Smooth muscle physiology Flashcards
Which type of smooth muscle is continuously active (tonic):
single or multi unit?
SINGLE
Is this a description of Single Unit or Multi Unit:
electrically coupled; stimulate one cell is followed by stimulation of adjacent smooth muscle cells; this results in a wave of contraction, as in peristalsis. The electrical signal may be initiated by a pacemaker cell.
Single
Is this a description of Single Unit or Multi Unit:
not electrically coupled. Eg. Vas deferens of the male genital tract and the iris of the eye.
Multi Unit
What are the 4 main differences of smooth muscle and skeletal?
- Apparatus attaches to DENSE BODIES
- No t-tubules
- Sarcolemma contains
caveolae, which represent invaginations of SL - Gap junction for electrical coupling and chemical communication
- smooth & skeletal both have actin & myosin
Instead of calcium induced muscle contraction, what does smooth muscle rely on?
- Calcium Calmodulin complex & phosphates & Kinases
State the general events that occur during SMOOTH muscle contraction
AP (doesn’t need one tho)
open voltage gated Calcium channels
increase Ca
Calcium binds to calmodulin( instead of troponin like in skeletal muscle)
Ca-Calmodulin activates Kinase
light chain activated
Myosin activated
Cross bridge formation
Tension
Does smooth muscle require an AP like skeletal muscle?
NO!
- but uses myosin
How can contraction be turned off?
- increase phosphates activity
- decrease kinase activity
- decrease amount of calcium
What are 3 excitation pathways involving Calcium?
- Hromon or NT IP3 gated
- Voltage gated - SR releasing calcium
- Ligand gated (Hormone or NT)
The 3 regulatory pathways in smooth muscle all result in what?
Increase in calcium
Describe the areas that fall under these categories:
- Normally contracted
- Normally partially contracted
- Phasically active
- Normally relaxed
- Sphincters
- Blood vessels, airways
- Stomach, intestines
- Esophogus, Urinary Bladder
What pathways DO NOT require membrane depolarization?
hormone receptor stimulation leading to formation of IP3, cAMP, cGMP or the activation of a ligand operated Ca2+ channel
How does NO cause smooth muscle relaxation?
- No released by endothelial cells in response to ACh
- causes VASODILATION
What are pathways that require alterations in membrane potential?
- Depolarization -induced Calcium entry into smooth muscle cells
- Voltage gated Ca
- Ligand Bound
- Ca entry by CA-CAM & MLCK
- spread of depolarization via gap junctions is important in SINGLE unit smooth muscle
What causes smooth muscle activation? Relaxation?
- Alpha-adrenergic stimulation
2. Beta - adrenergic = relaxation
What do all pathways require for smooth muscle activation?
activation of MLCK
- myosin light chain kinase to phosphorylate –> leading to cross-bridge formation (uses ATP)
What regulates phosphates?
cGMP
- regulated by NO release from endothelial cells
- if high = relaxation of blood vessels (viagra)
Name 3 ways to regulate smooth muscle:
- regulate calcium
- Regulate phosphotase
- Regulate kinase
What is the function of Angiotensin II?
CONTRACTION
What is the second messages for alpha-adrenergic receptors? Beta-adrenergic?
- IP3 (stimulate contraction)
2. cAMP ( stimulate relaxation)
What type of muscle requires somatic neural input? (not autonomic)
SKELETAL
- voluntary (the rest involuntary)
What type of hormonal control does the heart use?
EPINEPHRINE
What type of regulatory protein do the following bind:
- smooth muscle
- skeletal
- Cardiac
- Smooth = CALMODULIN
- Troponin
- Troponin
What two muscle types both have gap junctions?
- Cardiac
- Single-unit smooth muscle (NOT MULTI UNIT)
- both have pacemaker ability
