Chapter 10
Muscle Tissue
(Mostly Skeletal Muscle)
Muscle tissue:
skeletal
bones
cardiac
heart
smooth
“hollow organs”
Muscle tissue:
skeletal muscle functions
move skeleton
maintain balance/posture
support soft tissues
guard entrances/exits
maintain body temp
store nutrients
Muscle tissue:
muscle contains
muscle cells
connective tissue
nerves (axons)
blood vessels
muscle (and connective tissue)
surrounded by epimysium
subdivided into fascicles
surrounded by perimysium
fascicles contain myofibers
surrounded by endomysium
fig. 10-1
three connective tissues:
epimysium
perimysium
endomysiyum
blend into each other,
and the end of the muscle
blend into the tendon
three connective tissues:
contain: blood vessels
and 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
large
multinucleated
cells
(myofibers)
myofibers
cell membrane
sarcolemma
cytoplasm
sarcoplasm
filaments 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
myofibril
tc T tc
myofibers:
contain myofibrils
myofibrils:
contain myofilaments
thin filaments
thick filaments
actin
myosin
Thin filaments:
G actin (globular)
F
actin
(filamentous)
Other components:
Troponin (covers active site)
Tropomyosin
Nebulin
Thin filaments:
fig. 10-7b
fig. 10-7a, b
Thick filaments:
myosin
head
tail
Thick filaments:
binds to active site on
thin filaments
fig. 10-7d
fig. 10-7c, d
fig. 10-7c, d
to here
Monday 2/5
lec # 13
fig. 10-6
muscle
fascicles
myofibers
myofibrils
thick & thin
filaments
fig. 10-4
A band
I band
Z line
A band
I band
Z line
A
muscle structure terms
sarcomere
from Z line to Z line
A band
where myosin is
M line
center of A band
H zone
where actin isn’t
center of A band
I band
where myosin isn’t
Z line in center
overlap
actin and myosin
tc T tc
triad
titin
fig. 10-5
when muscle contracts:
A band
I band
H zone
Z lines
overlap
same
shrinks
shrinks
closer
increases
sliding filament theory
fig. 10-8
The contraction of skeletal m.
background physics:
tension
compression
pull towards
push away
overcome resistance
muscle cells only pull (produce tension)
generate force by getting shorter
OVERVIEW
motorneuron AP
release nt
AP in myofiber
release Ca2+
thick/thin interact
contraction
tension
fig. 10-9
control of skeletal muscle
motorneurons in CNS
synapse with myofiber
neuromuscular junction
aka myoneural junction
aka motor end plate (mep)
each myofiber is innervated by
a myelinated motorneuronfig. 10-9
neuromuscular junction (nmj)
axon terminal with ACh
synaptic cleft
postsynaptic membrane
(aka sarcolemma)
junctional folds
AChR and AChE
fig. 10-10
neuronal AP
myofiber AP
contraction ?
Excitation-Contraction Coupling
myofiber AP
(depolarization of sarcolemma)
depolarization
of 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)
remember structure:
fig. 10-7b
fig. 10-5
myosin
heads
fig. 10-11
Now we are ready for
the contraction cycle
(almost)
fig. 10-7
fig. 10-12
AP
AP
Ca2+
2
1
expose active site
fig. 10-12
form cross-bridges
“POWER STROKE”
4
3
cross bridge detachment
re”energize” the myosin
fig. 10-12
5
re energize myosin
fig. 10-12
As long as Ca2+ is present…
power stroke
re-energize
power stroke
re-energize
sarcomere shortens ~1%/cycle
tug-of-war
energize
reach
cross-bridge
grab
power stroke
pull
release release
tug-of-war
repeat cycle
reach
grab
pull
release
what if everybody released at
the same time?
actin
myosin
Z
line
sarcomere
Z
line
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 2/7
lec # 14
with contraction cycle…
each sarcomere get shorter…
…each myofiber is lots of
sarcomeres end to end…
…myofiber gets shorter…
…muscle gets shorter
As muscle gets shorter…
…it generates tension (pulls)
Skeletal muscles are attached
to bone at both ends
origin
insertion
actions
action:
flex at elbow
origin
insertion
fig. 11-2
How long will muscle contract ?
As long as:
continued stimulus at nmj
+ free Ca2+ in sarcoplasm
+ ATP to energize myosin…
…muscle will keep contracting
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 muscle
when 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.
death
no nutrients to muscle
ATP gets used up
Ca2+ pumps quit
myosin binds to actin
“freezes” muscle
rigor mortis
rigor mortis
occurs after a few hours
last for 15-25 hrs
until lyzozymal enzymes start to break
down muscle proteins
Have covered:
Muscle architecture
Mechanism of contraction
Still to come:
Tension Production
Energy Use
Muscle Performance
cardiac muscle
smooth muscle
Tension production
by myofibers
by muscles
Tension production
by myofibers:
Amount of tension produced
depends on number of
“power strokes” happening
Tension production
by myofibers:
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:
but…
“tension production at the level of the
individual cell does vary”
frequency of stimulation
resting length of fiber
Tension production
by myofibers:
resting length vs. tension in myofibers
Amount of tension produced
depends on number of
power strokes happening
resting length vs. tension in myofibers
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
tension produced
resting length vs. tension in myofibers
length of sarcomere
fig. 10-14
Tension production
by myofibers:
frequency of stimulation
resting length of fiber
frequency of stimulation
single stimulus (AP)
single contraction (twitch)
7-100 msec
frequency of stimulation
a single twitch has phases
latent phase
contraction phase
relaxation phase
Stimul
fig. 10-15
myogram
fig. 10-15
What if we stimulated a muscle cell,
let it contract and relax,
and then stimulated it again?
tension
time
fig. 10-16a
What if we stimulated a muscle cell,
let it contract and relax
(but not all the way),
and then stimulated it again?
tension
time
fig. 10-16b
tension
wave summation
time
fig. 10-16b
tension
time
fig. 10-16c
tension
incomplete tentanus
time
fig. 10-16c
tension
complete tentanus
time
fig. 10-16d
twitch
cycle
stimulation
rate
<
stimulation
rate
> twitch cycle
stimulation
rate
stimulation
rate
>
twitch
cycle
latent p
+
contraction p
>
treppe
1st
2nd
fig. 10-15
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 quickly
very little bleeding
Clostridium tetani
live is soil
(low O2 levels)
If it gets into the body:
divide
release tetanospasmin
(powerful neurotoxin)
carried to CNS by
retrograde transport
disables GABA-releasing
neurons (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
DTP
5X
(diptheria, tetanus, pertussis)
to here 2/9
lec # 15
Tension production
by myofibers
myofiber length
stimulation rate
by muscles
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 controlled
by a single neuron…
…motor
unit
size of motor unit…
(how many myofibers/unit)
…indication of how precisely
the muscle is controlled
for example
eye muscles
4-6 fibers/unit
leg muscles
1000-2000
within the muscle
myofibers are intermingled
fig. 10-17
think…
…move muscle
activate smallest motor units
keep thinking…
…move muscle
activate larger motor units…
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:
rotate which motor units are
being activated
asynchronous motor
unit summation
(can’t do it at max. tension)
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
isotonic
isometric
contractions
isotonic (equal tension)
rise in tension leads to
change in the muscle
length
fig. 10-18
isotonic contractions
concentric
muscle shortens
(overcomes resistance)
eccentric
muscle lengthens
(control)
contractions
isometric (equal measure)
•muscle length does
not change
•doesn’t produce
enough tension to
overcome resistance
isometric
fig. 10-18
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
inversely related
lighter resistance…
…faster speed of contraction
heavier resistance…
…slower speed of contraction
Returning a muscle to resting length
can’t actively lengthen muscle
can stretch it
opposing muscle
elastic forces
gravity
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
myosin (unenergized):
ATP
ADP + P
myosin (energized):
Energy use and Muscle activity
(as muscle uses ATP it makes ADP)
ATP
ADP + P
creatine
ADP +
phosphate
ATP + creatine
TABLE 10-2
Energy use and Muscle activity
(as muscle uses ATP it makes ADP)
ATP
ADP + P
creatine
ADP +
phosphate
CPK
ATP + creatine
Energy use and Muscle activity
CPK (or CK)
creatine phosphokinase
if muscle is damaged, CK
leaks 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
CO2
O2
ETS
ATP
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 ATP
use fatty acids for C source
lots of O2 available
extra ATP --->CP
glycogen is stored
at rest
fig. 10-20
Energy use and Muscle activity
moderate activity
higher demand for ATP
if enough of O2 available
mitochondria can supply ATP
via cellular respiration
fig. 10-20
Energy use and Muscle activity
high activity
anaerobic
enormous demand for ATP
no enough O2 delivered
(ETS will not work fast enough)
cells use ATP from glycolysis
make pyruvate
converted to lactic acid
pH
fig. 10-20
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
peak activity
hours
days-week
to here 2/12
lec # 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 acids
moderate 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 pyruvate
liver 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 heat
only 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 fibers
physical conditioning
Muscle Performance
Two factors influence performance
types of muscle fibers
fast fibers
intermediate fibers
slow fibers
Muscle Performance
fast fibers
contract very quickly after stimulation
large diameter
packed with myofibrils
large glycogen reserves
few mitochondria
fatigue easily
aka “white muscle fibers”
Muscle Performance
slow fibers
slower rate of contraction
1/2 diameter of fast fibers
more mitochondria (and what they need)
good blood supply
contain abundant myoglobin
more for extended contractions
aka “red muscle fibers”
Muscle Performance
intermediate fibers
in between
look like fast fibers
little myoglobin (pale)
but…
better blood supply than fast
more resistant to fatigue than fast
table 10-3
Muscle Performance
skeletal muscle
can have different percentages of the
different fiber types
hand/eye fast
back/calf slow
genetically determined
can be altered with exercise
Muscle Performance
skeletal muscle growth
repeated, exhaustive stimulation
more mitochondria
more glycolytic enzymes
more myofibrils
more filaments
cells get bigger
hypertrophy
Muscle Performance
skeletal muscle growth
non-stimulated muscles
get smaller
loose muscle tone
become weaker
atrophy
Muscle Performance
skeletal muscle growth
atrophy
temporary immobilization
(leg in a cast)
initially reversible
in 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] available
tolerance 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
fast fibers can take on
intermediate characteristics
improving CV performance
increased capillarity
accelerate blood flow
Muscle Performance
Physical conditioning
aerobic endurance improvement
does not promote hypertrophy
cross-training
combination aerobic and anaerobic
exercise for benefits of both
Cardiac Muscle
like skeletal:
striated (organized myofibrils)
unlike skeletal:
smaller cells
no triads
SR lacks terminal cisternae
dependent on aerobic metabolism
special cell-cell junctions
Cardiac Muscle
intercalated discs
junctions to hold the cells together
(adhering junctions)
junctions allowing for
cell-cell communication
(gap junctions)
functional syncytium (fused cells)
Cardiac Muscle
functional specializations:
•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
fig. 10-22
Smooth Muscle
forms sheets, bundles or sheaths
skin:
blood vessels regulate blood
flow to surface (thermoregulation)
cardiovascular:blood distribution
blood pressure
respiratory:
change airways / airflow
Smooth Muscle
forms sheets, bundles or sheaths
digestion: move material through
urinary:
urine production, transport…
reproduction: gamete movement
labor
Smooth Muscle
structure
small, single cells, central nucleus
no organized myofibrils
(no striations)
have thick and thin filaments
connected to neighbors
to here 2/14
lec # 17
Smooth Muscle
functional differences:
1. excitation-contraction coupling
calcium enters cells at stimulation
binds to calmodulin
activates an enzyme to
permits cross-bridges to form
Smooth Muscle
functional differences:
2. length-tension relationship
plasticity
ability to contract over a wide
range of lengths
Smooth Muscle
functional differences:
3. control of contractions
multiunit
similar to skeletal
iris m., arrector pili m., ….
visceral
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
injury to a ligament
strain
injury to a muscle to tendon
Muscle cramps
(via wikipedia)
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).
(postive feedback-next chapter)