Muscle

Question 1

Sarcoplasmic reticulum features

Answer 1

Networks around myofibrils, from one AI junction to the next. They meet at terminal cisterna. Reservoirs for ca2+.
PM invaginates transversely, forming T tubules. They separate cisternae. Pm has special voltage sensor proteins that activate when membrane depolarises, inducing sarcoplasmic reticulum to release ca2+.

Question 2

2 proteins associated with sarcomere. Functions

Answer 2

Nebulin extends from Z band, along one actin filament. Regulates actin length
Titin extends from z disc to m line. Maintains position of myosin generates tension via elastic extension during relaxation when sarcomere is stretched

Question 3

Mechanism of contraction

Answer 3

Ach release from motor end plate-> binds to na+ channels on pm & t tubule -> enters cell-> sarcoplasmic reticulum induced to release ca2+-> ca2+ binds to troponin-> tropomyosin pulled aside, actin binding sites exposed-> cross bridge formed-> atp binds to myosin -> myosin releases actin (relaxation) -> atp causes myosin head to bend 5nm, initiating atp breakdown -> myosin binds to new site, pi released -> increased binding affinity + power generation + adp lost-> reattachment to actin

Question 4

Muscle relaxation mechanism

Answer 4

Ca2+ ATPase pumps ca2+ back to sarcoplasmic reticulum-> ca release from troponin-> tropomyosin recovers binding sites

Question 5

Slow twitch muscle fibres

Answer 5

Function: postural 
Speed of development of maximum tension: slow
Myosin atp activity: slow
Fibre diameter: small 
Metabolism: aerobic
Capillary density: high
Mitochondria: high 
Endurance: fatigue resistant

Question 6

Type 2a muscle fibres

Answer 6

Function: phasic- walking 
Speed of development of maximum tension: intermediate 
Myosin atp activity: fast
Fibre diameter: medium 
Metabolism: glycolytic, aerobic possible
Capillary density: medium 
Mitochondria: moderate 
Endurance: fatigue resistant

Question 7

Type 2b muscle fibres

Answer 7

Function: phasic- jumping/running
Speed of development of maximum tension: fast
Myosin atp activity: fast 
Fibre diameter: large 
Metabolism: glycolytic / anaerobic 
Capillary density: Low
Mitochondria: few
Endurance: fatigues easily