Smooth Muscle (Exam III) Flashcards
What are smooth muscle cells lengths compared to skeletal muscle?
Do smooth muscle cells have a sarcomere?
Are smooth muscle cells attached to theskeleton?
- Shorter than skeletal muscle
- No
- No
What is the actin:myosin ratio of smooth muscle?
How does this compare to skeletal muscle?
- Smooth = 10 actin : 1 myosin
- Skeletal = 2 actin : 1 myosin
What functions as a replacement for the Z-disk in smooth muscle?
What is this structure made of?
- Dense Bodies
- Dense Bodies are made of collagen.
What is stronger, smooth muscle or skeletal muscle? How much more so?
Smooth muscle is 2x stronger per 100grams
How does the energy usage of smooth muscle compare to that of skeletal muscle?
- Smooth muscle is much more efficient
- 1/10 to 1/300 energy usage compared to skeletal muscle.
How does the speed of contraction of smooth muscle compare to that of skeletal muscle?
- Smooth muscle: 0.5 - 2 sec contraction speed
- Skeletal muscle: 0.15ms contraction speed
Where is actin anchored in smooth muscle cells?
Where are dense bodies located in smooth muscle cells?
How do smooth muscle cells connect to other smooth muscle cells?
- Dense bodies
- Dense bodies are attached to the cell wall.
- Smooth muscle cells attach to each other through their dense bodies.
Where do neurotransmitters send signals to trigger Ca⁺⁺ release in smooth muscle cells?
How does the sarcoplasmic reticulum of smooth muscles compare to that of skeletal muscle?
- Caveolae
- Smooth Muscle SR is limited comparatively and hangs out at the caveolae.
How much internal Ca⁺⁺ do smooth muscle cells store?
What does this mean clinically?
- Very little compared to skeletal muscle (depending on Ca⁺⁺ concentration of ECF)
- Hypocalcemia = ↓ BP due to ↓ SVR from smooth muscle’s inability to constrict.
Which “state” of cross-bridge cycling lasts longer in smooth muscle than skeletal muscle? Why?
- Released State
- Tension is maintained by myosin head holding on to actin longer even with ATP present.
Where might we see smooth muscle cells in the body?
GI system, ciliary muscle, GU tract, uterus
What is required for release of the myosin head from the actin in smooth muscle vs skeletal muscle?
- Skeletal Muscle: ATP binding to myosin head causes myosin head to detach from actin.
- Smooth Muscle: MLCP needed to dephosphorylate for myosin head to release.
How much more quickly do skeletal muscle contractions take place than smooth muscle contractions?
Skeletal muscle is 10 - 300 times faster.
To what degree can smooth muscle shorten its length? How does this compare to skeletal muscle?
- Smooth muscle: 80% of length shortening capability.
- Skeletal muscle: 30% of length shortening capability.
What structure of the skeletal muscle prevents length shortening to the same degree as the smooth muscle?
Skeletal muscle Z-disks
What are the two classifications of smooth muscle cells? Where are each found?
- Visceral (Unitary): larger organs (GI, GU, Blood vessels, resp, etc.)
- Multi-Unit: Ciliary muscles of the eye. (anywhere that fine control is needed)
What organ is unique in its composition of both smooth muscle and skeletal muscle?
Esophagus
What differentiates Visceral smooth muscle and Multi-unit smooth muscle?
Unitary (Visceral) Smooth muscle:
- Intercellular communication via gap junctions
- More common
Multi Unit Smooth Muscle:
- Insulated via glycoprotein fibrous coating
- No cell-cell communication
- Fine graded control
What are the layers of an artery (superficial to deep) and their alternate names?
- Tunica Externa (Adventitia)
- Tunica Media (Smooth muscle layer)
- Tunica Intima (Endothelium)
What is the composition of the Adventitia? How does this differ in arteries and veins?
Adventitia is composed of connective tissue.
- Arteries have more connective tissue (elastin) resulting in more resilience.
- Veins have less elastin and less resiliency.
How large is the endothelial layer of blood vessels?
How dependent is CV health on this layer?
What occurs with a diseased endothelium?
- 1 cell layer thick
- CV health is very dependent on the health of the endothelium.
- Blood vessels can’t dilate as well with a damaged endothelium.
How many layers of tissue do capillaries have?
One layer (Endothelium)
Which muscle cell type is able to “relax” more?
Smooth Muscle Cells
What is general Vᵣₘ for skeletal muscle?
-80mV
What troponin molecules does smooth muscle have?
None
Ca⁺⁺ combines with what molecule to activate MLCK?
Calmodulin
How does MLCK cause contraction?
Through phosphorylation of regulatory chain of Myosin molecule → Contraction.
What types of Ca⁺⁺ channels can influx Ca⁺⁺ in smooth muscle?
- Ligand-gated Ca⁺⁺ Channels
- VG Ca⁺⁺ Channels
- Leaky Ca⁺⁺ Channels
How does smooth muscle relaxation differ from smooth muscle contraction?
- Relaxation means less Ca⁺⁺ intracellularly
- ↓ Ca⁺⁺ ICF = No Calmodulin
- No Calmodulin = No Phosphorylation
- Myosin Phosphatase (MLCP) dephosphorylates Myosin Heads causing relaxation.
What receptors, located on endothelium, can start the process of NO creation?
mACh GPCRs or Bradykinin GPCRs
In an endothelial cell, what does the Ca⁺⁺CaM complex do?
- Uses eNOS to convert Arginine → Nitric Oxide (NO)
What conditions found in of lumen of the blood vessels cause endothelial cells to start producing more Nitric Oxide (NO) ?
- ↑ Flow/ Shear Stress
Nitric Oxide will dilate what primarily?
Veins (but has both arterial and venous activity)
Nitrates & nitrites cause increases release of what?
Nitric Oxide (NO)
Myosin Light Chain Kinase (MLCK) will do what to the regulatory chain of Myosin Light Chain?
Phosphorylate Myosin Light Chain causing cross-bridge cycling.
What inactivates phosphorylated myosin light chain?
MLCP (Myosin Light Chain Phosphatase)
Are action potentials always required for smooth muscle contraction? Why or why not?
What is an example of this concept?
- No, an oscillating Vᵣₘ can cause smooth muscle contraction.
- An example of this concept would be the “mixing” smooth muscles of the GI tract (Peristalsis?)
Where are α1 receptors located in the brain?
What is the consequence of this?
- No α1 receptors are in the brain.
- The brain is not responsive to pressors.
Where are α1 receptors not found in the CV system?
- Brain
- All capillaries
What mechanism causes myogenic constriction in the brain?
Na⁺ & Ca⁺⁺ stretch receptors responding to ↑ stretch from ↑ MAP.
What neurotransmitters are responsible for cerebral vasoconstriction/vasodilation?
Trick question. No NT’s, only Na⁺ & Ca⁺⁺ stretch receptors.
What is an example of an inverse response of smooth muscle being stretched resulting in increased dilation of said smooth muscle?
Bladder response to filling with urine
What does DAG do?
What is the result of this?
- Activates PKC (protein kinase C)
- PKC:
1. Potentiates MLCK
2. ↑ pCa⁺⁺
What does IP₃ do?
IP₃ potentiates Ca⁺⁺ release by binding to Ca⁺⁺ channel receptors on the sarcoplasmic reticulum.
What type of receptor is an α1 receptor?
What specific sub-type?
- GPCR
- Gₛ or Gq
What does Phospholipase do?
What activates phospholipase?
- PLC cleaves Phosphatidyl-Inositol to DAG & IP₃.
- PLC is activated by the active α-subunit of the G-protein.
What activates PKG?
What actions does PKG have?
- PKG activated by cGMP
- PKG potentiates MLCP & inhibits MLCK, causing relaxation.
