Skeletal Muscle Fibers

Characteristics of Skeletal Muscle Fibers

long & cylindrical

huge cells

length - several cm to dozens of cm

Multinucleated cells (Muscle needs ATP)

Myofibrils

long rods within a cytoplasm known as the sarcoplasm

What percent does the myofibrils made up the cytoplasm?

80%

What do the Myofibrils contains?

specialized, contractile proteins (actin & myosin)

Sarcomeres

are a long row of repeating segments & basic unit of contraction of skeletal muscle

Z-discs (Z line)

boundaries of each sarcomere

Thin (actin) filaments 

extend from z disc toward the center of the sarcomere 

Thick (myosin) filaments 

located in the center of the sarcomere & overlap inner ends of the thin filaments 

A-bands

full length of thick filaments & inner ends of thin filaments

H-zone

center part of A band where no thin filaments occur and it is thick filament only 

M-line

in center of H zone & contains tiny rods that hold thick filaments together

I-band 

region with only thin filaments & is part of two adjacent sacromeres 

Titin 

a spring-like molecule that resists overstretching 

Where does Titin molecules extend from? 

the Z-disc, to thick filaments, to the M-line 

What are the two-functions of Titin Molecules? 

hold thick filaments in place & unfolds when muscle is stretched

Sarcoplasmic Reticulum (SR)

a network of interconnecting tubules surround each myofibril

Sarcoplasmic Reticulum is best described as

a specialized smooth endoplasmic reticulum (ER)

What is the terminal ends called of Sarcoplasmic Reticulum (SR)

Terminal cisterns

Terminal cisterns

communicate with the sarcolemma through T-Tubules

T-Tubules

extensions & deep invaginations (fold the outer layer/formed a pocket) of the sarcolemma 

Triad 

T-tubule flanked by two terminal cisterns 

What happens if the electrical activity/movements of Ions that occur in the Sarcolemma?  

The activity/movement will travel to the T-tubules, then send information to the terminal cisterns, which then trigger the SR

What does Sarcoplasmic Reticulum contains?

calcium ions (released when muscle is stimulated to contract)

What role does the sarcoplasmic reticulum (SR) play in triggering the sliding filament mechanism?

Triggering the sliding filament mechanism by releasing calcium ions