1.12 Muscle Contraction

Question 1

How do action potentials pass along the muscle membrane?

Answer 1

Action potentials pass along the muscle membrane, in special invaginations of the sarcolemma called T tubules, which go deep into the muscle. They reach the sarcoplasmic reticulum and release Ca ions.

Question 2

Explain the calcium release in the sarcolemma…

Answer 2

Depolarisation along t-tubules activates the voltage sensitive calcium channels.
Mechanical coupling with SR causes SR calcium channels to open.
Calcium leaves SR and Ca also enters cell through calcium membrane channels.

Question 3

What are the types of calcium channels?

Answer 3

2 types of calcium channels;
• Calcium channel on t-tubule
○ L type channel
○ Also known as DHP receptor (dihydropyradines)
• Sarcoplasmic reticulum calcium channel
○ Ryanodine receptor - Inhibited by alkaloids ryanodine and caffeine

Question 4

What is this electrochemical coupling called?

Answer 4

There is an electromechanical coupling between the two - Calcium Induced Calcium Release.

Question 5

What is actin made up of?

Answer 5

Two actin strands fold into a double helix. Can be globilar or filamental

Question 6

What shape is tropomyosin?

Answer 6

Also helical

Question 7

What are the three types of troponin?

Answer 7

Troponin T - tropomyosin
Troponin I - actin
Troponin C - calcium

Question 8

What is myosin made up of?

Answer 8

Heavy chain - rod, hinge and hear

2 light chains - alkaline stabilising head - regulatory regulates ATPase

Question 9

Describe the structure of the sarcomere

Answer 9

Z line 
H zone - just myosin - thick 
I band - just actin - thin 
A band - one sarcomere - z to z
M line - middle

Question 10

What are stages of muscle contraction?

Answer 10

1. Release Calcium Sarcoplasmic reticulum
2. Calcium binds to troponin C
3. Confrontational change in troponin complex
4. Troponin I released from actin, troponin T moves from the myosin binding site
5. Myosin head free to interact the actin

Question 11

Explain the stages of cross bridge cycling…

Answer 11

1. ATP binds to myosin head and releases it
2. Myosin dissociates from actin
3. ATP hydrolysed and releases energy - myosin moves to a cocked state
4. Myosin then binds to a new place on the actin
5. Phosphate released - myosin performs power stroke and filaments slide
6. ADP released