Human Physiology - Midterm

• pacemaker potential = electrical
• cardiac action potential = muscle
• ECG = electrocardiogram
• cardiac output (CO) = volume of blood pumped per minute
• blood pressure (BP) = normal is 120/80
• if BP low: hypotension; death in minutes
• if BP high: hypertension; death in decades
• Baro reflex: raises BP when low
• to find cardiac output, CO = HR x SV
• to find blood pressure, BP = CO x PR (peripheral resistance)
• artery goes away from heart
• vein goes towards heart
• pulmonary circuit= lungs
• systemic circuit = rest of body
• AV valves: tricuspid (right side; 3) and bicuspid (left side; 2)
• semilunar valves: pulmonary and aortic
• the natural pacemaker of the body is SA node, which is located in the right atrium
• pacemaker --> conduction fibers --> contractile fibers
• conduction fibers are larger in diameter
• the atria/ventricles are separated by fibrous bundles
• the membrane potential never rests
• the heart will spontaneously depolarize and repolarize
• conduction pathway of the heart

  1. SA node - depolarizes the fasts
  2. internodal pathways - also functions as pacemaker
  3. AV node - next in line for pacemaker after SA
  4. AV bundle (bundle of His)
  5. right and left bundle branches
  6. Purkinje fibers - move out to contract
• cardiac muscle cells are electrically connected via Gap junctions
• desmosome - protein fibers that function to resist stretching
• desmosomes are important as it occurs every time the heart fills
• hypertrophy: reduced contraction
• gap junction: passage of current
• steps in conduction

  1. AP is initiated in the SA node
  2. AP is conducted throughout atria (rapid, large, low resistance)
  3. conduction slows at the AV node (small, allows for filling)
  4. AP travels rapidly through the bundle of His and bundles
  5. AP spread through ventricles (bottom to top)
  6. rest
• artificial pacemakers were line-powered that failed during power outages
• 1957 was the first battery-powered pacemaker
• older models of pacemakers stimulate at a fixed rate
• pacemakers sense heart rate and stimulate appropriately
• pacemakers use the same battery as a 787 plane
• Using a hybrid circuit, pulse generator, and lithium batteries, a dual chamber pacemaker has one lead/electrical wire stimulates the right atrium and one stimulates the right ventricle to beat properly
• 4 phases of a neuronal AP: threshold, depolarization, repolarization, hyperpolarization
• during the threshold, sodium channels open, potassium channels open (delayed rectifier) and the cell repolarizes the lost sodium channels
• during repolarization, there is a large influx of sodium so the cell becomes positive
• pacemaker cells do not have a steady resting potential
• potassium equilibrium potential: -94 mV