This document thoroughly explores the structure and function of various muscle types within the human body, focusing on their mechanisms of contraction and regulation. It details the differences and shared characteristics among skeletal, cardiac, and smooth muscles, emphasizing their unique structu...
Module
4:
Muscle
Introduction
and
Contraction:
Muscle
Types:
→
Three
main
muscle
types
in
the
body…
1.
Skeletal
Muscle
:
-
Striated
-
fibers/cells
are
large
in
diameter
and
also
length
-
Runs
the
entire
length
of
the
muscle
-
Multinucleated
cells
-
Controlled
by
the
somatic
nervous
system
2.
Cardiac
Muscle
:
-
Also
striated
-
Smaller
in
diameter
and
length
-
Specialized
junctions
between
the
cells
that
allow
the
cardiac
myocytes
to
contract
as
a
functional
unit
-
Controlled
by
the
autonomic
nervous
system
3.
Smooth
Muscle
:
-
Not
striated
-
Small,
single
nucleated
cells
-
Controlled
by
the
autonomic
nervous
system
-
Small
junctions
between
the
cells
for
cohesion
→
Shared
principles:
-
The
sliding
filament
mechanism
(myosin
filaments
bind
to
and
move
actin
filaments
to
shorten
the
muscle
cell)
-
Differences
in
organization
-
Myosin
and
actin
interactions
are
regulated
by
calcium
ions
-
Manner
will
be
different
between
the
three
muscle
types
-
Changes
in
the
membrane
potential
lead
to
contraction;
called
E-C
Coupling
(excitation
contraction
coupling)
Skeletal
Muscle:
-
Each
muscle
fiber
has
many
myofibrils,
which
number
determines
the
force
generating
capability
of
the
fiber.
-
Myofibrils
are
composed
of
many
sacomeres
that
are
in
series
(hundreds
of
thousands)
-
The
sarcomeres
are
what
contract Sarcomere
Structure:
-
Alternating
light
and
dark
portions
(responsible
for
striations)
-
Z
lines
:
ends
of
the
sarcomeres
-
Thin
filaments
:
actin
-
Thick
filaments
:
myosin
(motor
properties)
-
A
Band:
the
dark
area
which
includes
the
entire
length
of
the
myosin
thick
filaments
-
I
Band:
the
light
area
where
there
is
only
actin
Sliding
Filament
Model
of
Contraction:
1.
Attachment
:
Myosin
heads
om
the
thick
filaments
attach
to
specific
sites
of
the
actin
thin
filaments,
forming
cross-bridges
2.
Power
Stroke
:
The
myosin
heads
pivot,
pulling
the
actin
filaments
toward
the
center
of
the
sarcomere.
→
this
action
is
powered
by
ATP;
when
ATP
binds
to
myosin
it
is
hydrolyzed
into
ADP
and
phosphate,
releasing
energy
that
allows
to
myosin
head
to
perform
a
power
stroke.
3.
Detachment
:
Another
ATP
molecule
binds
to
the
myosin
head,
causing
it
to
detach
from
the
actin
filament
4.
Recovery
:
The
myosin
head
returns
to
its
OG
position,
ready
to
form
another
cross-bridge
with
actin
5.
This
cycle
of
attachment,
power
stroke,
detachment,
and
recovery
repeats
numerous
times
during
a
muscle
contraction.
Each
cycle
pulls
the
actin
filaments
slightly
further
over
the
myosin
filaments,
which
shortens
the
entire
length
of
the
sarcomere
and
thus
the
muscle
fiber.
→
Regulation
by
Calcium:
-
Tropomyosin
:
runs
in
parallel
along
the
actin
and
binds
actin
at
the
site
where
myosin
would
bind
-
Prevents
myosin
from
binding
to
actin
when
there
is
no
calcium
present
-
Troponin
:
the
binding
of
calcium
to
troponin
causes
a
change
in
its
conformation
which
causes
tropomyosin
to
move,
exposing
the
actin
to
myosin
heads
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