TH I N
Topic 4.1MOVEMENT ANALYSIS (4.1) NEUROMUSCULAR FUNCTION
T H ICK
Sliding Filament Theory
A ll
1. Draw and label or review diagram showing bands when (1) muscles are at rest and (2) muscles
are contracting
 Sarcomere, A band, H Zone, M Line, Z line [indicates the boundaries between
sarcomere] and note whether or not they change in length during contraction
2. Explain how skeletal muscle contracts by the sliding filament theory – you must produce very
detailed notes: Look at ‘Teach PE’ on the internet

You must include the terms myofibril, myofilament, sarcomere, actin and myosin, H
zone, A band, Z line, tropomyosin (protein), troponin protein which attaches to
tropomyosin), sarcomere, calcium ions and ATP.
Look at the internet as there are many great animations
Tip: Questions on the Sliding Filament Theory all relate to the bands and in particular, which
do or do not contract – so learn them 
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Topic 4.1MOVEMENT ANALYSIS (4.1) NEUROMUSCULAR FUNCTION
Revise terms for test
When muscle contracts the H-zone and Iband both decrease (shorten) as the z-lines
shorten and are pulled towards each other
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Topic 4.1MOVEMENT ANALYSIS (4.1) NEUROMUSCULAR FUNCTION
Sliding Filament Theory

Myofibril: A cylindrical organelle running the length of the muscle fibre, containing Actin and
Myosin filaments.

Sarcomere: The functional unit of the Myofibril, divided into I, A and H bands.

Actin: A thin, contractile protein filament, containing 'active' or 'binding' sites. It slides past
myosin casing contractions.

Myosin: A thick, contractile protein filament, with protusions known as Myosin Heads. Pulls
action filaments towards one another by means of cross bridges

Tropomyosin: An actin-binding protein which regulates muscle contraction.

Troponin: A complex of three proteins, attached to Tropomyosin.

Z Line: separates each sarcomere. It provides an anchor for proteins and also anchors the actin
filaments to the ends of the sarcomere

M Line: is the centre of the A band and it is where adjacent myosin filaments anchor to each
other [IB Exam Q: M Line not involved in muscle contraction as is described by the sliding
filament theory]

H Zone: is the centre of the sarcomere and has only myosin filaments

A Bands are also known as dark bands and has both actin and myosin microfilaments - stays the
same length during contraction [IB exam Q]

I Bands are also known as light bands and has only actin mircrofilaments
When muscle contracts the
H-zone and I-band both
decrease (shorten) as the zlines shorten and are pulled
towards each other
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Topic 4.1MOVEMENT ANALYSIS (4.1) NEUROMUSCULAR FUNCTION
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