20- Smooth Muscle Physiology Flashcards by Staci Thomas

Compare the histology of Skeletal Muscle vs. Smooth Muscle.

Skeletal Muscle = Large, multi-nucleated striated cells

Smooth Muscle = Small, single nucleus, no striations

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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

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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)

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Skeletal Muscle has (MORE/LESS) thin filaments than Smooth Muscle.

Less

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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!

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Skeletal Muscles has (MORE/LESS) thick filaments than Smooth Muscle.

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T/F. Smooth Muscle and Skeletal Muscle both us NMJ.

False. Smooth Muscle uses varicosities and has no endplate specialization.

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What NT and receptors does Smooth Muscle use?

ACh, Epinephrine, Norepinephrine

Muscarinic Cholinergic (Parasympathetic) 
Adrenergic (Alpha/Beta)

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Skeletal Muscle is innervated by alpha-motor neurons, what is Smooth Muscle innervated by?

Multiple things – including intrinsic and ANS

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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.

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What are the Calcium sources for Skeletal Muscle and Smooth Muscle?

Skeletal Muscle = Release from SR

Smooth Muscle = Release from SR and ECF influx

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For Skeletal Muscle, Calcium binds to Troponin C. However, Smooth Muscle does not have Troponin so Calcium binds to _________ to create a complex.

Calmodulin

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The Calcium-Calmodulin Complex activates what?

MLCK (Myosin Light Chain Kinase)

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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.

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What are the 2 major types of Smooth Muscle?

Mutli-Unit – uses one nerve per fiber

Unitary – a group of cells together

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Sometimes Smooth Muscle is subdivided into tonic and phasic, and its arrangement include…

- Circumferential
- Circumferential and Longitudinal
- Varied

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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

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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

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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

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

Latch Mechanism

Length-Tension