Week 13: (D) Coupling and Skeletal Muscle Contraction Flashcards
What 2 Transporters can take Calcium out of the cytosol?
Na/Ca2+ exchanger
Ca2+ ion pump
Where does the majority of Ca2+ in cytosol go and by what pump?
back to the SR
by a serca Ca2+ ATPases pump
What inhibits re-uptake of Ca2+?
High conc of Ca2+ in the SR lumen
What delays Ca2+ inhibition into SR?
binding to proteins in SR lumen
What protein binds to Ca2+ to delay inhibition?
Casequestrin: cardiac and some smooth muscle
Calreticulin: high conc in skeletal muscle
What happens when the cell is in full excitation (AP) of T-tubules/SR system?
causes Ca2+release, increase calcium= muscle contraction, Ca2+ in excess
What happens after excitation?
SERCA Ca2+ pumps depletes Ca2+ again
Does the contractile response lag behind the AP?
YES
because excitation contraction coupling must occur before cross bridge activity begins.
What is the delay in contractions called?
latent period
What is contraction time?
onset to peak contractile response
when does contractile response end?
ends when lateral sacs have taken up all Ca2+ released in response to AP
What are lateral sacs?
extended regions of the SR located on either side of the thin T-tubule
How quick is re-uptake?
time consuming
What is quicker the AP or the contractile response?
AP
what is a twitch summation?
Muscle doesn’t have time to fully relax and second twitch is added on to the first
What is tetanus?
Muscle fibres stimulated so rapidly it doesn’t have time to fully relax at all between stimuli
–>maximal sustained contraction
What fibres have high ATPase activity?
Fast fibres
What are the 3 types of fibre?
slow oxidative, fast glycolytic, fast oxidative
Where is an example of where slow oxidative would be found?
muscles on the back of the leg, provide support
Where is an example of where fast glycolytic would be found?
muscles of the arm, rapid forceful lifting movement
How to improve oxidative capacity in skeletal muscle?
regular aerobic endurance exercise promotes metabolic changes within oxidative fibres
increase in mitochondria and no. of capillaries. Fibres do not change in size
How to increase muscle hypertrophy?
Anaerobic, short-duration, high intensity resistance training leads to an increased diameter of fast glycolytic fibres (as a result of increased synthesis of actin and myosin).
What can increase actin and myosin
Influence of testosterone (promotes synthesis of actin and myosin).
Are slow and fast muscle fibres inconvertible?
Slow and fast fibres are not interconvertible.Whether a fibre is fast or slow twitch depends on the fibre’s nerve supply.
What type of neurones supply slow twitch fibres?
motor neurons that exhibit a low-frequency pattern of electrical activity.
What type of neurones supply fast twitch fibres?
innervated by motor neurons that display intermittent rapid bursts of electrical activity.
What can decrease muscle atrophy?
- Disuse atrophy… nerve supply intact-prolonged bed confinement
- Denervation atrophy… occurs after the nerve supply is lost.
