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Flashcards in Muscle Physiology COPY Deck (248)
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1

Name the three varieties of muscle in the body

  • Skeletal
  • Cardiac
  • Smooth

2

The contractile cells of muscle tissue

Myocytes/Myofibres

3

Another name for the skeletal muscle

Striated muscle

4

Skeletal muscle

5

Epimysium

6

Muscle fascicles

7

Muscle fascicle

8

Perimysium

9

Endomysium

10

Muscle Fibres

11

Muscle fibre

12

Sarcolemma

13

Fibril diameter

100 - 1000 µm

(1mm)

14

Myocyte diameter

10-100µm

15

Myofibril diameter

1µm

16

What is located between two Z-bands?

1 sarcomere

17

A-band

18

H-zone

19

1/2 I-bands

20

Z-bands

21

M-line

22

Sarcomere

23

Sarcoplasmic reticulum

24

Actin filament

25

H-zone

26

Z-disc

27

Myosin filament

28

I-band

29

A-band

30

M-line

31

Sarcolemma

32

Sarcoplasmic reticulum

33

Terminal cister

34

T-tubule

35

Triad

36

What permits the conduction of electrical impulses in the muscle fibre?

Narrow T-tubules

37

What regulates the intracellular levels of calcium?

Sarcoplasmic reticulum

38

The membrane triad of myocytes is composed of...

  • 2 x terminal cisternae
  • 1 x T-tubule

39

List the 3 additional proteins in the sarcomere

  • Titin
  • Nebulin
  • Alpha-actinin

40

Titin

  • Largest protein of the body
  • From Z-lines → Myosin bundles
  • Ensures precise return of actin and myosin bundles to original position

41

Nebulin

  • Determines the direction and placement of actin polymerisation (during development)
  • Protects actin fibres from rearranging

42

Alpha-actinin

  • Creates the Z-band
  • Net-like
  • Provides a binding site for actin complexes

43

Nebulin

44

Titin

45

Alpha-actinin

46

A motor unit

  • Motor neuron
  • Skeletal muscle fibres innervated by the neurone's axonal terminals

47

Summarise the pathway from neural activation to muscle contraction

  1. Generated AP→ Myoneural junction
  2. ACh-containing vesicles open at synaptic knobs
  3. ACh attach to the sarcolemma ACh-R
  4. ACh channel opens
  5. Naenters inner surface → Local end plate potential generated
  6. AP generated → Activates SR though T-system
  7. Ca2+ release into sarcoplasm → Actin-myosin contraction
  8. Ca2+ repumping into:
  • SR
  • Mitochondrium
  • EC

48

AP on the myolemma is generated only if...

The AP is stimulated through a nerve

49

Transmission of neural AP to the muscle takes place in the...

Myoneural junction

50

Give the summary of the processes that occur at the neuromuscular junction

  1. AP reaches nerve terminal → ACh release
  2. ACh → Nicotinic receptors on muscle membrane
  3. Ligand-activated cationic channels open
  4. EPP produced
  5. Voltage-gated Nachannels open
  6. AP formed in myolemma

51

Synaptic Vesicle

52

Synaptic Cleft

53

ACh receptor

54

  • ACh binding to its receptor
  • Ligand-activated cationic channel opens

55

ACh released by synaptic vesicle

Exocytosis

56

Lifecycle of neurotransmitter

Neurotransmitter synthesis

  • In cell body (cytosol)
  • In the terminal

57

Lifecycle of neurotransmitter

Neurotransmitter packaged into vesicles

58

Lifecycle of neurotransmitter

Neurotransmitter released

59

Lifecycle of neurotransmitter

Neurotransmitter binding

60

Lifecycle of neurotransmitter

Neurotransmitter diffused away

  • Catabolysed or transported back into the terminal

61

Give the actions when AP reaches the NMJ

  • Voltage-gated Ca2+ channels open, influx from EC space
  • [Ca2+] increases 100x → ACh exocytosis initiated

62

Clathrin

  • Protein on inner membrane
  • Stimulates endocytosis

63

What is shown?

Clathrin-dependent endocytosis

64

Composition of the nicotinic acetylcholine receptor

What does this allow?

  • Two alpha subunits
  • Two beta subunits
  • One delta subunit

Allows blocking effect of curare and bungarotixin

65

Give the 3 possible conductance states of the nicotinic acetylcholine receptor

  • Closed
  • Open
  • Inactivated

66

Which potential is amplitude-coded?

EPP

67

Which potential is frequency-coded?

AP

68

Decremental conduction

Decrease of signal strength with distance travelled

69

Role of Mg2+ in muscle contraction

  • Antagonises ACh receptor
  • Blocking function of sarcomere

70

Give the importance of Mg2+ in cattle

  • High Ca2+ secretion after calving → Low plasma Ca2+ levels
  • [Mg2+] becomes relatively high
  • Muscles relax: Parturient paresis

71

  • AP from axon
  • Ca2+ enters from EC, ACh vesicle release

72

Filling up with ACh

73

  • ACh binds to the receptor
  • EPP generated
  • AP generated, Ca2+ influx, contraction

74

Effect of nicotine on the neuromuscular junction

  • Same effect as ACh
  • Cannot be degraded by cholinesterase
  • Conc. therefore increases → Permanent depolarisation
  • Intensive spasm

75

Effect of cholinesterase inactivators on the neuromuscular junction

  • ACh not hydrolysed
  • High ACh accumulation
  • Repetitive stimulation of muscle fibres
  • Spasm/laryngeal spasm

76

Effect of curariform drugs on the neuromuscular junction

  • ACh receptor blocked
  • No depolarisation → No contraction
  • Paresis

77

Effect of botulin toxin on the neuromuscular junction

  • Blocking of ACh release
  • Pareisis

78

Effect of myasthenia gravis (autoimmune disease) on the neuromuscular junction

  • ACh receptor blocked by antibodies
  • No ACh binding
  • Paresis

79

Depending on the task of the given muscle, there can be variations in...

Nerve:muscle fibre ratio

  • Occular muscles (1:1)
  • Skeletal muscles (1:100)

80

The fusimotor system

  • Intrafusal fibres
  • Modified muscle fibres → Stretch detection
  • Also located in tendons → Golgi tendon receptor organs

81

Static fibres

Sensitive to static changes of tension (Length)

82

Dynamic fibres

Sensitive to dynamic changes of tension (length & velocity)

83

Intrafusal fibres

84

Extrafusal fibres

85

Sensory fibres

86

Myotatic reflex

  • (Contraction of stretched muscle)
  • Efferentation returns to the same muscle where afferentation occurs
  • Monosynaptic

87

Give the responses of Myotactic reflex

  1. Increased stretching causes increased tension (Servo-mechanism)
  2. Fusimotor activation

88

Give the steps of the servo-mechanism

  1. Muscle stretching → Muscle spindles stimulated
  2. Sensory neuron activated
  3. Information processing at motor neurone
  4. Motor neurone activation
  5. Muscle contraction

89

Co-activation

CNS participation (+servo-mechanism) in fusimotor system activation

90

Describe Co-Activation mechanism

  • α- + γ- motorneurones stimulated by cerebral centre (Co-acitivation)
  • Intrafusal & extrafusal fibres contract with the same rate and strength

91

Describe Co-Activation in the case of sudden increased load

  • Extrafusal fibre tension is stronger than intrafusal
  • AP frequencies accelerate in Ia and II afferents
  • Locally adjust the tension of extrafusal fibres (fine tuning)

92

1

AP → Myolemma

93

2

  • AP reaches L-type Ca2+ channels in the T-tubuli
  • L-type channels open

94

3

Ryanoid-Ca2+ open

95

4

Ca2+ enters the IC from the SR

96

5

  • Ca2+ channels open on myolemma
  • Ca2+ influx from the EC

97

6

  • IC Ca2+ high in and around the sarcomere
  • Contraction

98

Contraction and relaxation of muscle require...

ATP

99

The triad

100

Cardiac equivalent to the triad

Diad

101

Triad

  • Basis of excitation-contraction coupling
  • Where t-tubule is closest to the SR IC

102

What occurs at the triad?

  • AP → Change in L-type Ca2+ receptors
  • T-type ryanodin Ca2+ channels open
  • High amount of Ca2+  released from SR to IC space
  • Positive feedback:
    • Ca2+ opens SR Ca2+ channels
  • Increase in [Ca2+] → Cross-bridge cycle triggered
  • Calcium signal stimulates its own inactivation

103

Potential dependent DHP proteins

104

T-type (Ryanodin) calcium channel

105

Briefly describe the figure

  • Receptors in the T-tubule changing from their closed state to their opened state
  • Influx of Ca2+ ions into the triad

106

What is the main component of the actin-complex?

G-actin

107

Give the function of tropomyosin

Used in stimulation of ATPase activity of myosin

108

What is shown?

F-actin α-helix

109

G-actin subunit

110

Myosin binding site

111

Tropomyosin (Inactive)

  • Blocks 7 binding sites

112

Tropomyosin (Active)

  • Slides into the groove of α-helix, leaving binding sites free

113

What is shown?

Troponin-complex

114

Troponin-C

115

Troponin-T

116

Troponin-I

117

Describe activation of tropomyosin

  • Ca2+ binding → Removes tropomyosin to grove (Active)
  • Tn-complex binds to the tropomyosin attached to actin
  • Tropomyosin-troponin complex kept on the helix surface (inactive)

118

Describe the structure of myosin

1 bundle = 6 myosin molecules

  • 2 heavy chains (HC)
  • 2 light chains (LC)
  • Globular part (head/cross bridge)

119

Angle of myosin head with alpha helices

90°

120

Maximum bend angle of myosin heads

45°

121

Give the three types of ATPases

How do they differ in function?

  • LC-1
  • LC-2
  • LC-3

Difference determines the speed of ATPase activity

122

LC-2 ATPases are found in...

Fast twitch muscle

123

LC-3 ATPases are found in...

Slow-twitch muscle

124

  • Tail / Heavy chain
  • Formed by α-helix

125

Head Cross-bridge

126

Actin binding site

127

ATP binding site

128

Myosin filament composition

200 miosin units

129

Calcium transient

  1. IC [Ca2+] increased x1000
  2. Calcium (re)pumping mechanisms
  3. Calcium elimination from cytoplasm
  4. Ca2+ levels decrease near the sarcomere

130

Give the steps of the Cross-bridge cycle

  1. Relaxation/Resting
  2. Ca2+ release from AP
  3. Tropomyosin removed → myosin binding sites exposed
  4. Cross bridge binds to actin
  5. Contraction (head tilts, ADP released)
  6. Ca2+ removed from outside → Myosin detaches

131

ATP in the cross bridge cycle

  • Myosin head binds to ATP
  • Energy deliberated → ADP + P
  • Head tilts back to 90° (Cocked head)

132

  • Myosin head detached
  • ATP hydrolysed

133

ADP + P bound to myosin as myosin head attaches to actin

 

134

  • ADP + P release
  • Head changes position
  • Actin filament moves

135

  • ATP binding to head
  • Head returns to resting position

136

When ATP isn't present in the muscle

  • Myosin cannot dissociate from actin
  • Muscle becomes contracted and inactive

Rigor mortis → Autolysis follows after

137

When Ca2+ isn't present in the muscle

  • Tropomyosin slides over myosin
  • Activating part of the actin
  • Muscle relaxes
  • Myosin heads can't bind

138

The ratchet mechanism

Myosin filament cannot fall back

  • Myosin heads need to work asynchronously to contract

139

How is calcium removed from the cytosol

All are ATP dependent:

  • Na+/Ca2+ ion antiporter
    • Secondary active transport
  • Ca2+ repumping into the SR
  • Other
    • Cell organelles
    • Mitochondria

140

Composition of muscle tissue

  • 75% water
  • 20% protein

141

Describe the importance of the macroscopic structure of muscles

  • Most sarcomere orientations aren't parallel to the direction of macroscopic contraction
  • Skeletal muscle is wasteful but provides extreme spatial flexibility

142

Which metabolism is expressed in red/slow twitch muscle?

Oxidative

143

Which metabolism is expressed in white muscle?

Anaerobic

144

Which metabolism is expressed in pink muscle?

Mixed

145

Fast twitch muscle types

Pink and White

146

Atrophy

  • Decrease in skeletal muscle size
  • Myonuclear loss
  • Decreased myofibrillar proteins
  • Decreased CSA

147

Muscle Hypertrophy

  • Increase in skeletal muscle size
  • Myonuclear addition
  • Increased myofibrillar proteins
  • Increased CSA
  •  

148

The fibre spectrum of an individual is determined by...

  • Genetic factors
  • Usage of specified muscle

149

Which two factors contribute to hypertrophy

  • Sarcoplasmic hypertrophy - Increased glycogen storage
  • Myofibrillar hypertrophy - Increased myofibril size

150

Remodelling of 'slow' muscles

Mass of fibres increase slower than nutrient/energy storage of myocytes

151

Myocyte ATP concentration

5 mmol/l

152

List the energy sources of muscle contraction

  • Creatin-phosphate
  • Anaerobic glycolysis
  • Oxidative phosphorylation

 

153

Creatin phosphate

ADP + CrP → ATP + Cr

154

Creatin phosphate conc. in myocytes

20 mmol/l

155

Anaerobic Glycolysis as muscle energy source

In cases of outstanding load

  • Glycogen
  • Glucose

4 ATP produced

  • If more ATP is used than produced → Oxygen debt
  • Produced lactic acid inhibits contraction

156

Oxidative phosphorylation as a muscle energy source

Pyruvate → Acetyl-Coenzyme A

36 ATP produced

Process and contraction are slow

No oxygen debt

157

Working in an oxygen-free environment

158

Oxygen debt

159

Muscle can replenish glycogen and creatine phosphate by...

Oxygen consumption

160

Give the types of muscle contraction

  • Isotonic
  • Isometric
  • Mixed
    • Auxotonic
    • Preload
    • Afterload

161

Isotonic contraction

Contraction with constant tension

162

Isometric contraction

Contraction when only tension is changed, no length changes

e.g lifting an unliftable load

163

Auxotonic contraction

Working against increasing tension and resistance

e.g against a spring

164

Preload contraction

  • Muscle length is adjusted until equilibrium
  • Isotonic contraction follows

e.g locomotion related muscle work

165

Afterload contraction

  • Isotonic contraction until the contraction is blocked
  • Isometric contraction follows

e.g. m. masseter

166

The sum of observable and biological latency

Virtual latency

167

Which muscle elements reach equilibrium with the load first, why?

SEC elements, dues to the contraction of the contractile components

(only tension is increased at this stage)

168

Summation of muscle contraction

Addition of muscle contraction forms

  • Increase the contractile capacity of individual fibres
  • Recruits more fibres

169

Give the types of Summation

  • All or none law
  • AP Frequency
  • Quantal summation
  • Contraction summation
  • (Staircase effect)
  • Tetanus

170

All or none law

  • Applies for a single fibre
  • Adequate stimulus causes maximal contraction
  • Stimulus strength can't influence amplitude of contraction

171

AP frequency summation

  • Increased frequency
  • Prolonged Ca2+ release
  • Stronger contraction

172

Quantal summation

  • Increased AP frequency
  • More fibres contract

 

173

Contraction summation

  • Additional Ca2+ release before the end of Ca2+ transient
  • Increased amplitude of contraction

174

Staircase effect summation

  • Warmup phenomenon - not graded contraction
  • If new stimuli arrive after the end of the first twitch
  • Increased efficiency of ion channels
  • Ca2+ accumulation
  • Increased amplitude of contraction

175

Tetanus summation

  • Stimuli applied with increasing frequency
  • Muscle eventually reaches max contraction state (tetanus0

176

How is the length-tension curve obtained?

  • Stimulation of a muscle which is passively stretched with varying loads
  • Isometric, isotonic, preload and afterload experiments carried out

177

What does the length and tension diagram show?

The area where muscles execute normal work

178

Maximal tension value

3kg/cm2 muscle cross section

179

Tension (g) generated upon stimulation

180

Sarcomere length (µm) before stimulation

181

Overly contracted

182

Optimum resting length

183

Overly stretched

184

Length x Tension =

Work

185

Describe obtaining length-tension diagram in isotonic conditions

  • Muscle stretched to A, B, C distances (Above L0)
  • Muscle is stimulated with max single stimuli
  • The isotonic maximum (It) curve can be obtained

186

Describe obtaining length-tension diagram in isometric conditions

  • Shortening isn't possible
  • Only changes of tension can be measured
  • Isometric maximum (Im) curve achieved

187

Describe obtaining length-tension diagram in the preload experiment

  • Tension increase is followed by contraction
  • Preload maximum (Pm) curve achieved

188

Length-tension diagram in the afterload conditions

Afterload-maximum (Am) curve achieved

189

How is working range achieved from the 4 length-tension experiments?

Area is constructed on a graph

190

Compare 'normal working range' and 'length measured under max power' in skeletal muscle

Both are identical to eachother

191

Compare 'normal working range' and 'length measured under max power' in cardiac muscle

  • The normal working range is much below the length
  • Ensuring maximal tension

192

Velocity x Tension =

Power

193

As tension is...velocity becomes...during muscle work

Low; high

194

Unloaded muscle contracts with...velocity

Maximal

195

Overloaded muscle contracts with...velocity

Zero

196

Velocity related to an actual tension is determined by...

The type of muscle

  • Phasic (Fast)
  • Tonic (Slow)

197

Using the velocity-tension diagram rather than the length-tension diagram gives a better indication of...

The power of the muscle

198

Intermediate tension and intermediate velocity result in...

Maximal power

199

Describe the figure

Grey rectangles:

  • Small tension = High velocity
  • High tension = Small velocity

Red rectangle:

  • The optimal position where maximum power can be achieved

200

Max speed of muscle contraction

7 m/sec

201

Total force of skeletal muscle

200N

relative to 100kg mass

202

Efficiency of skeletal muscle

20%

203

Power maximum of skeletal muscle

  • Short term: 3-5000 W
  • Long term: 1200 W

204

How do muscles produce heat?

  • Contraction: ATP breakdown
  • After contraction: Synthetic processes create heat

205

When do phasic/fast/white fibres produce heat most?

During restoration/recovery

206

When do tonic/slow/red fibres produce heat most?

207

Give the phases of heat production

  • In resting (Muscle maintenance/BMR)
  • Initial heat production
    • Activation heat
      • Ca2+ release
      • Myosin-activation
    • Contraction heat
      • Sliding filament
      • Ca2+ repumping
  • Restitution heat

208

Muscle fatigue is dependent on...

Ratio of phasic and tonic fibres

209

Signs of fatigue on a mechanogram

210

In Vitro fatigue

  • Lack of O2
  • Lack of Transmitter

211

In Vivo fatigue

  • Peripheral
    • Decreased energy sources
    • Lactic acid
  • Central fatigue
    • Exhaustion of motor-unit
    • Exhaustion of myoneural junction

212

Subjective feelings of fatigue can be caused by...

  • Increased heat production
  • Decreased pH
  • Lactic acid
  • Dehydration
  • Hypoglycaemia

213

Fatigue develops earlier in...

Phasic fibres

214

Smooth muscle

Used in maintenance and form of visceral organs

  • Single-unit smooth muscles
  • Multi-unit smooth muscles

215

Multi-unit smooth muscle

  • Individual fibres not connected with gap junctions
  • Fibres under direct neural control (not by AP)
  • Capable of fast and accurate movements
  • Transmitters cause local depolarisation

Located in the eye

216

Single unit smooth muscle

  • Many hundreds of fibres
  • Form a functional syncytium
  • Fibres are innervated by varicosities

e.g muscle of vessels

217

What causes contraction of smooth muscle

  • Dense bodies and intermediate filaments
  • Networked through the sarcoplasm

218

Proportion of myosin:actin in smooth muscle

1:15

219

Give the steps of contraction in smooth muscle

  • If IC Ca2+ is high, MLCK enzyme is used
  • Actomyosin complex formation
  • Contraction stays continuous until MP enzyme triggers relaxation

Most muscles are in weak but continuous contraction

220

Summarise the structure of smooth muscle

  • No transverse tubular system
  • Poor blood supply
  • Non-striated
  • Small SR

221

What is shown?

Smooth muscle sarcomere

222

Calmodulin

223

Caldesmon

224

Describe the role of caldesmon in smooth muscle contraction

  • Ca2+ binds to the Calmodulin-Ca2+ complex
  • Removes tropomyosin from binding sites

225

Describe smooth muscle myosin

Heads contain a unique MLC subunit:

P-LCh

  • Phosphorylated = Actin binding → Contraction
  • Non-phosphorylated = No actin binding

 

 

226

In smooth muscle:

If there is no Ca2+ 

MLCK is inactive → P-LCh is not phosphorylated

227

Elimination of Ca2+ activates...

Myosin phosphatase (MP)

 

228

Activation of MP

Dephosphorylation of P-LCh → Relaxation

 

229

Characteristics of smooth muscle contraction

  • Prolonged tonic contraction (hours/days)
  • Energetically economic - low energy use
  • Length of contraction 30x longer than skeletal

230

Max contraction length of smooth muscle

66% of resting length

231

Varicosities

  • Series of axon-like swellings
  • From autonomic neurons
  • Form motor units in the smooth muscle

232

Example of multi-unit smooth muscle

m. ciliaris

233

Example of single unit smooth muscles

Gastrointestinal muscles

234

What is shown?

Special structure of smooth muscle SR

235

Sources of Ca2+ in the smooth muscle

  • Minor: SR
  • Major: EC-Space

236

Which channels can be found in the smooth muscle myolemma?

  • Voltage-gated Ca2+ channels
  • Ligand-gated Ca2+ channels

237

Describe AP in smooth muscle

  • Single-unit only
  • RMP = -50mV
  • Forms of AP:
    • Typical peak potential
    • AP with 'plato'

238

Importance of extremely prolonged repolarisation of smooth muscle

Prolonged contraction:

  • Myocardium
  • Uterus

239

Factors causing contraction of smooth muscle

  • AP
  • Binding of chemical ligands
  • IC IP3 release
  • G-Protein or phospholipase C (PLC) mediated Ca2+ influx

240

What stimulates relaxation of smooth muscle?

All stimuli which can increase IC cAMP or cGMP levels

  • Sympathetic beta2 receptor agonists

241

Chemical factors influencing smooth muscle contraction

  • Lack of O2
  • Excess of CO2
  • Increased H+
  • Increased K+

242

Bayliss effect

Extension of smooth muscles results in contraction

Not related to neural or hormonal influences

243

What is the mechanism of the Bayliss effect?

  • Stretching opens the mechano-sensitive cation-channels
  • Depolarisation

244

Where would the spontaneous generation of smooth muscle AP be observed?

In the gut

245

Spontaneous generation of smooth muscle AP is associated with...

The 'slow wave' rhythm

246

AP (Spike potential)

247

Slow wave potential

  • Not AP
  • Local potential
  • If above -35mV, AP is initiated

248

Each slow wave initiates...

More than one AP

(Also called pacemaker waves)