Characteristics of the Cardiac Muscles

1
Characteristics of the Cardiac Muscles

• Myocardial Cells
• Characteristics
• automaticity cells can depolarize without any
  impulse from outside source (self-excitation)
• excitability cells can respond to an electrical
  stimulus
• conductivity cells can propagate the electrical
  impulse from cell to another
• contractility the specialized ability of the
  cardiac muscle cells to contract

2
Cardiac Physiology

• 3 types of cardiac muscle cells
• Excitatory Cells
• SA node (in wall of RA)
• Contains pacemaker cells
• Cells of conducting system
• Transatrial Pathways
• AV node (between atria and ventricles)
• Conducting cells along internodal pahtways
• AV bundle (HIS)
• Bundle branches
• Purkinje fibers (distribute stimulus to
  ventricular myocardium)
• Contractile cells

3
The Neuromuscular Junction
4
Skeletal Muscle
Fast Na
Slow K
Stimulus
5
Cardiac Muscle
Slow K
Plateau ?
Fast Na
Slow Na/Ca
Leak Na
6
Self-Excitation

• Leak Na channels
• Slow Na/Ca channels (VG)
• Fast Na Channels

7
Impulse Conduction through the Heart
Figure 2013
8
Conduction

• Conduction depends on
• The size
• Length
• Width
• The intercalated discs
• Number
• Gap junction

9
Contractility

• Why these muscle fibers can perform better
  contraction?
• More Myosin More Sarcomeres
• STRONGER CONTRACTION