Week 1
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What is a muscle?
 Muscles are organs made of muscular and connective
tissues, which make up the Muscular System
 They attach to bones and other muscles so that when
they contract, they produce motion
 There are three different types of muscle:
 Skeletal
 Cardiac
 Smooth
Muscle Tissue
 Muscle tissue:
Collection of muscle
cells which contain
sarcomeres
 Sarcomere: a single
contractile unit made of
primarily actin, myosin,
and titin
Sarcomere
Myosin
Actin
 M-line
 Only myosin
 Doesn’t move
 Z-disk
 Perimeter of sarcomere
 Moves toward M-line with contraction
 I-band
 Actin + titin
 Spans width of titin
 Shrinks with contraction
 A-band
 Actin + myosin
 Spans width of myosin
 H-zone
 Only myosin
 Gets smaller with contraction
Sarcomere Proteins
 Actin
 G-actin: Globular individual pearl-like actin molecules
 F-actin: G-actin pearls assemble into a Filament of actin
 Myosin
pulls actin inward
 Contains head and tail units

Myosin head binds to actin, pulls it inward to contract
 Titin
pushes z-discs outward
 Elastic, holds myosin in place and helps re-extend
sarcomere upon relaxation
Video- Sarcomere Contraction
Click video to watch
Arrangement of Fibers
 Many sarcomeres together
make up a myofibril
 Many myofibrils make up a
muscle fiber (cell)
 Coated by endomysium
 Many fibers make up a
fiber bundle
 Coated by perimysium
 Many bundles make up the
entire muscle
 Coated by epimysium
Types of Muscle
 Skeletal
 Cardiac
 Smooth
*Connected to
muscle for voluntary
motion
*Only in the heart for
moving blood
*Found in organs (GI,
vessels) for
constriction
-Voluntary
-Striated
-Multinucleate
-Parallel fibers
-Involuntary
-Striated
-Mononucleate
-Branched Fibers
-Intercalated Discs
-Involuntary
-Non-striated
-Mononucleate
-Parallel fibers
Types of Muscle
Next Week- A Preview