smooth muscle Flashcards
Compare and contrast Skeletal muscle and smooth muscle: histology, and sarcoplasmic reticulum
skeletal muscle: Large, multinucleate striated cells
-large well developed SR with triads, well developed T tubules
smooth muscle: small, single nucleus, no striations
-poorly developed SR, T tubles have membrane with caveoli
Compare and contrast Skeletal muscle and smooth muscle: Thin filaments, thin filament number,
Skeletal muscle: actin, tropomyosin, toponin
lower number of thin filaments
smooth muscle: actin and tropomyosin
more number of thin filaments
Compare and contrast Skeletal muscle and smooth muscle: Thick filament, composition, number
Skeletal muscle: myosin, ATPase activity is faster
-greater number of thick filaments
smooth muscle: Myosin, ATPase activity is slow, myosin light chain prominence
-lesser number thick filaments
Compare and contrast Skeletal muscle and smooth muscle: Innervation, neurotransmitters, and neurotransmitter receptors
skeletal muscle: alpha motor neurons
- Acetylcholine-excitatory
- nicotinic cholinergic
smooth muscle: multiple including intrinsic and autonomic nervous system
- acetylcholine, epinephrine, norepinephrine (excitatory/inhibitory)
- muscarinic cholinergic, adrenergic, and others
Compare and contrast Skeletal muscle and smooth muscle: Transmission specialization, other forms of activation
skeletal muscle: Neuromuscular junction
-zero
smooth muscle: No NMJ- varicosities (pre-synaptic swelling) no endplate specialization
-blood-borne, paracrine, intrinsic
Compare and contrast Skeletal muscle and smooth muscle: Action potential, source of calcium, and role of calcium
skeletal muscle: Required
- release from SR
- Binds to troponin C
Smooth muscle: No-pacemaker activity, hormonal
- Release from SR and ECF influx
- binds calmodulin, activates MLCK
Compare and contrast Skeletal muscle and smooth muscle: Mechanism to allow actin and myosin binding, Relaxation
Skeletal muscle: Tropomyosin moved by troponin
-REmoval of Ca+ from troponin
Smooth muscle: Phosphorylation of myosin light chain
-Activation of light chain phosphatase, dephosphorylation
what are the two major types of Smooth muscle and how can they be arranged
Multi unit smooth muscle
Unitary smooth muscle
arrangements:
- Circumferential
- Circumferential and longitudinal
- Varied
Characteristics of Multi-unit smooth muscle
- Fibers operate individually
- Innervated by single nerve
- allows for more fine control
- examples: ciliary muscle of eye, iris, piloerector muscles
characteristics of Unitary smooth muscle
- Visceral smooth muscle or syncytial
- works together as a unit
- cell membranes adhere and contain gap junctions
- Examples: GI tract, bile ducts, uterus
what component on the smooth muscle allows for the muscle to pull together
since their are no true sarcomere structures
smooth muscle has actin attach to dense bodies/adherens junctions
these serve as anchors for the muscle that come together during contraction
what is the difference in smooth muscle for, cycling, force, and ATP demand compaired to skeletal muscle
in smooth muscle the cycling of myosin cross bridges is slower than skeletal muscle
but, the time myosin and actin are attached is greater making a greater force
and the the ATP demand for contraction is lower
Mechanism of COntraction of SMooth muscle
Ca+ enters cell via
- Sarcolemmal: L type voltage gated Ca+ or receptor activated Ca+ channels
- via the SR from Ryanodine receptors
- IP3 receptors
calcium binds reversibly CaM (calmodulin)
calmodulin-calcium complex activates the myosin light chain kinase
-contraction strength proportionate to Ca+ levels
the myosin light chain kinase (activated) will phosphorylate the myosin light chains so that now it can bind to actin to cause contraction
How does the relaxation process occur for smooth muscle
calcium pumps remove calcium from the cell
myosin light chain phosphatase removes the phospate from the myosin light chain which will stop binding to actin
need both to occur to stop contraction
what are the 4 stimulations of smooth muscle
nerves
hormones
stretch
environmental Ques
effects on smooth muscle: Norepinephrine/epinephrine? Acetylcholine? Angiotensin II, vasopressin, endothelin? Adenosine? Nitric oxide? Antidiuretic hormone?
Norepinephrine/epinephrine: excitatory or inhibitory depending on organ
Acetylcholine: excitatory or inhibitory depending on organ
- contraction is direct effect
- relaxation can be indirect effect
Angiotensin II, vasopressin, endothelin: contraction
Adenosine: relaxation
Nitric oxide: inhibitory = relaxation
antidiuretic hormone: vasoconstrict
other neurotransmitters and hormones that control smooth muscle and how?
Cholecystokinin (CCK)
Oxytocin
Serotonin
Histamine
actions through own receptors influence Ca+ channels
(all major role in GI tract not much in cardio)
How does increased metabolic activity affect smooth muscle, and what are some of those ques
Hypoxia Excess CO2 Increased H+ increased K+ Prostoglandins
lead to increase in Vaso dilation
how does an increase in sympathetic tone affect the smooth muscle
cause Vasoconstriction
how does Atrial natriuetic peptide affect smooth muscle
ANP released by atrium
tells body to vasodilate
how does the latch mechanism work
binding of slow fatigue myosin ATPase that can contract without burning though large amounts of AtP
After the initial depolarization with Ca+ to get the contraction started, the muscle can go to a tonic contraction by not releasing all the calcium to still hold the force for longer periods of time
attached cross bridges are still generating tension at 20/30 percent even after dephosphorylation of the light chain, thanks to the ca+
what is the resting membrane potential of smooth muscle
-50 to - 60 mv
what are the two forms of action potentials for smooth muscle activity
plateaus (hold force for long periods of time at specific increases of mv or by different agents increasing Ca+ concentrations)
Spike potentials (typical over threshold to increase contraction strength,)
how are spike potentials stimulated
stimulated by hormones
neurotransmitters
stretch
spontaneous