Physiology Exam 3 - Muscular System Flashcards
1
Q
What are the three types of muscle?
A
skeletal, smooth, cardiac
2
Q
Structure of skeletal muscle
A
- striated, tubular, and multinucleated
- multiple mitochondria
3
Q
Where skeletal muscle is found
A
attached to bones (tendon)
4
Q
Structure of smooth muscle
A
non-striated, spindle-shaped, and mononucleated
5
Q
Where smooth muscle is found
A
covering walls of internal organs
6
Q
Structure of cardiac muscle
A
striated, branched, and bi- or mononucleated
7
Q
Where cardiac muscle is found
A
covering walls of the heart
8
Q
Striation
A
occurs due to light and dark bands originating from difference in myofilaments
9
Q
What makes up a muscle fiber?
A
sarcolemma, sarcoplasm, and myofibrils
10
Q
Sarcolemma
A
plasma membrane
11
Q
Sarcoplasm
A
cytoplasm (almost entirely made up of myofibrils)
12
Q
Myofibrils
A
contractile structure of cell
13
Q
Transverse (T-) tubule
A
invaginations of sarcolemma into sarcoplasm (surround myofibrils)
14
Q
Action potentials go through the sarcolemma and travel into the muscle fiber via…
A
T-tubules
15
Q
Sarcoplasmic reticulum
A
internal membrane complex (smooth ER)
16
Q
Terminal cisternae
A
sacs at the end of sarcoplasmic reticulum adjacent to T-tubules
17
Q
Triad
A
T-tubule between two terminal cisternae
18
Q
What does the sarcoplasmic reticulum do?
A
Stores calcium (Ca2+ binding protein calsequestrin in the terminal cisternae allows for storage of a large quantity of Ca2+)
19
Q
What results in the contraction of a cell?
A
shortening of myofibrils
20
Q
What are myofilaments?
A
strands of protein used for contraction
21
Q
What is the thick filament?
A
myosin
22
Q
What is the thin filament?
A
actin
23
Q
Actin
A
globular protein that has a binding site for myosin
24
Q
Nebulin
A
might play a role in thin filament assembly (actin wraps around it)
25
Troponin
Ca2+ binding site and changes conformity of tropomyosin
26
Tropomyosin
covers the binding region of actin
27
Myosin
two large polypeptide heavy chains
28
Globular heads
at the end of myosin, form cross-bridges to make contact with actin
29
What does each globular head contain?
two light chains and two binding sites for actin and ATP
30
What does the ATP binding site on myosin function as?
an enzyme - myosin-ATPase
31
Sarcomere
structural and functional unit within a myofibril
32
What does a sarcomere contain?
overlapping thin and thick filaments
33
Where does a sarcomere span?
from one Z disc to the next
34
Z disc
protein that anchors thin filaments
35
What does contraction mean?
activation of cross-bridges, force-generating sites within a muscle fiber (Z discs come in)
36
What does relaxation mean?
mechanisms generating force are turned off and tension declines (Z discs expand)
37
M line
middle of sarcomere
38
H zone
thick filaments only
39
I band
thin filaments only
40
A band
thick and thin filaments
41
Motor unit
A motor neuron and all of the muscle fibers it innervates
42
How are action potentials initiated in skeletal muscle?
neurons are stimulated to a skeletal muscle
43
Alpha motor neurons
neurons whose axons innervate skeletal muscle fibers (cell bodies in brainstem and spinal cord)
44
What are the three subunits of troponin?
Troponin I (inhibitory)
Troponin T (tropomyosin binding)
Troponin C (Ca2+ binding)
45
What happens when Ca2+ binds to troponin?
its shape changes, it relaxes its inhibitory grip and allows tropomyosin to expose the myosin-binding stie on actin and starts contraction
46
What happens when Ca2+ is removed from troponin?
tropomyosin moves back into place to block the cross bridge binding sites, contraction stops
47
What happens when a muscle fiber shortens?
the overlapping thick and thin filaments move past each other in each sarcomere propelled by movements of cross-bridges
48
What happens to the lengths of filaments during shortening of sarcomeres?
they do not change in length, they change their amount of overlap
49
What is the mechanism for muscle contraction called?
sliding-filament mechanism
50
Structure of a neuromuscular junction
motor neuron axon (myelinated), axon terminal (synaptic vesicles and active zone), synaptic cleft (space between axon and sarcolemma), motor end plate (ACh receptors and junctional folds)
51
Steps of initiation of excitation-contraction coupling at the neuromuscular junction
1. The action potential arrives at the presynaptic terminal
2. Voltage-gated Ca2+ channels open
3. Ca2+ enters the terminal and causes vesicles to release ACh from synaptic vesicles to the synaptic cleft
4. ACh diffuses across the synaptic cleft
5. ACh binds to receptors on the muscle fiber membrane
6. ACh binding increases the permeability of Na+ channels.
7. Na+ enters the cell and depolarizes the membrane to produce an action potential
8. The action potential propagates over the muscle cell membrane
9. Ach is broken into acetic acid and choline by acetylcholinesterase
10. Choline is reabsorbed into the presynaptic cell and combines with acetic acid to form ACh
11. ACh enters synaptic vesicles
52
What do action potentials cause terminal cisterns to do?
release Ca2+
53
What happens at the end of an action potential?
1. Ca2+ ATPase pumps return Ca2+ ions to the sarcoplasmic reticulum by active transport
2. Ca2+ concentration around actin and myosin decreases
3. thick and think filaments disengage and the muscle relaxes
54
What two factors is muscle contraction based on?
force and length
55
Muscle tension
the force generation by a muscle on an object (contraction)
56
Muscle load
the force by an object on a muscle (its weight)
57
What are the two types of isotonic contraction?
concentric and eccentric
58
Isotonic contraction
the muscle changes length while the load on the muscle remains constant (when a muscle actively moves an object)
59
Concentric contraction
tension exceeds the load and shortening occurs
60
Eccentric contraction
when an unsupported load is greater than the tension generated by the sarcomeres, the load pulls the muscle to a longer length
61
Isometric contraction
muscle develops tension but does not shorten or lengthen (when a muscle supports a load in a constant position)
62
Twitch
single stimulus-contraction-relaxation sequence in a muscle fiber (mechanical response of one muscle fiber to one action potential)
63
What happens when you increase the load?
it shortens the action potential and diminishes the time of the twitch
64
Frequency-tension relation
NOTES
65
Tetanus
a maintained contraction in response to repetitive stimulation
66
Tetanus disease
- caused by Clostridium Tetani
- causes permanent contraction
- inhibits release of inhibitory neurotransmitters
67
Botulism
- caused by Clostridium Botulinum
- found in raw honey
- causes muscles to stay relaxed and flaccid
68
Summation
the increase in muscle tension from successive action potentials occurring during the phase of mechanical activity
69
What are the three ways a muscle fiber can form ATP?
- direct phosphorylation of ADP by creatine phosphate
- aerobic respiration of ADP in mitochondria
- anaerobic glycolysis - phosphorylation of ADP in cytosol
70
Muscle fatigue
when a skeletal muscle fiber is repeatedly stimulated, the tension will eventually decrease even though the stimulation continues
71
What are skeletal muscle fibers classified based on?
- their maximal velocities of shortening (fast or slow-twitch)
- their major pathway they use to form ATP (oxidative or glycolytic)
72
What are the three types of skeletal muscle fibers?
1. slow oxidative fibers - Type I
2. fast oxidative/glycolytic - Type IIa
3. fast glycolytic - Type IIb
73
What type of muscle fiber is best for long distance running?
Type 1
74
What type of muscle fiber is best for brisk running?
Type IIa
75
What type of muscle fiber is best for sprints?
Type IIb
76
What is the rate of fatigue in each skeletal muscle fiber?
1. Type I = almost nonexistent
2. Type IIa = 8 minutes
3. Type IIb = 2-4 minutes
77
Hypertrophy
increase in size of muscle fibers resulting from increase amounts of contractile activity (regular exercise)
78
Atrophy
muscle fibers get smaller due to decrease in exercise
79
What are the two types of atrophy?
1. disuse atrophy (arm in a cast)
2. denervation atrophy (nerve damage = loss of function)
