20- Smooth Muscle Physiology Flashcards
Compare the histology of Skeletal Muscle vs. Smooth Muscle.
Skeletal Muscle = Large, multi-nucleated striated cells
Smooth Muscle = Small, single nucleus, no striations
Compare the Sarcoplasmic Reticulum in Skeletal Muscle vs. Smooth Muscle.
Skeletal Muscle = Large, well-developed SR with triads. Well-developed t-tubules
Smooth Muscle = Poorly developed SR and t-tubules. Membrane with Caveoli
Compare the thin filaments in Skeletal Muscle vs. Smooth Muscle.
Skeletal Muscle = Actin, Tropomyosin, Troponin
Smooth Muscle = Actin and Tropomyosin (does not use Troponin, it uses Calmodulin)
Skeletal Muscle has (MORE/LESS) thin filaments than Smooth Muscle.
Less
Both Skeletal Muscle and Smooth Muscle use Myosin, but the ATPase activity in Smooth Muscle is (FASTER/SLOWER) than that in Skeletal Muscle.
Slower
***Smooth Muscle utilizes Myosin Light Chain!
Skeletal Muscles has (MORE/LESS) thick filaments than Smooth Muscle.
More
T/F. Smooth Muscle and Skeletal Muscle both us NMJ.
False. Smooth Muscle uses varicosities and has no endplate specialization.
What NT and receptors does Smooth Muscle use?
ACh, Epinephrine, Norepinephrine
Muscarinic Cholinergic (Parasympathetic) Adrenergic (Alpha/Beta)
Skeletal Muscle is innervated by alpha-motor neurons, what is Smooth Muscle innervated by?
Multiple things – including intrinsic and ANS
T/F. Skeletal Muscle requires an action potential to work, but Smooth Muscle can work with or without an action potential.
True
***Smooth Muscle can be activated via pacemaker activity or hormones.
What are the Calcium sources for Skeletal Muscle and Smooth Muscle?
Skeletal Muscle = Release from SR
Smooth Muscle = Release from SR and ECF influx
For Skeletal Muscle, Calcium binds to Troponin C. However, Smooth Muscle does not have Troponin so Calcium binds to _________ to create a complex.
Calmodulin
The Calcium-Calmodulin Complex activates what?
MLCK (Myosin Light Chain Kinase)
In Smooth Muscle, what allows the binding of actin and myosin?
Phosphorylation of Myosin and addition of ATP
***Remember, Skeletal Muscle binds actin and myosin by tropomyosin being moved by troponin.
What are the 2 major types of Smooth Muscle?
Mutli-Unit – uses one nerve per fiber
Unitary – a group of cells together
Sometimes Smooth Muscle is subdivided into tonic and phasic, and its arrangement include…
- Circumferential
- Circumferential and Longitudinal
- Varied
For this type of Smooth Muscle, fibers operate individually and are each innervated by a single nerve. Examples include ciliary muscles of eye, iris, and piloerector muscles. This muscle “fine-tunes”.
Multi-Unit
For this type of Smooth Muscle, it is visceral or syncytial. It works together as a unit and the cell membranes adhere and contain gap junctions. Examples include GI tract, bile ducts, and the uterus.
Unitary
Smooth Muscle has no true sarcomere structures. Actin attaches to ________ _______ or ________ ________, and Myosin heads have bi-directional arrangement.
Dense bodies
Adherens Junctions
***The Dense bodies can rearrange the positioning
The Smooth Muscle cycling of Myosin cross-bridges (attaches to Actin and walks along) is (FASTER/SLOWER) than Skeletal Muscle. However, the time Myosin and Actin are attached is (MORE/LESS), making the force greater.
Slower
More
In Smooth Muscle, because contractions can last longer the _______ demand is lower. This is because we don’t want Smooth Muscle to continuously use up the ATP to maintain contraction. Instead, its ________ levels stay increased. The term for this slow in excitation but remained contraction is the ________ ________.
ATP
Calcium
Latch Mechanism
Calcium enters the Smooth Muscle cytosol via the Sarcolemma (plasma membrane) and through the poorly develop SR. On the SR, what receptors release Calcium?
IP3-Gated Calcium Channels
Ryanodine Receptors
What type of receptors lie on the Sarcolemma for Calcium release?
L-Type Voltage-Gated Calcium Channels
Ligand-Gated Calcium Channels
***These can be activated via depolarization, NT, hormones, etc.
How does Calcium exit the Smooth Muscle cells?
SERCA
3Na+/Ca2+ Antiporter
Sarcolemmal Ca2+ ATPase
What are the steps to reach Smooth Muscle contraction?
1) Calcium enters cytosol via Sarcolemma and SR.
2) Calcium binds to Calmodulin
3) Calmodulin-Calcium complex activates MLCK.
4) MLCK phosphorylates Myosin.
5) Phosphorylated Myosin with ATP can bind to Actin.
6) Bound Myosin and Actin create muscle contraction.
There are 2 methods to cause Smooth Muscle relaxation, and we need both. What are they?
1) Calcium pumps remove Calcium from cytosol.
2) Myosin Light Chain Phosphatase removes phosphate group on Myosin light chain.
What are things that can stimulate Smooth Muscle?
Nerves
Hormones
Stretch
Environmental Ques
For nerve stimulation of Smooth Muscle (aka depolarization), __________ serve as NT release sites (sometimes called diffuse junctions). They don’t release only ACh, there are multiple NTs.
Varicosities
T/F. Distance between Varicosities and fibers differ depending on the number of Varicosities. There can be multiple for each cell, or one for multiple cells.
True
These NTs are adrenergic (use alpha/beta receptors) and they can either be excitatory or inhibitory depending on the organ.
Norepinephrine
Epinephrine
This NT is parasympathetic and cholinergic (uses muscarinic cholinergic receptors). It can excitatory or inhibitory depending on the organ.
ACh
ACh usually causes contraction as a (DIRECT/INDIRECT) effect and relaxation as a (DIRECT/INDIRECT) effect.
Direct
Indirect
For Smooth Muscle, Anigiotensin II, Vasopressin, and Endothelin all cause what?
Contraction
For Smooth Muscle, Adenosine will (CONTRACT/RELAX) it.
Relax
For Smooth Muscle, Nitric Oxide is (EXCITATORY/INHIBITORY) so it (CONTRACTS/RELAXES) the muscle.
Inhibitory
Relaxes
What hormones can control Smooth Muscle via the actions of their own receptors influencing Calcium?
CCK (Cholecystokinin)
Oxytocin
Serotonin
Histamine
Cardiovascular arterioles, meta-arterioles, and pre-capillaires all have smooth muscle and respond to environmental cues such as…
Hypoxia
Excess CO2
Increased H+
Adenosine, LA, Increased K+, etc.
What is the Resting Membrane Potential of Smooth Muscle?
-50 to -60 mV
Action potentials only occur in ________ Smooth Muscle, and the two forms of action potentials are ________ and ________ potentials.
Unitary
Plateaus
Spike
Spike potentials and Slow waves of action potentials are stimulated by what?
Varying amounts of Calcium influx (L-Type Voltage-Gated) and K+ efflux (Calcium-activated K+ channels).
Spike potentials can also be stimulated by hormones, NTs, stretch, or be spontaneous.
What are Smooth Muscle plateaus stimulated by?
NTs
Stretch
This mechanism is the way to increase tension while decreasing ATP usage. There is dephosphorylation of the light chain and the cycle proceeds slowly. Attached cross-bridges are still generating tension (hold on to more Calcium instead of ATP).
Latch Mechanism
The ________-________ relationship is similar to Skeletal Muscle, but it differs in that instead of just ripping when being stretched too much, Smooth Muscle can rearrange to allow for greater stretch and still be able to contract. An example is when you expand your stomach from eating a lot.
Length-Tension
Spike potentials and Slow waves of action potentials are stimulated by what?
Varying amounts of Calcium influx (L-Type Voltage-Gated) and K+ efflux (Calcium-activated K+ channels).
Spike potentials can also be stimulated by hormones, NTs, stretch, or be spontaneous.
What are Smooth Muscle plateaus stimulated by?
NTs
Stretch
This mechanism is the way to increase tension while decreasing ATP usage. There is dephosphorylation of the light chain and the cycle proceeds slowly. Attached cross-bridges are still generating tension (hold on to more Calcium instead of ATP).
Latch Mechanism
The ________-________ relationship is similar to Skeletal Muscle, but it differs in that instead of just ripping when being stretched too much, Smooth Muscle can rearrange to allow for greater stretch and still be able to contract. An example is when you expand your stomach from eating a lot.
Length-Tension
