Chapter 12: Muscles Flashcards
1
Q
are large, multinucleate cells that appear striped or striated under the microscope
A
skeletal muscle fibers
2
Q
-striated but they are smaller, branched, and uninucleate -Cells are joined in series by junctions called intercalated disks
A
cardiac muscle
3
Q
fibers are small and lack striations
A
smooth muscle
4
Q
moves bones closer together
A
flexion
5
Q
moves bones away from each other
A
extension
6
Q
- The tissue surrounding muscle (epimysium) and tendon connective tissue are continuous
- perimysium
- fascicles
A
skeletal muscles
7
Q
extends into the muscle body, dividing muscle into bundles (fascicles) of muscle cells
A
perimysium
8
Q
contain 100s-1000s of muscle cells—muscle fibers, which extend the length of the muscle
A
fascicles
9
Q
what are the components of a muscle fiber?
A
-many myofibrils
-sarcoplasmic reticulum
-many mitochondria ~ high energy
-transverse tubules (T tubules)
-lateral sacs (terminal cisternae)
~ Ca2+
-triad
10
Q
T tubule + 2 lateral sacs
A
triad
11
Q
-Give skeletal and cardiac muscle striated appearance
-Orderly arrangement of thick and thin filaments
~actin
~myosin
A
myofibrils
12
Q
due to thick and thin filaments that run parallel to the long axis
A
striations
13
Q
form sarcomeres
A
filaments
14
Q
what is the structure of a sarcomere?
A
- A band
- H zone
- M line
- I band
- Z line
15
Q
- dark band
- thick filaments
A
A band
16
Q
- thick filaments
- no overlap
A
H zone
17
Q
links thick filaments
A
M line
18
Q
- light band
- thin filament
- no overlapping
A
I band
19
Q
links thin filaments
A
Z line
20
Q
has acces- sory proteins that link the thin filaments together, similar to the accessory proteins shown for the M line
A
Z disk
21
Q
contractile protein
A
actin
22
Q
has binding site for myosin
A
each G actin
23
Q
- regulatory protein
- overlaps binding sites on actin for myosin
A
tropomyosin
24
Q
-regulatory protein
-complex of 3 proteins
~Attaches to actin
~Attaches to tropomyosin
~Binds Ca2+ reversibly
A
troponin
25
-Myosin tail is toward the M line
-Myosin head is toward the I band
-Myosin head binding sites
~actin binding site
~ATPase activity
thick myofilament
26
- Is a very elastic protein
- Supports protein in muscle
- Anchors thick filaments between the M line and the Z line
- Provides structural support and elasticity
titin
27
- crossbridge cycle
- excitation-contraction coupling
- muscle cell metabolism
sliding filament model
28
how muscles generate force
crossbridge cycle
29
how muscle contractions are turned on and off
excitation contraction coupling
30
how muscle cells provide ATP to drive the crossbridge cycle
muscle cell metabolism
31
* shortening of muscle
- thick & thin filaments overlap
- neither thick nor thin filaments shorten
- filaments slide past each other
muscle contraction
32
what happens within a sarcomere during contraction?
- A band stays the same length
- I band shortens
- H zone shortens
- Sarcomere shortens
33
due to cyclical formation and breaking of cross bridges = crossbridge cycle
sliding
34
what happens to actin and myosin during contraction?
do not change length but instead slide past one another
35
do not change length but instead slide past one another
Cyclical formation of links between actin and myosin
36
what happens to myosin during the cyclical formation of links between actin and myosin (sliding)?
*myosin head undergoes conformation changes
-high energy form
~ADP and Pi bound to myosin
~High affinity for actin
-low energy
~ADP and Pi released from myosin
*relies on hydrolysis of ATP
37
myosin head moves, propelling thin filament toward center of muscle
power stroke
38
detach when ATP binds
thick and thin filaments
39
returns to the initial cocked position when ATP is hydrolyzed.
myosin head
40
1. ATP binds to myosin; Myosin releases actin
2. Myosin hydrolyzes ATP; Energy from ATP rotates the myosin head to the cocked position. Myosin binds weakly to actin.
3. Power stroke begins when tropomyosin moves off the binding site.
4. Myosin releases ADP at the end of the power stroke.
contraction cycle
41
1. binding of myosin to actin
2. power stroke
3. rigor (myosin in low energy form)
4. unbinding of actin and myosin
5. cocking of the myosin head (myosin in high energy form)
crossbridge cycle
42
* Sequence of events whereby an action potential in the sarcolemma causes contraction
- Dependent on neural input from the motor neuron
- Requires Ca2+ release from the sarcoplasmic reticulum
excitation contraction coupling
43
what is the role of the neuromuscular juncton in excitation-contraction coupling?
-Each motor neuron innervates several muscle cells
-Each muscle fiber receives input from a single motor neuron
-Acetylcholine released
-Motor end plate
~High density of acetylcholine receptors
-End-plate potential
-Motor neuron AP always creates a muscle cell AP
44
what is the role of Ca2+ in excitation contraction coupling?
If no Ca2+ → troponin holds tropomyosin over myosin binding sites on actin
- no crossbridges form between actin & myosin
- muscle relaxed
45
what happens in excitation contraction coupling if Ca2+ is present?
If Ca2+ present → binds to troponin, causing movement of troponin, causing movement of tropomyosin, exposing binding sites for myosin on actin
- Crossbridges form between actin and myosin
- Cycle occurs; muscle contracts
46
what are the steps of excitation-contraction coupling?
1. Action potential in sarcolemma
2. Action potential down T tubules
3. DHP receptors of T tubules open Ca2+ channels (ryanodine receptors) in lateral sacs of SR
4. Ca2+ increases in cytosol
5. Ca2+ binds to troponin, shifting tropomyosin
6. Crossbridge cycling occurs
47
how is muscle action potential initiated?
1. somatic motor neuron releases ACh at neuromuscular junctions
2. Net entry of Na+ through ACh
receptor-channel initiates a
muscle action potential.
48
what are the 3 metabolic pathways to obtain energy?
- phosphocreatine breakdown
- anaerobic glycolysis
- aerobic respiration
49
short burst of energy
Phosphocreatine breakdown
50
- produces lactate and acid
| - quick, no oxygen required, small amount of energy released
anaerobic glycolysis
51
- citric acid cycle and electron transport chain
| - slow, requires oxygen, large amount of energy released
aerobic respiration
52
- psychological effects
| - protective reflexes
central fatigue
53
- decrease in neurotransmitter release
- decrease in receptor activation
- at neuromuscular junction
peripheral fatigue
54
change in muscle membrane potential
excitation-contraction coupling
55
what is the basis for skeletal muscle classification?
-velocity of contraction
-primary energy source
~oxidative vs glycolytic
56
what are the differences in speed of contraction?
- fast twitch
| - slow twitch
57
what are the differences in speed of contraction dependent on?
* dependent on rate of myosin ATPase activity
- ATP hydrolysis= rate limiting step of cycle
- Higher rate = faster crossbridge cycling
58
myosin with fast ATPase activity
fast fibers
59
myosin with slow ATPase activity
slow fibers
60
- contract 2-3 times more rapidly than slow fibers
| - relax more rapidly
fast fibers
61
why do fast fibers relax more rapidly?
rate of Ca2+-ATPase is faster
62
contractions last 10 times longer than fast fiber contractions
slow fibers
63
what are the 3 skeletal muscle fiber types?
- slow oxidative (type 1)
- fast oxidative-glycolytic (type 2A)
- fast glycolytic (type 2X)
64
-slow myosin ATPase
-high oxidative capacity-aerobic
~mitochondria
~rich blood supply
~myoglobin (red)
-small diameter
~little tension
-fatigue slowly
slow oxidative fibers (type 1)
65
-fast myosin ATPase activity
-high glycolytic capacity
~high glycogen stores
~many glycolytic enzymes
-no myoglobin (white)
-large diameter
~greater tension
-fatigue rapidly
fast glycolytic fibers (2X)
66
- intermediate myosin ATPase activity
- high oxidative capacity-aerobic
- myoglobin
- slow to fatigue, but more rapid than slow oxidative fibers
- intermediate diameter
fast oxidative fibers (type 2A)
67
what are the long term responses to aerobic exercise?
- increased oxidative capacity
- some fast glycolytic fibers can be converted to fast oxidative fibers
- increase in size & # of mitochondria
- increase in # of capillaries surrounding muscle fibers
68
what are the long term responses to high intensity exercise?
- decreased oxidative capacity
- some fast oxidative fibers can be converted to fast glycolytic fibers
- decrease in size & # of mitochondria
- increase in fiber diameter
- reduced resistance to fatigue
69
the mechanical response of an individual muscle cell to a single action potential.
twitch
70
Graded muscle contractions depend on two factors, what are they?
-tension produced by each fiber
~# of active crossbridges that bind to actin
~more crossbridges that bind-->more force
-number of fibers contracting
71
what are the Factors affecting the number of active crossbridges and thus the force generated by the contraction of individual muscle fibers?
- frequency of stimulation
- fiber diameter
- changes in fiber length
72
Frequency of stimulation: increases in the frequency of action potentials in muscle fibers increase tension in two ways, what are they?
- treppe
| - summation
73
-Amount of tension developed depends on amount of Ca2+ bound to troponin
-At high frequencies, release exceeds reuptake
~Ca2+ increases in cytosol
-eventually saturates system
~All troponin has Ca2+ bound to it
~Crossbridge cycling maxed out
~Maximum tetanic contraction
cause of summation and tetanus
74
how does fiber diameter affect force generating capacity?
-fiber diameter varies
-larger diameter--> more filaments --> more force
~more crossbridges --> more force
~more sarcomeres in parallel --> more force
75
Length of fiber at the onset of contraction affects force generated
fiber length
76
- Resting length of muscle at which the fiber can develop the greatest amount of tension
- Due to maximum overlap of thick filament crossbridges and thin filaments
optimal length
77
Decrease crossbridge overlap
nonoptimal lengths
78
what does more muscle fibers contracting result in/
greater force
79
-More fibers contracting → greater tension
-Recruit motor units
~Activation of the motor neuron activates all muscle fibers in the motor unit
~Increases in tension occur in steps proportional to the size of the motor unit
motor unit recruitment
80
what are motor unit sizes like?
-number of motor units varies in different muscles
~small: delicate movements (3-5 fibers)
~large: strength movements (100s-1000s)
-all muscle fibers in a single motor unit are of the same fiber type
~fast twitch
~slow twitch
81
```
-Order of motor unit recruitment is related to size of motor units
~small units recruited first
~large units recruited last
-asynchronous recruitment
~avoids fatigue and maintains tension
```
size principle
82
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-create force and moves a load
~concentric action
~eccentric action
-the muscle contracts,
shortens, and creates enough force to move the load.
```
isotonic contractions
83
is a shortening action
Concentric action
84
is a lengthening action
eccentric action
85
```
-create force without moving a load
~series elastic elements
~sarcomeres
-the muscle contracts
but does not shorten. The force created cannot move the load
```
isometric contractions
86
elastic components of muscles
Series elastic elements
87
what do sarcomeres and elastic elements do during isometric contractions?
Sarcomeres shorten while elastic elements stretch, resulting in little change in overall length
88
act as levers to enhance the speed or power of limb movements
long bones
89
any elongated, rigid object that rotates around a fixed point called a fulcrum
lever
90
occurs when an effort applied overcomes resistance (load) at some other point
rotation
91
what are the 2 advantages conferred by a lever?
-To exert more force against a resisting object than the force applied to the lever
~Human moving a heavy object with help of crowbar
-To move the resisting object farther or faster than the effort arm is moved
~movement of rowing a boat
92
- Has fulcrum in the middle between effort and resistance (EFR)
- Atlanto–occipital joint lies between the muscles on the back of the neck and the weight of the face
- Loss of muscle tone occurs when you nod off in class
first class lever
93
- Resistance between fulcrum and effort (FRE)
- Resistance from the muscle tone of the temporalis muscle lies between the jaw joint and the pull of the digastric muscle on the chin as it opens the mouth quickly
second class lever
94
- Effort between the resistance and the fulcrum (REF)
- Most joints of the body
- The effort applied by the biceps muscle is applied to the forearm between the elbow joint and the weight of the hand and the forearm
third class lever
95
- Lacks striations
- Found in internal organs and blood vessels
- Under involuntary control by the autonomic nervous system
- Spindle-shaped
- Small—approximately 1/10 the size of skeletal muscle
- Contains actin and myosin
- No sarcomeres
- Dense bodies
smooth muscle
96
located in Vascular, gastrointestinal, urinary, respiratory, reproductive, ocular systems
smooth muscle
97
what are the contraction patterns of smooth muscle?
- phasic (periodic)
| - tonic (continuously)
98
how does smooth muscle communicate with neighboring cells?
- Single-unit smooth muscle, or visceral smooth muscle
| - Multi-unit smooth muscle
99
example of a phasic smooth muscle that is usually relaxed
esophagus
100
example of a phasic smooth muscle that cycles between contraction and relaxation
intestine
101
example of a tonic smooth muscle that is usually contracted
a spinchter that relaxes to allow material to pass
102
a tonic smooth muscle whose contraction is varied as needed
vascular smooth muscle
103
are connected by
| gap junctions, and the cells contract as a single unit
Single-unit smooth muscle cells
104
are not electrically linked,
| and each cell must be stimulated independently.
Multi-unit smooth muscle cells
105
are the slowest to contract and relax
smooth muscles
106
-actin is more plentiful
-lacks troponin
-less myosin
~myosin filaments are longer
~entire surface of filament covered with myosin heads
-extensive cytoskeleton
~intermediate filaments and dense bodies
-amount of SR varies and is less organized
-no t-tubules but caveolae
smooth muscle
107
membrane invaginations
caveolae
108
-form a cytoskeleton
~Actin attaches to the dense bodies
~Each myosin molecule is surrounded by actin filaments
Intermediate filaments and protein dense bodies
109
has
| hinged heads all along its length
smooth muscle myosin
110
what does smooth muscle contraction begin with?
Begins with increase in cytosolic Ca2+
111
what happens in smooth muscle contraction after cytosolic Ca2+ increases?
Ca2+ binds to calmodulin and begins a cascade that results in contraction
112
during smooth muscle contraction, what happens after the cascade started by Ca2+?
Dephosphorylated myosin may remain attached to actin for a period of time during a latch state
113
Contraction (of smooth muscle) caused by electrical signaling (change in membrane potential)
electrochemical coupling
114
Contraction (of smooth muscle) caused by chemical signaling
pharmacomechanical coupling
115
the signal for contraction in smooth muscle
increased cytosolic calcium
116
the first step of relaxation of smooth muscle
removal of Ca2+ from the cytosol
117
fire action potentials when they reach threshold
slow wave potentials
118
always depolarize to threshold
pacemaker potentials
