Karius: Physio of Smooth Muscle Flashcards
When skeletal muscle is stretched, what happens to it’s ability to generate tension (force) ?
decreases
When skeletal muscle is stretched, what happens to it’s ability to generate tension (force) ?
WHY?
the cross bridges don’t have enough overlap
Considering skeletal muscle loses the ability to generate force the longer the muscles get, what would happen if the GI track were made of skeletal muscle?
the more it distended because of food, the less it would have the ability to recoil (retract)
muscles of the GUT, vasculature, and respiratory tract must be able to do 5 things
a. contract and maintain contraction for long periods of time, so they have to be energy efficient
b. contract periodically to mix contents of organ
c. maintain shape of organ
d. continue to generate active tension even when stretched
e. use relatively little ATP
in what locations do we find smooth muscle?
vasculature
GI
respiratory tract
urogenital tract
Skeletal muscles are innervated by
alpha motor neurons
smooth muscles are innervated by
intrinsic innervation
(GUT and TRACHEA)
neurons (Sensory and motor)
independent of CNS & PNS
extrinsic innervation
Autonomic nervous system allows CNS to control viscera
NT of Skeletal M.
acetylcholine
norepinephrine or epinephrine
causes contraction of vascular smooth muscle
inhibits gut smooth muscle
nitric oxide (NO)
major inhibitory influence on smooth muscle
acts via cGMP mechanism
from the slides
“one major difference between skeletal and smooth muscle is that smooth muscle can be…”
directly inhibited (caused to relax)
Varicosities
swellings in the axon where NT is released
muscarinic receptors are both
cholinergic and adrenergic (alpha and beta)
NO uses what kind of receptor?
it doesnt, it’s believed to diffuse across the membrane and act on the cGMP system
Skeletal muscle vs smooth m.
innervation
SK : alpha motorneurons
SM: multiple sources, intrinsic, AND, and sensory
Skeletal muscle vs smooth m.
NT
SK: acetylcholine
SM: ACh, Epinephrine/Norepinephrine, NO, others
Skeletal muscle vs smooth m.
excitatory or inhibitory
SK: ACh is exclusively +
SM: May be + or -
Skeletal muscle vs smooth m.
Specialized NMJ
SK: specialized NMJ
SM: varicosities, no motor end plate
Skeletal muscle vs smooth m.
ACh receptor is located at the…
SK: motor end plate
SM: Multiple receptor types located over cell membrane
Skeletal muscle vs smooth m.
activation
SK: only activated at NMJ
SM: may be activated by blood-borne substances
Control of Smooth muscle contraction
hormonal control, blood borne pathogens
Control of Smooth muscle contraction
Paracrine signaling in SM
endothelia secrete endothelium derived relaxing factor (NO), causing smooth muscle to contract
Control of Smooth muscle contraction
“other forms of activation”
STRETCHING!
SOME smooth muscle cells can be activated by stretch including some vasculature
The Latch Mechanism
4 steps
- dephosphorylation of light chain
- cycle proceding very slowly
- any attached crossbridges are still generating tension
- way of increasing tension and decreasing ATP usage
Tension/STRETCH curves for skeletal muscle
as active tension increases, passive tension increases due to the elasticity of the muscle membranes
as active tension decreases, passive tension increases
due to the elasticity of the muscle membranes
Tension/STETCH curve for smooth muscle
as the muscles stretch there is a momentary increase in passive tension due to the elasticity, followed quickly by dissipation because of the rearrangement of the actin-myosin fibers
as smooth muscle is stretched, the myosin heads, once free from the actin, will interact with a different thin filament
what is attached to the membrane in smooth muscle, thin or thick filaments?
thin
what is the purpose of thin and thick filaments randomly associating/dissociating?
it decreases passive tension build up by reducing tension build up on points of the membrane
allows the smooth muscle cell to continue to generate active tension over a wide range of length: there is always actin available for myosin heads to bind to
which maintains a longer muscle length: skeletal or smooth?
smooth (slide #40 of lecture)
