Muscle

Question 1

Key Properties of muscle

Answer 1

• Extensibility
• Elasticity
• Force production

Question 2

Cross-Bridge Activation in Smooth Muscle

Answer 2

1 - Ca2+ binds to calmodulin
2 - Complex binds to myosin light-chain kinase, activating the enzyme
3 - Uses ATP to phosphorylate myosin light chains in globular head
4 - Drives cross-bridge away from myosin filament backbone, allowing it to bind actin
5 - Occur as long as myosin light chains are phosphorylated
6 - To relax, myosin must be dephosphorylated by myosin light-chain phosphatase

Question 3

Structure of Smooth Muscle

Answer 3

• Spindle shaped
• Interconnected to form sheetlike layers
• Single nucleus
• Capacity to divide
• Myosin and actin filaments
• Actin filaments anchored to plasma membrane/dense bodies
• When actin shortens, regions of plasma membrane between points where actin is attached balloon out
• Significant force is generated over a relatively broad range of muscle lengths

Question 4

Membrane Activation of Smooth Muscle

Answer 4

• Spontaneous electrical activity
• Neurotransmitters released by autonomic nerve endings
• Hormones
• Local factors

Question 5

Proprioceptors in Skeletal Muscle

Answer 5

• Muscle spindles

- Golgi tendon organs

Question 6

Sliding Filament Theory

Answer 6

• Muscle force and length change generated by overlapping and interaction of filaments
• I Band reduced
• H Zone reduced
• Z lines closer to middle

Question 7

• Regulatory protein
• Overlaps binding sites on actin for myosin
• Inhibits interaction when relaxed

Answer 7

Tropomyosin

Question 8

• Regulatory protein

- Binds Ca2+ to pull tropomyosin from binding sites

Answer 8

Troponin

Question 9

Excitation-Contraction Coupling

Answer 9

1 - Muscle AP propagated into T-Tubules
2 - Ca2+ released from lateral sac
3 - Ca2+ binds troponin, pulling tropomyosin away
4 - Cross bridges bind and generate force
5 - Ca2+ taken up
6 - Ca2+ removal restores tropomyosin

Question 10

• If frequency of stimulation is high, a contraction occurs, where force remains constant for a period of activation
• Type of muscle force in functional activities

Answer 10

Tetanic Contraction

Question 11

Region of muscle fiber plasma membrane that lies directly under terminal portion of axon

Answer 11

Motor end plate

Question 12

Neuromuscular Junction

Answer 12

1 - Motor neurons AP
2 - Ca2+ enters voltage-gated channels
3 - Acetylcholine released
4 - Acetylcholine binding opens ion channels
5 - Na+ entry
6 - Local current between depolarised end plate and adjacent muscle plasma membrane
7 - Muscle fiber action potential initiation
8 - Acetylcholine degradation by acetylcholinesterase

Question 13

Period of time from AP to onset of contraction

Answer 13

Latent period

Question 14

Time that tension is developing

Answer 14

Contraction phase

Question 15

Time that tension is decreasing

Answer 15

Relaxation phase