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Physiology > Chapter 12: Muscle > Flashcards

Chapter 12: Muscle Flashcards

1
Q

Skeletal muscles are composed of

A

individual muscle fibers that contract

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2
Q

Skeletal muscles are stimulated by the

A

Somatic motor neurons

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3
Q

Skeletal muscles are usually attached to bone on each end by

A

tough connective tissue tendons

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4
Q

What causes movement of the bones at a joint?

A

The tension placed on tendons and attached bones by muscle contraction

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5
Q

What is an insertion?

A

The more movable bony attachment of a muscle. MOVEMENT IS TOWARD INSERTION

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6
Q

Less movable attachment of a muscle

A

Origin

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7
Q

What do flexor muscles do?

A

Decrease the angle of a joint

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8
Q

What do extensor muscles fo?

A

Increase the angle of their attached bones at the joint

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9
Q

Agonist muscle

A

The prime mover of any skeletal movement

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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

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11
Q

Antagonist muscles

A

Flexors and extensors that act on the same joint to produce opposite actions.

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12
Q

What does an abductor muscle do?

A

Moves limb away front he midline of the body

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13
Q

What does an adductor muscle do?

A

Moves limb toward the midline of the body

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14
Q

What does a legator muscle do?

A

Moves insertion upward

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15
Q

What does a depressor muscle do?

A

Moves insertion downward

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16
Q

What does a rotator muscle do?

A

It rotates a bone along its axis

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17
Q

What does a sphincter muscle do?

A

Constricts an opening

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18
Q

What is the epimysium?

A

A sheath of muscle tissue proteins within tendons which extend around the muscle in an irregular arrangement

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19
Q

What is a fascicle?

A

Connective tissue from the epimysium extending into the body of the muscle

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20
Q

What is the perimysium?

A

Tissue sheath surrounding fascicles

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21
Q

Sarcolemma

A

Plasma membrane surrounding the muscle fibers or myofibers

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22
Q

What is the endomysium?

A

Connective tissue layer surrounding sarcolemma

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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

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24
Q

Syncytium

A

Formed from the union of several embryonic myoblast cells

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25
Q

Most distinctive feature of skeletal muscle fibers

A

Striated appearance

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26
Q

Striated appearance of muscle cells are caused by :

A

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)

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27
Q

What is a motor unit?

A

A single motor neuron and all the muscle fibers it innervates. They all contract at once. Each consist of branched motor axon

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28
Q

Graded contractions

A

Varied contraction strength due to different numbers of motor units being stimulated

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29
Q

Nueromuscular junction

A

Site where a motor neuron stimulates a muscle fiber

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30
Q

Motor end plate:

A

Area of the muscle fiber sarcolemma where a motor neuron stimulates it using the neurotransmitter, acetylcholine

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31
Q

Control of motor unit

A

Contraction strength comes from motor unit recruitment

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32
Q

Fine muscle control requires

A

smaller motor units with fewer muscle fibers

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33
Q

How many muscle fibers/motor units in the eye?

A

~23 muscle fibers/units

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34
Q

Motor end plate

A

The specialized region of the sarcolemma of the muscle fiber at the neuromuscular junction, where acetylcholine is released for contraction of the muscle

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35
Q

Where is the cell body of a somatic motor neuron located?

A

In the ventral horn of the gray matter of the spinal cord, gives rise to a single axon

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36
Q

Recruitment of motor units

A

Process used when contractions of greater strength are required, larger motor units are activated

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37
Q

Process involved with increase force of muscle contraction:

A
  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.
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38
Q

What are myofibrils?

A

Subunits packed densely in each muscle fiber which run the length of the muscle fiber

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39
Q

What are myofibrils composed of?

A

Thick and thin myofilaments (the smallest unit)

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40
Q

What does each muscle fiber contain?

A

Nucleus, striations, sarcolemma, sarcoplasm, myofibrils, myofilaments

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41
Q

I band contains:

A

Only thin filaments, primarily of the protein ACTIN

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42
Q

A band contains:

A

All of the thick filaments with some thin filament overlap; the thin filament is the protein MYOSIN

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43
Q

H band are:

A

The center of the A band with no thin filament overlap

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44
Q

Z discs (lines) are found:

A

In the center of the each I band

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45
Q

What is the sarcomere?

A

The basic subunit of striated muscle contraction. Forms hexagonal pattern

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46
Q

What does a sarcomere contain?

A

Area from a Z disc to the next. It contains the A band, H band, and I band

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47
Q

What does titin do?

A

Protein which runs from the Z disc to the M line and allows elastic recoil

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48
Q

Where are M lines found?

What do they do?

A

In the center of each A band

Help hold down thick filament

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49
Q

Sliding Filament Theory of contraction

A

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)

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50
Q

How is the sliding of the filaments accomplished?

A

Asynchronous power strokes of myosin cross bridges, which pull the thin filaments (actin) over the thick filaments (myosin)

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51
Q

Shortening of the sarcomeres is accomplished by

A

Sliding of the myofilaments-the length of each filament remains the same during contraction

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52
Q

What are thick filaments composed of?

A

Myosin

53
Q

Myosin proteins contain

A

Two globular heads with actin-binding sites and ATP-binding sites (these are responsible for moving the thin filaments in contraction)

54
Q

Thin proteins are composed of/?

A

Actin

55
Q

Actin proteins contain

A

Tropomyosin (String) and troponin that prevent myosin binding at rest

56
Q

Action of sliding is caused by

A

Several cross bridges that form between myosin and actin

57
Q

What part of the myosin acts as the ATPase enzyme?

A

The myosin head, splitting ATP into ADP and inorganic P

58
Q

What does hydrolysis of ATP cause?

A

Allows the myosin head to bind to actin binding sites when the muscle is stimulated

59
Q

What causes the power stroke?

A

The release of inorganic P upon binding cocks the myosin head to pull the thin filament toward the center

60
Q

What happens after the power stroke?

A

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
Q

Two types of Actin

A

F (Filamentous) actin: String of many G actin

G (Globular) actin: round subunits

62
Q

How is actin arranged in thin filaments?

A

F actin is made up of 300-400 G actin units, arranged in a double row and twisted to form helix

63
Q

What can block cross bridges?

A

Tropomyosin (string which moves to attach to myosin head)

64
Q

Troponin complex composed of :

A

Troponin I inhibits binding of myosin
Troponin T binds to tropomyosin
Troponin C binds to calcium

65
Q

Role of Ca:

A

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
Q

What is the role of sarcoplasmic reticulum in muscle contraction?

A

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
Q

What are transverse tubules?

A

Found in the SR
They are narrow membranous tunnels formed from the sarcolemma
They are open to the extracellular environment and conduct action potentials.

68
Q

Excitation Contraction Coupling Summary

A

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
Q

What happens in muscle relaxation?

A

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
Q

How is muscle contraction studied?

A

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
Q

What is a twitch?

A

When a muscle quickly contracts and relaxes after a single electrical shock of sufficient voltage

72
Q

What is summation?

A

When a second shock is applied immediately after the firs, the second twitch will partially piggyback the first. Twitch increases with voltage increase.

73
Q

What is a latent period?

A

Time between the stimulus and the contraction. Also referred to as excitation-contraction coupling at cross bridges.

74
Q

Graded contractions?

A

Stronger contractions result in recruitment of more fibers, until all fibers are contracting.

75
Q

Incomplete tetanus

A

Increasing the frequency of electrical shocks decreases the relaxation time between twitches. Muscle never relaxes enough before being stimulated again

76
Q

Complete tetanus

A

At a certain frequency, there will be no relaxation. This is equivalent to a smooth, sustained contraction. The more twitch the better the result

77
Q

Treppe effect

A

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

78
Q

Types of muscle contraction:

A

Force velocity curve
Isotonic contractions
Isometric contractions

79
Q

Force velocity curve

A

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
Q

Isotonic contractions

A

Muscle fibers shorten when the tension produced is just greater than the load.

81
Q

Two subcategories of isotonic contractions

A

Concentric contractions

Eccentric contraction

82
Q

Concentric contractions

A

A muscle fiber shortens when force is greater than load

83
Q

Eccentric contraction

A

A muscle may actually lengthen, despite contraction, if the load is too great (going down a hill/lowering weight slowly)

84
Q

Isometric contraction

A

Muscles can’t shorten because the load is too great. Can be voluntary

85
Q

Muscle strength is determined by

A

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
Q

Tension is maximal when:

A

Sarcomeres are at normal resting length

87
Q

Increasing sarcomere length….

A

Decreases muscle tension. There are fewer interactions between myosin and actin. At some point, no tension will be generated

88
Q

Decreasing sarcomere length…

A

Decreases muscle tension due to fiber shortening and thickening. This increases fluid pressure and distance between the actin and myosin

89
Q

Energy is needed for:

A 
Myosin ATPase (70%)
Ca pump to actively return calcium to SR (30%)
90
Q

At rest and for mild exercise energy comes from?

A

Aerobic respiration of fatty acids

91
Q

For moderate exercise energy comes from?

A

Glycogen storage

92
Q

For heavy exercise energy comes from?

A

Blood glucose

With increased intensity or duration, FLUT4 channels are inserted into the sarcolemma to allow more glucose into cells

93
Q

Types of twitch?

A 
Slow twitch (Type I)
Fast twitch (Type IIx)
Intermediate twitch (Type IIa)
94
Q

Slow twitch

A

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
Q

Fast twitch

A

Type IIx: Faster contraction speed
Fatigue fast
Fewer capillaries, mitochondria, respiratory enzymes and myoglobin

96
Q

Intermediate twitch

A

Type IIa: Fast twitch but with high oxidative capacity; called fast oxidative fibers

97
Q

What reduces the ability to generate force?

A

Muscle fatigue

98
Q

Fatigue can be due to

A 
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
Q

What causes muscle decline with aging?

A

Reduced muscle mass (Type II fibers)
reduction in capillary blood supply
Fewer satellite cells
Increased myostatin production

100
Q

How do muscle cells repair themselves?

A

Using stem cells called satellite cells located newer muscle fibers

101
Q

Lower motorneurons

A

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
Q

Higher motorneurons

A

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
Q

Alpha motorneurons

A

Lower motor neurons whose fibers innervate ordinary (extrafusal) muscle fibers.

104
Q

Gamma motorneuons

A

Lower motor neurons whose fibers innervate the muscle spindle fibers (intrafusal/active stretch)

105
Q

Agonis/Antagonist muscles

A

A pair of muscles or muscle groups that inset on the same bone, the agonist being the muscle of reference

106
Q

Synergist

A

A muscle whose action facilitates the action of the agonist

107
Q

Ipsilateral/contralateral

A

Ipsilateral is located ion the same side, or the side of reference
Contralateral is located on the opposite side

108
Q

Afferent/Efferent

A

Afferent neurons are sensory

Efferent neurons are motor

109
Q

Golgi tendon organs respond to:

A

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

110
Q

Muscle spindle apparatus responds to :

A

Muscle length
Muscles that require more control have more spindles
Stretching a muscle causes spindles to stretch

111
Q

Two types of muscle sensory organs?

A 
Intrafusal fibers (Thin)
Extrafusal fibers (thick)
112
Q

Which is the simples reflex?

A

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

113
Q

Knee-Jerk Reflex:

A
  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
Q

Crossed extensor reflex:

A

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
Q

Upper Motor Neuron Control parts

A

Precentral gyrus
Neurons through extrapyramidal tracts
Cerebellum
Basal nuclei

116
Q

Role of pre central gyrus:

A

Sends neurons through pyramidal tracts by the lateral and ventral corticospinal tracts

117
Q

Role of neurons through extrapyramidal tracts

A

Reticulospinal tracts inhibit lower motor neurons

118
Q

Role of cerebellum

A

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

119
Q

Role of basal nuclei

A

Act to inhibit motor activity through the rubrospinal tract

120
Q

Types of paralysis

A 
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
Q

Babinski’s Reflex

A

Extension of the great toe when the sole of the foot is stroked along the lateral border

122
Q

Spastic paralysis

A

High muscle tone and hyperactive stretch reflexes; flexion of arms and extension of legs

123
Q

Hemiplegia

A

Paralysis of upper and lower limbs on one side (stroke)

124
Q

Paraplegia

A

Paralysis of the lower limbs on both sides as a result of lower spinal cord damage

125
Q

Quadriplegia

A

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
Q

Chorea

A

Random uncontrolled contractions of different muscle groups as a result of damage to basal nuclei

127
Q

Resting tremor

A

Shaking of limbs at rest; disappears during voluntary movements; produced by damage to basal nuclei

128
Q

Intention tremor

A

Oscillations of the arm following voluntary reaching movements; produced by damage to cerebellum

129
Q

Cardiac muscles are:

A

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

Physiology (3 decks)

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