Topic 11: Muscular System - Skeletal Muscle Fiber Structure

Question 1

What structure of cells are in skeletal muscle fibers?

Answer 1

large, multinucleated cells

Question 2

What are the 5 parts of a multinucleated cell?

Answer 2

1. sarcolemma
2. sarcoplasm
3. myofibrils
4. T-Tubules
5. Sarcoplasmic Reticulum

Question 3

What is sarcolemma?

Answer 3

cell membrane

Question 4

What is sarcoplasm?

Answer 4

• cytoplasm

Question 5

What are myofibrils? (2)

Answer 5

• intracellular structures
• composed of sarcomeres

Question 6

How many myofibrils are in each fibre?

Answer 6

• within each fibre are several hundreds to thousands

Question 7

What are the two types of myofilaments (proteins) in sarcomeres?

Answer 7

• thin filaments
• thick filaments

Question 8

What are the 3 components of thin filaments?

Answer 8

• actin
• tropomyosin
• troponin

Question 9

What is the function of actin?

Answer 9

• functions in contraction

Question 10

What is the function of troponin? (2)

Answer 10

• regulates contraction
• regulatory proteins

Question 11

Thick filaments are composed of ____, which functions in ___-

Answer 11

• myosin
• contration

Question 12

What are thick filaments attached to?

Answer 12

• attached to Z discs by protein titin

Question 13

What is the structure of thick filaments? (2)

Answer 13

• has rod-like tails with 2 globular heads
• head extends towards actin and attaches to it to form a crossbridge

Question 14

What do the myofilaments in sarcomeres form?

Answer 14

• dark and light bands called striations

Question 15

What is an A band? (2)

Answer 15

• dark = length of filament
• myosin + actin, with troponin + propomyosin

Question 16

What is the H zone? (2)

Answer 16

• lighter band at the center of A band
• myosin only (not overlapping w actin

Question 17

What is the I band? (2)

Answer 17

• light = actin (with troponin + tropomyosin) + titin
• note that it appears the lightest

Question 18

Where are Z discs located?

Answer 18

• in center of I band

Question 19

What protein filaments are in Z discs?

Answer 19

• actin and titin attach

Question 20

What is the function of Z discs?

Answer 20

• connect sarcomeres
• between 2 Z discs is one sarcomere

Question 21

What is the M line?

Answer 21

• where myosins tails (thick filaments) attaches to each other (center os sarcomere)

Question 22

Sarcomeres join end to end at Z discs to form ___

Answer 22

myofibrils

Question 23

Sarcomeres join end to end at Z discs to form ___

Answer 23

myofibrils

Question 24

What are T-tubules?

Answer 24

• continuations of sarcolemma that extend deep into fiber (cell)

Question 25

Where are T-tubules located?

Answer 25

• directly encircle myofilaments of myofibrils at junction of A and I bands (2/sarcomere)

Question 26

What is the sarcoplasmic reticulum? (2)

Answer 26

• smooth ER

Question 27

What is a triad?

Answer 27

• 2 enlarged areas of sarcoplasmic reticulum (terminal cisternae) and T-Tubules