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8/8/2019 LSB231.5 Muscle Tissue Physiology Student Version Slides
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LSB231-Ph siolo
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Muscle Ph siolo
Muscle tissueMuscle tissuena omy o s e e a musc esna omy o s e e a musc es
The neuromuscular junctionThe neuromuscular junction
Huxleys sliding filament theoryHuxleys sliding filament theory
ContractionContraction
o or un so or un s
Types of skeletal muscle fibresTypes of skeletal muscle fibres
Other muscle typesOther muscle types
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Muscle Ph siolo
Learning objectivesLearning objectives n ers an e ana omy o s e e a musc e ce sn ers an e ana omy o s e e a musc e ce s
Understand the function of:Understand the function of:
The neuromuscular junctionThe neuromuscular junction
Excitation / Contraction CouplingExcitation / Contraction Coupling
o or un so or un s
Types of skeletal muscle fibresTypes of skeletal muscle fibres
Other muscle typesOther muscle types
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Muscle Tissue T es
Converts chemical energy into mechanical energy.Converts chemical energy into mechanical energy.
Three basic types of muscle:Three basic types of muscle:
SkeletalSkeletal striatedstriated voluntary controlvoluntary control
r ir i riri inv l n r n r linv l n r n r lSmoothSmooth nonnon--striatedstriated involuntary controlinvoluntary control
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Muscle Tissue T es
2. Skeletal
1. Cardiac
3. Smooth
voluntary involuntary
involuntary
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Muscle Tissue Functions
Muscle tissue facilitates;
Body posture
Stabilisation of joints Movement of substances internally
Regulation of organ volume
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Root words: refixes & suffixes
Root words:
Muscle from the Latin forlittle mouse mus
myo or mys gk = muscle sarco sarx k = flesh
plasm gk = form or mould
lemma = k sheath or husk(refers to plasma membrane)
mere = se ment
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Anatom of Skeletal Muscle
Levels of structure:Levels of structure:
Fascicle = (bundles)Fascicle = (bundles)
MyoMyo--fibril: linkedfibril: linked sarcomeressarcomeresThick and thin filamentsThick and thin filaments
Thick: myosinThick: myosin
Thin:Thin: actinactin and othersand othersSarcoplasmic reticulumSarcoplasmic reticulum
Stores and releases CaStores and releases Ca2+2+
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Skeletal Muscle Cross-Section
Endomysium = fine layer
of connective tissue
fibre (cell)
Perim sium = la er of
fibrous connective tissuewhich surrounds each
fascicle
Epimysium = layer of
tissue surrounds muscle
sometimes blends with
deep facia betweenneighbouring muscles
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Anatom of Skeletal Muscle
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Skeletal Muscle Fibres Stained
Alternating A (dark) and I (light) bands seen underthe microscope. Striated
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Muscle Fibres Cells
Muscle cells:
-,
Multinucleated formed from hundreds of embr onic cells
Nuclei are pressed against sarcolemma (plasma membrane)
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Muscle Fibres Cells
Muscle cells:
Myoglobin used to transport O (similar to haemoglobin)
Contain many glycosomes (granules of glycogen)
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M ofibrils
Myofibrils:
Run the whole length of
30cm long!)
Are 1-2m
Are composed of repeating
units called sarcomeres
Give the muscle cell its
stri ed striated
appearance
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Sarcomeres
Sarcomeres:
Are the individualcontractile units of muscle
fibres
Mainly consist of two
Thick filaments Myosin
Thin filaments - Actin
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Sarcomere:- Ma or Com onents
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Thin Filament
Thin filaments:
5-6nm in , 1 m long
G-actin proteins (g=globular)
Two chains of these molecules
are wound into an F-actinhelix (f=filamentous)
Each F-actin is attached to
the Z-line.
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Thin Filament
The actin filament has a
number of other proteins
F actin
tro om osin
troponins nebulin
Troponin (3 proteins)
TnC binds Ca2+
TnI binds Actin
Tropomyosin changes shapewhen troponin binds Ca2+
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Thin Filament
,
tropomyosin + actin prevents
m osin from bindin G actin activesite
Active site binds myosin during
contraction not at rest
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Thick Filament
The thick filaments are composed ofmyosin proteins and
arranged such that the tails are linked in the middle
A titin protein runs through the centre of each thick filament
and traverses the sarcomere
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Thick Filament
Thick Filament
-
1.6 microns long
~
thick filament
2 myosin polypeptide
chains wound around each other
ATP/ADP + Pi binding sites
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Thick Filament
Titin:
Very Large protein Largest po ypept e
discovered
attaches them to Z line
stabilises filaments
with nebulin
helps resist stretch a stretchy protein
allows muscle to spring
within core of thickmyosin filament
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Along the F-actin are attachment sites for the myosin heads.
The binding of the myosin head to its actin binding site forms a
crossbridge
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Muscle Contraction
Each sarcomere that makes u the m ofibril
shortens when the muscle cell (fibre) contracts
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Muscle Contraction
cell
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Neural Control
CNS activates muscle somatic motor division
motor neurons
long axons m elinated
> 1m
nerve cell bod inspinal cord or brain
alwa s excitator
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Neural Control
Control over skeletal muscle
(connections cross over)
Contralateral
Motor cortex divided intoareas of the body
o or omuncu us
Stimulate - movement
precision and complexityof motor skills
Many other areas of brainalso involved
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The Neuromuscular Junction
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The Neuromuscular Junction
The neurotransmitter
is degraded by
acetylcholinesterase.
action potential which then
spreads over the whole surface of
the muscle cell.
The muscle cell starts to contract.
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Neuromuscular Junction vs S na se
1. Both separated by a synaptic cleft.1. Both separated by a synaptic cleft.
2. Neurotransmitter is released when calcium gates open.2. Neurotransmitter is released when calcium gates open.
. .. .
4. Neurotransmitter opens gates in the postsynaptic membrane.4. Neurotransmitter opens gates in the postsynaptic membrane.
5. The membrane potential change which results is graded.5. The membrane potential change which results is graded.
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Neuromuscular Junction vs S na se
erences
1. A synapse is a junction between two neurons.1. A synapse is a junction between two neurons.
A Neuromuscular Junction (NMJ) is between a neuron and aA Neuromuscular Junction (NMJ) is between a neuron and a
skeletal muscle cell.skeletal muscle cell.
2. There is always an action potential in a postsynaptic membrane2. There is always an action potential in a postsynaptic membrane
when neurotransmitter is released in an NMJ.when neurotransmitter is released in an NMJ.
A synapse needs summation of Excitatory Post synaptic Potentials.A synapse needs summation of Excitatory Post synaptic Potentials.
3. A NMJ is always excitatory.3. A NMJ is always excitatory.
A synapse may be excitatory or inhibitoryA synapse may be excitatory or inhibitory
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An action potential spreads rapidly over the muscle cell from
t e NMJ ut t ere is a rie atent perio 5 to 10 msecs
before contraction occurs
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Excitation
e ore a musc e ce can contract ca c um must e re ease
into the cytoplasm
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Com onents Needed For Excitation
The sarcolemma is the muscle cell membrane
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Com onents Needed For Excitation
T-tubules are extensions of the muscle cell membrane deep
into the cytoplasm of the muscle cell.
They are filled with extracellular fluid.
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Com onents Needed For Excitation
e sarcop asm c ret cu um s a networ o mem ranous
channels throughout the cytoplasm of the muscle cell.
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Com onents Needed For Excitation
the T-tubule to the sarcoplasmic reticulum
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Com onents Needed For Excitation
erm na c sternae are part o t e
sarcoplasmic reticulum which stores calcium
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Com onents Needed For Excitation
a c um c anne s ea rom t e sarcop asm c ret cu um nto
the cytoplasm. They are normally closed.
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Com onents Needed For Excitation
Calcium is continually being pumped from the
cytoplasm back into the sarcoplasmic reticulum.
This is an active transport process.
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Excitation Process
The action potential
spreads from theNMJ all over the
sarcolemma.
It spreads down into- .
It spreads throughthe junctional feetinto the
sarcop asm c
reticulum
E i i P
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Excitation Process
The calcium
channels are voltagegated and open.
a c um usesinto the cytoplasm.
Calcium binds to
troponin whichleads to the
attachment of
myos n ea s.
E it ti P
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Excitation Process
Myofibrils start to
contract.
Calcium is pumpedou o e
cytoplasm.
Myosin binding sites
are covered and themyofibrils relax.
Bi h i
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Biomechanics
.
.
To lift an object (i.e. shorten the muscle).
Bi h i
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Biomechanics
load unchanged (isotonic)
Tension = Load length unchanged isometric
Tension < Load muscle stretches eccentric
-bridges provide brake.
C t i i t i t ti
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Concentric isotonic contraction
resistance and the muscle shortens
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Isometric contraction
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Isometric contraction
Crossbridges cycle but can not overcome the
resistance wei ht
The muscle does not shorten
Eccentric contraction
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Eccentric contraction
the muscle gradually lengthens
Eccentric contraction
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Eccentric contraction
Stren th len th relationshi s
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Stren th len th relationshi s
Stretching a muscle too much results in a decreased force
generated
A Muscle Twitch
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A Muscle Twitch
A Muscle Twitch
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A Muscle Twitch
A single action potential will cause a muscle to contract
briefly then relax
Muscle Twitch
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Muscle Twitch
Muscle twitch has 3 phases
Latent Period ECC isoccuring and muscle tension
is building.
Period of Contraction X
bridges are active from onset
development, lasts 10-100ms.
10-100ms, initiated by re-
entry of Ca2+ to SR
Muscle Twitch
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Muscle Twitch
Muscle twitch is rapid in
some muscles and slower inothers.
Rapid, short duration
eyes
Slower lon er duration-Calf muscles
The effect of multi le stimulation
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The effect of multi le stimulation
called wave summation Due to additional stimulus before muscle has completelyrelaxed (repolarised)
Due to Ca2+ release from SR
The effect of multi le stimulation
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The effect of multi le stimulation
constant but is applied repeatedly Relaxation time between twitches becomes shorter [Ca2+] in sarcoplasm increases further
Degree of summation becomes greater
The effect of multi le stimulation
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The effect of multi le stimulation
muscle tension increases until maximum tension is reached Relaxation disappears & contractions are fused Result smooth, sustained contraction plateau
Skeletal muscle motor units
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Skeletal muscle motor units
The combination of the motor nerve cell (neuron) and all
the muscle cells it innervates is known as a motor unit
Skeletal muscle motor units
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Skeletal muscle motor units
Motor units are the functional divisions of a muscle.
Each muscle cell in a unit contracts at the same time.
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Skeletal muscle motor units
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Skeletal muscle motor units
usc es conta n many motor un ts
Act as individual entities - contract as individual units.
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Motor unit recruitment
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Motor units are not allexcited simultaneously
nsion
stimulated to contractmotor unit 3
recruited
uscleT
While some motor unitsare contracting andmotor unit 21recruited
recruited
ole-M
shortening within the
muscle belly, others willmotor unit 1W
lengthening
Motor unit recruitment
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More force is generated in a muscle by recruiting more motor
units
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Stren th of motor units
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The more fibres in a motor unit the stronger the unit
Motor units motor control
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FINE MOTOR CONTROL The motor units have a small number of
musc e ce s.
e.g. in muscle moving the eyeball only
GROSS MOTOR CONTROL The motor units have a large number of
muscle cells
e.g. n t e erector sp nae musc es o t eback 1000 3000 muscle cells in each
Lets watch a movie of muscles in action
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then discuss muscle energy requirements
Muscle ener & metabolism
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Muscle cells have about 4-6 sec of ATP reserves
reat ne nase regenerates rom reat nephosphate (CP) almost immediately following hydrolysis of
Together ATP and CP stores fuel maximum power for 10-15 sec
Muscle ener & metabolism
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T es of muscle fibres
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Muscle fibres can be classified according to
ze: ys ca ame er
a e o con rac on: a e o ase ac v y
myosin and calcium/ATPase pump
Major pathway used to produce ATP
mitochondria.
l col tic: via l col sis lar e store of l co en .
T es of muscle fibres
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Muscle fibres can be classified according to
ype . ma , ow, x a ve res.ype . ma , ow, x a ve res.
ypeype aa.. --s ze, as , x a ve res.s ze, as , x a ve res.
ypeype . arge, as ,. arge, as , yco y cyco y c res.res.
,generated.
myofibrils.
Cross-section of skeletal muscle
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Stained to show the slow twitch (type I) fibres
(dark blue, mitochondria)
Slow and fast-twitch muscles
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A single skeletal muscle ismade up of both major fibre
types:-
i.e. slow twitch (ST) and
as w c
into motor units.
Motor units never have amixture of fibre types.
Slow and fast twitch muscles
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On average muscles contain:- 50% ST and 50% FT
but the percentages do change in individual muscles
Fast & slow-twitch fibre differences
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Speed at which the myosin head splits ATP
fibre
Fast twitch fibres have larger diameter axons
Slow twitch motor units have 10 - 200 fibres whereas fasttwitch typically have 300 - 800 fibres
Fast twitch motor units generate more force than slow twitch
Fast twitch motor units fatigue more quickly than slow twitch
Slow twitch fibres
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twitch motor unit
These take about 110milliseconds to reach
pea ens on w en
excited
Sometimes these arecalled type I or slow
oxidative (SO) fibres
ey ma e up a s ow
twitch motor unit
F i i i
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A slow twitch (SO) fibre is fatigue resistant
Fast twitch fibres
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They make up a fast twitchmotor unit
milliseconds to reach peak
They can be furthersubdivided into FTa, FTb,
and FTc fibres
Sometimes these are called
Glycolytic(FG) and Fast
Oxidative/glycolytic (FOG)
Fast twitch motor units
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In general there are 300to 800 muscle fibres in a
In eneral fast twitchmotor units are stronger
than slow twitch ones
Motor units are fast to
but fatigue easily
Fati ue due to lactic acid
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A fast twitch (FG) fibre fatigues quickly
It generates most of the lactic acid
Fati ue due to lactic acid
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.
It generates lots of lactic acid.
Motor unit recruitment
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In general small motor units are recruited before larger ones
-
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ar ac ssue
-
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ar ac ssue - sto ogy
joined together and function
as a s nc tium
The striated appearance isue to sarcomeres
fibres
-
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moot musc e
-
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moot musc e - structure
Spindle shaped
e ac n an myos n are no
arranged into sarcomeres
Roughly central nucleus
-
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moot musc e - sto ogy
-
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moot musc e - sto ogy
Artery wall
Smoothmusc e
Overwhelmed??...dont be!
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Words of encouragement if your finding this a lot of
information to digest