muscles 1

Question 1

Cardiac muscle

Answer 1

• 200-300 micro metres long
  
  • Single nucleus
  • Striated
  • Involuntary
  • Responsible for contraction of the heart
  • Has intercalated disks

Question 2

intercalated disks

Answer 2

○ Cardiac muscle cells branch and are interconnected by intercalated disks
○ Connected by gap junctions - electrically connected

Question 3

Smooth muscle

Answer 3

• Involuntary
  
  • Lines internal structures eg. Digestive tract, veins/arteries, respiratory passage ways
  • Small elongated, thin spindle shaped cells
  • Single nucleus
  • Non-striated - smooth

Question 4

Muscle fibre

Answer 4

• Surrounded by endomysium
  
  • Contains myofibrils
  • The cell

Question 5

Myofibrils

Answer 5

• Surrounded by sarcoplasmic reticulum
  
  • Consists of sarcomeres
  • Thing inside the cell (100s of em)

Question 6

Sarcomere

Answer 6

• Contains
  ○ thick filaments
  ○ Thin filaments

Question 7

actin is attached to

Answer 7

Z disk

Question 8

actin is attached to Z disc by

Answer 8

a-actinin

Question 9

myosin thick filament is attached to

Answer 9

Z disk

Question 10

myosin thick filament is attach to Z disc by

Answer 10

titin

Question 11

how is tension created in the sarcomere

Answer 11

actin and myosin pull on each other

Question 12

Actin (thin) filaments

Answer 12

• Double helix of polymerised G-actin (F-actin)

- Tropomyosin and troponin complexes are embedded in the cleft of the twisted chains

Question 13

Tropomyosin

Answer 13

○ Tropomyosin is filamentous and spans the lengths of the filament

Question 14

Myosin (thick) filaments

Answer 14

• Thick filaments are comprised of many myosin molecules

○ 1.6 micro metres long x 12nm wide

Question 15

Sarcomeres change during contraction

Answer 15

• Shorted
  
  • I bands and H zone shorten
  • A bands do not change in length

Question 16

A bands

Answer 16

length of myosin thick filaments

Question 17

I bands

Answer 17

distance between mysosin thick filaments

Question 18

H bands

Answer 18

distance between actin think filaments

Question 19

4 steps of actin myosin cross bridge

Answer 19

1. Myosin binds actin
   - Myosin head attached reversibly to high affinity active sites on the actin thin filament
   
   2. Myosin ‘power stroke’ pulls actin filament, contracting sarcomere
      
      • ADP released, freeing ATP-binding site
   3. ATP binding releases myosin from actin
      
      • Conformational change
   4. ATP hydrolysis drives re-cocking of myosin to high energy state, but is not required for power stroke

Question 20

Sliding filament model

Answer 20

• The lever movement pulls on the actin filament relative to the myosin head (~5nm) producing force
  
  • Thick and thin filaments interdigitate and slide relative to each other

Question 21

tension is proportional to

Answer 21

○ Proportional to the number of actin-myosin crossbridges

○ Ie. Amount of overlap

Question 22

• Length-tension curve

Answer 22

○ The tension generated by a sarcomere can be predicted from sarcomere length ie. Overlap

Question 23

In relaxed muscle

Answer 23

§ Tropomyosin ™ blocks the myosin binding site on actin filaments preventing crossbridge formation
§ Tropomyosin is regulated by the tropomyosin complex

Question 24

troponin complex

Answer 24

Tn-T, Tn-I, Tn-C

Question 25

Tn-T binds to

Answer 25

tropomyosin

Question 26

Tn-I binds to

Answer 26

Tn-C and actin

Question 27

Tn-C binds to

Answer 27

Ca ions

Question 28

how does troponin work

Answer 28

○ When Tn binds Ca its conformation changes pulling tropomyosin out of the myosin binding site so myosin thick filament can bind

Question 29

How is Ca regulated

Answer 29

- Action potential -> opens dihydropyridine receptor (DHPR) -> opens ryanodine receptor (RyR) -> releases Ca2+ from the sarcoplasmic reticulum

Question 30

sarcoplasmic reticulum

Answer 30

endoplasmic reticulum and muscle | surrounds each myofibril

Question 31

SERCA

Answer 31

calcium ATPases / calcium pumps on the sarcoplasmic reticulum sequesters calcium to cause relaxation

Question 32

dihydropyridine receptor

Answer 32

on the outside of the cell | voltage gated

Question 33

ryanodine receptor

Answer 33

mechanically gated calcium channel gated by dihydropyridine receptor on the sarcoplasmic reticulum inside the cell

Question 34

DHPR does

Answer 34

voltage gated | mechanically pushes the RyR receptor

Question 35

T tubule

Answer 35

part of the plasma membrane that brings the action potential closer to the interior of the muscle fibre

Question 36

numero muscular junction

Answer 36

where the nerve talks to muscle motor end plate cholinergic synapse

Question 37

motor neurone secretes

Answer 37

acetyl choline

Question 38

Nicotinic Ach receptor

Answer 38

§ Ionotropic - ligand-gated Na+ channel § Always excitatory lets sodium into the cell to cause an action potential which travels down the T tubule

Question 39

How does contraction stop

Answer 39

- Motorneuron AP stops - Ach degraded at the synapse by AChE - Muscle AP stops - DHPR - RyR close - Ca -ATPase pumps remove cytoplasmic Ca so calcium sequestered back into the sarcoplasmic reticulum - Troponin-tropomyosin complex blocks cross bridges, causing relaxation (if ATP is present)

Question 40

excitation/contraction event called

Answer 40

- This whole event is called a twitch

Question 41

latent period

Answer 41

time between action potential and coupling

Question 42

excitation contraction coupling

Answer 42

Because a twitch is slow, theres time for >1 AP | Wave summation progressively increases [Ca2+] which increases tension

Question 43

maximum tension

Answer 43

- Maximum tension (tetanus) Is reached when all actin + myosin are forming crossbridges