smooth muscle Flashcards
is smooth muscle voluntary or involuntary control?
involuntary
smooth muscle contractions produce __________
constriction
smooth muscle is organized in _______________
multidirectional contractile units
how many nuclei do smooth muscle have?
one
how is smooth muscle classified?
1 - by location
2 - by contraction pattern
3 - by their communication with neighboring cells
what are the 2 contraction patterns of smooth muscles?
1 - phasic (ex. peristalsis)
2 - tonic (ex. sphincters)
what are the 2 classifications of communication between neighboring cells
1 - single-unit/unitary/visceral smooth muscle
2 - multiunit smooth muscel
__________ smooth muscle cells are connected by gap junctions, and the cells contract as a single unit
single-unit
_______ smooth muscle cells are not linked, and each cell must be stimulated independently
multi-unit
what is an example of a phasic smooth muscle that is usually relaxed?
esophagus
what is an example of a phasic smooth muscle that cycles between contraction and relaxation?
intestine
what is an example of a tonic smooth muscle that is usually contracted?
sphincter
what is an example of a tonic smooth muscle whose contraction is varied as necessary
vascular smooth muscle
smooth muscles are the _______ to contract and relax
slowest
(skeletal is the fastest and cardiac is in the middle)
T or F: smooth muscle has no sarcomeres
T
T or F: actin is more plentiful in smooth muscle
T
T or F: smooth muscle lacks troponin
T, but actin is still associated with tropomyosin in smooth muscle
T or F: myosin filaments are longer in smooth muscle and the entire surface of the filament is covered with myosin heads
T
T or F: smooth muscle has an extensive cytoskeleton consisting of intermediate filaments and dense bodies
T
T or F: in smooth muscle the amount of SR varies and is less organized
T
T or F: smooth muscle has t-tubules and caveolae
F, smooth muscle only has caveolae
_______ initiates smooth muscle contraction
calcium
increased _____________ is the signal for smooth muscle contraction
cytosolic calcium
describe the events for smooth muscle contraction
1 - intracellular Ca+ concentration increases
2 - Ca binds to calmodulin
3 - Ca-calmodulin activates myosin light chain kinase
4 - MLCK phosphorylates light chains
5 - active myosin crossbridges slide along actin (crossbridge cycling)
____________ is the first step in smooth muscle relaxation
removal of Ca+ from the cytosol
describe the steps of smooth muscle relaxation
1 - free Ca in cytosol decreases
2 - Ca unbinds from calmodulin
3 - myosin phosphatase removes phosphate from myosin light chains
4 - less myosin ATPase activity
contraction caused by chemical signaling is ________________ coupling
pharmacomechanical
what are the 3 different types of cell membrane ca entry in smooth muscle
1 - voltage gated
2 - ligand gated or receptor- operated ca channels (ROCC)
3 - stretch-activated
some smooth muscles have unstable membrane potentials including ________ and __________ potentials
slow-wave and pacemaker
membrane potentials _______ in smooth muscles
vary
_____________________: chemical signals change muscle tension through signal transduction pathways with little or no change in membrane potential
pharmacomechanical coupling
what are some ways chemical signals influence smooth muscle activity
- autonomic neurotransmitters and hormones
- paracrine signals
antagonistic control
both sympathetic and parasympathetic neurons
influence smooth muscle
tonic control
only a single autonomic branch controls smooth muscle
chemical signal
different effects in different tissues with different receptors (hormonal control)
most neurotransmitters and hormones act through:
G protein-linked receptors
what are two examples of paracrine signals that influence smooth muscel
histamine constricts airways. nitric oxide dilates
sympathetic + epinephrine + alpha receptor =
constriction of blood vessels, dilates etes, GI/bladder sphincters
sympathetic + epinephrine + beta 2 receptors =
relaxes airways, wall of stomach, small intestine, and bladder, some blood vessels
parasympathetic + acetylcholine + M receptors =
contracts airways
relaxes GI/bladder sphincters
relaxes via NO or CIP some blood vessels
__________ must operate over a range of lengths
smooth muscle
T or F: within an organ, the layers may run in several directions
T, like the stomach
smooth muscles contract and relax more ________ than skeletal muscle
slowly
smooth muscle uses ________ energy to generate and maintain a given force than skeletal muscle
less
T or F: smooth muscle can sustain contractions for extended periods without fatiguing
T
T or FL smooth muscles have small, spindle-shaped cells with multiple nuceli
F - single nucleus
T or F: smooth muscle contractile fibers are arranged in sarcomeres
F
Contraction in smooth muscle may be initiated by:
electrical or chemical signals or both
T or F: smooth muscle is controlled by the somatic nervous system
F: autonomic
T or F: smooth muscle lacks specialized receptor regions
T
T or F: the Ca+ for contraction comes from the extracellular fluid as well as from the SR
T
T or F: the Ca+ signal initiates a cascade that ends with phosphorylation of myosin light chain and activation of myosin ATPase
T
