Chapter 9 EXAM 2 Flashcards
(128 cards)
1
Q
What do muscles do?
A
contract
maintain posture
heat production
glycogen storage
2
Q
What does contraction of muscles lead to?
A
movement of the whole body, walking, running.
manipulation of external object, picking up books, etc.
emptying of contents, bladder, uterus during birth, etc.
3
Q
What are the two types of functional classifications of skeletal, cardiac, and smooth muscle?
A
voluntary and involuntary.
4
Q
Describe the voluntary classification of muscles.
A
can be consciously controlled. Predominantly skeletal muscle.
5
Q
Describe the involuntary classification of muscles.
A
has little or no conscious control.
smooth muscle.
cardiac muscle.
6
Q
Describe unstriated muscle.
A
microscopically has no visible patterns or lines of distinction.
7
Q
Describe striated muscle.
A
has distinct lines when examined under a microscope.
skeletal and cardiac muscle
8
Q
Describe nucleated muscle.
A
skeletal-multinucleated, due to fusion of myoblasts during embryonic development.
smooth and cardiac-single nucleus
9
Q
What is epimysium?
A
the connective tissue covering that covers the entire muscle and forms attachments to the bone called tendons.
10
Q
What is perimysium?
A
connective tissue that covers fascicles (bundles of muscle fibers).
11
Q
What is endomysium?
A
connective tissue layer that covers individual muscle cells (myofibers, muscle fibers).
12
Q
Describe the connective tissues of tendons.
A
epimysium, perimysium, and endomysium is continuous.
13
Q
What is the purpose of the continuity of connective tissue?
A
when muscles contract, they do not pull out of their tendons.
14
Q
What are myofibrils?
A
the bulk of the intracellular contents of a myofiber.
Contains characteristic dark and light staining bands that provide the striated appearance of skeletal and cardiac muscle, nuclei are pushed out to periphery of muscle fiber.
15
Q
Describe thick filaments.
A
make up part of the A band.
composed of myosin molecules.
H zone (strictly thick filaments) has a central M line that anchors the thick filaments.
16
Q
Describe thin filaments.
A
make up the I band.
contains actin, tropomyosin, and troponin molecules.
anchored together by the Z line.
slide relative to or interdigitate with the myosin molecules.
17
Q
What are the two accessory proteins of muscles?
A
titin and nebulin.
18
Q
Describe the sarcomere.
A
a functional unit.
extends from z line to z line.
19
Q
Where are cross bridges?
A
exist on the ends of the myosin molecules.
20
Q
Describe myosin heads
A
contain actin binding sites as well as myosin ATPase site
21
Q
Describe myosin tails
A
long helical molecules that are in the center of the myosin molecules.
22
Q
Describe actin
A
thin filaments
form a helix of globular proteins that have attachment sites for myosin binding.
tropomyosin
troponin
23
Q
Describe tropomyosin
A
spirals along the helix of actin. covers myosin binding sites
24
Q
Describe toponin
A
associated with tropomyosin. Formed by three components:
- troponin C
- troponin I
- troponin T
25
Describe Troponin C
contains a calcium binding site.
26
Describe Troponin I
binds to the actin fiber.
27
Describe Troponin T
binds to tropomyosin.
28
Describe the sliding-filament mechanism of skeletal muscle contraction.
actin and myosin molecules interdigitate.
the H zone may completely disappear with contraction
The I band will also narrow during contraction.
29
Describe the interdigitation of actin and myosin molecules.
all sarcomeres of a muscle fiber shorten simultaneously.
decreases overall length of muscle cell
heads of myosin bind to specific binding sites on actin.
mediated by calcium
myosin undergoes a conformational change that physically pulls the thin filaments toward the center of the thick filaments.
during skeletal muscle contraction there are multiple cross bridges cycling.
30
What is the mechanism for contraction?
calcium is released from the sarcoplasmic reticulum.
calcium binds to the calcium receptors on troponin C
binding of myosin to actin initiates the power stroke.
31
what is the sarcoplasmic reticulum?
the endoplasmic reticulum of the muscle cells.
32
What are terminal cisternae?
specialized modifications of the sarcoplasmic reticulum.
| blind pouches that hold calcium.
33
What is the sarcolemma?
the plasma membrane of the muscle cells
34
What are T tubules?
invaginations of the sarcolemma that are in between two terminal cisternae.
35
What is a triad?
the three structures (2 terminal cisternae and 1 T tubule).
| are located above the A band-I band junction.
36
What does an action potential in the muscle cell initiate?
the opening of calcium channels of the sarcoplasmic reticulum for a few milliseconds.
Calcium leaves sarcoplasmic reticulum and enters cytoplasm.
37
What is dihydropyridine?
a drug that blocks calcium channels from opening by binding to T tubule receptors.
38
describe how T tubule receptors work?
an action potential travels over the sarcolemma dn down into T tubules, activates the voltage-sensitive T tubule receptors.
the T tubule receptors (dihydropyridine receptors) trigger the opening of foot protein calcium channels in the terminal cistern.
39
What are foot proteins?
special calcium channels that span the gap from terminal cisterna to T-tubule
also called ryanodine receptors, locked open by plant chemical ryanodine.
40
What happens when calcium binds to the troponin C calcium receptors?
troponin undergoes a conformational change or rearrangement, which initiates movement of tropomyosin.
movement of tropomyosin uncovers myosin binding sites on actin molecules.
41
What does binding of myosin to actin initiate?
the power stroke.
42
What are the steps of the power stroke?
1. when ATP is bound to myosin head, it assumes a high energy or cocked position.
2. binding with actin releases the energy which causes the myosin head to tilt, assuming a low energy conformation.
3. ADP and Pi are released.
4. the change in conformation of the myosin head pulls the thin filament toward the center of the thick filament.
5. the linkage between myosin and actin is broken when a new ATP molecule binds to the ATPase site on myosin. This returns the myosin head to its high-energy conformation and continued contraction is possible if a binding site is available.
43
Describe the process of muscle relaxation.
1. calcium is actively resequestered by the sarcoplasmic reticulum. This is accomplished by a calcium ATPase pump.
2. a reduction in cytoplasmic calcium causes troponin to revert to its original conformation and allows tropomyosin to cover over the myosin binding sites of actin.
3. contraction stops, but the myosin heads remain in the high energy conformation.
44
What is rigor mortis?
lots of calcium is available from released storage, but little ATP is available for myosin to become unbound from actin.
45
Describe the timing of a skeletal muscle contraction.
1. an action potential lasts 1 to 2 msec
2. latent period-delay of onset of contraction, lasts only a few milliseconds. due to the time required for diffusion of calcium to its site of action and generation of tension within the muscle fiber.
3. contraction time-50 msec. from initiation to peak of contraction.
4. relaxation time-50 to 100 msec. due to reuptake of calcium.
46
What is a twitch?
a single action potential on a muscle fiber.
| does not normally occur in the body.
47
What is variability in muscle activity based on?
1. number of fibers contracting
| 2. amount of tension being produced.
48
What is a motor unit?
a single neuron and all of the muscle fibers innervated by it.
49
Describe coarsely controlled muscles.
have high numbers of muscle fibers per axon.
| Postural muscles, etc.
50
Describe finely controlled muscles.
have relatively few muscle fibers per axon.
| those of the face and hands.
51
What is motor unit recruitment?
increasing the number of motor units called upon to contract.
will increase the strength of contraction.
52
What is asynchronous recruitment?
allows for rest of fatigued muscle fibers during sustained activity. Alternating motor units are used to maintain a submaximal concentration. Force is not increased.
53
What does increased frequency of stimulation do?
increases tension.
54
Describe temporal (twitch) summation.
a second stimulus is given to the muscle before it relaxes.
| muscle cells cannot summate action potentials.
55
What can lack of relaxation be attributed to?
persistence of calcium in the cytosol.
56
What is tetanus?
fusion of twitches, with no time for relaxation, results in a smooth sustained muscle contraction of maximal strength.
57
Describe how fiber length influences tension.
there is an optimal length, Io.
myosin heads are in optimal alignment with the actin binding sites.
contraction strength decreases markedly as muscle length changes by more than 30% of Io.
58
What happens if the muscle is stretched too much?
myosin cant bind to actin.
59
What happens if the muscle is too shortened?
1. thin filaments from the opposing sides of the sarcomere can become overlapped, decreasing the number of binding sites available for the myosin heads (cross bridges).
2. thick filaments can run into the Z-line therefore limiting contraction.
60
What three things can influence tension?
length of fiber
extent of fatigue
thickness of fiber.
61
How does the thickness of the fiber influence tension?
the thickness of fiber=the diameter of the fiber.
| the larger the diameter, the more myofibrils, then the greater the tension generated with each muscle fiber contraction.
62
How does the brain coordinate muscle movement.
by controlling combinations of muscles contracting by stimulating tetanic cointractions and shifts in asynchronous motor unit recruitment within muscles (to execute smooth movements).
63
Describe series-elastic elements.
non-contractile portions of the muscle (tendons, connective tissue, etc.). tension develops within sarcomeres, muscle shortening then pulls bones via tendons.
these connective tissues exhibit inherent elasticity.
elasticity must be overcome for movement to occur.
64
What is an isometric muscle contraction?
muscle contracts but remains at the same length, therefore no work is accomplished.
65
What is an isotonic muscle contraction?
muscle contracts and work or movement is accomplished.
concentric
eccentric
66
What is a concentric contraction?
muscle contracts and the insertion is brought closer to the origin and the muscle is shortened.
67
What is an eccentric contraction?
the muscle contracts and lengthens at the same time.
68
What are the four actions during muscle contraction that require energy?
1. release of cross bridge (same ATP molecule that cocks the myosin head).
2. cocking of the myosin heads for the power stroke.
3. active transport of calcium back into the sarcoplasmic reticulum.
sodium potassium pump to re-establish these ions at their normal extra and intracellular concentrations following the action on the muscle cell.
69
What are the four sources of energy?
1. storage of energy-ATP
2. storage of energy-creatine phosphate
3. glycolysis
4. oxidative phosphorylation
70
Describe how creatine phosphate creates energy.
adds a high energy phosphate group to ADP.
requires creatine kinase.
can rapidly supply ATP
very short duration (few seconds of maximum exertion).
71
What is the creatine phosphate equation during contraction?
creatine phosphate + ADP ----> creatine + ATP
72
What is the creatine phosphate equation during relaxation?
Creatine + ATP ----> Creatine phophate + ADP
73
When does glycolysis occur?
when there is no oxygen present.
74
Describe glycolysis.
glucose is stored in the muscle as glycogen.
glucose is split into two pyruvic acid molecules.
forms 2 ATP per glucose molecule.
pyruvic acid can be converted to lactic acid that can be recycled to glucose or can be used in the Krebs cycle.
supplies energy for a few minutes.
75
When does oxidative phosphorylation occur?
when oxygen is present.
76
Describe the oxidative phosphorylation process.
aerobic metabolism.
supplies 36 ATP/glucose molecule.
extra oxygen is stored by a myoglobin (pigment). This can also increase the rate of transfer of oxygen from the blood to the muscle.
can provide energy for long durations.
slower than glycolysis because more enzymes are involved.
77
What is muscle fatigue?
a build-up of lactic acid, which may alter the pH of the cell, inhibiting enzymatic reactions.
Depletion of ATP can lead to fatigue.
not due to tissue damage.
78
What is neuromuscular fatigue?
a lag in production (and therefore release) of acetylcholine.
79
What is central (physiological) fatigue?
may be due to pain associated with muscle use, decreased motivation or boredom.
80
What is oxygen debt?
the amount of oxygen required to replenish the ATP used during exercise.
81
What is EPOC?
excess postexercise oxygen consumption.
82
Describe muscle soreness.
initial pain in muscles and soreness during exercise is due to lactic acid.
Damage felt the next few days after a workout are probably due to reversible structural damage of muscle.
83
Describe slow-oxidative fibers.
```
have low myosin-ATPase activity.
slow contraction
highly resistant to fatigue.
high oxidative phosphorylation capacity.
low intensity of contraction, small fiber diameter.
found in postural muscles.
```
84
Why do slow-oxidative fibers have high oxidative phosphorylation capacity?
high levels of mitochondria and myoglobin.
many capillaries
low glycogen content
low glycolytic enzyme content.
85
Describe fast-oxidative fibers.
```
has high myosin-ATPase activity.
fast contraction
intermediate resistance to fatigue.
high oxidative phophorylation capacity.
intermediate intensity of contraction and fiber diameter.
found in most muscles
```
86
Why do fast-oxidative fibers have high oxidative phosphorylation capacity?
high levels of mitochondria and myoglobin.
many capillaries
intermediate glycogen content
intermediate glycolytic enzyme content.
87
Describe fast-glycolytic fibers.
high myosin-ATPase activity.
fast contraction.
low resistance to fatigue, fatigues relatively quickly.
low oxidative phosphorylation capacity.
high glycogen content and high glycolytic enzyme contents.
high intensity of contraction and large fiber diameter.
found in muscles used for rapid movement.
88
What kinds of neurons do motor units contain?
neurons of all the same type of fiber.
89
What is hypertrophy?
increase in muscle size due to an increase in fast-glycolytic fiber diameter.
90
What is hyperplasia?
increase in uscle size due to an increase in myofiber numbers.
can split or tear under stress, and then heal.
91
What is testosterone?
a hormone that increases the synthesis and assembly of myosin and actin fibers.
92
What is atrophy?
decrease in muscle fiber size due to disuse or loss of nerve supply.
93
What are satellite cells?
muscle cell stem cells, which can become myoblasts. Myoblasts fuse to form mature multinucleated muscle cells.
limited repair method.
94
what happens after extensive muscle damage?
the remaining healthy muscle cells hypertrophy to fill in the space of the lost muscle cells.
95
Describe the primary motor cortex and corticospinal motor system.
pyramidal cells (upper motor neuron) in the frontal lobe stimulate the lower motor neurons (LMN).
sends information on fine, discrete, voluntary movements to the hands and fingers.
works in concert with extrapyramidal system.
96
Describe the extrapyramidal system.
a multi-system interlink that receives input from the brainstem, basal nuclei, cerebellum, premotor area and supplementary motor areas, parietal lobes.
sends information on posture.
involves large muscle groups.
97
What is coordination of muscle movements based on?
a balance between excitation and inhibition.
98
What is spastic paralysis?
unopposed excitatory input causes it.
99
What is flaccid paralysis?
loss of excitatory input.
100
Who are the mcCaughey Septuplets?
two have cerebral palsy.
one has overexcited muscles, stiff.
one has under excited muscles, limp.
both have trouble learning to walk and crawl.
101
What do the muscle spindles and golgi tendon organs do?
monitor change in muscle length and tension.
apprise the motor areas of the brain of length and tension.
alter length and tension via negative feedback.
102
Describe the muscle spindles.
found in the belly of muscles.
lie parallel to ordinary muscle fibers (extrafusal)
contain non-contractile elements in the center, with contractile elements on either side.
has its own efferent (gamma motor neuron) and afferent nerve supply.
103
What are the two receptors in the afferent nerve of muscle spindles?
primary (annulospiral) endings
| secondary (flower-spray) endings
104
what do annulospiral endings detect?
change in length as well as the rate at which they change. Located at the central portion of the intrafusal fibers.
105
What do flower-spray endings detect?
change in length only and are located at the end segments of intrafusal fibers.
106
What happens when a muscle is stretched?
hammer hits tendon, stretches the muscle, muscle contracts reflexively. the afferent neurons are excited and directly excite alpha motor neurons to the extrafusal fibers. This reflex initiates muscle contraction.
107
What are gamma motor neurons?
keep the intrafusal fibers taut so that they can detect changes in length of the entire muscle.
108
What is the doctor testing when he tests reflexes?
afferent neuromuscular junction and efferent muscle.
109
What does loss of knee jerk reflex indicate?
CNS problem is possible.
110
Describe the golgi tendon organs.
located within the tendons of muscles.
respond to changes in externally applied tension.
afferent fibers are intertwined with the tendon fibers.
sends information to the brain for proprioceptive processing.
synapse on alpha neuron by means of an inhibitory interneuron.
111
What does the synapse on alpha neuron by inhibitory interneuron in the golgi tendon organs allow for?
reflex relaxation of the muscle to prevent damage to the muscle and associated tendon.
112
What are the similarities between (cardiac and smooth) and skeletal muscle?
calcium is required for contraction.
ATP is the energy source for contraction.
contain contractile fibers (actin and myosin).
113
Where is smooth muscle found?
walls of hollow organs, tubular structures (intestines), and blood vessels.
114
What does smooth muscle contain?
long myosin molecules (thick filaments)
thin filaments that lack troponin.
has more actin molecules than skeletal muscle.
intermediate filaments (non-contractile).
dense bodies that act as Z-lines.
115
What are thin filaments usually composed of?
actin, tropomyosin and troponin.
116
What are intermediate filaments?
unique to smooth muscle.
| non-contractile, but play a role in the inherent elasticity of smooth muscle.
117
Describe contraction in smooth muscle.
requires calcium.
myosin must be phosphorylated to interact with actin.
phosphorylation is accomplished by increases in intracellular calcium which activates calmodulin.
calmodulin binds and activates myosin light chain kinase (myosin kinase) which phosphorylates myosin.
cross-bridge cycling begins when calcium moves into the cell and ends when calcium is removed.
118
describe the sarcoplasmic reticulum and T tubules in smooth muscle.
poorly developed sarcoplasmic reticulum.
No T tubules of sarcolemma.
most calcium comes from extracellular sources.
119
Describe excitation in multi-unit smooth muscle.
neurogenic.
has discreet nervous input.
myoneural junctions are different.
the axon terminates in several varicosities instead of terminals.
nerve supply is via autonomic nervous system, not motor neurons.
120
Describe excitation in single-unit smooth muscle.
myogenic.
muscle fibers operate dependently.
cells are interconnected via gap junctions and action potentials spread from cell to cell, "function syncytium"
121
What does myogenic mean?
single-unit smooth muscle.
undergo action potentials without nervous input.
do not maintain a constant resting potential, but the membrane potential fluctuates.
pacemaker activity.
slow-wave potentials.
once an action potential is generated, the entire smooth muscle contracts.
122
What is pacemaker activity?
Single-unit smooth muscle.
| when pacemaker cells gradually depolarize the membrane due to passive ion fluxes.
123
What are slow-wave potentials.
single-unit smooth muscle.
automatic cyclical changes in the transport of sodium ions causes oscillations from hyperpolarization to hypopolarization.
124
Describe tone in smooth muscle cells.
tone is due to low levels of calcium present all the time.
| cross-bridges are still bound to actin.
125
What is the stress-relaxation response?
while most muscle contracts vigorously when stretched, smooth muscle tends to relax and accomodate for stretching by maintaining a relatively constant tone.
This allows for organs to fill without great increases in tone or evenutal loss of tone (bladder).
126
Describe energy in smooth muscle.
uses aerobic and anaerobic metabolism.
uses less energy than skeletal muscle.
strength of contraction is equal.
speed of contraction is much slower.
127
what does cardiac muscle contain?
thin filaments with actin, tropomyosin and troponin.
thick filaments composed of myosin molecules.
sarcomeric arrangement (same as skeletal).
sarcoplasmic reticulum and T tubules are present.
128
Describe pacemaker cells in cardiac muscle.
generate action potentials without any external influence.
| gap junctions propogate the action potential through the heart.
