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biol2480 > skeletal muscle > Flashcards

skeletal muscle Flashcards

1
Q

what are the 5 functions of skeletal muscle

A
  • body movement
  • maintenance of posture
  • protection and support
  • regulating elimination of materials
  • heat production
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2
Q

how do muscles generate body movements

A

through contractions

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3
Q

which 5 skeletal muscles contract to maintain posture

A
  • trunk
  • pelvis
  • legs
  • neck
  • head
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4
Q

how do skeletal muscles protect the internal organs within the abdominopelvic cavity

A
  • skeletal muscles are arranged in layers within the walls of abdominal cavity
  • and the floor of the pelvic cavity
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5
Q

how do skeletal muscles regulate passage of material

A

contraction and relaxation of sphincters

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6
Q

describe sphincters

A

circular muscle bands

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7
Q

why are skeletal muscles responsible for heat production

A

energy is required for tissue contraction and heat is always produced by this energy

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8
Q

what are the

5 characteristics of skeletal muscles

A
  • excitability
  • conductivity
  • contractility
  • extensibility
  • elasticity
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9
Q

what is the definition of excitability as it relates to skeletal muscle

A

the ability of a cell to respond to a stimulus

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10
Q

what does the stimulus cause in excitable cells

A

it causes a local change in the rmp (resting membrane potential) by triggering movement of ions across the plasma membrane

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11
Q

when is the response of skeletal muscle cells to the movement of ions across the plasma membrane of excitable cells

A

its receptors bind to a neurotransmitter, which is released from a motor neuron

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12
Q

why is muscle excitability important

A

it ensures that the muscle can conduct or transmit electrical impulses

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13
Q

what is conductivity of a muscle

A

it involves an electrical signal being propagated along the plasma membrane as voltage-gated channels open during an action potential

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14
Q

what is the role of electrical signals in conductivity

A

they functionally connect the plasma membrane of the muscle cell to the interior of the muscle cell

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15
Q

why is conductivity necessary for in skeletal muscle

A

to propagate the electrical signal across the muscle

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16
Q

when is contractility of muscle displayed

A

it’s exhibited when contractile proteins within skeletal muscle cells slide past one another

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17
Q

what does contractility of muscle allow

A

muscle cells to cause body movement and to perform the other functions of muscles

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18
Q

what is extensibility of muscle

A

it’s the lengthening of a muscle cell

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19
Q

how is the lengthening of muscle possible

A

the contractile proteins slide past one another to decrease their degree of overlap

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20
Q

when is muscle extensibility exhibited

A

when we stretch our muscles

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21
Q

what is elasticity of muscles

A

the ability of a muscle cell to return to its original length following either shortening or lengthening of muscles

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22
Q

what is elasticity of muscle cells dependent upon

A

the release of tension in the springlike connecting protein associated with contractile proteins

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23
Q

what else can muscle fibers be referred to as

A

myofibers

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24
Q

is a skeletal muscle a tissue or organ

A

organ

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25
Q

what are the 4 components of skeletal muscle

A
  • skeletal muscle fibers
  • connective tissue layers
  • blood vessels
  • nerves
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26
Q

how are muscle fibers being binded

A

within a fascicle

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27
Q

what are the 3 layers of connective tissue within the muscles

A
  • epimysium
  • perimysium
  • endomysium
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28
Q

what connective tissue is epimysium made of

A

dense irregular connective tissue

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29
Q

what connective tissue is perimysium made of

A

dense irregular connective tissue

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30
Q

what connective tissue is endomysium made of

A

areolar connective tissue

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31
Q

what forms the tendon/aponeurosis of a skeletal muscle

A

epimysium, perimysium and endomysium collectively extend past the muscle fibers to form it

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32
Q

what’s the difference between a tendon and aponeurosis

A
  • tendon is a thick, cordlike structure composed of dense regular connective tissue
  • aponeurosis is a thin, flattened sheet of dense regular connective tissue
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33
Q

what is another connective tissue component not present within the skeletal muscle

A

deep fascia

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34
Q

what else can the deep fascia be referred to as (2)

A

visceral or muscular fascia

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35
Q

what connective tissue is the deep fascia composed of

A

expansive sheet of dense irregular connective tissue external to the epimysium

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36
Q

what are the 4 functions of deep fascia

A
  • separates individual muscles
  • binds together muscles with similar functions
  • contains nerves, blood vessels and lymph vessels
  • fills space between muscles
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37
Q

what is the deep fascia internal to

A

superficial fascia

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38
Q

what is the superficial fascia composed of (2)

A
  • areolar connective tissue

- adipose connective tissue

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39
Q

what does the superficial fascia do

A

separates muscle from skin

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40
Q

how far do the blood vessels in skeletal muscle reach

A

extend through epimysium and perimysium to reach the endomysium

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41
Q

what are the smallest blood vessels in skeletal muscle

A

capillaries

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42
Q

what is skeletal muscle innervated by

A

motor neurons

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43
Q

what is the role of motor neurons in skeletal muscle

A

control skeletal muscle contraction

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44
Q

how far does the motor neuron axons extend through skeletal muscle

A

they extend through all 3 connective tissue layers to almost make contact with an individual muscle fiber

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45
Q

what is the junction between the axon and the muscle fiber called

A

neuromuscular junction

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46
Q

what are the primary cells forming a skeletal muscle

A

skeletal muscle fibers

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47
Q

what is the cytoplasm in skeletal muscle called

A

sarcoplasm

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48
Q

what is the typical diameter for skeletal muscle fiber

A

between 10 and 500 micrometers

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49
Q

what is the length of skeletal muscle typically

A

100 micrometers to 30 centimeters

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50
Q

what are embryonic muscle cells termed

A

myoblasts

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51
Q

what do myoblasts do to reach their length

A

they fuse to form single skeletal muscle fibers during development

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52
Q

why are skeletal muscle cells multinucleated

A

when myoblasts fuse, each myoblast nucleus contributes to the eventual total number of nuclei in the fiber

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53
Q

what are satellite cells

A

when myoblasts don’t fuse with muscle fibers during development

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54
Q

what may satellite cells do if a skeletal muscle cell is injured

A

stimulated to differentiate, fuse with damaged cell and assist it to a limited extent in repair and regeneration

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55
Q

what is the plasma membrane of a skeletal muscle fiber called

A

sarcolemma

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56
Q

what are T(transverse)-tubules

A

deep invaginations of the sarcolemma

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57
Q

what channels are located within both the sarcolemma and t-tubules

A

voltage-gated

  • Na+
  • K+
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58
Q

what composes 80% of the volume of a skeletal muscle fiber

A

myofibrils

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59
Q

what structure in skeletal muscle fibers is similar to smooth er

A

sarcoplasmic reticulum

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60
Q

what do terminal cisternae serve as

A

reservoirs for calcium ions

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61
Q

2 terminal cisternae and a centrally located t-tubule form what structure

A

triad

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62
Q

what do the t-tubule membranes within the triad contain

A

voltage-sensitive calcium ion channels

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63
Q

what do the terminal cisternae membranes contain

A

calcium ion release channels (ryanodine receptors)

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64
Q

where does the connection occur between the electrical signals propogated and the release of calcium from the SR

A

the calcium ion release channels

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65
Q

what else is embedded within the SR membrane

A

calcium ion pumps which move calcium from the cytosol into the SR

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66
Q

how is calcium stored in the SR

A

bound to specialised proteins

  • calmodulin
  • calsequestrin
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67
Q

how do calcium pumps function in the SR

A

active transport; they maintain low cytosol levels of Ca

these pumps return Ca+ to the terminal cisternae of the SR after its release to initiate muscle contraction

68
Q

what are myofilaments

A

contractile proteins that are bundled within myofibrils

69
Q

what are the 2 types of myofilaments

A

thick and thin

70
Q

how many myosin protein molecules make up thick filaments

A

200 to 500

71
Q

what does the myosin head of thick filaments contain

A
  • a binding site for actin of thin filaments

- catalytic atpase site where atp molecule splits into adp + pi

72
Q

what is the diameter of thick filaments

A

11nm

73
Q

what is the diameter of thin filaments

A

5 - 6nm

74
Q

what are thin filaments primarily composed of

A

2 strands of actin protein twisted to form a helix

75
Q

what does each G-actin molecule of thin filaments have

A

a myosin binding site

76
Q

what happens to the myosin head and binding site during muscle contraction

A

the head attaches to the binding site

77
Q

what are the 2 regulatory proteins within thin filaments

A
  • troponin

- tropomyosin

78
Q

what does troponin in thin filaments contain

A

the binding site for calcium ion

79
Q

what is the length of sarcomeres

A

2 micrometers

80
Q

what are sarcomeres

A

repeating cylindrical units

81
Q

what is each sarcomere composed of

A

overlapping thick and thin filaments

82
Q

what are the 4 regions in which thick and thin filaments overlap within a sarcomere

A
  • I band
  • A band
  • H zone/band
  • M line
83
Q

where can I bands be located

A

extending from both directions of a Z disc and are bisected by a Z disc

84
Q

what do I bands contain

A

only thin filaments

85
Q

what causes the I bands to disappear during maximal muscle shortening

A

thin filaments being pulled parallel along the thick filaments

86
Q

where can the A band be found on the sarcomere

A

central region

87
Q

what does the A band in the sarcomere contain

A

the entire thick filament

88
Q

what overlaps the thick filament in the A band

A

thin filament on each end of the A band

89
Q

does the A band change in length during muscle contraction

A

no

90
Q

where can the H zone be located on the sarcomere

A

the most central portion of the A band in a resting sarcomere

91
Q

does the H zone have thin filament overlap

A

no

92
Q

what happens during maximal muscle shortening in the H zone

A

this zone disappears as thin filaments are pulled past thick filaments

93
Q

what is the M line in a sarcomere

A

a thin transverse protein meshwork structure in the center of the H zone

94
Q

what does the M line serve as

A

an attachment site for the thick filaments and keeps them aligned during contraction and relaxation

95
Q

what causes muscle fiber striations

A

repeating light and dark bands of overlapping myofilaments which are caused by size and density difference between thick and thin filaments

96
Q

what are the 2 other structural and functional proteins in muscle fibers

A
  • connectin

- dystrophin

97
Q

where can connectin be found

A

extending from the z discs to the m line through the core of each thick filaments

98
Q

what does connectin do

A

stabilises the position of thick filaments and maintains thick filaments alignment

99
Q

what shape can connectin be

A

springlike to return the sarcomere to its normal position

‘muscle elasticity’

100
Q

what is dystrophin

A

part of a protein complex that anchors myofibrils adjacent to the sarcolemma proteins

101
Q

where do the proteins of the sarcolemma extend to

A

the connective tissue of the endomysium

102
Q

what is the role of dystrophin

A

links internal myofilament proteins of a muscle fiber to external proteins

103
Q

how many mitochondrion does skeletal muscle fibers have approximately

A

300

104
Q

what is myoglobin

A

a reddish, globular protein

105
Q

what does myoglobin do

A

binds oxygen when the muscle is at rest and releases it for use during muscle contraction

106
Q

what are somatic motor neurons

A

nerve cells that transmit electrical signals from the brain/spinal cord to control skeletal muscle activity

107
Q

how are numerous skeletal muscle fibers innervated

A

the axon of each motor neuron divides into many individual branches

108
Q

what is a motor unit

A

a single motor neuron and the skeletal fibers it controls

109
Q

what determines the degree of control of the motor unit

A

the size of the motor unit

110
Q

are the motor neurons innervating the eye muscles large

A

no, they’re small for greater control

111
Q

what is the strength of contraction of the stimulation of a motor unit

A

weak over a wide area

112
Q

where can a neuromuscular junction typically be found

A

in the mid region of the skeletal muscle fiber

113
Q

what are the 3 parts of a neuromuscular junction

A
  • synaptic knob
  • motor end plate
  • synaptic plate
114
Q

what is the synaptic knob of a motor neuron

A

an expanded tip of an axon which enlarges and flattens to cover a large surface area of the sarcolemma

115
Q

what does the synaptic knob cytosol house

A

numerous synaptic vesicles filled with neurotransmitter molecules, acetylcholine

116
Q

what are the 3 points to note about the synaptic knob

A
  1. Ca2+ pumps embedded within the plasma membrane of the synaptic knob - establishes a concentration gradient with more Ca2+ outside of the knob than inside before the arrival of the electric signal
  2. voltage-gated Ca2+ channels embedded within the plasma membrane of the synaptic knob - channels open, allows Ca2+ to flow into the knob, triggering exocytosis of vesicles containing ACh
  3. the vesicles with ACh are normally repelled from the synaptic knob plasma membrane
117
Q

what is the motor end plate

A

a specialised region of the sarcolemma of a skeletal muscle fiber

118
Q

how does the motor end plate increase the membrane surface area covered by the synaptic knob

A

it has numerous folds and indentations

119
Q

what does the motor end plate have

A

chemically gated ion channels, ACh receptors

120
Q

what does the binding of ACh do

A

opens the ACh receptor channels, allowing Na+ entry into the muscle fiber and K+ out

121
Q

what is the synaptic cleft

A

an extremely narrow fluid filled space separating the synaptic knob and the motor end plate

122
Q

what enzyme resides in the synaptic cleft

A

acetylcholinesterase (AChE)

123
Q

what is the role of acetylcholinesterase

A

they quickly break down ACh molecules following their release into the synaptic cleft

124
Q

at rest, relative to the interstitial fluid, is the cytosol negative or positive in comparison

A

negative

125
Q

what is the RMP of the skeletal muscle fibers at rest

A

-90mV

126
Q

how is the RMP of the skeletal muscle fiber maintained at rest

A

by leak channels and Na+/K+ pumps

127
Q

what is the primary function of Na+/K+ pumps in skeletal muscle fibers

A

maintain the concentration gradients for Na+ and K+ with more Na+ outside the cell and more K+ inside the cell

128
Q

in the relaxed position, which acetylcholine receptors are closed (3)

A
  • within the motor end plate
  • voltage-gated Na+ channels
  • voltage-gated K+ channels
    in the sarcolemma and T-tubules
129
Q

where are Ca2+ ions stored in the relaxed position

A

within the terminal cisternae of the sarcoplasmic reticulum

130
Q

where do the events of skeletal muscle contraction occur at (3)

A
  • neuromuscular junction
  • sarcolemma, t-tubules, sarcoplasmic reticulum
  • sarcomeres
131
Q

what is the first physiological event of skeletal muscle contraction

A

muscle fiber excitation by a somatic motor neuron

132
Q

what are the 3 steps to muscle fiber excitation at the neuromuscular junction

A
  • Ca2+ entry at synaptic knob
  • release of ACh from the synaptic knob
  • binding of ACh to ACh receptor at motor end plate
133
Q

what does the nerve signal trigger at the synaptic knob

A

the opening of voltage-gated Ca2+ channels, allowing flow of Ca2+ into the knob, binding with membrane proteins (synaptotagmin) exposed on external surface of synaptic vesicles

134
Q

what does the binding of Ca2+ to synaptic vesicles cause

A

exocytosis of ACh into synaptic cleft, at 300 vesicles per nerve signal (thousands of ACh in each vesicle)

135
Q

what causes excitation of skeletal muscle fiber

A

ACh binding to ACh receptors on the motor end plate

136
Q

how many nerve signals are propagated per second

A

10 to 40

137
Q

what is the second physiologic event of muscle contraction

A

excitation-contraction coupling

138
Q

what are the 3 events that occur during excitation-contraction coupling

A
  • development of end-plate potential at motor end plate
  • initiation and propagation of an action potential along the sarcolemma and T-tubules
  • release of Ca2+ from the sarcoplasmic reticulum
139
Q

what is the end-plate potential (EPP)

A

the minimum voltage change in the motor end plate that can trigger opening of voltage-gated channels in the sarcolemma to initiate action potential

140
Q

when ACh receptors open, does more Na+ flow in than K+ diffuse out or the other way around

A

more Na+ flows in than K+ diffuses out

141
Q

when is an end-plate potential produced

A

when there is sufficient gain of positive charge to change the RMP from -90mV to -65mV

142
Q

what 2 events encompasses an action potential

A
  • depolarization

- repolarization

143
Q

what is depolarization

A

inside of sarcolemma becomes positive due to influx if Na+

144
Q

what is repolarization

A

returning of inside of sarcolemma to its rel. negative RMP due to K+ flowing out

145
Q

what is the change in RMP during depolarization

A

-65mV to 30mV

146
Q

how long does the propagation of depolarisation reach

A

to the end of the skeletal muscle fiber

147
Q

when do the voltage-gated K+ channels (sarcolemma and T-tubules) open

A

immediately after the opening of voltage-gated Na+ channels

148
Q

what is the change in RMP during repolarization

A

30mV to -90mV

149
Q

what does repolarization allow

A

the skeletal muscle fiber to propagate a new action potential when stimulated again by a motor neuron

150
Q

what does the refractory period include

A

period of time taken for depolarisation and repolarisation

151
Q

what cannot occur during the refractory period

A

a new action potential

152
Q

what 2 things occur when the action potential reaches the sarcoplasmic reticulum

A
  • stimulating a change to voltage-gated channels (dihydropyridine receptors) in T-tubule membrane
  • cause change in Ca2+ release channels (ryanodine receptors) in the terminal cisternae of the SR, causing them to open, allowing Ca2+ to diffuse out of cisternae into the cytosol
153
Q

what does the third physiologic event involve (2)

A
  • binding of Ca2+

- crossbridge cycling

154
Q

what are the 4 things that happens during Ca2+ binding prioir to crossbridge cycling

A
  1. Ca2+ binds to a subunit of globular troponin
  2. inducing a conformational change in troponin
  3. the entire troponin-tropomyosin complex is moved, exposing myosin binding sites of actin
  4. crossbridge cycling is initiated
155
Q

what are the 4 steps to crossbridge cycling

A
  1. crossbridge formation
  2. power stroke
  3. release of myosin head
  4. resetting of myosin head
156
Q

how are crossbridges formed

A

‘cocked’ myosin heads attach to exposed myosin binding sites of actin

157
Q

describe a power stroke of myosin heads

A

the head swivels/ratchets

158
Q

what does the myosin head power stroke achieve (2)

A
  • pulling the thin filament past the thick (towards the centre of the sarcomere)
  • ADP and Pi are released so ATP binding sites become available again
159
Q

what causes the release of myosin head

A

ATP binds to the ATP binding site on the myosin head

160
Q

what resets the myosin head

A

myosin ATPase splits ATP into ADP + Pi which provides the energy to reset the head

161
Q

what causes the sarcomere to shorten

A

the repetitive steps in crossbridge cycling

162
Q

what happens to the H zone, I band and Z discs when muscle contracts

A
  • H zone disappears
  • I band narrows, may disappear
  • Z discs move closer together
163
Q

what are 2 examples of muscle paralysis caused by toxins

A
  • tetanus

- botulism

164
Q

what bacterium causes tetanus

A

clostridium tetani

165
Q

what does the toxin produced by C. tetani do

A

blocks the release of glycine, causing excessive muscle contractions

166
Q

what bacterium causes botulism

A

clostridium botulinum

167
Q

what does the toxin produced by C. botulinum do

A

prevents the release of ACh

biol2480 (15 decks)

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