exam 1 lecture 8 Smooth muscle Flashcards
Primary pathologies of smooth muscle in veterinary medicine are very ___ and have yet to be identified
rare
many diseases result in changes in smooth muscle activation or ___, resulting in pathology AND
relaxation
smooth muscle can be innervated by ___
Additionally, neurotransmitters and endocrine and paracrine factors can both stimulate and inhibit contraction
smooth muscle contracts quickly or slowly?
slowly
anatomy and chemistry of smooth muscle has eliminated speed as a characteristic of excitation-contraction coupling
what type of muscle has an all or nothing response
skeletal
where to find smooth muscle
Lines hollow organs
GI tract
Urinary Bladder
Endothelium
Uterus
Vas Deferens
Bronchioles ………
smooth muscle is normally is sheet shapes, where is it in bundles?
eye
smooth muscle is always covered by ___
protective cell layer- epithelium
muscle cell shape
spindled
single cell
single nucleus
shorter and smaller than skeletal muscle
why irregular pattern in smooth muscle?
generate force over huge changes in length
example: urinary bladder- works if a drop or is a liter of urine is present
___ muscle undergoes extensive tissue damage if stretched and also doesn’t generate force if the overlap between the thick and thin filaments is damaged.
Skeletal
___ help transfer force from thick and thin filaments onto the surface of smooth muscle cells
dense bodies
Z lines in skeletal muscle are similar to ___ in smooth muscle
dense body
distribute force
smooth muscle is stimulated to contract by affecting either calcium or ___
myosin light chain kinase or phosphatase
two distinct sources of neural stimulation of smooth muscle
extrinsic: ANS
Intrinsic: within the organ (enteric NS)
extrinsic innervation of smooth muscle
Autonomic Nervous System
Parasympathetic and Sympathetic
Organ specific (Vascular smooth muscle almost exclusively sympathetic)
intrinsic innervation of smooth muscle
Neural plexuses within organs
Motor, sensory and interneurons
Allows function if CNS input lost - doesn’t need brain to tell it what to do
example: Myenteric plexus
Generally ___ neural stimulation provides primary control of the smooth muscle and ____ input modifies activity
intrinsic
extrinsic
describe multi-unit neural stimulation of smooth muscle
each muscle cell has its own nerve and acts independently of other smooth muscle cells
1:1 muscle to nerve
(eye muscles: iris, piloerector muscles, some vascular smooth muscle)
describe single unit neural stimulation of smooth muscle
Gap junctions between smooth muscle cells exist to allow direct signaling between muscle cells
1 nerve impulse gets spread to other cells by gap junctions
(urinary bladder, GI, uterus, vascular smooth muscle)
example for single unit neural stimulation of smooth muscle
urinary bladder
Gap junctions between smooth muscle cells exist to allow direct signaling between muscle cells
example for multi-unit neural stimulation of smooth muscle
eye muscle
each muscle cell has its own nerve and acts independently of other smooth muscle cells
True or false
smooth muscle have motor endplates
false
no motor endplates, they have synaptic troughs, the axon released neurotransmitters to many muscle cells through varicosities
what neurotransmitter is released for parasympathetic stimulation of smooth muscle
acetylcholine
(rest and digest)
what neurotransmitter is released for sympathetic stimulation of smooth muscle
Norepinephrine
(fight or flight)
what are some neurotransmitters released at the synaptic troughs of smooth muscle?
Acetylcholine (parasympathetic- rest and digest)
Norepinephrine (sympathetic- fight or flight)
Nitric oxide
two types of receptors for acetylcholine
muscarinic- smooth muscle, CNS, G-protein linked (slower)
Nicotinic- skeletal muscle, CNS, no second messenger (fast)
which acetylcholine receptor is used in smooth muscle and why?
muscarinic
CNS
second messenger system- G protein linked
makes it a slower reaction
example of paracrine stimulation of smooth muscle
(particularly vascular smooth muscle)
Nitric oxide
Prostacyclin
Adenosine
Endothelin
endocrine stimulation of smooth muscle is by ___
Epinephrine
Angiotensin
all smooth muscle cells have ___ cell surface receptors
many different
(muscarinic, adrenergic, nitric oxide etc.) meaning that smooth muscle can respond appropriately to many different physiological stimuli, and that some conditions will result in an over-expression of the receptors.
Some factors will cause contraction of ___ in one tissue and relaxation in another (i.e. histamine and epinephrine/norepinephrine) Balancing these effects will be critical in therapeutic use of the drugs.
smooth muscle
example of a factor that causes contraction in one type of smooth muscle and relaxation in another smooth muscle
histamine
contractions- bronchi
dilation- blood vessels
where does smooth muscle get calcium?
Sarcoplasmic reticulum
extracellular calcium
there is more calcium inside or outside the cell?
outside- if you open a gate calcium will flow into the cell
two types of calcium channels
ligand-gated calcium channels
voltage-gated calcium channels
-calcium induced calcium release (no voltage gated sodium channels)
how is myosin in smooth muscle different than smooth muscle in skeletal muscle
smooth muscle:
2 regulatory myosin light chains
these control activation
how do regulatory myosin light chains work in smooth muscle
4 calcium bind to calmodulin which activates myosin light chain kinase which phosphorylates (adds a phosphate) to the Regulatory myosin light chain. When this happens the myosin heavy change undergoes a conformation change and allows actin-myosin interaction
myosin light chain kinase does what in smooth muscle?
adds phosphate group/ phosphorylates the regulatory myosin light chain which causes the myosin heavy chain to change shape and allow for actin-myosin interactions
in smooth muscle, calcium binds to ___ to cause actin-myosin interactions
calmodulin
calmodulin triggers myosin light chain kinase
phosphylated Regulatory myosin light chain causes
myosin heavy chain to change shape
this allows actin-myosin interactions
when regulatory myosin light chain is phosphorylated, the smooth muscle is ___
contracted
when regulatory myosin light chain is not phosphorylated, smooth muscle is ___
relaxed
what enzyme relaxes smooth muscle
myosin light chain phosphatase
what % of myosin is working at maximum?
50%
never fully relaxes- 5% still working
Calcium, through Calmodulin only affects MyLC ___ activity. It does not affect MyLC ___.
kinase (only forward to contraction)
phosphatase (relaxation)
increased myosin light chain kinase leads to what in smooth muscle
more contracting from the regulated myosin light chain.
balance between kinase and phosphatase= amount of force generated by the smooth muscle
why does smooth muscle not have an all or none response
some always have to work or else they would just pull on the relaxed one and nothing would move
example: heart and vessels, if they all relaxed- blood would pool and not move
tonic form of myosin heavy chain encodes for a ___
slower, more energy efficient contraction (aorta)
phasic form of myosin in smooth muscle produces a ___
faster contracting muscle (bladder)
phasic smooth muscle is much __ than slow skeletal muscle
slower
phasic is fast contracting smooth muscle but even so it is much slower than skeletal muscle
the aorta has what isoform of myosin heavy chain
tonic
slower, more energy efficient
the bladder has what isoform of smooth muscle myosin heavy chain?
phasic
faster contracting
Enzymatic inhibition of ___ results in a shift towards muscle contraction, with no change in calcium
MyLC phosphatase
(stop the relaxation of a smooth muscle)
explain latch mechanism for smooth muscle
Actin-myosin complexes remains attached and force generating despite the loss of ATP from the myosin pocket
explain calcium sensitization of smooth muscle
keep a smooth muscle contracted without using calcium but stopping/inhibiting the backwards reaction by myosin light chain phosphatase
true or false. a drug will affect all smooth muscle the same way.
false
can have different reactions/side effects in different tissues or different areas of the body.
Feline asthma is a type I hypersensitivity reaction to an inhaled allergen, that causes the the immune system to release histamine which causes constriction of ___
smooth muscle: bronchus/airways
can breathe in but oxygen can’t transfer
treatment of asthma
glucocorticoids (suppress immune system)- primary problem
bronchodilators (relax smooth muscle of airways)- secondary response
in a long term obstruction of the urinary bladder what can happen?
atonic(flaccid bag) bladder due to massive distension of bladder wall.
damage is actually to the nerves, which do not stretch as well as the smooth muscle of the bladder wall
treatment for urinary tract obstruction
bethanechol- muscarinic agonist with selective activity in the detrusor muscle
help bladder contract
muscarinic- type of acetylcholine receptor for smooth muscle- second messanger- g protein linked
does not effect skeletal muscle
dystocia
abnormal delivery of pups
long delivery-
uterus uses up all the extracellular calcium→ decrease in calcium influx into the muscle cell
↓ Calcium calmodulin complex→ ↓ MLC kinase activation → ↓ Myosin activation and force
treatment: give calcium slowly
similar to milk fever
milk fever is similar to ___ in dogs
dystocia
Early in heart failure, increasing vascular resistance is a good thing, maintaining tissue perfusion. Eventually the resistance exceeds the hearts ability to adequately push blood out of the ___. Death ensues rapidly
ventricles
treatment for canine heart failure
nitroprusside → decrease blood pressure, heart doesn’t have to work as hard
paracrine transmitter to smooth muscle- cNOS is an enzyme that causes vasodilation through a second messenger signaling pathway that lowers intracellular calcium
what kind of muscle lack all-or-none response?
smooth
allows either pharmacological increase or decrease in smooth muscle activation
The ability to generate force over tremendous changes in fiber ___ are critical to smooth muscle function
length
Tissue ___ activation or relaxation is critical to therapeutic success
specific
have to know what drug will do to different types of smooth muscle throughout the body, can have bad side effects.
