Muscle 2 Flashcards
What does excess fatigue cause?
Rigor, new cross bridges cannot form
What does muscle fatigue depend on?
Length of contraction, fibre type and fitness of the individual
What factors contribute to fatigue?
Rising extracellular potassium levels - failure of cell depolarisation
Lactic acid - acidifies proteins
Increasing concentration of ADP + Pi delaying myosin detachment from actin
Decrease in glucose and glycogen
Dehydration
Central command fatigue - cerebral cortex cannot excite motor neurones - there is no will
Describe the ATPase activity of myosin in fast muscle fibre
High activity
Describe the features of oxidative muscle fibres
More mitochondria since more oxidative phosphorylation
More vascularisation to deliver oxygen and nutrients
Fibres are red with small diameters
Describe glycolytic fibres
Few mitochondria
More glycolytic enzymes and glycogen
Lower blood supply
White fibres with larger diameters
Describe the three types of muscle fibres and their resistance to fatigue
Slow oxidative - High resistance to fatigue
Fast oxidative - Intermediate resistance to fatigue
Fast Glycolytic - Low resistance to fatigue
What is recruitment?
When the load increases, Increasing the number of motor units - a cluster of fibres activated by the same action potential
What can lead to muscle mass loss?
Denervation atrophy (damaging the nerve or nmj)
Disuse atrophy
What is the effect of aerobic respiration on muscle development?
Increases mitochondria, vascularisation, fibre diameter, facilitation of oxidative phosphorylation
What is the effect of anaerobic respiration (strength training)?
Increase in diameter increase in glycolysis
What is smooth muscle innervated by?
The ANS and not the NS
Does smooth muscle have striations?
NO
Where can you find smooth muscles?
GI Tract, Uterus, airways, ducts
Describe the nucleus of smooth muscle?
Mononucleate
How are filaments arranged in smooth muscle?
Diagonally across the cell
Describe the cross bridge cycle in smooth muscle
Increase in calcium ions
Calcium binds to calmodulin
Calmodulin binds to Myosin Light Chain Kinase
Kinase phosphorylates the cross bridges activating them - bind to actin and cause contraction, ATP used to release the myosin from the actin
There is no blocking tropomyosin in smooth muscle
What causes the relaxation of the smooth muscle?
Myosin light chain phosphatase
What’s the result of dephosphorylating the cross head when the myosin is still bound to the myosin?
Inhibits the cross bridge cycle, decreases the rate of ATP splitting, maintenance of tension with low ATP consumption, useful in blood vessel walls that need to stay open for long periods of time.
What are the sources of cytosolic calcium?
Sarcoplasmic reticulum, (less in smooth muscle, no t- tubules)
Extracellular Ca+ - Voltage activated calcium channels
What pumps calcium out the cell and into the SR?
Calcium ATPases - slower than in skeletal muscle
What factors affect contractile activity of smooth muscle?
Pacemaker activity
Autonomic neurotransmitters
Hormones
Local factors (paracrine agents, pH, osmolarity, Ions)
Stretch
How many action potentials is needed in skeletal muscle to saturate all troponin sites?
1
In smooth muscle what does the GRADE of contraction depend on?
The number of action potentials received, there is a constant level of contraction in smooth muscles
Where can you find single unit smooth muscle types?
GIT, uterus, Small blood vessels
How are cells in single unit muscle types linked?
Gap junctions
What evokes contraction in single unit smooth muscle
Stretch
How do cells coordinate their actions with one another in single unit muscle type?
Gap junctions allow signals to travel between cells
They contract synchronously
Contain pacemaker cells
Where do you find multiunit smooth muscle?
Arteries, airways hair
Does multiunit smooth muscle contain gap junctions?
Yes but only very few
Describe innervation by the ANS in multiunit smooth muscle
Rich
Does multiunit smooth muscle respond to stretch?
no
Why are muscles in organs a mixture of single an multiunit muscle?
An organ can have a mixture of properties in different areas
