Muscular System Flashcards
1
Q
What kind of cells are muscles made of?
A
cells that can shorten or contract
2
Q
What does myo- mean?
A
refers to muscle generally
3
Q
What does myology mean?
A
the study of muscles
4
Q
What does myositis mean?
A
inflammation of muscle tissues
5
Q
What does sarco- refer to?
A
muscle cells, such as sarcoplasm (the cytoplasm of a muscle cell)
6
Q
What are the functions of skeletal muscle?
A
- produce skeletal movement
- maintain posture and body position
- support and protect soft tissues
- guard entrances and exits of digestive and urinary tracts
- maintain body temperature
7
Q
Describe the anatomy of the skeletal muscle.
A
- muscle tissues (skeletal muscle cells or fibers)
- connective tissues (dense)
- nerves
- blood vessels
- adipose tissue (marbling)
8
Q
What are the three layers of connective tissue?
A
epimysium, perimysium, endomysium
9
Q
What does the epimysium do?
A
surrounds the entire muscle
10
Q
What does the perimysium do?
A
divides the skeletal muscle into a series of compartments (fascicle)
11
Q
What does the endomysium do?
A
surrounds the individual skeletal muscle fibers and interconnects adjacent muscle fibers
12
Q
What do the collagen fibers of the three layers of the connective tissue do?
A
They come together to form a bundle (tendon) or a broad sheet (aponeurosis)
13
Q
Describe skeletal muscle fibers (cells)
A
- are very long
- develop through fusion of mesodermal cells (myoblasts)
- become very large
- contain hundred of nuclei
14
Q
What is the sarcolemma?
A
- Plasma membrane of muscle fibers surrounding the sarcoplasm
- has characteristic transmembrane potential (-95 mV)
15
Q
How are transverse tubules (T tubules) formed?
A
- formed by inward extensions of the sarcolemma. Have same properties of sarcolemma.
16
Q
What do transverse tubules do?
A
Transmit action potential through cells, allow entire muscle fiber to contract simultaneously
17
Q
What are myofibrils?
A
- cylindrical structures
- each muscle fiber contains hundreds to thousands of myofibrils
- consist of bundles of myofilaments (thin and thick filaments)
18
Q
What are thin filaments formed by?
A
actin
19
Q
What are thick filaments formed by?
A
myosin
20
Q
What is the sarcoplasmic reticulum (SR)
A
- network of tubules and sacs around each individual myofibril
21
Q
What does the sarcoplasmic reticulum do?
A
continually pumps calcium ions from the sarcoplasm into its sacs.
22
Q
What are the two parts of the sarcoplasmic reticulum?
A
terminal cisternae and triad
23
Q
What are the terminal cisternae?
A
expanded chambers on either side of a T tubule
24
Q
What is a triad?
A
a pair of terminal cisternae and T tubule
25
What is a sarcomere?
segment of myofibril between two successive lines. Structural units of myofibrils. Contractile unit of skeletal muscle fibers.
26
What does each myofibril consist of?
Many sarcomeres (~10,000) end to end
27
What do sarcomeres do?
form visible patterns within myofibrils
28
What is the A ban in a sarcomere?
the entire length of the thick filaments
29
What is the M line of the sarcomere?
the central portion of each thick filament is connected to its neighbors by proteins of the M line.
30
What is the H zone of the sarcomere?
contains no thin filaments.
31
What is the zone of overlap of the sarcomere?
thin filaments are situated between the thick filaments
32
What is the I band of a sarcomere?
the ends of the thin filaments where they do not overlap the thick filaments
33
What is the Z line/ Z disc of a sarcomere?
marks the boundary between adjacent sarcomeres and interconnect thin filaments of adjacent sarcomeres
34
What is the titin of the sarcomeres?
extends from the tips of the thick filaments to attach sites at the Z line
35
What are the 4 proteins of the thin filaments?
F actin, nebulin, tropomyosin, troponin
36
Describe F actin
- is two twisted rows of globular G actin
- each G actin contains an active site that can bind to a thick filament
37
Describe Nebulin
- a long strand of nebulin spirals along the F actin strand in the cleft between the rows of G actin and hold them together
38
Describe tropomyosin
- cover the active sites and prevent actin myosin interaction
- is a double-stranded protein
39
Describe troponin
- consists of three subunits
- noe subunit binds to a tropomyosin
- a second subunit binds to one G-actin and hold troponin-tropomyosin complex in position
- the third subunit has a receptor that binds to a calcium ion
40
What do thick filaments contain?
- contain twisted myosin subunits
- contain titin strands that recoil after stretching
41
What are the two parts of the myosin molecule? Describe them.
tail: binds to other myosin molecules
head: myosin heads are arranged in a spiral, each facing one of the surrounding thin filaments
- projects outward toward the nearest thin filament
- is a cross-bridge for interaction between thin and thick filaments
- the H zone includes a central region with no myosin heads
42
What are muscle contractions caused by?
interactions of thick and thin filaments
43
What determine interactions of muscle contractions?
structures of protein molecules determine interactions
44
What is the sliding filament theory?
Thin filaments of sarcomere slide toward M line between thick filaments. The width of A zone stays the same and z lines move closer together
45
What is involved in the process of contraction?
Neural stimulation of the sarcolemma causes excitation-contraction coupling. The cisternae of SR release Ca2+, which triggers interaction of thick and thin filaments, consuming ATP and producing tension.
46
Describe the neuromuscular junction.
A single axon branches within the perimysium to form a number of fine branches. Each branch ends at an expanded synaptic terminal.
47
What does the synaptic terminal contain and what does it do?
It contains vesicles filled with acetylcholine (ACh) and it can alter the permeability of the sarcolemma and trigger the muscle fiber contraction.
48
What is the synaptic cleft?
A narrow space separating the synaptic terminal from the opposing sarcolemmal surface (motor end plate)
49
What does the motor end plate contain?
Contains membrane receptors that bind to ACh, junctional folds, and acetylcholinesterase (AChE)
50
What do junctional fold do?
Increase its surface area and receptor numbers
51
What does acetylcholinesterase (AChE) do?
Break down acetylcholine (ACh).
52
How does the neuromuscular junction work?
1. a neuron sends an action potential
2. exocytosis of ACh into the synaptic cleft
3. binding
4. action potential - sodium ions
5. sweep of the impulse across the entire membrane surface and travel along each T tubule
53
How does the excitation-contraction coupling work?
an action potential triggers the temporary release of calcium ions from the cisternae of SR at the triads. This results in a 100-fold increase of calcium ion concentration in and around the sarcomere. Then calcium binds to troponin and the initiation of the contraction cycle starts.
54
What are the steps of the contraction cycle?
1. exposure of active sites: calcium ions enter the sarcoplasm -> bind to troponin -> exposure of active sites on thin filaments
2. attachment of cross-bridges: myosin cross bridges bind to exposed active sites on thin filaments
3. pivoting: the myosin head pivots towards the M line
4. detachment of cross bridges: ATP binds to the myosin head -> detachment of cross bridges
5. reactivation of myosin: ATP splits into ADP + P -> relocking of the myosin head -> repeating the cycle
55
How does relaxation of the muscle occur?
AChE breaks down ACh and limits the duration of stimulation. The contraction continues until either 1. calcium concentrations return to resting levels by active transport into the SR or 2. the muscle fiber runs out of ATP
56
What is the relevance of rigor mortis?
Rigor mortis is the rigidity of a body after death, usually lasting from one to four days. When death occurs, no ATP is produced. Ca2+ continues to leak into the cytosol and cannot be pumped back to SR. A few hours after death, the Ca2+ concentration in cytosol will be high enough to cause binding of thin and thick filaments until the muscles themselves start to decompose.
57
How does tension production work?
the all-or-none principle: as a whole, a muscle fiber is either contracted or relaxed. Tension of a whole muscle depends on: the frequency of stimulation and the total number of muscle fibers stimulated (motor units)
58
What constitutes a motor unit?
All the muscle fibers controlled by a single motor neuron. Contain hundred of muscle fibers that contract at the same time
59
Describe the energetics of muscle contraction
A single muscle fiber may contain 15 billion thick filaments; each breaks down roughly 2500 ATP per second --> enormous ATP demand for a contracting muscle
60
What are the sources of energy in a typical muscle fiber?
1. ATP: ATP --> ADP + P
2. CP (creatine phosphate)
- at rest: ATP + creatine --> ADP + CP
- during a contraction: ADP + CP --> ATP + creatine (recharge)
3. glycogen: major energy storage
61
What are the two ways that cells produce ATP?
aerobic metabolism of fatty acids in the mitochondria and anaerobic glycolysis in the cytoplasm
62
What is anaerobic metabolism (glycolysis)?
The breakdown of glucose to pyruvic acid in the cytoplasm of a cell.
- glucose = 2 pyruvic acid (pyruvate) + 2 ATP
- does not require oxygen
- glucose comes from glycogen reserves
63
What is aerobic metabolism?
- CO2 and water, via pyruvic acid; requires mitochondria and O2
- one glucose produces 38 ATP
64
Describe the energy use in a resting muscle
- more than enough oxygen is available
- fatty acids --> ATP by aerobic metabolism
- ATP --> CP + glycogen for energy storage
65
Describe the energy use for a muscle at moderate activity
- ATP and rate of oxygen consumption
- oxygen availability is not a limiting factor yet
- ATP is generated primarily bu the aerobic metabolism of pyruvic acid from glycolysis
- All ATP generated is used with no surplus
66
Describe energy use for a muscle at peak levels of activity
- oxygen availability becomes limited
- 1/3 of the ATP is produced by aerobic metabolism; 2/3 by glycolysis which is an inefficient way to generate ATP
- lactic acid conversion lowers the intracellular pH --> alter functional characteristic of key enzymes --> can not continue to contract
67
What is the cause of muscle fatigue?
- exhaustion of ATP and CP
- drop in pH that accompanies the build up of lactic acid
- physical damage
68
What does normal muscle function require?
- substantial intracellular energy reserves
- blood and oxygen
69
What is the recovery period?
the time required after exertion for muscle to return to normal when oxygen becomes available
70
What is oxygen debt?
the amount of oxygen required to restore normal, pre exertion condition
71
How is lactic acid removed?
lactic acid diffuses out of the muscle fibers into the bloodstream and is converted to glucose by liver
72
What is muscle performance considered as?
- power: the maximum amount of tension produced by a particular muscle or muscle group
- endurance: the amount of time for which the individual can perform a particular activity
73
What is muscle performance determined by?
- the types of skeletal muscle fibers in the muscle
- physical conditioning or training
74
What are the three types of skeletal muscle fibers?
1. slow fibers (red fibers)
2. fast fibers (white fibers)
3. intermediate fibers
75
What type of fibers are fast fibers?
white, type IIb
76
What are the characteristics of white fibers?
- contract very quickly
- have large diameter, densely packed myofibrils, large glycogen reserves, few mitochondria
- have strong contractions, fatigue quickly
77
What type of fibers are slow fibers?
red, type I
78
What are the characteristics of slow fibers?
- are slow to contract and slow to fatigue
- have smaller diameter, more mitochondria
- have more capillaries and high oxygen supply
- contain mitochondria (red pigment, binds to oxygen)
79
What kind of fibers at intermediate fibers?
type IIa
80
What are the characteristics of intermediate fibers?
- are mid-sized
- have low myoglobin
- have more capillaries than fast fibers, slower to fatigue
81
What are the seven structural characteristics of cardiocytes?
1. are small
2. have a single nucleus
3. have short, wide T tubules
4. have no triads
5. have SR with no terminal cisternae
6. are aerobic
7. cells are branched and have intercalated discs
82
What are the 4 functional characteristics of cardiac tissue?
1. automaticity
- contraction without neural stimulation
- controlled by pacemaker cells
2. variable contraction tension
- controlled by nervous system
3. extended contraction time (~ 10 times longer), do not readily fatigue
4. prevention of wave summation and tetanic contractions by cell membranes
83
What are the 8 structural characteristics of smooth muscle cells?
1. long, slender, and spindle shaped
2. have a single, central nucleus
3. have no tendons or aponeuroses
4. have no T tubules, myofibrils, or sarcomeres
5. have scattered myosin fibers
6. myosin fibers have more heads per thick filament
7. have thin filaments attached to dense bodies
8. dense bodies transmit contractions from cell to cell
