CH 12 - muscles Flashcards
(73 cards)
1
Q
What are skeletal muscles surrounded by?
A
Fibrous epimysium
2
Q
What are the subdivisions of the perimysium?
A
Fascicles
3
Q
What divides the skeletal connective tissue?
A
Perimysium
4
Q
What is inside fascicles?
A
Myofibers
5
Q
What surrounds myofibers?
A
Endomysium
6
Q
What are the 4 main fiber structures/characteristics in muscles? (not all specific names)
A
a. Have the same organelles found in other cells
b. Sarcolemma
c. Are multinucleated; form a syncytium
d. Are striated
7
Q
What are the 3 band names in striated skeletal muscle?
A
I bands: light bands
A bands: dark bands
Z-lines (discs): dark lines in the middle of the I bands
8
Q
What are the light bands in skeletal muscle?
A
I bands
9
Q
What are the dark bands in skeletal muscle?
A
A bands
10
Q
What are the dark lines in the middle of light bands in skeletal muscle?
A
Z-lines
11
Q
What is the plasma membrane in muscle fibers called?
A
Sarcolemma
12
Q
What is the site where a motor neuron stimulates a muscle fiber?
A
Neuromuscular junction
13
Q
What is the area of the muscle fiber sarcolemma where a motor neuron stimulates it using the neurotransmitter, acetylcholine?
A
Motor end plate
14
Q
a single motor neuron (with its collateral branches) and all the muscle fibers it innervates
A
Motor units
15
Q
How do motor units contact?
A
All at once
16
Q
What is varied contraction strength due to different numbers of motor units being activated?
A
Graded contractions
17
Q
What type of muscle control requires fewer motor units?
A
Fine muscle control
18
Q
Contraction strength comes from?
A
Motor unit recruitment
19
Q
What are myofibrils composed of?
A
Myofilaments
20
Q
What are the 4 layers of muscle fibers (outside to inside)
A
Sarcolemma
Sarcoplasm
Myofibrils
Myofilaments
21
Q
What is the dark blob in skeletal muscle?
A
Nucleus
22
Q
What protein is I bands composed of primarily?
A
actin
23
Q
What protein is A bands composed of primarily?
A
myosin
24
Q
Which band is thin filament?
A
I band
25
Which band is thick filament?
A band
26
What is inside of A bands?
H bands
27
The basic subunit of striated muscle contraction that runs from one Z disc to the next?
Sarcomere
28
Protein that runs from the Z disc to the M line that contributes to the force of contraction due to elastic recoil and the refolding of unfolded elements?
Titin
29
What lines are inside A bands?
M lines
30
What do M lines do?
Help hold down thick filaments
31
What 3D shape do sarcomere form?
Hexagonal patterns
32
What does sarco mean?
Muscle/flesh
33
When do sarcomere shorten?
Muscle contraction
34
Do A bands shorten?
No, but they move together
35
Do I bands shorten?
Yes
36
Do actin or myosin shorten?
N o :)
37
What is thin filament?
Actin
38
What is thick filament?
Myosin
39
Where do thin filaments go in muscle contraction?
They slide towards the H band
40
What happens to the H bands in muscle contraction?
Shortens or even disappears
41
What is sliding filament theory?
When a muscle contracts, sarcomeres shorten
42
How does sliding filament theory work?
Sliding is produced by several cross bridges that form between myosin and actin.
43
How do myosin and actin make cross bridges?
a) The myosin head serves as a myosin ATPase enzyme, splitting ATP into ADP + Pi.
b) This allows the head to bind to actin when the muscle is stimulated.
44
How does the myosin head help the sliding filament theory?
Release of Pi upon binding cocks the myosin head, producing a power stroke that pulls the thin filament toward the center.
45
What is the full descriptive way that sliding filament theory works?
After the power stroke, ADP is released and a new ATP binds.
This makes myosin release actin.
The new ATP is split.
The myosin head straightens out and rebinds to actin farther back.
Continues until the sarcomere has shortened
46
How many ATP molecules are needed to create a power stroke?
2
47
What are the 3 parts of the troponin complex?
a. Troponin I inhibits binding of myosin.
b. Troponin T binds to tropomyosin.
c. Troponin C binds to calcium.
48
What does tropomyosin do?
Blocks cross bridges
49
What does calcium do when muscles are stimulated?
When muscle cells are stimulated, Ca2+ is released inside the muscle fiber.
Some attaches to troponin C, causing a conformational change in troponin and tropomyosin.
Myosin is allowed access to form cross bridges with actin.
50
In muscles, what is the modified endoplasmic reticulum that stores calcium?
Sarcoplasmic reticulum (SR)
51
At the end of a contraction, what happens to calcium?
It is pumped back into the Sarcoplasmic reticulum (SR)
52
When muscles are stimulated, what happens to calcium?
Ca2+ diffuses out of calcium release channels (ryanodine receptors).
53
In muscles, what are calcium release channels?
ryanodine receptors
54
Narrow membranous tunnels formed from the sarcolemma
Transverse Tubules (T tubules)
55
In muscles, what contains voltage-gated calcium channels (dihydropyridine, DHP) receptors that respond to membrane depolarization?
Transverse Tubules
56
What can transverse tubules do?
Conduct action potentials
57
What happens in muscle stimulation according to Excitation-Contraction Coupling ?
a. Acetylcholine is released from the motor neuron.
b. End plate potentials are produced.
c. Action potentials along the sarcolemma and down the T tubules are generated (All-or-none event).
d. Voltage-gated calcium channels in transverse tubules change shape, couple to SR calcium channels, and cause them to open.
e. Calcium is released and can bind to troponin C.
58
Why is excitation-contraction coupling described as an electromechanical release mechanism?
Because the voltage-gated calcium channels and the calcium release channels are physically (mechanically) coupled
59
What is calcium induced release mechanism?
channels in the SR membrane that respond to increased cytoplasmic Ca2+ concentration to release more Ca2+
60
What happens during muscle relaxation according to the excitation-contraction coupling
a. Action potentials cease.
b. Calcium release channels close
c. Sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) pumps move Ca2+ back into SR (active transport).
d. No more Ca2+ is available to bind to troponin C
e. Tropomyosin moves to block the myosin heads from binding to actin
61
What is a twitch?
Twitch: when a muscle quickly contracts and relaxes after a single electrical shock of sufficient voltage
62
What is summation?
a. Increasing the voltage increases the strength of the twitch up to a maximum.
b. When a second shock is applied immediately after the first, a second twitch will partially piggyback the first. This is called summation.
63
What is the latent period in twitching?
Latent period – time between the stimulus and the contraction (excitation-contraction coupling to the attachment of myosin cross bridges to actin)
64
What are graded contractions in twitching?
Graded contractions – stronger contractions result in recruitment of more fibers, until all fibers are contracting.
65
What is incomplete tetanus?
Increasing the frequency of electrical shocks decreases the relaxation time between twitches. This is called incomplete tetanus.
66
What is complete tetanus?
At a certain frequency, there will be no relaxation. This is called complete tetanus, a smooth, sustained contraction.
67
what are some properties of smooth/cardiac muscles?
a. Involuntary
b. Regulated by autonomic nervous system
c. Like skeletal muscle, contraction is due to myosin/actin cross bridges stimulated by calcium
68
What are some characteristics of cardiac muscle?
~Striated
~Myosin and actin filaments form sarcomeres.
~Contraction occurs by means of sliding filament mechanism
~Unlike skeletal muscle fibers, these fibers are short, branched, and connected via gap junctions called intercalated discs (electrical synapses that permit impulses to be conducted cell to cell).
69
What is myocardium?
myocardium is a mass of cardiac muscle cells connected to each other via gap junctions. (atrium and ventricles)
70
What does myocardium do?
b. Action potentials that occur at any cell in a myocardium can stimulate all the cells in the myocardium.
c. It behaves as a single functional unit.
d. The atria of the heart compose one myocardium, and the ventricles of the heart compose another myocardium.
71
What is pacemaker potential?
a. Cardiac muscle can produce action potentials automatically (without innervation).
Begin in a region called the pacemaker
b. Heart rate is influenced by autonomic innervation and hormones.
72
What type of muscle is found in blood vessel walls, bronchioles, digestive organs, urinary and reproductive tracts?
Smooth muscles
73
What are some characteristics of smooth muscle? (fix bc its copy pasted and a lot of words)
a. Both circular and longitudinal smooth muscle layers occur in tubular structures
b. Alternating contractions of the circular and longitudinal muscles produce peristaltic waves to propel contents of these organs
~No sarcomeres, but still contain large amounts of actin and myosin
~Long actin filaments attached to dense bodies or regions of the plasma membrane
~Myosin filaments are stacked vertically and can form cross bridges with actin its entire length
~Arrangement allows contraction even when greatly stretched
