ELM17: Muscle 2 Flashcards
What are the characteristics of a muscle twitch and why does this happen?
Longer and delayed
More time for calcium concentration to rise and decrease
What is the tetanus state of a muscle?
The state where a muscle is maximally stimulated
What is Hennemans size principle?
When a muscle is stimulated motor neurons are recruited in order of size
What is the function of muscles using Hennemans size principle?
Can regulate the force of contraction
Can make small or large contractions
What are the three types of skeletal muscle?
Slow twitch oxidative
Fast twitch glycolytic
Fast twitch oxidative
What are the properties of slow fibre skeletal muscle?
Posture maintenance
Myoglobin red as oxygen store
Many mitochondria
What are the properties of fast fibre skeletal muscle?
Fast myosin isoform
Fast
Ca transient
Rapid shortening at high energy cost as ATP hydrolysed quickly
What are type IIA fibres?
Fast oxidative
Lots of mitochondria
Good blood supply
Good glycogen stores
Resist fatigue
What are type IIB fibres?
Fast glycolytic fibres
Lactate accumulation and acidosis can limit contraction
What is duchenne muscular dystrophy?
X linked disorder caused by dystrophin gene mutation
Skeletal muscle not linked to ECM properly
Excess calcium enters and muscle fibres die
Progressive muscle weakness
What happens in animals with myostatin deficiencies?
Extra muscle mass and little fat
What are the differences between cardiac and skeletal muscle?
Branched syncytium
Cells not fused completely
Joined by intercalated discs
Different control mechanisms
Only in heart
What causes the rising phase in cardiac muscle?
Opening of sodium channels
What causes the broad plateau phase in cardiac muscles?
Opening of voltage gated calcium channels
What is the process of excitation contraction coupling in cardiac muscle?
- L type calcium channel on membrane lets calcium in
- Calcium induced calcium release from sarcoplasmic reticulum using ryanodine receptor
How is contraction initiated in cardiac muscle?
Myogenic as pacemaker potentials generated
What are pacemaker potentials?
Slow depolarisation of the membrane that happens independently
What occurs when the slope of pacemaker potential steepens?
SNS is activated
What occurs when the slope of the pacemaker potentials unsteepens?
PNS is activated
What determines the force of contraction?
Degree of stretch of cardiac muscle
Concentration of cytoplasmic reticulum
Why is smooth muscle different?
No striations
No T tubules
Gap junctions or independent
Where is smooth muscle usually found?
In hollow organs
What is the function of smooth muscle?
Propel contents
Regulate flow
Usually controlled by ANS
What is the difference in the contraction mechanism of smooth muscle?
Slowly
More energy efficient
Contracts well over greater range
What is the first mechanism of excitation contraction coupling in smooth muscle?
- Depolarisation
- L type calcium channels open and calcium enters
- Triggers calcium induced calcium release from ryanodine receptor
What is the second mechanism of excitation contraction coupling in smooth muscle?
- Agonist binds to GPCR
- Activates phospholipase C
- Activates IP3
- Releases calcium
What is the third mechanism of excitation contraction coupling in smooth muscle|?
- SR runs out of calcium and signals store operated calcium channels
- Open and calcium enters
What is the role of calcium in smooth muscle?
Increase the low ATPase activity of smooth muscle myosin heads
How does calcium increase the ATPase activity in smooth muscle?
- Calcium binds to calmodulin
- Interacts and activates MLCK
- MLCK phosphorylates regulatory light chains
- Switches on ATPase activity
How is smooth muscle excited?
Myogenic
Initiated by AP from neuronal stimulation
APs superimposed on myogenic activity
Graded response to depolarisation
Modulated by NTs and hormones
