Smooth Muscle Flashcards
(37 cards)
What is smooth muscle named for?
It is named because the cells do not have striations.
Where is smooth muscle found in the body?
In the walls of hollow organs and passageways, such as:
* Urinary bladder
* Uterus
* Stomach
* Intestines
* Arteries and veins
* Respiratory, urinary, and reproductive tracts
What is the shape and size of smooth muscle fibers?
Spindle-shaped, ranging from about 30 to 200 μm.
What type of connective tissue do smooth muscle fibers produce?
Endomysium.
What contractile proteins do smooth muscle fibers contain?
Actin and myosin.
What are dense bodies in smooth muscle analogous to?
Z-discs of skeletal and cardiac muscle fibers.
What regulates cross-bridge formation in smooth muscle?
Calmodulin.
What activates myosin light chain kinase in smooth muscle contraction?
The Ca++-calmodulin complex.
How do thin filaments affect muscle contraction in smooth muscle?
They pull on dense bodies, causing contraction.
Do smooth muscle fibers have T-tubules?
No, T-tubules are not required.
What is the primary source of Ca++ for smooth muscle contraction?
Extracellular Ca++ ions and release from the sarcoplasmic reticulum.
What happens to Ca++ ions after muscle contraction?
They are actively transported back into the SR and out of the cell.
What mechanism allows smooth muscle to maintain tone with little energy expenditure?
Latch-bridges between myosin heads and actin.
Is smooth muscle under voluntary control?
No, it is involuntary muscle.
What triggers smooth muscle contraction?
Hormones, neural stimulation by the ANS, and local factors.
What do pacesetter cells do in smooth muscle?
They can spontaneously trigger action potentials and contractions.
What is the role of varicosities in smooth muscle?
They release neurotransmitters into the synaptic cleft.
Fill in the blank: Smooth muscle contraction can be triggered by _______.
[stretching the muscle]
True or False: Smooth muscle has a highly organized neuromuscular junction (NMJ) like skeletal muscle.
False.
What is the stress-relaxation response in smooth muscle?
Stretching the muscle can trigger its contraction.
What is the contraction energy output of smooth muscle compared to skeletal muscle?
Power output is relatively low but can continue without large amounts of energy.
What are varicosities in autonomic neurons?
A series of axon-like swelling that form motor units through smooth muscle.
What are the two types of smooth muscle?
Single-unit smooth muscle and multiunit smooth muscle.
Where is single-unit smooth muscle commonly found?
In the walls of all visceral organs except the heart.
