SM 1 Flashcards
1
Q
Sarcomeres Shorten During Contraction
• Zone of Overlap —
• I-Band —
• H-Zone —
A
Increases
Decreases
Decreases
2
Q
The thin filament
A
is composed of actin (with G-actin molecules, the active site which binds myosin), tropomyosin, and troponin (which binds actin, tropomyosin, and calcium).
3
Q
The myosin (thick) filament
A
has multiple cross-bridges where the “heads” can bind to the G-actin molecule. Myosin also functions as an ATPase enzyme.
4
Q
Dystrophin Protein connects thin filaments to
A
glycoproteins in sarcolemma
5
Q
Dystrophin-Glycoprotein Complex provides
A
scaffolding
for sarcomeres
6
Q
Muscular Dystrophies (5)
A
a. Duchenne
b. Beckers
c. Myotonic
d. Oculopharyngeal
e. Limb Girdle
7
Q
The alpha motor neuron
releases – which binds to
a
A
ACh
nicotinic ACh receptor (NM)
on the muscle fiber
8
Q
Botulinum toxin A inhibits the
release of
A
ACH at the neuromuscular junction. Botox can be used in dentistry (Bruxism, Sialorrhea, Masseteric Hypertrophy, etc.
9
Q
For contraction to occur, the intracellular calcium
in the muscle fiber must —
A
increase
10
Q
in resting muscle,
tropomyosin prevents a
strong bond between the
A
myosin head and G-actin
molecules
11
Q
When troponin binds to cytosolic Ca++, tropomyosin is pulled away from the myosin binding site, and allows for the
A
power stroke
12
Q
Sarcoplasmic Reticulum (SR):
A
modified ER that sequesters Ca2+
13
Q
Transverse (T)-Tubules:
A
invaginations of sarcolemma
14
Q
Terminal Cisternae:
A
Portion of SR that contact T-tubules
15
Q
Calcium is released from the Sarcoplasmic Reticulum (2)
A
a.The AP travels down the membrane, down T-tubules, & activates
voltage-sensitive dihydropyridine (DHP) receptors on the T-
tubules. These in turn open calcium channels (ryanodine
receptors) on the SR. Calcium goes from SR to the sarcoplasm.
b.The intracellular structure of myocytes ensures spread of action
potential (and calcium) throughout the cell
16
Q
ATP is Necessary for Contraction (3)
A
- ATP binding to the myosin head breaks the cross-bridge
(connection between actin and myosin). - Energy released from ATP hydrolysis by the myosin head
provides energy for cocking the myosin head (myosin is
now in the high energy form). - Release of inorganic phosphate from the myosin head
provides energy for the POWER STROKE (myosin head
pulling actin towards the center of the sarcomere). This
shortens the sarcomere.
17
Q
Muscle cells only have enough ATP for ~– twitches.
A
8
18
Q
Both (2) produce ATP for muscle
fibers.
A
Aerobic and Anaerobic Metabolism
19
Q
However, the contribution of each in a specific muscle fiber depends on (2)
A
(1) the metabolic enzymes are present in the cell (ex. glycolytic
fibers versus oxidative fibers)
(2) the intensity of the exercise.
20
Q
Sources of ATP (3)
A
aerobic/anaerobic metabolism
phosphocreatine
21
Q
Measurement of Creatine
Kinase (CK) levels in the
blood is done to determine if
A
damage to muscle tissue (skeletal and cardiac) has occurred (ex. heart attack or muscular dystrophy). Different isoforms of CK are found in skeletal versus cardiac muscle.
22
Q
Fatigued muscles: (3)
A
1.have decreased tension generation,
2.take longer to contract
3.relax more slowly and may not completely
relax.
23
Q
SKIPPED
Theories for fatigue: (6)
A
- Change in membrane potential
- Decreased ACH
- Blockage of blood flow
- Central Fatigue
- Increased metabolic byproducts
- Depleted glycogen
24
Q
Both (2) must be present for cross-bridge
cycling.
A
Calcium and ATP
25
SKIPPED
| Cross-Bridge Cycling (Sliding Filament Theory) (5)
A. Rigor State: myosin and actin are tightly bound
B. ATP binds myosin, decreases its affinity for
actin, and the two separate
C. Myosin head moves in the direction of the Z line,
ATP is hydrolyzed
D. Myosin binds the next actin (one closer to Z line)
and power stroke occurs (pulls actin toward the
M Line)
E. ADP is released and the actin and myosin
resume the brief rigor state
26
Relaxation of Skeletal Muscle (2)
* The alpha motor neuron must stop firing
| * Cytosolic (intracellular) calcium concentrations must decrease
27
Cytosolic (intracellular) calcium concentrations must decrease (3)
A. Calcium ATPases on SR remove calcium from
cytosol
B. Tropomyosin moves, and covers actin’s myosin-
binding site
C. Actin slowly slides back to its original resting place
and the sarcomere returns to its original length.
28
For relaxation to occur, --- must be removed,
but --- must be present to release myosin from
actin. Otherwise, rigor state is maintained.
Rigor Mortis?
Calcium
| ATP
29
Diversity of Skeletal Muscle Fibers
| 3 Types
Slow-Twitch: Type I
Fast-Twitch:
Oxidative-Glycolytic: Type IIA
Glycolytic: Type IIB
30
Changes in Size (3)
1. Hypertrophy
2. Atrophy
3. Sarcopenia
31
The thickness of the jaw muscles decreases
| significantly with
age, which is caused primarily by a
decrease in the cross-sectional area of their
fibers. These
changes might be explained by the
progressive reduction in the number and the
total duration of activity bursts per day with
age.
32
Certain Characteristics of Skeletal Muscle Fibers
| Can Change in Response to Use (2)
changes in size
| changes in fiber types
33
Human jaw muscles are different from
other skeletal muscle. Human jaw
closing muscles are composed of a
relatively homogenous mixture of
type I
and II fibers, the type II fibers being
much smaller than the type I
34
```
The fibre-type composition of the
jaw muscles also changes with age.
In the jaw-closing muscles of
elderly subjects, the proportion of
pure type -- fibres decreases, while
the proportion of pure type -- fibres
and that of hybrid fibres increase
```
I
| II
35
Motor Units:
a motor unit is the alpha motor neuron
| and the muscle fibers it innervates
36
Motor units are recruited in order of size (2)
a. Small motor units are
recruited first
b. Smallest motor units
control fewer fibers
37
```
An increase in the number
of motor units activated
increases the total tension
produced by contraction of
a muscle—
```
SPATIAL
| SUMMATION
38
--- Recruitment
Asynchronous
39
Small motor units (X) are composed of
slow-twitch
oxidative fibers. They have the lowest threshold for
firing and are recruited first.
40
Larger motor units (Z) are composed of
fast-twitch
glycolytic fibers. They have the highest threshold
and are recruited last
41
Motor units in jaw muscles are
restricted to specific areas of the
jaw muscles, which permits
differential control of separate
| muscle portions.
42
Types of Contraction: the amount of (2) determines the type of
contraction
load and the
| force the muscle generates
43
ISOMETRIC CONTRACTION.
Force produced is
| less than the load; no movement.
44
ISOTONIC CONTRACTION.
Force produced is
| great enough to move a load
45
```
The force of
contraction
increases until
the isometric
contraction
becomes an
```
isotonic
contraction—
NOT always
possible!
46
```
The contraction with
the -- gram load is
isometric because the
muscle is not strong
enough to move the
load and shorten. The
maximum isometric
contraction only
produces -- grams of
tension.
```
20
| 17
47
ncrease total force by (2)
(1) increasing the frequency of fiber activation
and/or
(2) increasing the number of muscle fibers contracting (motor
unit recruitment).
48
An increase in the frequency of α motor neuron
| stimulation will increase the amount of
tension produced.
The tension produced in response
to each action potential will sum if the muscle
has not yet completely relaxed.
49
For a single muscle twitch (one muscle fiber), the
| tension developed is altered by
sarcomere length
50
Optimal length is where there is the best degree of overlap
| between the
thick and thin filaments.
51
```
At the optimal length
the greatest number of
actin/myosin cross-
bridges can form,
which results to
```
maximal tension
| production.
52
```
Tension is reduced if
the muscle (2)
```
is not
stretched enough or if it
stretched too much.
53
The velocity of contraction (distance moved/time)
| depends on the
load a fiber is contracting against.
54
The greater the load, the
-- the speed of
contraction.
SLOWER
55
Load isn’t the only factor that dictates the speed of contraction. --- dictates it, too. For example,
Fiber Type
Type I fibers have an isoform of myosin with
slower ATPase activity while type II fibers have fast myosin ATPase.
56
Skeletal Muscle Reflexes (2)
A. Stretch Reflex (Muscle Receptors)
B. Golgi Tendon Reflex (Tendon
Receptors)
57
Extrafusal Fibers
Skeletal muscle fibers/cells that produce the
| contraction.
58
Alpha Motor Neuron:
Efferent neuron that
releases ACh and causes contraction of
the extrafusal fiber (skeletal muscle).
59
Muscle Spindle
Small structure within the extrafusal fibers that
contains Intrafusal Fibers that have sensory
nerve endings wrapped around them that are
sensitive to CHANGES IN MUSCLE LENGTH.
60
Gamma Motor Neuron:
Efferent neuron
that causes contraction of intrafusal
fibers so they mimic what the EF fibers
are doing.
61
```
Jaw --- have
a lot of muscle
spindles.
Jaw --- have
few to none.
```
closers
| openers
62
Components of the Muscle Spindle:
| sensitive to
muscle length
63
SKIPPED
| The Stimulus for the Muscle Spindle Reflex is Stretch
1. When the muscle stretches, the sensory fibers of the muscle
spindle are squeezed.
2. Afferent information enters the spinal cord and
a. Activates the alpha motor neuron.
i. This stimulates muscle (extrafusal fiber) contraction.
ii. There is also simultaneous inhibition of the alpha motor
neuron of antagonistic muscles.
b. Also activates the gamma motor neuron.
i. This stimulates intrafusal fiber contraction.
ii. If the intrafusal fibers did not contract, the sensory fibers
would not be able to sense a further change in muscle
length since they would be slack.
64
The Effect of Muscle Spindle Activation is
Contraction.
The reflex has dynamic (immediate) and static (maintains
tone—constant contraction) reflex components
65
Anytime the alpha motor neuron is activated, the -- motor
| neuron is also activated.
gamma
66
```
Anytime the alpha motor neuron is activated, the gamma motor
neuron is also activated.
This allows the
muscle spindle to
maintain
```
sensitivity
to changes in
muscle length.
67
if the intrafusal fibers did not contract, the sensory fibers would not
be able to sense a further change in
muscle length since they
| would be slack.
68
Golgi Tendon Organs:
```
Mechanosensitive receptors
found at the junction of
tendons and muscle.
Sensitive to a change in
FORCE.
```
69
The Golgi Tendon
Organ Reflex is a
--- reflex.
protective
70
SKIPPED
The Stimulus for the Golgi Tendon Organ
(GTO) Reflex is Tendon Stretch (2)
```
1. Tendons stretch in response to
contraction (particularly isometric
—maximal—contractions)
2. Extreme stretch of the tendon will
squeeze the GTO and afferent
neurons will send information into
the spinal cord
a. Stimulates an inhibitory
interneuron.
b. This neuron decreases the
activity of the alpha motor
neuron
c. Skeletal muscle contraction is
decreased (relaxation)
```
71
SKIPPED
| control of mastication (4)
• A mix of voluntary, reflex and central (subconscious)
processes.
• Requires coordination of muscles controlling lips, tongue
and cheeks.
• Voluntary control is usually bilateral, although people tend
to favor one side of the mouth over the other.
• Central component; mastication is a cyclical movement
with develops early in life. It is controlled by the Central
Pattern Generator (CPG) of the brainstem, which when
stimulated, elicits rhythmic, coordinated activation and
inactivation of jaw-closers and jaw-openers.
72
The --- cannot by itself adjust muscle force to
deal with changing conditions that occur when different foods are
chewed. Reflexes are important modifiers of force.
Central Pattern Generator
73
Input from higher cortical regions can regulate
| the CPG frequency via the
Corticobulbar
| Pathway
74
Jaw opening reflex (2)
– Pain inhibits the alpha motor neuron of jaw closing muscles such as
when you bite down on your tongue, a metal spoon, with your
incisors
– Jaw opens
75
Jaw jerk reflex (3)
```
– Strong tap to the chin stretches the
jaw closers
– The jaw closers respond by
contraction so the jaw closes
– Stretch reflex
```
76
SKIPPED
How do you determine the force needed to
take a bite of something hard?
• CPG starts chewing by activating jaw closing muscles
• When the jaw closing muscles connect with the food (ex.
carrot), they initially meet with resistance:
– The force of contraction is initially insufficient to
overcome the load (carrot) – isometric contraction
– Intrafusal fibers in muscle spindle are still contracting and
stretching the muscle spindle so this signals further
contraction of jaw closing muscles
• Constant feedback from the muscle spindle in the jaw
closing muscles is sufficient to overcome the load of the
carrot --- isotonic contraction
77
With subsequent chewing strokes, the response is greater and
matches the load of the food with appropriate force more ---.
quickly
78
SKIPPED
| Protection by Muscle Spindles
• To crack a nut, a tremendous amount of force is required.
Once the nut cracks, there is potential to damage the intra-
oral structures.
• Muscle spindles decrease the contraction in these
situations.
– When the nut cracks, the force is now greater than the
load (nut).
– At this point, there is more slack in the muscle spindle
which leads to less activation of the muscle (due to
decreased alpha/gamma co-activation).
79
Powerful isometric contractions stimulate both jaw closing and
opening muscles. The jaw openers keep the jaw from
snapping shut.
