Topic 13: Muscles Flashcards
Describe the roles of muscles
- Movement
- Thermoregulation
- Energy metabolism and storage
- Appetite regulation
- Endocrine functions
- Drug storage
Describe some properties of muscles
- Muscles mass deline with age and men have more skeletal muscles than women.
- Contractility: able to contract with a force (actively)
- Excitability: able to respond to electrical stimulation
- Extensibility: able to be stretched to normal resting length and beyond to a limited extent
- Elasticity: return/recoil to resting position when relaxed
Differentiate different types of muscles
- Skeletal muscles: attached to skeleton - responsible for movement (voluntary)
+ multiple peripheral nuclei
+ highly organized sacromeres & triads
+ hypertrophy
+ long tube-shaped
+ have striations - Cardiac (myocaridum): forms heart - responsible for pumping heart (involuntary)
+ multiple central nuclei
+ intercalated discs with adhesion and gap junctions
+ hypertrophy
+ long, branching cells
+ have striations - Smooth: line within tissues - control diameter of structures and peristalsis (involuntary)
+ single central nucleus
+ without striations
+ spindle shaped cells
+ hypertrophy
Describe the structure of muscles
Contractile proteins (filaments) are bounded by Z disks to make up sacromere.
- Myosin - thick filament: have heads pointing towards binding sites of actin
- Actin - thin filament: have binding sites for myosin heads
A bundle of sacromeres make up myofibril.
A bundle of myofibril make up muscle fibre/muscle cell.
A bundle of muscle fibres make up fascicle.
A bundle of fascicles make up muscle bundle.
Describe how myosin and actin work together to produce muscle contraction (in different types of muscles)
- Skeletal/Myocardium muscle contraction:
+ Trypomyosin locks binding sites on actin
+ ATP is dephosphorylated, and electrical excitation of the muscle cell releases Ca2+ from sacroplasmic reticulum (SR)
+ Ca2+ binds to troponin and moves trypomyosin out of the way to allow myosin heads binding with actin
+ Release of P in ATP dephosphorylation bind to myosin head, making it move along with actin and be pulled towards center of sacromere
+ At en of excitation, calcium pumps back into SR allowing tropomyosin to block myosin binding again - Smooth muscle contraction:
+ Ca2+ comes from SR and ECF via channels
+ Ca2+ binds calmodulin in sarcoplasm
+ Ca2+/calmodulin complex activates MLCK which phosphorylated myosin heads –> cross-bridge formation
Describe the structure of motor units
1 muscle fibre is supplied by 1, and only 1 neuron
1 neuron can supply many muscle fibres
1 neuron and all muslce fibres it supplies is 1 motor unit.
Describe how action potential affects muscle contraction and how summation works
1 action potential generates 1 contraction/twitch.
If another muscle is contracted while the previous twitch is still happening, the 2nd twitch will be stronger.
Summation is the add-up of muscle contraction due to multiple electrical stimulus.
Describe different stages of muscle contraction and explain how it is different in summation
- Normal:
+ Latent phase: action potential is being sent and Ca2+ ions being released
+ Contraction phase: cross-bridge formation and contraction
+ Relaxation phase: Ca2+ is pumped back into SR, cross-bridge stops - If there is continuous electrical stimulus, the muscle will continue the contraction phase for a longer time.
Describe different stages of muscle contraction and explain how it is different in summation
- Normal:
+ Latent phase: action potential is being sent and Ca2+ ions being released
+ Contraction phase: cross-bridge formation and contraction
+ Relaxation phase: Ca2+ is pumped back into SR, cross-bridge stops - If there is continuous electrical stimulus, the muscle will continue the contraction phase for a longer time.
Differentiate fast and slow twitch
- Type 1: slow twitch
+ more efficient, so always being used first
+ contract slowly, so slow fatigue
+ use aerobic metabolism, needs a large amount of oxygen - adpat to bring oxygen to mitochondria via myoglobin - Type 2: fast twitch
+ less efficient
+ contract very quickly, rapid fatigue
+ more actin and myosin
