1
Q
types of muscle tissue
A
- skeletal
- cardiac
- smooth
2
Q
- Attached to bones and skin
- multinucleated, long, cylindrical cells
- Striated
- voluntary (i.e., conscious control)
A
skeletal muscle tissue
3
Q
- Heart muscle
- Striated; intercalated disks (gap_ junctions)
- mononucleated_, branched cells
- Involuntary (i.e., conscious_ control)
A
cardiac muscle tissue
4
Q
- In the walls of hollow organs, e.g., stomach , urinary bladder, and airways
- oblong nucleus, Spindle-shaped cells
- Not striated
- Involuntary (i.e., unconscious control)
A
smooth muscle tissue
5
Q
- excitability (responsiveness or irritability): ability to receive and respond to stimuli
- contractibility : ability to shorten when stimulated
- extensibility : ability to be stretched
- elasticity : ability to recoil to resting length
A
special characteristics of muscle tissue
6
Q
- Movement of bones or fluids (e.g., GI tract, blood)
- maintaining posture and body position
- Stabilizing joints
- Heat generation (especially skeletal muscle)
A
muscle functions
7
Q
Each muscle is served by one artery , one nerve , and one or more veins
A
skeletal muscle
8
Q
- epimysium : dense regular connective tissue surrounding entire muscle
- perimysium : fibrous connective tissue surrounding fascicles (groups of muscle fibers)
- endomysium : fine areolar connective tissue surrounding each muscle fiber
A
connective tissue sheaths of skeletal muscle
9
Q
fibrous connective tissue surrounding fascicles (groups of muscle fibers)
A
perimysium (connective tissue sheath in skeletal muscle)
10
Q
dense regular connective tissue surrounding entire muscle
A
epimysium (connective sheath of skeletal muscle)
11
Q
fine areolar connective tissue surrounding each muscle fiber
A
endomysium (connective tissue sheath of skeletal muscle)
12
Q
- ______—epimysium of muscle is fused to the periosteum of bone or perichondrium__ of cartilage
- ______—connective tissue wrappings extend beyond the muscle_ as a ropelike tendon or sheetlike aponeurosis
A
directly/ indirectly
13
Q
- cylindrical_cell 10 to 100um in diameter, up to 30 cm long
- Many mitochondria [to generate force in skeletal muscle]
- Multiple peripheral nuclei [to generate myofibrils to develop proteins]
- Glycosomes for glycogen storage, myoglobin for O2 storage
- Also contain myofibrils, sarcoplasmic reticulum, and T tubules
A
microscopic anatomy of a skeletal muscle fiber
14
Q
- contractile organelle of muscle fiber
- densely packed, rodlike elements
- ~80% of cell volume
- Exhibit striations: perfectly aligned repeating series of dark A bands and light I bands
A
myofibrils
15
Q
- Network of smooth endoplasmic reticulum surrounding each myofibril
- Pairs of terminal cisternae form perpendicular cross channels
- Functions in the regulation of intracellular Ca2+ levels
A
sarcoplasmic reticulum
16
Q
- Continuous with the sarcolemma
- penetrate the cell’s interior at each A band–I band junction
- Associate with the paired terminal cisternae to form triads that encircle each sarcomere
A
T(transverse) tubules
17
Q
- _ _____ conduct impulses deep into muscle fiber
- Integral proteins protrude into the intermembrane space from T tubule and SR cisternae membranes
A
t tubules
18
Q
t tubule proteins : ______ ______
A
voltage sensors
19
Q
gated channels that regulate Ca2+ release from the cisternae
A
SR foot proteins
20
Q
Shortening occurs when tension generated by cross bridges of the two contractile proteins: ____ and ____
A
actin and myosin
21
Q
- Composed of the protein myosin
- Myosin heads contain:
- 2 smaller, light polypeptide chains form cross bridges
- Binding sites for actin of thin filaments
- Binding sites for ATP
- ATPase enzymes
A
ultrastructure of THICK filament
22
Q
- Composed of the protein_ actin
- Composed of two regulatory proteins:
- Troponin (bind Ca+2)
- tropomyosin (cover crossbridge binding site
A
ultrastructure of THIN filament
23
Q
- Smallest contractile unit (functional unit) of a muscle fiber
- The region of a myofibril_ between two successive Z discs
- Composed of thick and thin myofilaments made of contractile proteins
A
sacromere
24
Q
- thick filaments: run the entire length of an A band
- Thin filaments : run the length of the I band and partway into the A band
- Z disc: coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another
- M line: line of protein myomesin_ that holds adjacent thick filaments together (structural protein)
A
features of sarcomere
25
In what state does thin and thick filaments overlap only slightly
relaxed state
26
during \_\_\_\_\_\_, myosin heads bind to actin , detach , and bind again, to propel the thin filaments toward the M line
contraction
27
As _ zones shorten and disappear, sarcomeres shorten, muscle cells shorten, and the whole muscle shortens
H
28
1. activation : neural stimulation at aneuromuscular junction
2. Excitation-contraction coupling:
* generation and propagation of an action potential along the sarcolemma
* final trigger: a brief rise in intracellular Ca2+ levels
Requirements for Skeletal Muscle Contraction
29
* skeletal muscles are stimulated by somatic motor neurons
* Axons of \_motor\_\_ neurons \_travel\_ from the central \_\_nervous\_ system via nerves to skeletal muscles
* Each axon forms several branches as it enters a muscle
* Each \_axon\_ ending forms a \_neuromuscular\_\_ junction with a single muscle\_ fiber
events at the neuromuscular junction
30
* situated midway along the length of a muscle\_fiber
* Axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft
* synaptic vesicles of axon vesicles contain the neurotransmitter \_acetylcholine (ACh)
* juntional folds of the sarcolemma contain ACh
neurmuscular junction
31
* nerve\_ impulse arrives at axon \_terminal\_\_
* ACh is released and binds with \_receptors\_\_ on the sarcolemma\_
* Electrical events lead to the generation of an action potential
events at neuromuscular junction
32
* ACh effects are quickly rteerminated\_ by the enzyme acetylcholinesterase\_
* Prevents continued muscle fiber contraction\_ in the absence of additional stiumulation
destruction of acetylcholine
33
the 2 light polypeptide chains in a myosin molecules head link the thick and thin filaments together, forming \_\_, and swivel around their point of attachment during contraction
cross bridges
34
Sequence of events\_ by which \_transmission\_\_ of an AP along the sarcolemma leads to sliding of the myofilaments
Excitation-Contraction (E-C) Coupling
35
Latent period:
time\_\_ when E-C coupling events occur
Time between AP initiation and the beginning of contraction
excitation contraction coupling LATENT PERIOD
36
* Continues as long as the Ca2+ signal\_ and adequate \_ATP\_ are present
* cross\_ bridge formation — high-energy myosin\_ head attaches to thin filament
* Power stroke — \_mysosin\_ head pivots and pulls thin filament toward M line
cross bridge cycle
37
ATP attaches to myosin head and the cross bridge detaches
cross bridge detachment
38
energy from the hydrolysis of ATP cocks the myosin head into the high energy state
cocking of the myosin head
39
* no shortening; muscle tension increases but does not exceed the load
* once sufficient tension develops , tension remains relatively constant through rest of contractile period
isometric contraction
40
muscle shortens because muscle tension exceeds the load
isotonic contraction
41
1. Same principles apply to contraction of a single fiber and a whole muscle
2. contraction\_produces tension , the force exerted on the load or object to be moved
3. Contraction does not always shorten a muscle:
* isometric contraction: no shortening; muscle tension increases but does not exceed the load
* isotonic contraction: muscle shortens because muscle tension exceeds the load
4.Force and duration of contraction vary in response to stimuli of different frequencies and intensities
principles of muscle mechanics
42
a motor neuron and all (four to several hundred) muscle fibers it supplies
motor unit : the nerve muscle functional unit
43
\_\_\_\_ motor units in muscles that control fine movements (fingers , eyes)
small
44
\_\_\_\_\_\_ motor units in large weight-bearing muscles (thighs, hips)
large
45
* Muscle fibers from a ___ \_\_\_are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle
* Motor units in a muscle usually contract asynchronously ; helps prevent fatigue
motor unit
46
Response of a muscle to a single, brief threshold stimulus
simplest contraction observable in the lab (recorded as a myogram)
muscle twitch
47
* Latent period: events of excitation-contraction coupling
* Period of contraction: cross bridge formation; tension increases
* Period of relaxation : Ca2+ reentry into the SR; tension declines to zero
3 phases of a twitch
48
Different strength and duration of twitches are due to
variations in metabolic properties and enzymes btw muscles
49
* Variations in the degree of muscle contraction
* Required for proper control of skeletal movement
Responses are graded by:
1. Changing the frequency of stimulation
2. Changing the strength of the stimulus
graded muscle responses
50
a single stimulus results in a single contractile response- muscle twitch
response to change in stimulus frequency
51
Ca2+ release stimulates further contraction /further increase in stimulus frequency
temporal (wave) summation/ unfused (incomplete) tetanus
52
motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments
sequence of events for muscle contractions
53
funtional unit of a skeletal muscle is called
sarcomere
54
contractile units of skeletal muscle
myofibrils
55
surrounds the individual muscle cell?
endomysium
56
composed of myosin
thick filaments
57
During muscle contraction, myosin cross bridges attach to which active sites
actin filaments
58
What produces the striations of a skeletal muscle cell?
arrangement of myofilaments
59
The major function of the sarcoplasmic reticulum in muscle contraction is to \_\_\_\_\_\_\_\_.
regulate intracellular calcium concentration
60
What structure in skeletal muscle cells functions in calcium storage?
sarcoplasmic reticulum
61
Which muscle cells have the greatest ability to regenerate?
smooth
62
What is the role of tropomyosin in skeletal muscles?
Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules.
63
When a muscle fiber \_\_\_\_\_, the I bands diminish in size, the H zones disappear, and the A bands move closer together but do not diminish in length.
contracts
64
The effect of a \_\_\_\_\_\_on the muscle cell membrane is to modify its ion permeability properties temporarily.
neurotransmitter
65
An increase in the calcium ion level in the sarcoplasm starts the sliding of the thin filaments. When the level of calcium ions declines, ___ \_\_\_
sliding stops
66
stimulus stength at which the first observable muscle contraction occurs
threshold stimulus
67
contraction force is precisely controlled by _______ , which brings more and more muscle fibers into action
recruitment (multiple motor unit summation)
68
* Constant, slightly contracted\_ state of all muscles
* Due to spinal reflexes that activate groups of motor units alternately in response to input from stretch receptors in muscles
* Keeps muscles firm, healthy, and ready to respond
muscle tone
69
isotonic contractions are either ____ or \_\_\_\_\_
* concentric contractions—the muscle shortens and does work
* eccentric contractions—the muscle contracts as it lengthens
70
* The load is greater than the tension the muscle is able to develop
* tension\_ increases to the muscle’s capacity, but the muscle neither shortens nor lengthens
isometric contractions
71
* Direct phosphorylation of ADP by creatine phosphate (CP)
* Anaerobic pathway (glycolysis )
* aerobic respiration
how ATP is regenerated by
72
glycolysis in cytosol, pyruvic acid, lactic acid released to blood
anaerobic pathway
73
this pathway :
* Produces 95% of ATP during rest and light to moderate exercise
* Fuels: stored glycogen , then bloodborne glucose, pyruvic acid from glycolysis , and free fatty acids
aerobic pathway
74
* physiological inability to contract
Occurs when:
* ionic imbalances (K+, Ca2+, Pi) interfere with E-C coupling
* Prolonged exercise damages the SR and inteferes with Ca2+ regulation and release
* Total lack of ATP occurs rarely, during states of continuous conraction , and causes contractures (continuous contractions )
muscle fatigue
75
* Extra O2 needed after exercise for:
* Replenishment of oxygen\_ reserves, glycogen stores,ATP and CP reserves, Conversion of lactic acid to pyruvic acid, glucose, and glycogen
oxygen deficit
76
\_\_\_\_\_\_ __ \_\_\_\_\_ is affected by:
number of muscle fibers stimulated (recruitment )
Relative size of the fibers—hypertrophy of cells increase strength
* Frequency of stimulation —increase frequency allows time for more effective transfer of tension to noncontractile components
* Length-tension relationship—muscles contract most strongly when muscle fibers are 80–120% of their normal resting length
force of contraction
77
velocity and duration of contraction influenced by...
muscle fiber type, load, recruitment
78
1.Speed of contraction : slow or fast, according to:
* speed at which myosin ATPases split ATP
* Pattern of electrical activity of the motor neurons
2.Metabolic pathways for ATP synthesis:
* Oxidative fibers—use aerobic pathways
* Glycolytic fibers—use anaerobic glycolysis
classification of muscle fiber according to these 2 characteristics
79
aerobic (endurance ) exercise leads to increased....
* muscle capillaries
* number of mitochondria
* myoglobin synthesis
* results in greater endurance, strength, resistance to fatigue
80
Resistance exercise (typically anaerobic) results in:
* Muscle hypertrophy (due to increase in fiber size)
* Increased mitochondria , myofilaments, glycogen stores, and connective tissue
81
* \_\_\_\_\_\_\_layer contracts; organ dilates and shortens
* _____ layer contracts\_ ; organ constricts and elongates
longitudinal/ circular
82
\_\_\_\_\_\_\_ nerve fibers innervate smooth muscle at diffuse junctions
autonomic
83
\_\_\_\_\_\_ are (bulbous swellings) of nerve fibers store and release neurotransmitters
varicosities
84
* Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:2)
* thick filaments have heads along their entire length
* No troponin complex; protein calmodulin binds Ca2+
* Myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner
* Dense bodies: proteins that anchor noncontractile\_ intermediate filaments to sarcolemma at regular intervals
mylofilaments in smooth muscle
85
* Slow, synchronized contractions
* Cells are electrically coupled by gap junctions
* Some cells are self-excitatory (depolarize without external stimuli); act as pacemakers for sheets of muscle
* Rate and intensity of contraction may be modified by neural and chemical stimuli
contraction of smooth muscle
86
* Stress-relaxation response:
* responds to stretch only briefly, then adapts to new length
* Retains ability to contract on demand
* enables organs such as the stomach and bladder to temporarily store contents
* Length and tension changes:
* Can contract when between half and twice its resting length
special features of smooth muscle contraction
87
* sheets contract rhymthmically as a unit (gap junctions)
* Often exhibit spontaneous action potentials
* Arranged in opposing sheets and exhibit stress-relaxation response
single unit visceral smooth muscle
88
* located in large airways, large arteries , arrector pili muscles, and iris of eye
* gap junctions are rare
* Arranged in motor units
* Graded contractions occur in response to neural stimuli
multiunit smooth muscle
89
in excitation contraction coupling the action potential is propagted down the \_ ______ causing calcium to en released from the SR into the cytosol
t tubules
90
Anatomy & Physiology
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