Structure of Muscle part 2

Question 1

What is the sarcoplasm?

Answer 1

Muscle cell cytoplasm

Question 2

What is the sarcolemma?

Answer 2

Muscle cell membrane

Question 3

What are the characteristics of the sarcolemma?

Answer 3

• excitable
• motor end plate
• T-tubule (transverse tubules)

Question 4

What are the motor end plates of the sarcolemma?

Answer 4

Contact surface with axon terminal

Question 5

What are T-tubules?

Answer 5

Extension of sarcolemma into the sarcoplasm
- ‘holes’ into the cytoplasm

Question 6

What does the structure of the T-tubules allow?

Answer 6

Allows the depolarising signal (for contraction) to conduct deep into the muscle fibre.

Question 7

What is the sarcoplasmic reticulum?

Answer 7

Specialised form of the endoplasmic reticulum that surrounds the myofibrils

Question 8

What are cisternae?

Answer 8

Areas of the endoplasmic reticulum dedicated to Ca2+ storage

Question 9

What is a triad?

Answer 9

Structure within the skeletal muscle consisting of the T-tubule and cisternae

Question 10

What is a myofibril?

Answer 10

Bundle of myofilaments surrounded by cisternae
(slide 4)

Question 11

How far does a myofibril extend?

Answer 11

Same as mucle fibre, one end of muscle to the other

Question 12

What is a sarcomere?

Answer 12

Repetitive, contractile units of the muscle fiber in the myofibril

Question 13

What is a Z line in a sarcomere?

Answer 13

Zigzag line that marks end of each sarcomere

Question 14

What is a M line in a sarcomere?

Answer 14

Middle of sarcomere

Question 15

What surrounds both sides of the M line?

Answer 15

• thick and thin filaments
• thin filaments (and titin)
  (slide 5)

Question 16

What is the zone of overlap in a sarcomere?

Answer 16

Overlap of thick and thin filaments

Question 17

What is the H band?

Answer 17

Has thick filaments either side of the M line, bisecting A band

Question 18

What is the A band?

Answer 18

Area containing thick and thin filaments on both sides of the M line

Question 19

What is the I band?

Answer 19

Area containing thin filaments (and titin) bisected by the Z line

Question 20

What do thick filaments within the sarcomere consist of?

Answer 20

Many myosin molecules per filament
- golf club shape
- long tail topped by a head
- head forms cross-bridges with the thin filament

Question 21

What are the 2 conformations of myosin?

Answer 21

• low energy conformation (flexed/bent)
• high energy conformation (entended)

Question 22

How does the myosin go from low to high energy conformation?

Answer 22

ATP attaches to the head of myosin

Question 23

What do thin filaments within the sarcomere consist of?

Answer 23

3 different proteins:
- actin - G actin ball containing myosin-binding site
- tropomyosin - string covering myosin-binding site
- troponin - complex attached to actin

Question 24

What is the actin protein in a thin filament?

Answer 24

Binds to myosin heads

Question 25

What is the tropomyosin protein in a thin filament?

Answer 25

Long, fibrous molecule (string)
- blocks interaction between actin and myosin when relaxed, by lying directly on the myosin-binding site

Question 26

What is the troponin protein in a thin filament?

Answer 26

• binds reversibly to Ca
• moves tropomyosin away from the actin active site