Chpt. 49
Muscles &
Motor Locomotion
Why Do We
Need All
That ATP?
Function of
• To convertMuscles:
chemical energy of ATP into
•
•
•
•
mechanical work,
To get around…
To get your food
To digest your food
To pump your heart
so that oxygen can
get to that
mitochondria
QuickTime™ and a
decompressor
are needed to see this picture.
Types of Muscle
Tissue:
• 1) Cardiac
rapid contraction
• 2) Skeletal
rapid contraction
• 3) Smooth
slow sustained contraction
QuickTime™ and a
decompressor
are needed to see this picture.
involuntary,
striated
auto-rhythmic
voluntary,
striated
heart
moves bone
multi-nucleated
evolved first
involuntary,
non-striated
digestive system
arteries, veins
QuickTime™ and a
decompressor
are needed to see this picture.
As a side
QuickTime™ and a
decompressor
are needed to see this picture.
…
• Insect flight muscles
contract more rapidly than
ANY OTHER
• 1,000
contractions/second
• Highest metabolic rate
• Contain more
mitochondria than any
other tissue
• HOW get oxygen???
HOW DO
WE MOVE
THESE 206
BONES?
SKELETAL MUSCLE
skeletal muscles move bones by
pulling…not pushing, therefore they
come in antagonistic pairs:
So in other words, in order to flex, you must contract your
flexor muscles… and in order to, relax, you must contract
the antagonistic muscle
flexor vs. extensor
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Extensor
(quadracep)
Notice the TENDON
connects the muscle to the
bone.
One bone is pulled
towards another bone
upon contraction.
Vertebrate
Skeletal
Muscle
composed of smaller & smaller & smaller units
skeletal muscle
Structure:
nuclei
plasma
membrane
tendon
muscle fiber (cell)
myofibrils
myofilaments
Vertebrate
Skeletal
Muscle
each muscle fiber =
one long, cylindrical,
multinucleated cell
Vertebrate
Skeletal Muscle
Muscle fiber cells
composed of:
bundles of myofibrils
(threadlike
structures)
QuickTime™ and a
decompressor
are needed to see this picture.
Bundle of fibers
Myofibrils are
basically parallel
“contractile units”
QuickTime™ and a
decompressor
are needed to see this picture.
Myofibrils consist of
even smaller
structures:
thick filaments
thin
myofibrils have a
regular arrangement
regular arrangement
regular arrangement
regular arrangement
regular arrangement
sarcomere = basic
unit of a myofibril hundreds are
connected end to end
& make up the
myofibril
sarcomeres are made of these proteins:
thick filaments
thin
filaments
Thin filaments: actin
• Complex (bunch) of
proteins:
– braid of actin molecules & tropomyosin
fibers
• tropomyosin fibers secured with
troponin complex
• these are proteins
Thick filaments:
• Single protein
myosin
– myosin molecule
• long protein with globular head
bundle of myosin proteins:
globular heads aligned
Thick & thin filaments
• Myosin tails aligned together & heads
pointed away from center of sarcomere
sarcomere = basic
unit of a myofibril hundreds are
connected end to end
& make up the
myofibril
SARCOMER
E
making up the
sarcomere…
Z-lines = the borders
of the
sarcomere
(actin)
at rest, the thick
myosin & thin
actin filaments in
the sarcomere do not
overlap completely:
area inwhich only thick
myosin filaments = H
zone
Area inwhich only
thin actin
filaments =
I band
Area in which both:
thin actin
filaments & thick
myosin filaments = A
band
More muscle anatomy: SARCOLEMMA = plasma membrane
QuickTime™ and a
decompressor
are needed to see this picture.
More muscle anatomy: T tubule = inward extension of the
plasma membrane
QuickTime™ and a
decompressor
are needed to see this picture.
More muscle anatomy: mitochondrion = ohh, there are plenty!
QuickTime™ and a
decompressor
are needed to see this picture.
More muscle anatomy: sarcoplasmic reticulum = another name
for endoplasmic reticulum
QuickTime™ and a
decompressor
are needed to see this picture.
How does the Muscle
Contract?
Sliding
Filament
Model
Motor Unit
QuickTime™ and a
decompressor
are needed to see this picture.
(Usually hundreds of muscle fibers)
NEUROMUSCULAR JUNCTION
QuickTime™ and a
decompressor
are needed to see this picture.
NEUROTRANSMITTOR ~
ACETYLCHOLINE released as action
potential moves to synaptic terminal
QuickTime™ and a
decompressor
are needed to see this picture.
of muscle fiber
The acetylcholine causes the action
potential to continue in the muscle fiber
QuickTime™ and a
decompressor
are needed to see this picture.
The action potential spreads into T-Tubules
(invaginations in the membrane of the muscle fibers)
QuickTime™ and a
decompressor
are needed to see this picture.
The a.p. opens Ca+2 channels in the
sarcoplasmic reticulum (e.r.)
QuickTime™ and a
decompressor
are needed to see this picture.
The special type of smooth endoplasmic reticulum found in
smooth and striated muscle fibers whose function is to
store and release calcium ions.
Ca+2 flows & binds to a protein in
the actin filament
QuickTime™ and a
decompressor
are needed to see this picture.
Sliding
Filament
Model
Thin actin filament
has myosin binding
sites…
At rest myosin
binding sites are
blocked (with
trypomyosin)
Sliding
Filament
Model
Thin actin filament
has myosin binding
sites…
myosin binding sites are
opened when Ca+2 binds to
the troponin.
(Ca+2 is released as a result
of acetylcholein rushing
through the T-tubules)
Sliding
Filament
Model
At rest, myosin head
is bound to an ATP
-ATP
Sliding
Filament
Model
when Ca+2 floods into the cell,
Myosin head hydrolyzes
(breaks) ATP to ADP and P --.
Sliding
Filament
Model
Myosin binds to Actin --





this forms a cross-bridge
When this occurs, the myosin
Sliding
Filament
Model
the myosin head changes shape
and releases the ADP + P
Sliding
Filament
Model
The thin actin filament is
pulled toward the center of the
sarcomere…
Sliding
Filament
Model
Sliding
Filament
Model
ATP
cross-bridge broken
when ATP binds back
to the myosin head
Cleaving ATP  ADP + P allows
myosin head to bind to actin filament
ADP
1
ATP
2
form
cross
bridge
4
release
cross
bridge
shorten
sarcomere
ADP expelled
3
What is the Stimulus that
causes muscle to contract?
Synapse with
Neuron &
Muscle
Synaptic Terminal of
neuron releases
acetylcholine
Synapse with
Neuron &
Muscle
Ca++ released
Binding sites on actin
are now exposed.
Myosin head now
binds to the actin
Synapse with
Neuron &
Muscle
Muscles do not relax
until the Ca++ is
pumped back into the
sarcoplasmic
reticulum
ATP
1
Acetylcholine released
Put it all together…
2
Action potential travels
3
a.p, travels through
T-Tubules
ATP
7
Ca+2 pumped back
into s.r. / ATP
required
6
4Ca+2 released & binds
to troponin complex
Ca+2 depleates; cross
bridge broken/ ATP
back on myosin head
Cross bridge formed
ATP
5
Put it all together…
1
2
3
ATP
7
4
6
ATP
5
Muscle limits:
• Muscle fatigue
– lack of sugar
• lack of ATP to restore Ca2+ gradient
– low O2
• lactic acidcauses pH drop which
interferes with protein function
– synaptic fatigue
• loss of acetylcholine
• Muscle cramps
– build up of lactic acid
– ATP depletion
– ion imbalance
• massage or stretching
increases circulation
Rigor mortis
• So why are dead people “stiffs”?
–
–
–
–
–
–
–
no life, no breathing
no breathing, no O2
no O2, no aerobic respiration
no aerobic respiration, no ATP
no ATP, no Ca2+ pumps
Ca2+ stays in muscle cytoplasm
muscle fibers continually
contract
• tetany or rigor mortis
– eventually tissues breakdown
& relax
• measurement for time of death
Money for Beauty
• What is Botox?
– Toxin derived from Closteridium botulinum
– blocks the release of acetylcholine
– Muscles relax… which
takes away the wrinkle
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
*The transmission of an impulse from a nerve to the
surface of a resting muscle initiates a contraction in that
muscle. Biochemical and biophysical studies of muscle
tissue have resulted in an explanation for muscle
contraction known as the sliding-filament theory.
a. Describe the chemical changes that occur when a
nerve impulse is transmitted to the surface of a
resting muscle cell.
b. Describe the internal structure of a muscle fiber
as revealed by electron microscopy.
c. On the basis of this structure, explain the slidingfilament theory.
*7. Discuss the mechanism by which a muscle cell
contracts or a nerve cell transmits an impulse. Include in
your discussion the relationship between cell structure and
function.
• Action potential causes Ca2+ release from SR
– Ca2+ binds to troponin
• Troponin moves tropomyosin uncovering myosin
binding site on actin
ATP
• Myosin binds actin
– uses ATP to "ratchet" each time
– releases, "unratchets" & binds to next actin
• Myosin pulls actin chain along
• Sarcomere shortens
– Z discs move closer together
• Whole fiber shortens  contraction!
• Ca2+ pumps restore Ca2+ to SR  relaxation!
– pumps use ATP
ATP