Biology Support & Movement MDCAT 2015
PMDC Verified Question 74 of 75
According to sliding filament theory, when muscle fibers are stimulated by nervous system, which of the following changes occurs?
A
I-bands shorten
B
Z-lines move further apart
C
H-zone becomes more visible
D
A-bands shorten
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: I-bands shorten
Concept:

Changes in sarcomere banding during contraction.

Formula:

N/A (Conceptual)

Solution:

  • According to the sliding filament theory, myofilaments themselves do not change length; rather, the thin filaments slide deeply into the A-band.


  • As the Z-lines are pulled closer together, the region containing only thin filaments (the I-band) noticeably shortens.


Why other options are incorrect:

Z-lines move closer together, not further apart. The H-zone (center gap) narrows and disappears, rather than becoming more visible. The A-band remains completely unchanged in length because the thick filaments do not shrink.

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