Smooth Muscle Flashcards by An Nakamura

Q

Definition of autacoid

A

Physiologically active factor released by cells which typically acts locally and briefly on other cells

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Q

Definition of local hormone

A

Any regulatory substance released by cells acting in an autocrine/paracrine fashion

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Q

Definition of ANS

A

Autonomic nervous system, a branch of the nervous system that controls activity of the heart, visceral organs, blood vessels and glands

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Q

Definition of unitary

A

Not all cells have synaptic input, excitation spread through tissue via gap junctions
Allows for coordinated cell contraction

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Q

Definition of multiunit

A

Each smooth muscle has synaptic input, allows for finer control of muscle

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Q

Location
Function
Shape
Regulation of SM
Properties

A

Wall of hollow organs, including blood vessels except capillaries

Acts as body conduits for transport

Spindle

ANS/Hormones/Pacemaker cells

No striations
Dense bodies which anchor actin filaments
SR
More actin : myosin than to striated muscle

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Q

Smooth muscle containing organs

A

Blood vessels
GI tract
Detrusor in bladder, ureters, urethra
Myometrium in uterus
Respiratory system
Vas deferens, corpus cavernosum
Fallopian tube
Iris and ciliary body

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Q

Function of smooth muscle in blood vessels

A

Diameter control, vascular resistance, blood flow distribution and BP

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Q

Function of smooth muscle in GI tract

A

Controls mixing, propulsions of GI contents

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Q

Function of smooth muscle in detrusor, ureters, urethra

A

Controls urine storage and micturition

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Q

Function of smooth muscle in myometrium of uterus

A

Responsible for labour

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Q

Function of smooth muscle in the respiratory system

A

Controls diameter of airways

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Q

Function of smooth muscle in vas deferent, corpus cavernosum

A

Erection, ejaculation control

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Q

Function of smooth muscle in fallopian tube

A

Mediates egg movement from ovaries to uterus

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Q

Function of smooth muscle in iris and ciliary body

A

Controls pupil diameter, lens focusing

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Q

How is the contraction of smooth muscle regulated in the vascular system

Does it respond to action potentials

A

ANS
Autacoids
Vascular endothelium
Blood bourne substances

Sometimes

Q

How is the contraction of smooth muscle regulated by the airways

Does it respond to action potentials

A

ANS
Autacoids

No

Q

How is the contraction of smooth muscle regulated by intestinal cells

Does it respond to action potentials

A

Intestinal cells of Cajal
ANS regulates rhythms
Autacoids

Yes

Q

How is the contraction of smooth muscle regulated by myometrium

Does it respond to action potentials

A

Intrinsic rhythmicity
Autacoids

Yes

Q

How is the contraction of smooth muscle in the detrusor

Does it respond to action potentials

A

ANS
Autacoids

Yes

Q

How is vasoconstriction initiated in vascular smooth muscle

A

Noradrenaline, angiotensin II, other vasoconstrictors bind to a1 receptors
Activates phospholipase C and rho kinase with +ve currents
Rho kinase increases Ca2+ sensitization

Phospholipase C hydrolyses PIP2 into IP3 and DAG
IP3 causes SR to release Ca2+
DAG opens RGC, influx of Ca2+ and Na+

SAC causes Na+ influx, membrane depolarization, spreads excitation to neighboring cells via gap junctions
Also causes VGCC to open, influx of Ca2+

Q

How is vasodilation initiated by NO

A

NO released by endothelial cell
Causes GTP conversion into cGMP by GC

cGMP causes Ca2+ to be reabsorbed into SERCA, leave cell via PMCA and increase Ca2+ desensitization
cGMP also causes K+ channel to open, K+ efflux, leads to membrane hyperpolarization
Membrane hyper polarization causes VGCC to close

Q

How is vasodilation initiated by cAMP

A

Adrenaline, adenosine prostacyclin binds to b2 receptor

Activated AC converts ATP to cAMP

cAMP activates SERCA and PMCA to decrease Ca2+ in cell
cAMP also activates K+ channels, K+ efflux, membrane hyperpolarization
cAMP activates PDE, converted into AMP

Q

Smooth muscle cross bridge cycle and its regulation in comparison to striated muscle

A

Crossbridge cycling slower in SM than striated

Lower ATP requirement => contract indefinitely without fatigue

What happens when there is a high conc of Ca2+ in the active complex of myosin light chain kinase and calmodulin

Forms myosin phosphate, binds with actin | Formation of actin myosin, cross bridge cycling occurs

What happens when there is a low conc of Ca2+ in active complex and myosin phosphotase

Myosin light chain formed from the dephosphoryation of myosinPi (via myosin phosphatase) Calmodulin also formed

Action of NO via cGMP on myosin phosphotase

Promotes Ca2+ desensitization, relaxation | Formation of myosin from myosinPi

Action of antagonists via rho kinase on myosin phosphatase

Promotes Ca2+ sensitization, contractions | Formation of myosinPi

Regulation of tension development in smooth muscle, latch bridges

Latch bridge formation allows smooth muscle to maintain force w less ATP MyosinPi is dephosphorylated by myosin phosphatase, maintains force via cross bridges Latch bridges detach v slowly

Describe electrical activity of smooth muscle | 2 types

Varies between organs Resting potential is stable in vascular, Show spontaneous visceral oscillations=slow waves driven by Interstitial cells of Cajal in GI

Effects of AP in slow waves and non slow waves

Increased frequency of stimuli => depolarization/increase in slow wave amplitude Visceral Some vascular smooth muscles

What is depolarization and repolarization due to

AP upstroke due to VGCC | Repolarization due to K+ channels

Graded depolarisations and their effects | Are AP generated

Lower levels of stimuli => contraction, AP not generated Any depolarization tends to open VGCCs, cause contraction

Other causes of contraction via pathways not dependent on depolarizations and VGCC

Hormone, autacoids, NT

Describe unitary smooth muscle Describe multiunitary smooth muscle Where can these types be found

1 synapse => excitation spread through gap junctions => coordinated contraction GI tract, genitourinary, airways, most vascular Many synapses => fine muscle control Iris, ciliary body, piloerectors