctions between muscle cells
c) one nerve controls many different muscle cells, wave-like contraction
c) individual muscles with separate
motor nerves