Chapter 6
Muscular Tissue
1.
General description
1) components:
---cell: muscle fiber-myofiber
elongated thread-liked
Sarcolemma
Sarcoplasm
sarcoplasmic reticulum: SER
---extracellular G.S: CT with BV, LV and N
2) classification
According to the structure and function
skeletal muscle: striated, voluntary
cardiac muscle: striated, involuntary
smooth muscle: unstriated, involuntary
2. Skeletal muscle
Muscle is an organ, consists of muscle
fiber and CT, fixed on bone by tendons
CT:
epimysium: DCT
Perimysium
Endomysium
muscle satellite cell: differentiate and
proliferate
function: supporting, connecting, nourishing
and regulating
1)
microstructure
of skeletal muscle fiber
① long cylindrical 10-100um
in diameter,1-40mm long
② multinucleate, nuclei are ovoid, distributed
under sarcolemma
③ filled with longitudinal parallel-arranged
myofibrils
myofibril:
1-2um in diameter
cross striation: light band -I(isotropic) band,
dark band- A(anisotropic) band
--A band: M-line, H-band
--I band: Z-line
* sacromere: a segment of myfibril
extending from one Z line to next Z line,
which is composed of 1/2 I band, A
band and 1/2 I band ,is the smallest
structural and functional unit of myofibril
2) Ultrastructure of myofiber
① myofibril: composed of
---thick myofilament:
1.5 um long, 15nm in
diameter
composed of myosin:
-rob: in bundles
-head:
cross
bridgebinding
site(ATPase activity)
---thin myofilament:
1um long, 5nm in diameter
composed of:
A.
actinspherical
monomers of globularactin arranged in two row
and twisted- filamentous
actin, each monomer has
binding site
B.tropomyosin:
filamentous protein of
two
polypeptide
chains
C. troponin: three subunits:
-Tn
T:
bind
to
tropomyosin
-Tn C: binds to
calcium ions
-Tn I: inhibite actinmyosin interaction
② Transverse tubule (T
tubule):
---definition:
sarcolemma
and basement membrane
invaginate
into
sarcoplasm to form a
transverse
distributed
tubular system
---location: A-I junctional part
---function:
transfer
the
information into cytoplasm
③
Sarcoplasmic reticulum:
---definition: A longitudinal distributed tubular
system formed by smooth endoplasmic
reticulum
---structure:
H-A band: longitudinal enclose myofibril-longitudinal tubule
A-I junction: enlarge to form flattened sac—
terminal cisternae
* triad: one T-tubule +two terminal cisternae
---function: there are calcium pump proteins
(ATPase) on membrane, so it can store and
release calcium ions
④
Mitochondria, glycogen, lipid
droplet
3) Sliding filament hypothesis
During
the
contraction, the A band
remained constant in
length, whilst the I band
and H band both
decreased in width,
which suggest that the
actin
filament
slide
along
the
myosin
toward the M –line.
a.
b.
c.
Myoneural junction transfer the impulse
from NF to sarcolemme.
The impulse spreads to interior part of cell
by T- tubule, then through the triad, impulse
is transferred to sarcoplasmic reticulum, the
calcium ions are released by sarcoplasmic
reticulum.
Calcium bind to Tn C, troponin and
tropomyosin change their position and
structure, the binding site on actin and
myosin is exposed
d. Binding site on actin and myosin combine,
ATP(adenosine triphosphate) are splitted
into ADP(adenosine diphosphate) by
ATPase on head of myosin, and energy are
release. The energy is provided to band the
head in the direction of M-line, and actin
filament are pulled toward to M line.
e. After contraction, calcium ions in
sarcoplasm are withdrawed into
sarcoplasmic reticulum. A new ATP
molecules bind to the myosin, the actinmyosin separated, troponin-tropomyosin
cover the binding site, the myofiber relax.
3.Cardiac muscle
1) Microstructure of
cardiac muscle
① short column in shaped, 100um long,15um
in diameter, with branches, the branches
associated with each other to form a network
② 1-2 ovoid nuclei, centrally-located
③ striated, but no very clear
④ intercalated disc: junctional part
LM: dark striation across the cardiac fibers
2)
Ultrastructure
of
cardiac muscle
similar to skeletal
muscle, composed of
thick, thin filament and
have sarcomere
①
myofibril have
different diameter, the
boundary of myofibril is
not very clear
② thansverse tubule are
thicker, located at Z-line
level
③ sarcoplasmic reticulum is
not well-developed, form
less terminal cisternae
* diad: one T-tubule + one
terminal cisternae
④ intercalated discs
step-liked structure
transverse portion:
-intermediate junction
-desmosome
-connection
longitudinal portion:
-gap junction
-communication
⑤rich in
mitochondria
glycogen
pigment
4. Smooth muscle
1)
microstructure of
smooth muscle
①
elongated, spindle-shaped cells, 8um
in diameter, 200( 20-500)um long
② rob-liked or ovoid nucleus
③ no striation, no myofibril
2) ultrastructure of
smooth muscle
① caveola: sarcolemme
invaginate into cytoplasm
②
/dense patch: under sarcolemma
/dense bodya: in sarcoplasm
③ intermediate filament:
/composed of desmin
/10nm in diameter
/connect between dense body
④ /thick filament: myosin, 15 nm
/thin filament: actin, 5 nm- fixed on
dense patch or body
percentage: thick/thin filament=1/12-30
contractile unit: several thick filament
and thin filament aggregate