Smooth Muscle

• What type of muscle is smooth muscle?

  Involuntary muscle

  
• Where is smooth muscle primarily located?

  In walls of hollow structures and organs
• What is a key characteristic of smooth muscle?

  Not striated
• How are contractile filaments arranged in smooth muscle?

  In loose bundles

  
• What is the role of smooth muscle in homeostasis?

  Control fluid and act as sphincters
• What type of contractions do smooth muscles exhibit?

  Tonic contractions

  
• What is a characteristic of smooth muscle contractions?

  They are slow and cause little fatigue
• How do smooth muscles compare to skeletal muscles in size?

  Much smaller than skeletal muscle

  
• What is the arrangement of actin and myosin in smooth muscle?

  In a lattice/criss-cross arrangement

  
• What must happen for smooth muscle contraction to occur?

  Myosin light chain kinase must phosphorylate myosin

  
• What initiates the contraction of smooth muscle?

  Ca2+ -mediated change in thick filaments

  
• What complex forms when calcium levels increase in smooth muscle?

  Ca/calmodulin complex

  
• What is required for smooth muscle relaxation?

  Decreased [Ca2+]i and increased myosin phosphatase activity

  
• What is the role of myosin light chain kinase (MLCK) in smooth muscle?

  Phosphorylates myosin light chains for contraction

  
• What happens to smooth muscle in the absence of CaCM?

  It remains quiescent and inactive
• What is the effect of elevated CaCM levels on smooth muscle?

  Induces MLCK activity and contraction

  
• What must occur for smooth muscle contraction to happen?

  Phosphorylation of p-light chains and removal of caldesmon

  
• How does adrenaline affect smooth muscle contraction?

  It raises cAMP and modulates contraction strength
• What is the role of RhoA/Rho kinase signaling in vascular smooth muscle contraction?

  Regulates thick filament activity

  
• What is the effect of inhibiting Rho-kinase on vascular smooth muscle?

  It would reduce contraction strength
• What are the two types of smooth muscle?

  • Single-unit: all fibers contract together
  • Multi-unit: fibers contract independently

  
• What are the characteristics of smooth muscle compared to skeletal muscle?

  • Smaller size
  • No different fiber types
  • Longer actin and myosin filaments
  • Higher actin/myosin ratio
  • Lattice arrangement of filaments
  • Attached to dense bodies
  • Contracts into a ball-like shape

  
• What are the mechanisms of smooth muscle contraction and relaxation?

  Contraction:

  • Ca2+/calmodulin activates MLCK
  • Phosphorylation of myosin light chains
  • Activation of actomyosin ATPase

  
  

  Relaxation:

  • Decreased [Ca2+]i
  • Increased myosin phosphatase activity

  
• What are the regulatory mechanisms governing vascular smooth muscle contraction?

  1. Thick filament regulation by RhoA/Rho kinase
  2. Thin filament regulation by protein kinase C/ERK signaling

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

  Single-unit:

  • All fibers contract together
  • Found in hollow organs

  
  

  Multi-unit:

  • Fibers contract independently
  • Found in blood vessels and respiratory tract

  
• What is the significance of the p-light chain in smooth muscle?

  • Exists in phosphorylated and non-phosphorylated states
  • Phosphorylation determines contraction

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

  • Binds to thin filaments
  • Freeing myosin binding sites for contraction

  
• How does calcium influence smooth muscle contraction?

  • Elevation of calcium induces contraction
  • Formation of Ca2+/calmodulin complex activates MLCK

  
• What is the relationship between MLCK and smooth muscle contraction?

  • MLCK phosphorylates myosin light chains
  • Essential for muscle contraction

  
• What happens to smooth muscle when calcium levels decrease?

  • Muscle relaxes
  • Myosin phosphatase activity increases

  
• What is the effect of cAMP on smooth muscle contraction?

  • Modulates contraction strength
  • Reduces MLCK affinity for CaCM

  
• What is the significance of the actomyosin ATPase activity in smooth muscle?

  • Essential for muscle contraction
  • Activated by phosphorylated myosin light chains

  
• What is the role of myosin phosphatase in smooth muscle relaxation?

  • Dephosphorylates myosin light chains
  • Promotes muscle relaxation

  
• What is the effect of increased myosin phosphatase activity on smooth muscle?

  • Promotes relaxation of smooth muscle
  • Reduces contraction strength

  
• What is the role of IP3 in vascular smooth muscle contraction?

  • Activates phospholipase C
  • Increases intracellular calcium levels

  
• What is the relationship between RhoA and smooth muscle contraction?

  • RhoA activates Rho-kinase
  • Inhibits myosin phosphatase, enhancing contraction

  
• What is the significance of the myosin light chain in smooth muscle physiology?

  • Key regulator of contraction
  • Phosphorylation state determines muscle activity

  
• What are the effects of calcium on smooth muscle contraction and relaxation?

  • High calcium levels induce contraction
  • Low calcium levels promote relaxation

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

  • Binds calcium
  • Activates MLCK for contraction