Smooth Muscle Flashcards
What are the two types of smooth muscle?
Multi-unit smooth muscle and Unitary Smooth muscle
Describe Multi-unit smooth muscle
Fibers operate individually
Each fiber is innervated by a single nerve
Not electrically connected (no gap junctions)
Provide ability for fine motor movements
Examples: ciliary muscles of the eye, iris, piloerector muscles (raise hair follicles)
Describe unitary smooth muscle
Muscle cells work as a unit
Cell membranes adhere and contain gap junctions
Examples: visceral smooth muscle; GI tract, bile ducts, urterus
What makes a smooth muscle cell different from cardiac and skeletal muscle?
No true sarcomere structures
Actin attaches to Dense Bodies/Adherens Junctions
Myosin heads have bi-directional arrangement
No striations
What is special about contraction of smooth muscle compared to the other muscle fibers?
Cycling of myosin cross-bridges is slower
The time that myosin and actin are bound is greater (which allows for greater force production)
ATP demand is lower
When excitation slows, contraction remains - Latch Mechanism
Describe the contraction mechanism of smooth muscle cells
Ca2+ enters the cytosol and binds to Calmodulin (CaM)
Ca - CaM complex activates Myosin Light Chain Kinase (MLCK)
MLCK phosphorylates the Myosin heads, allowing them to interact with actin which causes a contraction
Describe the relaxation mechanism of smooth muscle cells
Relaxation occurs as a result of removing Ca2+ from the cytosol via pumps
Relaxation also occurs as a result of Myosin Light Chain Phosphatase, which dephosphorylates the myosin heads, preventing them from binding with actin and can no longer cause a contraction.
What signals induce produce actions in smooth muscle?
Nerves (neurotransmitters)
Hormones
Stretch
Environmental cues
What are the effects of Norepinephrine/Epinephrine on smooth muscle?
Excitatory or inhibitory depending on the target organ
What is the effect of Acetylcholine on smooth muscle?
Can be excitatory or inhibitory depending on the target organ
Contraction is typically the direct effect
Relaxation is typically the indirect effect
Angiotensin II causes smooth muscle to do what?
Constriction
Vasopressin causes smooth muscle to do what?
Constriction
Endothelin causes smooth muscle to do what?
Constriction
What is Adenosine and what does it cause smooth muscle to do?
It is a metabolite and it causes relaxation
Nitric Oxide does what to smooth muscle?
Inhibitory
Causes relaxation
NO is a potent vasodilator
Hypoxia causes smooth muscle to do what?
Relaxation
Excess CO2 causes smooth muscle to do what?
Relaxation
Increased H+ causes smooth muscle to do what?
Relaxation
What is the effect of increased K+ on smooth muscle?
Relaxation
What does Antidiuretic Hormone (ADH) do to smooth muscle?
Constriction
What does Atrial Natriuretic Hormone do to smooth muscle?
Relaxation
What does stretching induce smooth muscle to do?
Constriction
How do GPCRs influence Ca2+ concentration in the smooth muscle cell?
GPCRs will increase production of IP3, which activate IP3 Receptor channels in the Sarcoplasmic reticulum.
IP3 causes the channels to open, allowing Ca2+ to enter the cytoplasm.
