Chapter 12: Muscle Flashcards
(129 cards)
1
Q
Skeletal muscles are composed of
A
individual muscle fibers that contract
2
Q
Skeletal muscles are stimulated by the
A
Somatic motor neurons
3
Q
Skeletal muscles are usually attached to bone on each end by
A
tough connective tissue tendons
4
Q
What causes movement of the bones at a joint?
A
The tension placed on tendons and attached bones by muscle contraction
5
Q
What is an insertion?
A
The more movable bony attachment of a muscle. MOVEMENT IS TOWARD INSERTION
6
Q
Less movable attachment of a muscle
A
Origin
7
Q
What do flexor muscles do?
A
Decrease the angle of a joint
8
Q
What do extensor muscles fo?
A
Increase the angle of their attached bones at the joint
9
Q
Agonist muscle
A
The prime mover of any skeletal movement
10
Q
What is the agonist muscle in flexion?
A
The flexor muscle. THIS IS THE MAIN MUSCLE RESPONSIBLE FOR MOVEMENT IN A GIVEN DIRECTION. ALSO KNOWN AS PRIME MOVER
11
Q
Antagonist muscles
A
Flexors and extensors that act on the same joint to produce opposite actions.
12
Q
What does an abductor muscle do?
A
Moves limb away front he midline of the body
13
Q
What does an adductor muscle do?
A
Moves limb toward the midline of the body
14
Q
What does a legator muscle do?
A
Moves insertion upward
15
Q
What does a depressor muscle do?
A
Moves insertion downward
16
Q
What does a rotator muscle do?
A
It rotates a bone along its axis
17
Q
What does a sphincter muscle do?
A
Constricts an opening
18
Q
What is the epimysium?
A
A sheath of muscle tissue proteins within tendons which extend around the muscle in an irregular arrangement
19
Q
What is a fascicle?
A
Connective tissue from the epimysium extending into the body of the muscle
20
Q
What is the perimysium?
A
Tissue sheath surrounding fascicles
21
Q
Sarcolemma
A
Plasma membrane surrounding the muscle fibers or myofibers
22
Q
What is the endomysium?
A
Connective tissue layer surrounding sarcolemma
23
Q
What is the only difference between any other cells in the body and the muscle cell?
A
The muscle cell is multi nucleated, syncytium
24
Q
Syncytium
A
Formed from the union of several embryonic myoblast cells
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Most distinctive feature of skeletal muscle fibers
Striated appearance
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Striated appearance of muscle cells are caused by :
Dark bands: A bands (think A in dark)
Light bands: I bands (think I in light)
Thin dark lines between A band and I band: Z lines (disks)
27
What is a motor unit?
A single motor neuron and all the muscle fibers it innervates. They all contract at once. Each consist of branched motor axon
28
Graded contractions
Varied contraction strength due to different numbers of motor units being stimulated
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Nueromuscular junction
Site where a motor neuron stimulates a muscle fiber
30
Motor end plate:
Area of the muscle fiber sarcolemma where a motor neuron stimulates it using the neurotransmitter, acetylcholine
31
Control of motor unit
Contraction strength comes from motor unit recruitment
32
Fine muscle control requires
smaller motor units with fewer muscle fibers
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How many muscle fibers/motor units in the eye?
~23 muscle fibers/units
34
Motor end plate
The specialized region of the sarcolemma of the muscle fiber at the neuromuscular junction, where acetylcholine is released for contraction of the muscle
35
Where is the cell body of a somatic motor neuron located?
In the ventral horn of the gray matter of the spinal cord, gives rise to a single axon
36
Recruitment of motor units
Process used when contractions of greater strength are required, larger motor units are activated
37
Process involved with increase force of muscle contraction:
1. motor unit stimulated asynchronously at greater frequency
2. recruitment of additional larger motor units with more muscle fibers per motor neuron to increase the force of contraction.
38
What are myofibrils?
Subunits packed densely in each muscle fiber which run the length of the muscle fiber
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What are myofibrils composed of?
Thick and thin myofilaments (the smallest unit)
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What does each muscle fiber contain?
Nucleus, striations, sarcolemma, sarcoplasm, myofibrils, myofilaments
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I band contains:
Only thin filaments, primarily of the protein ACTIN
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A band contains:
All of the thick filaments with some thin filament overlap; the thin filament is the protein MYOSIN
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H band are:
The center of the A band with no thin filament overlap
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Z discs (lines) are found:
In the center of the each I band
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What is the sarcomere?
The basic subunit of striated muscle contraction. Forms hexagonal pattern
46
What does a sarcomere contain?
Area from a Z disc to the next. It contains the A band, H band, and I band
47
What does titin do?
Protein which runs from the Z disc to the M line and allows elastic recoil
48
Where are M lines found?
| What do they do?
In the center of each A band
| Help hold down thick filament
49
Sliding Filament Theory of contraction
When muscle contacts, sarcomere shorten.
A band do not shorten but move closer together!!
I band do shorten!! but thin filaments do not!
Thin filaments slide toward the H band
H band shortens or disappears ( I and H bands shorten)
50
How is the sliding of the filaments accomplished?
Asynchronous power strokes of myosin cross bridges, which pull the thin filaments (actin) over the thick filaments (myosin)
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Shortening of the sarcomeres is accomplished by
Sliding of the myofilaments-the length of each filament remains the same during contraction
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What are thick filaments composed of?
Myosin
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Myosin proteins contain
Two globular heads with actin-binding sites and ATP-binding sites (these are responsible for moving the thin filaments in contraction)
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Thin proteins are composed of/?
Actin
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Actin proteins contain
Tropomyosin (String) and troponin that prevent myosin binding at rest
56
Action of sliding is caused by
Several cross bridges that form between myosin and actin
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What part of the myosin acts as the ATPase enzyme?
The myosin head, splitting ATP into ADP and inorganic P
58
What does hydrolysis of ATP cause?
Allows the myosin head to bind to actin binding sites when the muscle is stimulated
59
What causes the power stroke?
The release of inorganic P upon binding cocks the myosin head to pull the thin filament toward the center
60
What happens after the power stroke?
The ADP is released and a new ATP binds causing the myosin head to release the actin.
ATP is split again.
Myosin straightens out and rebind to actin further back
61
Two types of Actin
F (Filamentous) actin: String of many G actin
| G (Globular) actin: round subunits
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How is actin arranged in thin filaments?
F actin is made up of 300-400 G actin units, arranged in a double row and twisted to form helix
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What can block cross bridges?
Tropomyosin (string which moves to attach to myosin head)
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Troponin complex composed of :
Troponin I inhibits binding of myosin
Troponin T binds to tropomyosin
Troponin C binds to calcium
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Role of Ca:
Muscle cells are stimulated by release or Ca inside the muscle fiber
Some attach to troponin C causing conformational change in troponin and tropomyosin
Myosin is allowed access to form cross bridges with actin
66
What is the role of sarcoplasmic reticulum in muscle contraction?
SR is modified to store Ca when muscle is at rest.
Most is stored in terminal cisternae.
When muscle fiber is stimulated Ca diffuses out of calcium reuse channels.
At the end of contraction, Ca is actively pumped back into the SR.
67
What are transverse tubules?
Found in the SR
They are narrow membranous tunnels formed from the sarcolemma
They are open to the extracellular environment and conduct action potentials.
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Excitation Contraction Coupling Summary
ACh released from somatic motor neuron
In sarcolemma: ACh binds to nicotinic ACh receptors, opens ligand gated channels -> Na diffuses in, producing depolarizing stimulus -> Action potential is produced
In transverse tubules: Action potentials conducted along transverse tubules -> Action potentials open voltage gated Ca channels.
In sarcoplasmic reticulum: Ca release channels in SR open -> Ca diffuses out into sarcoplasm
In myofibrils: Ca binds to troponin, stimulating contraction
69
What happens in muscle relaxation?
Action potential cease
Calcium release channels close
Ca ATPase pumps move Ca back into SR
No more Ca is available to bind to troponin C
Tropomyosin moves to block the myosin heads from binding to actin
70
How is muscle contraction studied?
in vitro where one end of the muscle is fixed and the other is movable. Using electrical stimulations and contractions are displayed in currents
71
What is a twitch?
When a muscle quickly contracts and relaxes after a single electrical shock of sufficient voltage
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What is summation?
When a second shock is applied immediately after the firs, the second twitch will partially piggyback the first. Twitch increases with voltage increase.
73
What is a latent period?
Time between the stimulus and the contraction. Also referred to as excitation-contraction coupling at cross bridges.
74
Graded contractions?
Stronger contractions result in recruitment of more fibers, until all fibers are contracting.
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Incomplete tetanus
Increasing the frequency of electrical shocks decreases the relaxation time between twitches. Muscle never relaxes enough before being stimulated again
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Complete tetanus
At a certain frequency, there will be no relaxation. This is equivalent to a smooth, sustained contraction. The more twitch the better the result
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Treppe effect
Staircase effect seen when a fresh muscle is stimulated with several shocks at maximum voltage, each twitch will be progressively stronger. There is a maximum value reached
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Types of muscle contraction:
Force velocity curve
Isotonic contractions
Isometric contractions
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Force velocity curve
For muscle to contact, they must generate force that is greater than the opposing forces (gravity/weights). The greater the force the slow the contraction.
80
Isotonic contractions
Muscle fibers shorten when the tension produced is just greater than the load.
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Two subcategories of isotonic contractions
Concentric contractions
| Eccentric contraction
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Concentric contractions
A muscle fiber shortens when force is greater than load
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Eccentric contraction
A muscle may actually lengthen, despite contraction, if the load is too great (going down a hill/lowering weight slowly)
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Isometric contraction
Muscles can't shorten because the load is too great. Can be voluntary
85
Muscle strength is determined by
Number of fibers recruited to contract
Frequency of stimulation
Thickness of each muscle fiber ( the thicker the stronger)
Initial length of the fiber at rest
86
Tension is maximal when:
Sarcomeres are at normal resting length
87
Increasing sarcomere length....
Decreases muscle tension. There are fewer interactions between myosin and actin. At some point, no tension will be generated
88
Decreasing sarcomere length...
Decreases muscle tension due to fiber shortening and thickening. This increases fluid pressure and distance between the actin and myosin
89
Energy is needed for:
```
Myosin ATPase (70%)
Ca pump to actively return calcium to SR (30%)
```
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At rest and for mild exercise energy comes from?
Aerobic respiration of fatty acids
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For moderate exercise energy comes from?
Glycogen storage
92
For heavy exercise energy comes from?
Blood glucose
| With increased intensity or duration, FLUT4 channels are inserted into the sarcolemma to allow more glucose into cells
93
Types of twitch?
```
Slow twitch (Type I)
Fast twitch (Type IIx)
Intermediate twitch (Type IIa)
```
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Slow twitch
Type I: Slower contract speed; can sustain contraction for Longer periods without fatigue
Rich capillary supply
More mitochondria
More respiratory enzymes
More myoglobin
ALSO CALLED RED FIBERS OR SLOW OXIDATIVE FIBERS
95
Fast twitch
Type IIx: Faster contraction speed
Fatigue fast
Fewer capillaries, mitochondria, respiratory enzymes and myoglobin
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Intermediate twitch
Type IIa: Fast twitch but with high oxidative capacity; called fast oxidative fibers
97
What reduces the ability to generate force?
Muscle fatigue
98
Fatigue can be due to
```
Reduced SR Ca release
Lack of ATP
Buildup of ADP
Fatigue in CNS (Also called central fatigue)
Lactic acid accumulation/lower pH
Depletion of glycogen
```
99
What causes muscle decline with aging?
Reduced muscle mass (Type II fibers)
reduction in capillary blood supply
Fewer satellite cells
Increased myostatin production
100
How do muscle cells repair themselves?
Using stem cells called satellite cells located newer muscle fibers
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Lower motorneurons
Neurons whose axons innervate skeletal muscles
Cell bodies in ventral horn of spinal cord or brain stem
Travel down via ventral root or spinal nerves
Influenced by sensory feedback and stimulation from higher motor neurons or brain
102
Higher motorneurons
Neurons in the brain that are involved in the control of skeletal movements and that act by facilitating or inhibiting the activity of the lower motor neurons.
103
Alpha motorneurons
Lower motor neurons whose fibers innervate ordinary (extrafusal) muscle fibers.
104
Gamma motorneuons
Lower motor neurons whose fibers innervate the muscle spindle fibers (intrafusal/active stretch)
105
Agonis/Antagonist muscles
A pair of muscles or muscle groups that inset on the same bone, the agonist being the muscle of reference
106
Synergist
A muscle whose action facilitates the action of the agonist
107
Ipsilateral/contralateral
Ipsilateral is located ion the same side, or the side of reference
Contralateral is located on the opposite side
108
Afferent/Efferent
Afferent neurons are sensory
| Efferent neurons are motor
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Golgi tendon organs respond to:
Tension a muscle puts on a tendon
Constantly mojito tension in tendons
Sensory neuron stimulates interneuron in spinal cord, interneuron inhibits motor neuron, tension in tedon is reduced
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Muscle spindle apparatus responds to :
Muscle length
Muscles that require more control have more spindles
Stretching a muscle causes spindles to stretch
111
Two types of muscle sensory organs?
```
Intrafusal fibers (Thin)
Extrafusal fibers (thick)
```
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Which is the simples reflex?
Monosynaptic stretch reflex
Only involves one sensory neuron synapsing on one motor neuron in the spinal cord
Stimulated by striking the patellar ligament in the knee
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Knee-Jerk Reflex:
1. Striking patellar ligament stretches tendon and quadriceps femoris muscle
2. Spindle is stretched, activating sensory neuron
3. Sensory neuron activates alpha motor neuron
4. Alpha motorneuron stimulates extrafusal muscle fibers to contract
114
Crossed extensor reflex:
Type of double reciprocal innervation seen when you step on a tack;
1. Flexor contracts and extensor relaxes to withdraw foot
2. Extensor contracts and flexor relaxes in contralateral leg to support weight
115
Upper Motor Neuron Control parts
Precentral gyrus
Neurons through extrapyramidal tracts
Cerebellum
Basal nuclei
116
Role of pre central gyrus:
Sends neurons through pyramidal tracts by the lateral and ventral corticospinal tracts
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Role of neurons through extrapyramidal tracts
Reticulospinal tracts inhibit lower motor neurons
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Role of cerebellum
Receives info from muscle spindles and golgi tendon organs as well as other senses
also inhibits region sod the basal nuclei; red nuclei and vestibular nuclei
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Role of basal nuclei
Act to inhibit motor activity through the rubrospinal tract
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Types of paralysis
```
1. Flaccid paralysis: caused by damage to lower motor neurons.
Reduced muscle tone
Depressed stretch reflexes
Atrophy
2. Spastic paralysis: caused by damage ot upper motor neurons.
Increased muscle tone
Exaggerated stretch reflexes
Hyperactivity
```
121
Babinski's Reflex
Extension of the great toe when the sole of the foot is stroked along the lateral border
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Spastic paralysis
High muscle tone and hyperactive stretch reflexes; flexion of arms and extension of legs
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Hemiplegia
Paralysis of upper and lower limbs on one side (stroke)
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Paraplegia
Paralysis of the lower limbs on both sides as a result of lower spinal cord damage
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Quadriplegia
Paralysis of upper and lower limbs on both sides as a result of damage to the upper region of the spinal cord or brain
126
Chorea
Random uncontrolled contractions of different muscle groups as a result of damage to basal nuclei
127
Resting tremor
Shaking of limbs at rest; disappears during voluntary movements; produced by damage to basal nuclei
128
Intention tremor
Oscillations of the arm following voluntary reaching movements; produced by damage to cerebellum
129
Cardiac muscles are:
Involuntary
Regulated by autonomic nervous system
Contraction if due to myosin/actin cross bridges in sarcomeres
Stimulated by Ca
Striated
Fibers are short, branched and connected via gap junctions called INTERCALATED DISCS
