Muscles 2 Flashcards
Whats ATP used for in muscle contraction?
ATP is hydrolysed for energising X-bridges.
Also powers Ca2+ATPase
What does fatigue depend on?
Fibre type
Length of contraction
Fitness
What can cause fatigue in high-intensity short duration exercise?
- rise in [K+] causes depolarisation and conduction failure
- Rise in [lactic acid] acidifies proteins
- Rise in [adp] & [Pi] inhibits X-bridge cycle, delaying myosin detachment from actin filaments.
What can cause fatigue in long-term, low intensity exercise?
- drop in muscle glycogen
- drop in blood glucose
- Dehydration
Central command fatigue?
Cerebral cortex cannot excite motor neurons
What characterises skeletal msucle fibre types?
Whether theyre fast or slow shortening
Whether they use oxidative or glycolytic ATP forming pathways.
Whats different about oxidative fibres?
More mitchondria
More vascularisation
Myoglobin for O2 delivery
Red fibres small diameter
Whats different about glycolytic fibres?
Few mitochondria
more Glycolytic enzymes & glycogen
Low blood supply
White fibres with large diameters
What are 3 muscle fibre types?
Slow oxidative (I) - resist fatigue Fast oxidative (IIa) - some resistance to fatigue Fast Glycolytic (IIb) - Fatigue quickly
What is muscle fibre recruitment?
An increase in the number of active motor units
What causes muscle fibre recruitment?
And icnrease in load
In what order are muscle fibres recruited?
I
then IIa
Then IIb
How does exercise type determine the type of fibres you have?
Anaerobic exercise increases glycolysis and fibre diameter
Aerobic exercise increases mitochondria and vascularisation
What is differnet about smooth muscle?
No striATIONS
Innervated by ANS not the Somatic NS
Mononucleate
Where is smooth muscle found?
Hollow organs
What shape are smooth muscle cells?
Spindle-shaped
How is the smooth muscle x-bridge cycle different to skeletal muscle?
The Ca2+ binds to calmodulin
- the complex binds to myosin light chain kinase
- kinase phosphorylates myosin x-bridges with ATP
- Phosphorylated X-bridges bind to actin filaments and contract.
How is smooth muscle relaxed?
Myosin light chain phosphatase dephosphorylates X-bridges
What is different about Ca2+ supply in smooth muscle?
Little SR with no T-tubules so most Ca2+ is sourced extracellulaly from voltage gated Ca2+ channels.
How is Ca2+ removed from smooth muscle
Pumped into SR and out of cell by Ca2+ ATPase (slower process than in skeletal muscle)
How is contraction graded in smooth muscle cells?
1 AP doesnt release enough calcium to saturate all the troponin sites.
So the no of APs can grade the contraction
What does the tone of smooth muscle refer to?
There is a basal level of Ca2+ in smooth muslce causing a constant level of tension which can be increased or decreased.
What factors affect contractile activity in smooth muscle?
- hormones
- local factors (pH, O2, osmolarity etc)
- Stretch
- autonomic neurotransmitters from varicose veins
- spontaneous electrical activity in muscle membranes
Where are single unit smooth muscle types?
GI tract, Uterus, small vesells
Whats special about single unit muscle smooth muscle?
- many cells linked by gap junctions
- signals travel between cells
- May contain pacemaker cells
- Stetch evokes contraction
- Contract synchronously
Where are multiunit smooth muscle types found?
Airways
large arteries
hairs
Whats special about multiunit smooth muscle?
- Few or no gap junction
- richly innervated by ANS
- Dont respond to stretch
