Unit 4
The Muscular System
Muscle Cells
There are 3 types of muscle cells
– Cardiac, Smooth, and Skeletal
All muscles can contract
(shorten)
When muscles contract, part of
the body moves
Cardiac Muscles
Striated, tubular, and branched
Have one nucleus per cell
Contract involuntarily
Found in the walls of the heart
Smooth Muscles
Non-striated, arranged in sheets
Have one nucleus per cell
Contract involuntarily, and can
sustain prolonged contractions
Smooth Muscles
Found in the walls of internal
organs (cavities and tubes) such
as:
– Blood vessels, iris of the eye,
internal organs such as the stomach,
intestines, uterus, and esophagus for
peristalsis
Skeletal Muscles
Striated and tubular
Have many nuclei per cell
Attached to the bones of the
skeleton
Skeletal Muscles
Contract voluntarily, controlled
consciously by the nervous
system
Due to structure and having
many nuclei they are referred to
as fibres
Compare the muscle types!
Type
Cardiac
Smooth
Skeletal
Structure
Voluntary/
Location
Involuntary? in the Body
Type
Structure
Voluntary/
Involuntary
?
Location
in the Body
Cardiac
Tubular, arranged
in a branched
network, striated,
one nucleus per
cell
involuntary
Heart
Smooth
Long, tapered,
arranged in
sheets, nonstriated, one
nucleus per cell
involuntary
Walls of
digestive
system, blood
vessels, other
internal organs
Skeletal
Tubular, very long, voluntary
striated, many
Attached to
the bones of
nuclei per cell.
the skeleton,
Muscle Contraction
Muscles contract  they shorten!
Muscles can only pull they cannot
push
Muscles that permit movement are
found in pairs, as each muscle in the
relaxed state needs an opposite
muscle to stretch it.
Antagonistic muscles- pairs of
muscles that work against each other
to make a joint move
Muscle contraction –
bundle of fibres
Skeletal muscles consist of many
bundled muscle fibres held
together with connective tissue
Muscle fibre consists of:
– Myofilaments a thread of contractile
proteins found within muscle fibres
Muscle Contraction bundles of fibres
Two types of Myofilaments
– Thick filament – fine myofilament
composed of bundles of protein
called myosin. Each myosin
molecule consists of two
polypeptide chains wrapped around
each other. Binds to actin
Two types of Myofilaments
Thin filament – fine myofilament
composed of strands of protein
called actin. Consist of globular
actin proteins. Binds to myosin
Myofilament Contraction
Four steps:
1. The myosin head is attached
to actin
Myofilament Contraction
2. The myosin head flexes,
advancing the actin filament
Myofilament Contraction
3. The myosin head releases and
unflexes, powered by ATP.
Myofilament Contraction
4. The myosin reattaches to actin
farther along the fibre
Sliding Filament Model
Actin is anchored in the striated
muscle tissue called the Z-Line
Since it is ‘anchored’ like this,
when actin moves it drags the Zline with it, toward the myosin
This causes the entire muscle to
contract
Sliding Filament Model
The heads of the two ends of the
myosin filament are orientated in
opposite directions. When the heads
attach to the actin, they bend toward
the centre of the myosin.
Sliding Filament Model
As one end of the myosin
filament draws the actin filament
and its attached Z line toward
the centre, the other end of the
myosin filament does the same
Sliding Filament Model
Both Z lines move toward the
centre, and contraction occurs