External recordings permit monitoring of electrical activity in the body
  Impt medical diagnostic tools - quick, painless, noninvasive

     EEG -  electroencephalogram - brain
     EMG - electromyelogram  - muscle

     ECG/EKG  Electrocardiogram  - visualizing the electrical events 
                of the heart    Fig 20; W&D

     ECG tracings depict the sum of all electrical potentials generated
         by all cardiac muscle cells at a specific moment; 
         actually measures currents produced in EC fluid   

        Each part of the ECG reflects depol. or repol. of a heart region
        Since depolarization is the signal for contraction, portions 
         of the ECG may be correlated with mechanical (pumping) events 

        Einthoven's triangle  -  placement of electrodes [rt and left 
            wrists and left ankle]; modern measurements of heart 
            electrical activity utilizes 12 leads

Three major parts of ECG:  [patterns vary with electrode placement]
         
        P wave - atrial depolarization
        QRS complex - progressive wave of ventricular depol
        T wave  - ventricular repolarization; end of plateau

Correlating ECG, ventricular action potential and ventricular contraction 
 F 20 and 23

Cardiac cycle - atrial and ventricular contractions and relaxations,0.8 sec
    Phases reflect ventricular activity

       systole - ventricular contraction, blood is pumped out of 
                  both  ventricles
                 stroke volume - amt bl ejected
       diastole -  ventricles relax and fill with blood
     
    Examine   F 25  [left side of heart - systemic circ]
      At the end of diastole - 
        1] heart at rest - all chambers relaxed; atria filling with bl 
           from veins since AV valves open, ventricles also filling;
           aortic pressure falling as bl move away from heart

        2] SA fires - atria depolarize [P wave] and contract forcing 
           last portion of bl into ventricles
              
        3] concommitant rises in
                  atrial pressure (blue)
                  ventricular pressue (magenta) 
                  ventricular blood volume (red) 

        Depolarization wave spreads to AV node; AV node depol.
             spreads via BH and PF

      Systole - ventricles contract, ventr pressure rises, AV valves  close -
                brief isovolumetric ventr pressure, then aortic  valve opens 
                and  bl exits;     
                ventricular vol and pressure drop

      Beginning of diastole - repolarization of ventr [T wave]

    Pulmonary circulation is low pressure but = vol system, 
      rt ventr less muscular
----------------
 Cardiac Output  -  vol of bl pumped out of the ventricle per min
                      CO  =  HR  x   SV
                          =  72 beats/min  x  0.07 L/beat
		          =   5.0 L/min
         with moderate to strenuous exercise  20 - 35 L/min
----------------
Control of Heart RATE

     Autonomous discharge of SA node would give 100 beats/min
     Regulation - neural and hormonal    F  28

       Stimulation:  
          sympathetic neurons - release norepinephrine
               stim opening of Na+ channels,  incr slope of pacemaker 
               potential; 
               cells of AV node reach threshold faster        
               heart rate increases 
          epinephrine - from adrenal medulla -
      
       Inhibition:
          parasympathetic neurons - release ACh
               close Na+ channels and hyperpolarizes plasma membrane so 
               pacemaker potential is more neg                              

     Signal transduction mechanisms activated by NT or hormone ligand
           opening of pm Ca++  channels
           activate of Ca++ ATPase (pumps) returning Ca++ to SR
           alter binding of Ca++ and troponin
--------------          
Control of Stroke Volume                                F  33
    May be increased by an incr in end-diastolic volume (vol of bl in 
ventricles  before contraction)
    Also affected by
       amt of input from sympathetic  NS
       afterload - arterial "back"-pressure

=================================
SEC  D  --  Vascular System

All vascular vessels are lined with squamous epithelium -  endothelium
   Capillaries have this cellular layer and variable # of pericytes
   Arteries and veins have smooth muscle and varying amounts of 
     connective tissue
   Veins have less muscle and can be expanded to hold more blood
      Compliance - how much a vessel may be stretched

Arteries - highly elastic, large radii; low resistance; pressure reservoir
               
Arterial Blood Pressure  -  avg S/D  =  125/75 mm Hg
     Max - systolic pressure - peak ventr ejection
     Min  - diastolic pressure - just before ventr ejection     

     Magnitude of this ratio affected by -
             stroke vol
             speed with which stroke vol exits ventr
             compliance

      MAP (mean arterial pressure) driving force thruout cycle

Arterioles - contribute to MAP; regulate flow into individual organs; 
                  have increased resistance since smaller radius

                     F organ  =   MAP  / Resistance organ

                  continued next section