Flashcards in Muscle 2 Deck (37)
What 2 processes does ATP power in muscle contraction?
- unbinding of myosin to actin so that a new cycle may begin
-Ca2+-ATPase in the sarcoplasmic reticulum. calcium gets pumped back into the sarcoplasmic reticulum and contraction ends
What causes muscle fatigue?
repeated muscle stimulation
What does muscle fatigue prevent?
muscles using up too much ATP
What 3 factors during high intensity, SHORT duration exercise can lead to muscle fatigue?
- conduction failure due to increase in concentration of potassium ions
- increase in lactic acid concentration which can acidify the proteins
- increase in the concentrations of ADP and Pi inhibit X bridge cycle
What 3 factors during low intensity, LONGTERM exercise can lead to muscle fatigue?
- decrease in muscle glycogen
- decrease in blood glucose
What is meant by 'central command fatigue'?
cerebral cortex cannot excite motor neurones
How are skeletal muscle fibre types characterised?
based on whether the fibres are slow or fast shortening which is dependent on whether the oxidative or glycolytic ATP forming pathways are used
Comment on the ATPase activity of myosin in fast muscle fibres.
Comment on the ATPase activity of myosin in slow muscle fibres.
Give 4 properties of oxidative muscle fibres.
- lots of mitochondria for oxidative phosphorylation
- greater vascularisation to deliver more 02 and nutrients
- contain myoglobin to increase oxygen delivery
- fibres are red and have low diameters
Give 4 properties of glycolytic fibres.
- few glycolytic fibres
- greater glycolytic enzymes and glycogen
- lower blood supply
white fibres with larger diameters
What are the 3 types of muscle fibres? Comment on their susceptibility to fatigue.
- Slow oxidative- resist fatigue
-Fast oxidative - intermediate resistance to fatigue
- Fast glycolytic - fatigue quickly
What is muscle fibre 'recruitment'?
if there is an increase in load then we require to activate more motor units
the increase in number of active motor units is known as recruitment
In what order are the different types (oxidative etc) of muscle fibre activated?
1. slow oxidative fibres
2. fast oxidative
3. fast glycolytic
What 2 factors is neural control of muscle tension dependent on?
1. frequency of APs to motor unit
2. recruitment of motor units
What 2 things can lead to a decrease in muscle mass?
- denervation atrophy - destroy nerve/NMJ
- disuse atrophy - muscle not used
What causes muscle hypertrophy?
What determines the type of muscle fibres you have?
the type of exercise you do
What type of muscle fibre would you expect to have a lot of if you do a lot of aerobic exercise?
What type of muscle fibres would you expect to have if you do a lot of anaerobic (strength) exercise?
How is smooth muscle innervated?
By the autonomic nervous system
Give 3 general properties of smooth muscle appearance.
- spindle shaped
- not striated
How does smooth muscle differ from skeletal muscle in terms of repair?
smooth muscle cells divide through life
How do the myofilaments in smooth muscle differ in arrangement compared to skeletal muscle?
still have thick myosin and thin actin filaments that use the cross bridge, sliding filament model of contraction
- but filaments are arranged diagonally and are anchored to membranes and cell structures by dense bodies
Describe the 6 steps involved in the smooth muscle X-bridge cycle activation.
1. increase in calcium concentration
2. calcium binds calmodulin
3. calcium- calmodulin binds to Myosin Light Chain Kinase
4. kinase phosphorylates myosin X bridge with ATP
5. phosphorylated X bridges bind to actin filaments
6. contraction and tension
How does smooth muscle relax?
by action of myosin light chain phosphatase which dephosphorylates X - bridges
How can smooth muscle maintain tension for a long time with low ATP consumption?
by x bridges being dephosphorylated when still being bound to actin
decreases the rate of ATP splitting and slows cross bridge cycle
Where are the sources of cytosolic calcium in smooth muscle?
sarcoplasmic reticulum - less SR than in skeletal muscle and NO T tubules
How is calcium removed from the cytosol?
by pumping it back in to the SR and out of the cell by calcium ATPases