Topic 11: Muscular System - Skeletal Muscle Fiber Structure Flashcards
What structure of cells are in skeletal muscle fibers?
large, multinucleated cells
What are the 5 parts of a multinucleated cell?
- sarcolemma
- sarcoplasm
- myofibrils
- T-Tubules
- Sarcoplasmic Reticulum
What is sarcolemma?
cell membrane
What is sarcoplasm?
- cytoplasm
What are myofibrils? (2)
- intracellular structures
- composed of sarcomeres
How many myofibrils are in each fibre?
- within each fibre are several hundreds to thousands
What are the two types of myofilaments (proteins) in sarcomeres?
- thin filaments
- thick filaments
What are the 3 components of thin filaments?
- actin
- tropomyosin
- troponin
What is the function of actin?
- functions in contraction
What is the function of troponin? (2)
- regulates contraction
- regulatory proteins
Thick filaments are composed of ____, which functions in ___-
- myosin
- contration
What are thick filaments attached to?
- attached to Z discs by protein titin
What is the structure of thick filaments? (2)
- has rod-like tails with 2 globular heads
- head extends towards actin and attaches to it to form a crossbridge
What do the myofilaments in sarcomeres form?
- dark and light bands called striations
What is an A band? (2)
- dark = length of filament
- myosin + actin, with troponin + propomyosin
What is the H zone? (2)
- lighter band at the center of A band
- myosin only (not overlapping w actin
What is the I band? (2)
- light = actin (with troponin + tropomyosin) + titin
- note that it appears the lightest
Where are Z discs located?
- in center of I band
What protein filaments are in Z discs?
- actin and titin attach
What is the function of Z discs?
- connect sarcomeres
- between 2 Z discs is one sarcomere
What is the M line?
- where myosins tails (thick filaments) attaches to each other (center os sarcomere)
Sarcomeres join end to end at Z discs to form ___
myofibrils
Sarcomeres join end to end at Z discs to form ___
myofibrils
What are T-tubules?
- continuations of sarcolemma that extend deep into fiber (cell)
Where are T-tubules located?
- directly encircle myofilaments of myofibrils at junction of A and I bands (2/sarcomere)
What is the sarcoplasmic reticulum? (2)
- smooth ER
What is a triad?
- 2 enlarged areas of sarcoplasmic reticulum (terminal cisternae) and T-Tubules
