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Physiology > Muscles > Flashcards

Muscles Flashcards

1
Q

is skeletal muscle striated or unstriated

A

striated

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2
Q

is skeletal muscle voluntary or involuntary

A

voluntary

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3
Q

where is skeletal muscle found

A

attached to bones of skeleton

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4
Q

function of skeletal muscle

A

movement of body in relation to external environment

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5
Q

is cardiac muscle striated or unstriated

A

striated

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6
Q

is cardiac muscle voluntary or involuntary

A

involuntary

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7
Q

where is cardiac muscle found

A

wall of the heart

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8
Q

function of cardiac muscle

A

pumping blood out of the heart

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9
Q

is smooth muscle striated or unstriated

A

unstriated

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10
Q

is smooth muscle voluntary or involuntary

A

involuntary

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11
Q

where is smooth muscle found

A

in walls of hollow organs and tubes such as the stomach and blood vessels

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12
Q

function of smooth muscle

A

movement of contents within hollow organs

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13
Q

muscle

A

a group of fascicles

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14
Q

what are fascicles

A

groups of muscle fibres

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15
Q

sarcolemma

A

cell membrane that encloses each muscle cell

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16
Q

endomysium

A

connective tissue that wraps each muscle fibre

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17
Q

perimysium

A

connective tissue that wraps fascicles

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18
Q

epimysium

A

the connective tissue that wraps the whole muscle

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19
Q

fascia

A

a layer of thickened connective tissue covers the entire muscle and which is located over the layer of epimysium

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20
Q

where does communication of neurotransmitters in muscle occur

A

at the neuromuscular junciton (NMJ)

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21
Q

motor unit

A

an axon and the muscle fibres it communicates with

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22
Q

what part of the nervous system supplies skeletal muscle

A

the efferent arm of the somatic nervous system

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23
Q

motor end plate

A

specialised site on a muscle cell, where an α-motorneuron forms a synapse

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24
Q

terminal buttons

A

fit into shallow depressions of the sarcolemma of individual muscle fibres

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25
Q

the cleft

A

the space between the terminal button and the motor end plate

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26
Q

transverse (T) tubules

A

folds of the sarcolemma

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27
Q

sarcoplasm

A

cytoplasm, contains many myofibrils

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28
Q

sarcoplasmic reticulum

A

smooth ER

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29
Q

what is a muscle fibre made from

A

composed of myofibrils which are made of repeating units of sarcomere which in turn are made of regular arrays of thick and thin filaments

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30
Q

what gives skeletal muscle a striated appearance

A

the thick and thin filaments in myofibrils

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31
Q

H zone of sarcomere

A

thick filament only

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32
Q

A band of sarcomere

A

thick filament and overlapping thin filament

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33
Q

I band of sarcomere

A

thin filament

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34
Q

name two contractile proteins

A

actin and myosin

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35
Q

name two structural proteins

A

titin and dystrophin

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36
Q

name two regulatory proteins

A

troponin-complex and tropomyosin

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37
Q

what are thin filaments made of

A

actin

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38
Q

F-actin

A

contractile protein

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39
Q

G-actin

A

has a binding site for myosin

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40
Q

three troponin-complex proteins

A

T, I and C

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41
Q

TnI function

A

binds to actin to hold the troponin-tropomyosin complex in place

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42
Q

TnT function

A

binds to tropomyosinm interlocking them to form a troponin-tropomyosin complex

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43
Q

TnC function

A

binds to calcium ions to produce conformational change in TnI

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44
Q

where is myosin head

A

towards I band

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45
Q

where is myosin tail

A

towards M line

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46
Q

what does the myosin head contain

A
  • actin binding site
  • nucleotide binding site for ATP and ATPase
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47
Q

what does the myosin tail contain

A

flexible hinge regions where they combine with other tails

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48
Q

how many myosins per thick filament

A

300

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49
Q

how many actin can one myosin bind to

A

6

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50
Q

titin functions

A
  • supports protein in muscle
  • anchors thick filaments between M line and Z line
  • provides structural support and elasticity
  • template for myosin assembly
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51
Q

what is happening to actin at rest

A

myosin binding sites are blocked by tropomyosin

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52
Q

what happens when Ca2+ is exposed to actin

A
  • Ca2+ binds to TnC
  • There is a conformational change in TnC
  • this moves tropomyosin
  • thus exposes myosin binding sites
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53
Q

cross bridge explanation

A
  1. Actin binding: myosin cross bridge binds to actin
  2. Power stroke: cross bridge bends pulling thin microfilament inward
  3. Detachment: cross bridge detaches at end of power stroke and returns to original conformation
  4. Binding: cross bridge binds to more distal actin molecle; cycles repeats
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54
Q

explain sliding filament mechanism

A
  • needs overlapping thick and thin filaments
  • neither thick nor thin filaments shorted
  • filaments slide past eachother
  • sliding is due to the cyclical formation and breaking of cross bridges
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55
Q

what happens within a sarcomere during contraction

A
  • A band stays the same length
  • I band shortens
  • H zone shortens
  • Sarcomere shortens
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56
Q

what does the cross bridge cycle depend on

A

ATP and Ca2+

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57
Q

explanation of the cross bridge cycle

A
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58
Q

steps from excitation to contraction

A
  1. action potential in sarcolemma
  2. action potential dowm T tubules
  3. DHP receptors of T tubules open Ca2+ channels (ryanodine receptors)
  4. Calcium increases in cytosol
  5. Calcium binds to troponin shifting tropomyosin
  6. Cross bridge cycling occurs
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59
Q

what happens if Ca2+ is maintained

A
  • cross bridge cycle continues
  • However, Ca2+ is rapidly pumped back into the SR by the SR/ER Ca2+ ATPase (SERCA)
  • Therefore, based on the time-scale of the events there is a need for a continuous cycle of Excitation-Contraction to maintain the force
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60
Q

how does the cross bridge cycle use ATP

A
  • splitting of ATP by myosin ATPase (for power stroke)
  • binding of fresh ATP to myosin to cause dissociation
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61
Q

three sources of ATP for muscle

A
  • immediate system - ATP and Creatine Phosphate
  • Short term system - anaerobic or non-oxidative glycolysis
  • Long term system - oxidative phosphorylation
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62
Q

use balanced equations to explain creatine phosphate and atp system

A

Creatine phosphate + ADP ← creatine kinase → Creatine + ATP
ATP + H2O ← ATPase → ADP + Pi+ H+ + energy

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63
Q

creatine phosphate and ATP system

A
  • Creatine phosphate is the first source of ATP (10-30 seconds)
  • Can provide 4-5 times the amount of ATP present in cell at rest
  • One step process - very rapid
  • Very limited amount - used up rapidly
64
Q

use a balanced equation to explain anaerobic or non-oxidative glycolysis

A

Glucose → 2 lactic acid + 2 ATP

65
Q

anaerobic or non-oxidative glycolysis

A
  • When oxygen supply to muscle is limited (during intense exercise), anaerobic glycolysis is the primary source of ATP
  • Breakdown of glucose, O2 is absent
  • High intensity exercise (12-120 seconds)
  • Rapid source of ATP
66
Q

drawbacks of anaerobic or non-oxidative glycolysis

A
  • only 2 ATP per glucose molecule
  • limited glucose availability
  • build up of lactic acid
67
Q

oxidative phosphorlyation

A
  • Primary energy source for light/moderate exercise (>2 mins)
  • Muscles store a limited amount of glucose as glycogen
    • Substrate of oxidative phosphorylation up to 30 minutes
  • Glucose and fatty acids delivered to muscle by blood
    • Dominant after 30 minutes
  • Oxygen supply is adequate
  • Occurs in mitochondria
68
Q

twitch contraction

A

contraction produced in a muscle fibre in response to a single action potential

69
Q

name the three phases of a muscle twitch

A
  1. latent period
  2. contraction phase
  3. relaxation phase
70
Q

explain the latent period of a twitch

A
  • time from action potential in muscle to onset contraction
  • few milliseconds
  • exitation-contraction coupling
71
Q

explain the contraction phase of a muscle twitch

A
  • tension is increasing
  • 10-100 milliseconds
  • cross bridge cycle takes place repeatedly
72
Q

explain relaxation phase of muscle twitch

A
  • tension is decreasing back to zero
  • longer than contraction phase
  • calcium reuptake
73
Q

isotonic contraction

A

load remains constant as muscle changes length

74
Q

isometric contraction

A

muscle is prevented from shortening si tension develops at constant muscle length

75
Q

explain how isometric and isotonic contractions occur together

A
  • even if load is constant, isometric precedes isotonic phase of contraction
  • as tension increases the isometric contraction continues until tension exceeds the load
  • then isotonic contraction begins
  • tension remains constant as muscle shortens
76
Q

why is the load not generally constant

A

load changes as limb position changes

77
Q

two things the level of force generated by muscle depends on

A
  • factors affecting the force or tension generated by individual muscle fibres
  • regulation of the force or tension generated by the whole muscle
78
Q

name the factors that affect force or tension generated by individual muscle fibres

A
  • frequency of stimulation
  • fibre diameter
  • changes in fibre length
  • extent of fatigue
79
Q

what regulates the force or tension generated by the whole muscle

A

the number of fibres contracting ie. recruitment

80
Q

what is frequency of stimulation

A

frequency of action potentials in muscle fibres

81
Q

two ways tension is increased

frequency of stimulation

A
  • treppe
  • summation and tetanus
82
Q

treppe

A

when independent twitches follow one another closely; peak tension increases to a constant level

83
Q

causes of summation and tetanus

A
  • Amount of tension developed depends on amount of calcium bound to troponin
  • At high frequencies, release exceeds reuptake
    • Calcium increases in cytosol
  • Eventually saturate system
    • All troponin molecules are bound to calcium
    • Cross bridge cycle maxes out
    • Maximum tetanic contraction
84
Q

what is force generation capacity

A

inherent ability of muscle to generate force

85
Q

what does force generation capacity depend on

A

the number of cross bridges in each sarcomere and geometrical arrangement of sarcomeres

86
Q

what happens when there are more cross bridges in a sarcomere

A

more force is generated

87
Q

what happens when more sarcomeres are in parallel

A

more force is generated

88
Q

what happens when there is a greater fibre diameter

A

more filaments are present in the fibre and thus more force is generated

89
Q

optimum length

A
  • resting length of muscle at which fibres can develop greatest amount of tension
  • sue to maximum overlpa of thick filament cross bridges and thin filaments
90
Q

what causes a length greater than optimum

A

a decrease in cross bridge overlap

91
Q

what causes a muscle length less than optimum

A
  • thin filaments overlap eachother
  • Z lines contact thin filaments
92
Q

explain recruitment of motor units

A
  • activation of motor neuron activates all muscle fibres in the motor unit
  • increase in tension occurs in steps proportional to the size of motor units
93
Q

motor unit size in muscles for delicate movements

A

small

94
Q

motor unit size in muscles for strength

A

large

95
Q

small fibre diamter

A

needed for weaker movements

96
Q

large fibre units

A

needed for stronger movements

97
Q

relation of motor unit and fibre diameter

A
  • Small motor units → small fibres
  • Large motor units → large fibres
98
Q

motor unit size principle

A

small motor units are recruited first and large motor units are recruited last

99
Q

what does muscle contraction speed depend on

A

rate of mysosin ATPase activity

100
Q

3 types of muscle fibre

contraction speed

A
  • slow oxidative
  • fast oxidative
  • fast glycolic
101
Q

slow oxidative fibre size and force

A

smallest

102
Q

fast oxidative fibre size and force

A

intermediate

103
Q

fasy glycolic fibre size and force

A

largest

104
Q

composition of muscle fibre types within muscle

A

one muscle is made of a mixture of all three fibre types at different proportions depending on the function of the muscle

105
Q

recruitment order of muscle fibre types

A
  • slow oxidative
  • fast oxidative
  • fast glycolic
106
Q

muscle fatigue

A

decline in a muscle’s ability ti maintain a constant contraction force during repetition

107
Q

seven causes of muscle fatigue

A
  • low intensity exercise
  • high intensity exercise
  • very high intensity exercise
  • strong and sustained contractions
  • central fatigue
  • build up of inorganic phosphates
  • changes in ion distribution
108
Q

low intensity exercise

muscle fatigue

A

depetes energy reserves

109
Q

high intensity exercise

muscle fatigue

A

build up of lactic acid

110
Q

very high intensity exercise

muscle fatigue

A

depletion of acetylcholine

111
Q

trong and sustained contractions

muscle fatigue

A

compression of blood vessels

112
Q

central fatigue

muscle fatigue

A

psychological/neural fatigue

113
Q

how do muscles increase in size

A
  • no cell division
  • increase in myofibrils
114
Q

disuse atrophy

A

decrease in size due to loss of myofibrils

115
Q

denervation atrophy

A

motor neuron is destoryed, meaning there is no excitation - atrophy due to misuse

116
Q

hypertrophy

A
  • increase in muscle size due to increase in myofibrils
  • increase in production of actin and myosin
117
Q

two skeletal muscle receptors

A
  • muscle spindle
  • golgi tendon organ
118
Q

where are muscle spindles found

A

within muscle

119
Q

what do muscle spindles detect

A

muscle length

120
Q

where are golgi tendon organs found

A

within tendon

121
Q

what do GTOs detect

A

muscle tension

122
Q

what are extrafusual fibres found in

A

contractile cells of the muscle

123
Q

what are extrafusal fibres innervated by

A

alpha motor neurons

124
Q

where are intrafusal fibres found

A

muscle spindles

125
Q

what are intrafusal fibres innervated by

A

gamma motor neurons

126
Q

two types of sensory fibres found in muscle spindle

A
  • Type Ia
  • Tyoe II
127
Q

describe type Ia sensory fibres

A

annulospiral endings that wrap around the central portion of the spindle

128
Q

what do type Ia sensory fibres detect

A

muscle length and velocity

129
Q

describe type II sensory fibres

A

flower-spray endings that are located around either end of the spindle

130
Q

what do type II sensory fibres detect

A

onlt muscle length

131
Q

two steps of the stretch reflex pathway

A
  • afferent input from sensory endings of muscle spindle fibre
  • alpha motor neuron output to regular skeletal muscle fibre
132
Q

explain alpha-gamma coactivation

A
  • stretch reflex pathway
  • gamma motor neuron output to contractile end portions of spindle fibre
  • descending pathways coactivate alpha and gamma motor neurons
133
Q

how do GTOs sense muscle tension

A
  • They are afferent fibres lying within the tendons
  • Respond to alterations in muscle tension
  • Muscle tension causes tendon tightening and uplift to joint
  • The increased tension in the tendon stretches GTO
  • Stretch intensity increases action potential frequency (afferent signals delivered centrally and therefore interpreted consciously)
    • Meaning we can feel muscle tension but not muscle length
134
Q

where are smooth muscles found

A

walls of hollow organs

135
Q

what type of contractions do smooth muscles produce

A
  • continuous contractions of relatively low force
  • contraction of whole muscle mass
136
Q

what kind of control does smooth muscle have

A

involuntary - influenced by nervous system, hormones and local metabolites

137
Q

describe a smooth muscle cell (5 points)

A
  • contractile units
  • one nucleus
  • dense bodies
  • slow myosin ATPase
  • little sarcoplasmuc reticulum
138
Q

phasic

A

smooth muscle which contracts in bursts

139
Q

tonic

A

smooth muscle which maintains tone

140
Q

neurogenic

A

initiation of contraction is orginated in nervous tissue

141
Q

describe single unit smooth muscle

A
  • most common type
  • tonic or phasic
  • muscle fibres are activated synchronously
  • they contract together as a single unit
142
Q

where are single unit smooth muscles found

A

digestive, reproductive and urinary tracts and small blood vessels

143
Q

how are fibres in single-unit smooth muscles connected

A

gap junctions

144
Q

how are fibres in single-unit smooth muscles connected

A

gap junctions

145
Q

describe multi-unit smooth muscle

A
  • phasic and neurogenic
  • discrete units which function independently
  • few, if any gap junctions
146
Q

where is multi-unit smooth muscle found

A

walls of large blood vessels, small airways of lung, muscles of eye, base of hair follicles

147
Q

describe the innervation of multi-unit smooth muscle

A

each functional unit is activated separately ie. recieves its own innervation

148
Q

steps of excitation-contraction coupling of smooth muscle

A
  1. opening of calcium channels in plasma membrane
  2. Calcium triggers release of calcium from sarcoplasmic reticulum
  3. Calcium binds to calmodulin
  4. Ca2+-Calmodulin activates MLCK enzyme (myosin light chain kinase)
  5. MLCK phosphorylates myosin
  6. Cross-bridge cycling
149
Q

describe relaxation of smooth muscle

A
  1. Phosphatase enzyme removes phosphate from myosin
  2. Calcium removed from cytoplasm
150
Q

why is a high level of Ca2+ needed to activate MLCK

A

because phosphatase is continuously active and cometes with MLCK

151
Q

descrive neural regulation of smooth muscle contraction

A
  • Innervated by autonomic nervous system
  • May be excitatory or inhibitory
  • Target cell response depends on receptor type
  • Neurotransmitter is released from varicosities
  • Gap junctions allow transmission of electrical signal from one cell to neighbouring cells
152
Q

descrive non-neural regulation of smooth muscle contraction

A
  • Some smooth muscles are able to actively exert tension in absence of external stimulus
  • If intracellular Ca2+ levels are high enough to maintain constant level of cross-bridge activity - thus maintaining tone
  • Sometimes smooth muscles are able to contract by hormonal/other chemical stimulation
153
Q

similarities between skeletal and cardiac muscle

A
  • Striated - contains sarcomeres
  • Troponin and tropomyosin regulation
  • Has T tubules
  • Has sarcoplasmic reticulum although it’s not as well developed
  • Similar to slow oxidative fibres
    • Myoglobin
    • Mitochondria
    • Fatigue resistant
154
Q

similarities between smooth and cardiac muscle

A
  • Gap junctions (within intercalated discs)
  • Pacemaker cells
  • Innervated by autonomic nervous system
  • Influenced by hormones, paracrines (influenced by adjacent cells)
  • Calcium comes from ECF and SR
155
Q

why is there no summation in cardiac muscle

A
  • action potential lasts almost as long as tension
  • thus ling refractory period
156
Q

benefit of no summation of cardiac muscle

A

summation would not allow the heart to relax after each beat to fill with blood

Physiology (6 decks)

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