Cardiac

1
Cardiac Smooth Muscle

• Chapter 12

12-76
2
Cardiac Muscle (Myocardium)

• Contractile apparatus similar to skeletal
• Striated multinucleate (skeletal) but
  involuntary (smooth)
• Branched adjacent myocardial cells joined by
  intercalated disks (gap junctions)
• Allow APs to spread throughout cardiac muscle

Fig 12.31
12-77
3
Smooth Muscle

• no sarcomeres
• gap junctions
• 16X more actin than myosin
• greater stretching contracting
• Actin filaments anchored to dense bodies

Fig 12.33
12-78
4
Smooth Muscle Contraction

• Controlled by Ca but different from striated
• little SR no troponin/tropomyosin
• Ca enters thru channels in plasma membrane
• Binds with calmodulin
• Ca-calmodulin complex activates myosin light
  chain kinase (MLCK)
• phosphorylates activates myosin
• Myosin forms crossbridges with actin

12-79
5
Fig 12.34
12-81
6
Smooth Muscle Contraction

• Relaxation Ca concentration decreases
• Myosin dephosphorylated by myosin phosphatase
• Myosin can no longer form crossbridges
• Smooth muscle has slower contractions than
  striated
• Can form a state of prolonged binding of myosin
  to actin (latch state)
• Maintains force using little energy

12-80
7
Fig 12.34
12-81
8
Single Multiunit Smooth Muscle

• Single unit spontaneously active (myogenic)
• Some cells are pacemakers
• Many gap junctions to spread electrical activity
• Multiunit requires nerve stimulation by ANS
• NT released along a series of synapses
  varicosities
• Called synapses en passant (in passing)

12-82
9
Fig 12.35
12-83