Muscle Flashcards
Key Properties of muscle
- Extensibility
- Elasticity
- Force production
Cross-Bridge Activation in Smooth Muscle
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
Structure of Smooth Muscle
- 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
Membrane Activation of Smooth Muscle
- Spontaneous electrical activity
- Neurotransmitters released by autonomic nerve endings
- Hormones
- Local factors
Proprioceptors in Skeletal Muscle
- Muscle spindles
- Golgi tendon organs
Sliding Filament Theory
- Muscle force and length change generated by overlapping and interaction of filaments
- I Band reduced
- H Zone reduced
- Z lines closer to middle
- Regulatory protein
- Overlaps binding sites on actin for myosin
- Inhibits interaction when relaxed
Tropomyosin
- Regulatory protein
- Binds Ca2+ to pull tropomyosin from binding sites
Troponin
Excitation-Contraction Coupling
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
- 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
Tetanic Contraction
Region of muscle fiber plasma membrane that lies directly under terminal portion of axon
Motor end plate
Neuromuscular Junction
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
Period of time from AP to onset of contraction
Latent period
Time that tension is developing
Contraction phase
Time that tension is decreasing
Relaxation phase
