Biology 1001A Study Guide - Quiz Guide: Qrs Complex, Pulmonary Artery, Aorta
Electrocardiography: Electrical Activity of the Heart
External Innervation Regulating Heart Function
1. heart can beat without external innervation
2. external innervation is from AUTONOMIC SYSTEM
parasympathetic - (acetylcholine) DECREASES rate of contractions
cardioinhibitory center (medulla) ->
vagus nerve (cranial X) ->
heart
sympathetic - (norepinephrine) INCREASES rate of contractions
cardioacceleratory center (medulla) ->
lateral horn of spinal cord to preganglionics Tl-T5 ->
postganlionics cervical/thoracic ganglia ->
heart
A. Deflection Waves of ECG
1. P wave - initial wave, demonstrates the depolarization from SA Node
through both ATRIA; the ATRIA contract about 0.1 s after start of P
Wave
2. QRS complex - next series of deflections, demonstrates the depolarization
of AV node through both ventricles; the ventricles contract throughout the
period of the QRS complex, with a short delay after the end of atrial
contraction; repolarization of atria also obscured
3. T Wave - repolarization of the ventricles (0.16 s)
4. PR (PQ) Interval - time period from beginning of atrial contraction to
beginning of ventricular contraction (0.16 s)
5. QT Interval the time of ventricular contraction (about 0.36 s); from
beginning of ventricular depolarization to end of repolarization
V. The Normal Cardiac Cycle
A. General Concepts
1. systole - period of chamber contraction
2. diastole - period of chamber relaxation
3. cardiac cycle - all events of systole and diastole during one heart flow
cycle
