Objective 20 Flashcards
How is smooth muscle arranged?
typically organized into two layers (longitudinal and circular)
Where are smooth muscles found?
in the walls of hollow organs (except the heart)
What is perstalsis?
The movement created by alternating contractions and relaxations of these muscle layers in the GI tract
Smooth Muscle Microscopic Anatomy:
What do the fibers of smooth muscle look like and how are they connected?
They are short spindle-shaped fibers, connected in sheets
Smooth Muscle Microscopic Anatomy:
Are there fibrous middle or outer CT layers in smooth muscle?
No. Smooth muscle has endomysium only – (no fibrous middle or outer CT layers)
Smooth Muscle Microscopic Anatomy:
How does SR of smooth muscle compare to skeletal muscle?
SR is less developed in smooth muscle; no T tubules
Smooth Muscle Microscopic Anatomy:
What are caveolae?
pouchlike infoldings in plasma membranes
Where is Ca2+ sequestered?
In the extracellular space near the caveolae (much less in the limited SR)
Are there sarcomeres in smooth muscle?
No. Thick and thin filaments are present but there are no visible striations; arranged in a spiral so muscle contracts in a corkscrew-like fashion
What protein acts as the binding site in smooth muscle?
Calmodulin acts as the calcium binding site. There is no troponin complex
What resists tension and creates anchoring points for actin?
A dense body-intermediate filament cytoskeleton network
Describe how smooth muscle is innervated.
Autonomic nerve fibers innervate smooth muscle at diffuse junctions
What are varicosities?
Bulbous swellings that release neurotransmitters into wide synaptic clefts
What happens when whole sheets of smooth muscle exhibit slow, synchronized contraction
Contraction of smooth muscle
When smooth muscle contracts, how are cells electrically coupled?
Cells are electrically coupled with gap junctions
