Transcript Thin Filaments - Mount Carmel Academy

Microscopic Anatomy of Skeletal Muscle
MUSCLES – PART 2
Anatomy of Skeletal Muscle
 Sarcolemma – The plasma membrane in
muscle cells
Anatomy of Skeletal Muscle
 Myofibrils – Long ribbon-like contractile organelles
found in the cytoplasm of muscle cells
 Composed of bundles of myofilaments
 Contain light (I) and dark (A) bands along the length
of the perfectly aligned myofibrils.
 Gives the muscle cell as a whole its striped or
striated appearance.
Light I and Dark A Bands
Contain the Following:
 The Light I Band
has a midline
interruption, a
darker area called
the Z discs.
 The Dark A Band
has a lighter
central area called
the H zone.
Sarcomeres
 Sarcomeres – Tiny contractile units
 Myofibrils are actually chains of sarcomeres.
 Sarcomeres are aligned end-to-end like
boxcars in a train.
Myofilaments
 Myofilaments –
Filaments (threadlike
protein) composing
the myofibrils.
 2 Types:
1. Thick Filaments
(Myosin Filaments)
2. Thin Filaments
(Actin Filaments)
Thick Filaments
 Thick Filaments
(Myosin Filaments) –
Made mostly of
bundled molecules of
the protein myosin


Also contain ATPase
enzymes, which split
ATP to generate the
power for muscle
contraction.
Extends the entire
length of the Dark A
Band
Cross Bridges
on Myosin
Filaments
 Notice that the midparts of myosin filaments are
smooth, but their ends are studded with small
projections, or cross bridges.
 Cross Bridges (myosin heads) – Projections found of
myosin filaments that link the thick and thin
filaments together during contraction.
Thin Filaments
 Thin Filaments (Actin
Filaments) - Composed
of the contractile
protein called actin
 Also contains some
regulatory proteins that
play a role in allowing or
preventing myosin heads
from binding to actin.
 Are anchored to the Z disc
 When contraction occurs, the actin-containing
filaments slide toward each other.
Thin Filaments
 The light I bands
only contains thin
filaments.
 The thin
filaments overlap
the ends of the
thick filaments
but do not extend
into the H Zone
(bare zone).
Sarcoplasmic Reticulum
 Sarcoplasmic Reticulum – A specialized smooth
endoplasmic reticulum.
 The interconnecting tubules and sacs of the SR
surround each and every myofibril.
 Similar to a sleeve surrounding your arm
 Major Role: Store calcium and to release it “on
demand” when the
muscle fiber is
stimulated to contract.
What Happens During
Contraction