smooth muscle

• What are the three types of muscle tissue?

  Smooth, cardiac, and skeletal muscle
• What distinguishes smooth muscle from cardiac and skeletal muscle?

  Smooth muscle is non-striated and lacks characteristic markings

  
• What is the structure of smooth muscle cells?

  • Spindle-shaped cells with central nuclei
  • Arranged closely to form sheets
  • No striations (not arranged in sarcomere pattern)

  
• Where is smooth muscle located in the body?

  In walls of hollow organs, blood vessels, eye, glands, uterus, and skin
• What is the primary function of smooth muscle?

  To propel substances or objects along internal passageways
• How is smooth muscle controlled?

  By involuntary control of the Autonomic Nervous System and hormones
• What type of contraction does smooth muscle exhibit?

  Slow, wave-like contraction

  
• What are gap junctions in visceral smooth muscle?

  They allow for communication between adjacent smooth muscle cells

  
• What are dense bodies in smooth muscle cells analogous to?

  1. discs of skeletal and cardiac muscle fibers

  
• What is the role of caveolae in smooth muscle cells?

  They may act as T-tubules to modulate smooth muscle cell contraction
• How does the sarcoplasmic reticulum in smooth muscle compare to that in skeletal muscle?

  It is poorly developed, comprising about 5% of the total cell volume
• Where does the calcium needed for smooth muscle contraction come from?

  From the extracellular fluid surrounding the cell
• What types of filaments are present in smooth muscle cells?

  Thick myosin filaments, thin actin filaments, and intermediate filaments

  
• What is the role of calmodulin in smooth muscle contraction?

  It is a regulatory protein that helps with muscle contraction

  
• What are the steps involved in the contraction of smooth muscle?

  1. Membrane depolarization opens L-type calcium channels
  2. Extracellular calcium enters the cell
  3. Calcium binds to calmodulin, forming a complex
  4. Complex activates myosin light chain kinase (MLCK)
  5. MLCK phosphorylates myosin heads
  6. Myosin heads attach to actin-binding sites
  7. Thin filaments slide past thick filaments, causing contraction

  
• How does relaxation of smooth muscle occur?

  Through dephosphorylation of the myosin head mediated by myosin light chain phosphatase

  
• What maintains muscle tone in smooth muscle?

  A low concentration of calcium present within the sarcoplasm
• What are latch-bridges in smooth muscle?

  Specialized cross-bridges that remain between myosin heads and actin

  
• What happens to calcium during relaxation of smooth muscle?

  Calcium is pumped out of the cell or back into the sarcoplasmic reticulum
• How does the mechanism of contraction differ between smooth and skeletal muscle?

  Smooth muscle uses calmodulin, while skeletal muscle uses troponin

  
• What are the main differences between multiunit and single-unit smooth muscle?

  • Multiunit smooth muscle:
  • Neurologic
  • Consists of discrete units
  • Requires separate nerve stimulation
  • Found in large blood vessels and airways

  
  

  • Single-unit smooth muscle:
  • Myogenic
  • Auto-excitable
  • Electrically linked by gap junctions
  • Found in the gastrointestinal tract and uterus

  
• What is the primary characteristic of tonic contraction in smooth muscle?

  Maintains a state of partial contraction for a long time
• What is the primary characteristic of phasic contraction in smooth muscle?

  Contraction in bursts, rapid and transient

  
• How does smooth muscle differ in its neuromuscular junction compared to skeletal muscle?

  Smooth muscle lacks elaborate neuromuscular junctions

  
• What is the role of pinocytosis in smooth muscle cells?

  It allows neurotransmitters to be taken into the cells
• Describe the corkscrew-like mechanism in smooth muscle contraction.

  • Arrangement of thick and thin filaments in contracted and relaxed states
  • Allows for efficient contraction and relaxation