Flashcards in Muscle physiology Deck (48):
Which of the three muscle types have pacemaker cells?
Smooth m (in single-unit muscle)
List the three muscle types in order of increasing speed of contraction.
Smooth, cardiac, skeletal
Which of the three muscle types have T tubules?
Skeletal and cardiac
What are muscle fascicles?
Groups of muscle fibres, surrounded by perimysium
Name four scaffold proteins in muscle fibres.
Desmin, titin, obscurin, nebulin
What is the function of desmin?
Intermediate filament that:
Forms scaffolds between Z lines
Allows side-side organisation and large force generation
Connects mitochondria and the nucleus to the Z-disks and
Binds the myofibrils to the sarcolemma
What is titin?
Scaffold protein that:
Stabilises the myofibril
Anchors the thick filament to the Z disk
Acts as a tension sensor, allowing an appropriate response.
Largest protein in the body.
What is obscurin?
Connects the myofibril to the sarcoplasmic reticulum, allowing communication
What is nebulin?
Scaffold protein with own kinase activity; interacts with desmin to determine Z disk width and stabilise actin filaments.
How long does the creatine store in muscle lasts?
How long does the glycogen store in muscle last?
From 10 seconds to a few minutes
Can the amount of time the glycogen supply in muscle is used for be altered by training?
By a small amount
For how long can muscle use oxidative, aerobic pathway?
What is the colour difference between fast and slow twitch muscles?
Fast twitch- pale
Slow twitch - dark due to myoglobin
Do larger diameter motor neurons lead to more rapid or slower contraction?
Do sarcomeres shorten in length during muscle contraction?
Describe the positioning of the sliding filaments at rest.
Myosin heads are cocked, with is ATP-dependent
Describe thick filaments
Polypeptides made of 2 large heavy chains and 4 light chains with two globular heads containing an ATP binding site each, with a long tail.
What is tension in a muscle fibre and therefore, produced force, proportional to?
Number of cross-bridges between thick and thin filaments
What are the two roles of ATP in cross-bridge cycling?
Hydrolysis of ATP is required for the power-stroke
ATP binding is required for release of filament binding
What is the role of Ca2+ in cross-bridge cycling?
Binds to troponin to change orientation of tropomyosin to expose myosin binding sites.
How does the actin-myosin motility assay work?
Line up myosin heads, and run and actin filament through in the presence of Ca2+
Where is the major supply of Ca2+ in skeletal muscle from?
Where is the major supply of Ca2+ in cardiac muscle from?
What type of transport is used to transport Ca2+ into sarcoplasmic reticulum following contraction?
Active transport via pumping.
Which proteins allow vesicle binding to the axon membrane to allow ACh release?
SNARE proteins - SNAP-25 and vesicle-associated membrane protein (VAMP)
Which botulinum toxin drug targets which SNARE protein?
Botox - SNAP-25
Discort - VAMP
What is the target of organophosphate pesticides?
Compare isotonic and isometric contraction.
Isotonic - constant tension, muscle changes length
Isometric - constant length, no work done
In a contraction cycle, which size muscles are recruited first?
What causes a plateau in the force of muscle contraction?
The maximum number of fibres recruited
Constant contraction due to temporal summation of stimuli
In which fibres are sarcomeres most disrupted?
Fast glycolytic fibres
Which speed order are motor units recruited during contraction?
Slow (S), then medium fast resistant (FR), then rapid fast fatiguing (RR).
Muscle fibres that are the thickest and fastest are of which type?
What is the importance of phosphocreatine?
Serves as an ATP reservoir via activity of creatine kinase
What are the effects of exercise on blood glucose levels?
GLUT4 transporters increase in muscle, increasing capacity for muscle to transport glucose, decreasing blood glucose levels.
Citrate synthase increases in muscle
Treatment of metabolic disease
What is the brief mechanism of GLUT4 upregulation with exercise?
Ca2+ causes CaMKI upregulation
ATP depletion increases AMPK
Together, these cause GLUT4 upregulation
When do fast twitch fibres develop?
Adolescence. Prior to this, there is little to no anaerobic activity, and it should not be used.
How does the relative number of muscle fibre types change in puberty?
Before puberty, most muscle fibres are of oxidative capacity. Following puberty, there is an increase in muscle mass, proportion of fast-twitch fibres and glycolytic and CrP storage capacity.
What are the two phenomenons that occur in muscle with age?
Sarcopenia - loss of skeletal muscle fibres
Dynapenia - loss of strength
Are age-related sarcopenia and dynapenia modifiable?
Yes, with exercise to an extent
What is the effect of mTOR activity on protein synthesis?
Increases protein synthesis
What are negative regulators of mTOR?
Hypoxia, corticosteroids, alcohol
Low energy intake
What are the positive regulators of mTOR?
Name two factors that determine whether muscle regeneration or muscle degeneration dominates in muscle injury?
Age, extent of injury
Expression of which gene causes a satellite cell to divide into a satellite cell?