Transcript COMPARISON OF SKELETAL & SMOOTH MUSCLE …

SMOOTH MUSCLE
Dr. Ayisha Qureshi
MBBS, MPhil
Assistant Professor
CLASSIFICATION OF SMOOTH MUSCLES
1.
2.
3.
4.
UNITARY/ SINGLE
UNIT/SYNCYTIAL/VISCERAL
Muscles of visceral organs .e.g.
GIT, uterus, ureters & some of
the smaller blood vessels.
Form a sheet or bundles of
tissue.
Cell membranes show gap
junctions that allows AP to pass
rapidly from cell to cell.
AP spreads rapidly throughout
the sheet of cells – cells
contract as a single unit.
MULTI-UNIT
1.
2.
3.
4.
Iris & Ciliary body of the eye,
large arteries, Piloerector
muscles
Showing discrete, individual
smooth muscle fibers.
Smooth muscle cells not
electrically linked. Each muscle
fiber innervated by a single
nerve ending. NT itself can
spread and lead to an AP.
Selective activation of each
muscle fiber that can then
contract independently of each
other.
Latch mechanism
It is a state in which the dephosphrylated
myosin remains attached to actin for
prolonged period of time. This produces
sustained contraction without consuming ATP
& thus enables the smooth muscle to sustain
long-term maintenance of tone without
fatigue. E.g. urinary bladder full of urine.
COMPARISON OF SKELETAL &
SMOOTH MUSCLE CONTRACTION:
COMPARISON OF SKELETAL &
SMOOTH MUSCLE CONTRACTION:
S.NO
CHARACTERISTICS
SKELETAL MUSCLE
SMOOTH MUSCLE
1.
Location
Attached to the
skeleton
Blood vessels,
hollow organs, eye
2.
Mechanism of contraction
Sliding filament
Sliding filament
3.
Nerve supply
Motor neurons
Autonomic nervous
system
4.
Level of control
Under Voluntary
control
Under Involuntary
control
5.
Presence of Thick & Thin
filaments
Yes
Yes
6.
Presence of Tropomyosin
Yes
Yes
7.
Presence of Troponin
Yes
No
8.
Presence of T-tubules
Yes
No
9.
Level of development of
Sarcoplasmic Reticulum
Well Developed
Poorly Developed
S.no CHARACTERISTICS
SKELETAL MUSCLE
SMOOTH MUSCLE
10.
Source of Calcium
Sarcoplasmic Reticulum (SR)
ECF & SR
11.
Overlap of Actin & Myosin
Overlap of actin & myosin
seen only in part of the Aband
Continuous overlap of
actin & myosin, b/c of
side-polar cross
bridges
12.
ATP used directly by
contractile apparatus
Yes
Yes
13.
Myosin ATPase activity;
speed of contraction
Fast or slow depending on
type of fiber
Very slow
14.
Site of Calcium regulation
Troponin in thin filaments
Myosin in thick
filaments
15.
Mechanism of Calcium
action
Physically repositions
troponin-tropomyosin
complex to uncover actin
cross-bridge binding site
Chemically brings
about phosphorylation
of myosin cross
bridges so they can
bind with actin
S.no
CHARACTERISTICS
SKELETAL MUSCLE
SMOOTH MSUCLE
16.
Duration of contraction
100- 200 msec
Upto 5 sec
17.
Presence of Gap junctions
No
Yes
18.
Latch mechanism
No
Yes
19.
NMJ
Yes
No
20.
Neurotransmitter
Ach only
Ach &
Norepinephrine