Cardiac contraction

Question 1

What is function of cardiac myocyte?

Answer 1

1) Pumping action depend contractile proteins
2) ATP derived energy required for mechanical work move blood
under pressure
3) Activation contractile protein by excitation-contraction coupling
- action potential arrives, leads to influx Ca++ into cytosol
- binds receptor contractile apparatus- leads to passive
movement of Ca++
- Ca++ out of cell leads to heart relaxing

Question 2

What is the sarcomere defined by?

Answer 2

Z line on either side

Question 3

What is structure of myocardial cell?

Answer 3

Cross-striated myofibrils
Plasma membrane- regulate excitation-contraction

Question 4

What is the thick filament composed of?

Answer 4

Myosin

Question 5

What is the thin filament made of?

Answer 5

Actin- acts along with tropomyosin and troponin

Question 6

What is H zone?

Answer 6

Region sarcomere only has thick filament

Question 7

What is I band composed of?

Answer 7

Thin filament- binds Z disc

Question 8

What is A band composed of?

Answer 8

Large portion sarcomere
Overlap between thick and thin filament

Question 9

What is M line composed of?

Answer 9

Proteins connect central points thick filament

Question 10

Function of C-Zone?

Answer 10

Crosslinks thick filament and titin

Question 11

Funtion of Z disc?

Answer 11

Anchoring point thin actin filaments

Question 12

Function titin?

Answer 12

Responsible for elasticity of muscle
Allow muscles recoil to normal form
Prevents muscle fibres being overstretched

Question 13

What is responsible for elasticity/recoil of muscle?

Answer 13

Titin

Question 14

What is structure myosin?

Answer 14

Thick filament
2 large heavy chains, 4 smaller chains
2 globular heads on myosin end- join with actin
Globular head at 40 degrees- maximise chance connecting wit hactin
ATPase in head of myosin

Question 15

What structure is actin?

Answer 15

Thin filament
Globular protein, double stranded
Polymerise other monomers form helical structure
Has myosin binding site- partially covered by tropomyosin, held place by troponin (clamp)

Question 16

What is function of tropomyosin?

Answer 16

Binds along actin filaments
Regulates actin-myosin interaction in

Question 17

What are 3 sub-units of troponin?

Answer 17

TnI
TnT
TnC

Question 18

Explain TnI function?

Answer 18

Inhibitory
Inhibit actin and myosin interaction

Question 19

Explain TnT function?

Answer 19

Tropomyosin binding
Troponin bins to tropomyosin

Question 20

Explain TnC function?

Answer 20

Calcium binding
High affinity calcium binding sites
Signal contraction
Drives TnI from myosin binding site
Allow interaction between actin and myosin

Question 21

Why is TnC linked to TnI?

Answer 21

When calcium binds to TnC- TnI moved from groove allowing the myosin heads to interact

Question 22

How is the groove blocked via TnI?

Answer 22

ATP hydrolysis breaks TnC-Calcium bondy
Allows groove blocked by TnI

Question 23

Label?

Answer 23

Question 24

Define sarcolemma?

Answer 24

Plasma membrane of muscle

Question 25

What are transverse tubules?

Answer 25

Extensions cell membrane that penetrates into centre skeletal/ cardiac muscle cells

Question 26

Explain contraction?

Answer 26

ATPase on membrane
Hydrolysis ATP into ADP+P
Allows protein conformation
Allows Ca2+ inside
Once activated release stored Ca2+
Ca2+ binds troponin- induce actin-myosin complex- contractile proteins

Question 27

Where does hydrolysis of ATP into ADP+P occurs?

Answer 27

Sarcoplasmic reticulum

Question 28

Outline how contraction occurs?

Answer 28

1) Action potential arrives along sarcolemma
2) AP pass down t tubule, depolarises membrane
3) Leads release Ca++ from sarcoplasmic reticulum into cytosol
4) Ca++ binds to TnC
5) Pulls TnI away from groove along with tropomyosin
6) Allows globular head of myosin interact with groove of thin-actin
filament. Crossbridge formation.
7) ATP required for contraction and ATP hydrolysis
8) ATPase on myosin breaks apart Ca++-TnC bond
9) Groove of actin is blocked by tropomyosin and TnI
10) Power stroke action by myosin leads to sliding action of actin along
myosin
11) Shortens sarcomere- causes contraction
Crossbridge formation and release of Ca++ from TnC requires ATP hydrolysis.
ATPase on myosin breaks apart Ca++-TnC bond
Groove of actin is blocked by tropomyosin and TnI

Question 29

Outline how contraction occurs?

Answer 29

Depolarisation and Calcium Ion Release
1) Acetylcholine initiates depolarisation within sarcolemma
2) Spread through muscle fibre via T tubules
3) Depolarisation causes sarcoplasmic reticulum release stores of Ca2+(ryanodine)

Actin and Myosin Cross-Bridge Formation
1) Actin binding sites for myosin covered by troponin/tropomyosin
2) Calcium ions bind to troponin, reconfigure complex, expose binding
sites for myosin heads
3) Myosin heads form cross-bridge with actin filaments

Sliding Mechanism of Actin and Myosin
1) ATP binds to myosin head- breaks cross-bridge between actin and
myosin
2) ATP hydrolysis causes myosin heads to swivel- move closer to next actin
binding site
3) Myosin heads bind to new actin sites, return to original conformation
4) Reorientation drags actin along myosin in sliding mechanism
5) Myosin moves actin filaments- power stroke

Sarcomere Shortening
1) Repeated reorientation of myosin heads drags actin filaments along
length of myosin
2) Actin filaments anchored to Z lines
3) Dragging of actin pulls Z lines closer, shortening sarcomere
4) Individual sarcomeres become shorter, the muscle fibres contract

Question 30

Muscle contraction animation
https://ib.bioninja.com.au/higher-level/topic-11-animal-physiology/112-movement/muscle-contraction.html

Answer 30

https://ib.bioninja.com.au/higher-level/topic-11-animal-physiology/112-movement/muscle-contraction.html

Question 31

Where does muscle contraction occur?

Answer 31

Sarcolemma

Question 32

What ion is pivotal in muscle contraction?

Answer 32

Ca2+
Binds to TnC, pulls the TnI away from the groove along with the tropomyosin

Question 33

What does crossbridge formation require?

Answer 33

ATP hydrolysis