Post on 27-Dec-2015
Chapter 10
Muscle Tissue(Mostly Skeletal Muscle)
skeletal
cardiac
smooth
bones
heart
“hollow organs”
Muscle tissue:
Muscle tissue:
skeletal muscle functions
move skeletonmaintain balance/posturesupport soft tissuesguard entrances/exitsmaintain body tempstore nutrients
muscle cellsconnective tissuenerves (axons)blood vessels
Muscle tissue:
muscle contains
surrounded by epimysium subdivided into fascicles
surrounded by perimysium fascicles contain myofibers
surrounded by endomysium
muscle (and connective tissue)
fig. 10-1
three connective tissues:
epimysiumperimysiumendomysiyum
blend into each other,and the end of the muscle
blend into the tendon
three connective tissues:
contain: blood vesselsand nerves
that supply the muscle
skeletal muscle
voluntary muscle
although many are also controlled subconsciously too
skeletal muscle
formation and structure
fig. 10-2
myoblast fuse
forming
largemultinucleated
cells(myofibers)
myofibers
cell membrane sarcolemmacytoplasm sarcoplasmfilaments organized into myofibrils
T-tubules (transverse)-extensions of the sarcolemma
to the interior of the cell-surround myofibrils
fig. 10-3
sarcoplasmic reticulum (SR)
•modified sER(smooth endoplasmic reticulum)
•also surrounds myofibrils•expanded ends called
terminal cisternae•gather and store Ca2+
fig. 10-3
myofibriltc tcT
myofibers:
contain myofibrils
myofibrils:
contain myofilaments
thin filamentsthick filaments
actinmyosin
G actin (globular)
Factin
(filamentous)Other components:Troponin (covers active site)TropomyosinNebulin
Thin filaments:
fig. 10-7b
Thin filaments:
fig. 10-7a, b
Thick filaments:
myosin
tail
head
fig. 10-7d
Thick filaments:
binds to active site onthin filaments
fig. 10-7c, d
fig. 10-7c, d
to hereMonday 2/5lec # 13
muscle
fascicles
myofibers
myofibrils
thick & thinfilaments
fig. 10-6
fig. 10-4
Z line Z line
I band I bandA bandA band A band
from Z line to Z linesarcomere
M line
H zone
A band
overlap
I band
where myosinmyosin is
center of A band
where actin isn’tcenter of A band
where myosinmyosin isn’tZ line in center
actin and myosinmyosinmusc
le s
truct
ure
term
s
titin
T tctctriad
fig. 10-5
when muscle contracts:
A band sameI band shrinksH zone shrinksZ lines closeroverlap increases
sliding filament theory
fig. 10-8
The contraction of skeletal m.
background physics:
tension pull towardscompression push away
overcome resistance
muscle cells only pull (produce tension)generate force by getting shorter
fig. 10-9
motorneuron APrelease ntAP in myofiberrelease Ca2+
thick/thin interactcontraction
tension
OVERVIEW
fig. 10-9
control of skeletal muscle
motorneurons in CNS
synapse with myofiber
neuromuscular junctionaka myoneural junctionaka motor end plate (mep)
each myofiber is innervated by a myelinated motorneuron
neuromuscular junction (nmj)
axon terminal with ACh
synaptic cleft
postsynaptic membrane(aka sarcolemma)
junctional foldsAChR and AChE
fig. 10-10
neuronal AP
myofiber AP
contraction ?
Excitation-Contraction Coupling
myofiber AP(depolarization of sarcolemma)
depolarizationof the T-tubules
release of Ca2+
from sacroplasmic reticulum
release of Ca2+
from sacroplasmic reticulum
Ca2+ interacts with troponin(on thin filaments)
exposing active site(myosin will now bind)
fig. 10-7b
remember structure:
fig. 10-5
fig. 10-11
myosinheads
Now we are ready forthe contraction cycle
(almost)
fig. 10-7
fig. 10-12
APAP
Ca2+
1 2
fig. 10-12
expose active site form cross-bridges
34
fig. 10-12
cross bridge detachmentre”energize” the myosin
“POWER STROKE”
5
fig. 10-12
re energize myosin
As long as Ca2+ is present…
power stroke
re-energize
power stroke
re-energize
sarcomere shortens ~1%/cycle
tug-of-war
reachgrab
pull
energizecross-bridge
power strokereleaserelease
tug-of-war
reachgrab
pullrelease
repeat cycle
what if everybody released at the same time?
myosinactin
Zline
Zline
sarcomere
cross bridge formation
power stroke
release
energize
cross bridge formation
power stroke
release
energize
cross bridge formation
power stroke
release
energize
cross bridge formation
power stroke
to here 2/7lec # 14
…each myofiber is lots of sarcomeres end to end…
with contraction cycle…each sarcomere get
shorter…
…myofiber gets shorter……muscle gets shorter
As muscle gets shorter……it generates tension (pulls)
Skeletal muscles are attachedto bone at both ends
origin
insertion
action:flex at elbow
origininsertionactions
fig. 11-2
How long will muscle contract ?
continued stimulus at nmj+ free Ca2+ in sarcoplasm+ ATP to energize myosin…
…muscle will keep contracting
As long as:
If stimulus disappears:
ACh broken down by AChE
sarcolemma returns to RP
Ca2+ is reabsorbed by SR
active sites covered by troponin
What happens to the musclewhen contraction stops ?
muscle cannot lengthen on its own
muscles are “paired”
agonist muscle that does action
antagonist has opposite action(stretches agonist)
Muscle cannot lengthen on its own…
…it has to be stretched.
bic
ep
s b
rach
ii
tric
eps
bra
chii
flex forearm
ext
end f
ore
arm
death
no nutrients to muscleATP gets used upCa2+ pumps quitmyosin binds to actin“freezes” muscle
rigor mortis
rigor mortis
occurs after a few hourslast for 15-25 hrs
until lyzozymal enzymes start to break down muscle proteins
Muscle architectureMechanism of contraction
Have covered:
Tension ProductionEnergy UseMuscle Performance
cardiac musclesmooth muscle
Still to come:
Tension production
by myofibersby muscles
Tension production
by myofibers:
Amount of tension produceddepends on number of“power strokes” happening
Cannot vary the amount of tension produced by a myofiber by varying number of sacromeres being used.
Tension production
by myofibers:
A single myofiber is either
stimulated “on”
or
relaxed (off)
Tension production
by myofibers:
“tension production at the level of the individual cell does vary”
Tension production
by myofibers:
frequency of stimulation resting length of fiber
but…
Tension production
by myofibers:
resting length vs. tension in myofibers
Amount of tension produceddepends on number ofpower strokes happening
the number of cross-bridges forming will depend on the degree of overlap between the thin and thick filaments(zone of overlap)
only those myosin molecules that can form cross-bridges will produce tension
resting length vs. tension in myofibers
fig. 10-14
resting length vs. tension in myofibers
length of sarcomere
ten
sion
pro
du
ced
Tension production
by myofibers:
frequency of stimulationresting length of fiber
single stimulus (AP)
frequency of stimulation
single contraction (twitch)
7-100 msec
a single twitch has phases
frequency of stimulation
latent phasecontraction phaserelaxation phase
fig. 10-15
Stimul
fig. 10-15
myogram
What if we stimulated a muscle cell,
let it contract and relax,
and then stimulated it again?
fig. 10-16a
time
tensi
on
What if we stimulated a muscle cell,
let it contract and relax(but not all the way),
and then stimulated it again?
fig. 10-16b
time
tensi
on
fig. 10-16b
time
tensi
on
wave summation
fig. 10-16c
time
tensi
on
fig. 10-16c
time
tensi
on
incomplete tentanus
fig. 10-16d
time
tensi
on
complete tentanus
stimulationrate < twitch
cycle
stimulationrate > twitch
cycle
stimulationrate >twitch cycle
stimulationrate >
latent p+
contraction p
fig. 10-15
1st 2nd
treppe
an aside…
Don’t play around rusty nails !
Don’t run around barefoot outside!
Have you had your tetanus shot ?
What is tetanus ?
Tetanus
prolonged contraction of muscle
Why rusty nails ?
puncture wound
closes very quicklyvery little bleeding
Clostridium tetani
live is soil(low O2 levels)
If it gets into the body:
dividerelease tetanospasmin
(powerful neurotoxin)
carried to CNS byretrograde transport
disables GABA-releasingneurons (inhibitory nt)
overstimulation of motorneurons
If it gets into the body:
overstimulation of motorneurons
sustained, powerful contraction of skeletal muscle throughout body
“lockjaw”
Sir Charles Bell ,1809
Not much of a problem in developed nations…
immunizations&
booster shots
DTP5X
(diptheria, tetanus, pertussis)
return from aside
to here 2/9lec # 15
Tension production
by myofibers
by muscles
myofiber lengthstimulation rate
Tension production
by muscles
tension from myofibers# myofibers stimulated
“The amount of tension produced by a muscle as a whole is the sum of the tensions generated by the individual muscle fibers,” (pg 304)
Tension production
•each muscle - 1000’s of fibers
•muscle fibers - controlled by neurons•motorneurons - control many myofibers
all the fibers controlledby a single neuron…
…motor unit
size of motor unit…
…indication of how precisely
the muscle is controlled
(how many myofibers/unit)
for example
eye muscles
leg muscles
4-6 fibers/unit
1000-2000
within the muscle
myofibers are intermingled
fig. 10-17
think… …move muscle
activate smallest motor units
activate larger motor units…
keep thinking… …move muscle
smooth, steady increase in tension
smooth, steady increase in tension
recruitment
peak tension is produced when all motor units are in complete tetany
(can’t do it for long)
in sustained contractions:
(can’t do it at max. tension)
rotate which motor units are being activated
asynchronous motor unit summation
fig. 10-17
Key (pg 305)
“All voluntary muscle contractions and intentional movements involve sustained contractions of skeletal muscle fibers. The force exerted can be increased by increasing the frequency or motor neuron action potentials or the number of stimulated motor units (recruitment).”
muscle tone
resting muscle…
…always has some fibers contracting
don’t produce enough tension to cause movement, but they tense and firm the muscle
muscle tone
•holds bones in place•keeps body balanced(position)•prevent sudden movements•shock absorption•a muscle with good tone will
burn more Calories than one with poor muscle tone
contractions
isotonicisometric
contractions
isotonic (equal tension)
rise in tension leads to change in the muscle length
fig. 10-18
isotonic contractions
concentric
eccentric
muscle shortens(overcomes resistance)
muscle lengthens(control)
contractions
isometric (equal measure)
•muscle length does not change
•doesn’t produce enough tension
to overcome resistance
fig. 10-18
isometric
isometric contractions
although whole muscle does not shorten…
individual fibers do
isometric contractions
when would it be used?
…hold head up…carrying books…maintaining posture
Resistance and speed of contraction
lighter resistance…
…faster speed of contraction
inversely related
heavier resistance…
…slower speed of contraction
Returning a muscle to resting length
can’t actively lengthen muscle
can stretch it
opposing muscleelastic forcesgravity
Energy use and Muscle activity
single myofiber:
may have 15 billion thick filaments
each thick filament:
uses 2500 ATP molecules/sec
~ bazillion
Energy use and Muscle activity
muscle need lots of ATP
but ATP is for short-term storage
hot $ ?
Energy use and Muscle activity
ATP + creatine
ADP +creatine
phosphate(CP)
Energy use and Muscle activity
ATP ADP +
myosin (unenergized):
P
myosin (energized):
Energy use and Muscle activity
ATP ADP + P
ADP + creatinephosphate
ATP + creatine
(as muscle uses ATP it makes ADP)
TABLE 10-2
Energy use and Muscle activity
ATP ADP + P
ADP + creatinephosphate
ATP + creatine
CPK
(as muscle uses ATP it makes ADP)
Energy use and Muscle activity
CPK (or CK)
creatine phosphokinase
if muscle is damaged, CKleaks out of the cell into the blood ( high [CK] = muscle damage)
Energy use and Muscle activity
Aerobic metabolism(living with oxygen)
Most ATP demands (at rest) are met through TCA and ETS
organic molecules from cytoplasm
TCA
ETS ATP
O2
CO2
ß oxidation
of fatty acids
Energy use and Muscle activity
during contraction
swtiches to pyruvate as entry point into TCA
Where does pyruvate come from?
glycolysis
Energy use and Muscle activity
during contraction
What do we need to do glycolysis?
glucose
What does glucose come from?
glycogen in myofibers
Energy use and Muscle activity
at rest
low demand for ATPuse fatty acids for C sourcelots of O2 availableextra ATP --->CPglycogen is stored
fig. 10-20
at rest
Energy use and Muscle activity
moderate activity
higher demand for ATPif enough of O2 availablemitochondria can supply ATPvia cellular respiration
fig. 10-20
Energy use and Muscle activity
high activity
enormous demand for ATPno enough O2 delivered
(ETS will not work fast enough)cells use ATP from glycolysismake pyruvateconverted to lactic acid
anaerobic
fig. 10-20
pH
Energy use and Muscle activity
muscle fatigue
when the muscle can no longer perform at the required level
Energy use and Muscle activity
muscle fatigue
•depletion of energy reserves•damage to cell membrane, etc•decline in pH of myofibers
(decrease Ca2+ binding)
Energy use and Muscle activity
normal muscle function needs:
•intracellular energy reserves•normal blood supply•normal O2 levels•normal blood pH
interfere with any one of them…
…premature muscle fatigue
Energy use and Muscle activity
recovery period:
time needed for muscle to return to pre-exertion conditions
moderate activity hourspeak activity days-week
to here 2/12lec # 16
review 1
muscles cells contract… or ……don’t
vary tension by: ??
muscles have motor units:
vary tension by:
maximum tension is called
review 2
isotonic contraction: concentric?
isometric contraction:
Energy use by muscles
need ATP
stored as ??
review 3
Energy use by muscles
at rest fatty acidsmoderate work aerobic metab.heavy work anaerobic
(leads to build up of ?)
recovery period
Energy use and Muscle activity
removal of lactic acid (LA)
with O2, can be converted back to pyruvateliver can convert LA to glucose which goes back to the muscle
Cori cycle
Energy use and Muscle activity
Oxygen debt
supply O2 to tissues and allow for restoring pre-exertion levels of ATP, CP, glycogen,…
Energy use and Muscle activity
Heat production
~58 % of energy produced is lost as heatonly 42% goes to producing ATP
Energy use and Muscle activity
Hormones
GH and testosterone
stimulate synthesis of muscle tissue
TSH
stimulate energy consumption by muscle tissue
Energy use and Muscle activity
Hormones
epinephrine
stimulate muscle metabolism and contraction
Muscle Performance
How much force can be produced
tension produced by a muscle or group of muscles
How long can the muscle continue
endurance
Muscle Performance
Two factors influence performance
types of muscle fibersphysical conditioning
Muscle Performance
Two factors influence performance
types of muscle fibers
fast fibers
slow fibersintermediate fibers
Muscle Performance
fast fibers
contract very quickly after stimulationlarge diameterpacked with myofibrilslarge glycogen reservesfew mitochondriafatigue easilyaka “white muscle fibers”
Muscle Performance
slow fibers
slower rate of contraction1/2 diameter of fast fibersmore mitochondria (and what they need)good blood supplycontain abundant myoglobinmore for extended contractionsaka “red muscle fibers”
Muscle Performance
intermediate fibers
in betweenlook like fast fibers
little myoglobin (pale)but…
better blood supply than fastmore resistant to fatigue than fast
table 10-3
Muscle Performance
skeletal muscle
can have different percentages of the different fiber types
hand/eye fastback/calf slow
genetically determinedcan be altered with exercise
Muscle Performance
skeletal muscle growth
repeated, exhaustive stimulation
more mitochondriamore glycolytic enzymesmore myofibrilsmore filaments
cells get bigger
hypertrophy
Muscle Performance
skeletal muscle growth
non-stimulated muscles
get smallerloose muscle tonebecome weaker
atrophy
Muscle Performance
skeletal muscle growth
atrophy
temporary immobilization(leg in a cast)
initially reversiblein extreme cases: permanent
physical therapy
Muscle Performance
Physical conditioning
improve power (ability to generate tension)
improve endurance
Muscle Performance
Physical conditioning
anaerobic endurance
how long the muscle can work supported by glycolysis and stored ATP and CP
Muscle Performance
Physical conditioning
anaerobic endurance
limited by:
amount of ATP and CP stored[glycogen] availabletolerance to lactic acid
sprint work, pole vault, short events
Muscle Performance
Physical conditioning
anaerobic endurance
training:
frequent, brief,intense workouts
stimulate hypertrophy
Muscle Performance
Physical conditioning
aerobic endurance
how long the muscle can work supported by mitochondrial activity
Muscle Performance
Physical conditioning
aerobic endurance
limited by:
availability of substrates for aerobic respiration
dependent on blood supply
jogging, distance running, swimming, etc.,don’t require peak tension production
Muscle Performance
Physical conditioning
aerobic endurance improvement
changing characteristics of fibers
improving CV performance
fast fibers can take on intermediate characteristics
increased capillarityaccelerate blood flow
Muscle Performance
Physical conditioning
aerobic endurance improvement
does not promote hypertrophy
cross-trainingcombination aerobic and anaerobicexercise for benefits of both
Cardiac Muscle
like skeletal:striated (organized myofibrils)
unlike skeletal:smaller cellsno triadsSR lacks terminal cisternaedependent on aerobic metabolismspecial cell-cell junctions
Cardiac Muscle
junctions to hold the cells together(adhering junctions)
junctions allowing forcell-cell communication
(gap junctions)
functional syncytium (fused cells)
intercalated discs
Cardiac Muscle
•contract without neural stimulation
(beat is intrinsic)•nervous system can alter “pace”
and adjust tension produced•contractions are slower than
skeletal•wave summation and tetany don’t
occur
functional specializations:
fig. 10-22
Smooth Muscle
forms sheets, bundles or sheaths
skin: blood vessels regulate blood
flow to surface (thermoregulation)
cardiovascular: blood distributionblood
pressure
respiratory: change airways / airflow
Smooth Muscle
forms sheets, bundles or sheaths
digestion: move material through
urinary: urine production, transport…
reproduction: gamete movementlabor
Smooth Muscle
structure
small, single cells, central nucleusno organized myofibrils
(no striations)have thick and thin filamentsconnected to neighbors
to here 2/14lec # 17
Smooth Muscle
functional differences:
1. excitation-contraction coupling
calcium enters cells at stimulationbinds to calmodulinactivates an enzyme to
permits cross-bridges to form
Smooth Muscle
functional differences:
2. length-tension relationship
ability to contract over a wide range of lengths
plasticity
Smooth Muscle
functional differences:
3. control of contractions
multiunit
visceral
similar to skeletaliris m., arrector pili m., ….
contraction spreads in waves(peristalsis in gut)
Smooth Muscle
functional differences:
4. smooth muscle tone
neural and hormonal control
table 10-4
fig. 10-23
Muscle strains(pulls, tears)
sprain
strain
injury to a ligament
injury to a muscle to tendon
There are two basic causes of cramping. One is inadequate oxygenation of muscle,
and the other is lack of water or salt.
Electrolyte disturbance may cause cramping and tetany of muscles,
particularly hypokalemia (a low level of potassium) and hypocalcemia (a low level
of calcium).
Muscle cramps(via wikipedia)
(postive feedback-next chapter)