Dr Ayisha Qureshi MBBS MPhil Assistant Professor CLASSIFICATION OF SMOOTH MUSCLES UNITARY SINGLE UNITSYNCYTIALVISCERAL Muscles of visceral organs eg GIT uterus ureters amp some of the smaller blood vessels ID: 405459
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Slide1
SMOOTH MUSCLE
Dr.
Ayisha
Qureshi
MBBS, MPhil
Assistant ProfessorSlide2
CLASSIFICATION OF SMOOTH MUSCLES
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
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.Slide3Slide4
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.Slide5
COMPARISON OF SKELETAL & SMOOTH MUSCLE CONTRACTION:Slide6
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
DevelopedSlide7
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 A-band
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 Slide8
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