Extrinsic Innervation of the Heart

The nervous system can modify the basic heart rate set by the intrinsic conduction system

Acts most strongly on SA and AV nodes


Extrinsic Regulation of Heart Function

Nervous system

PNS -dominant influence on heart during rest (acetylcholine) [vagal innervation]

decreases heart rate

little effect on contractility

SNS - activated during stress, excitement, exercise (epinephrine, norepinephrine)

increases heart rate

increases contractility

Other Regulation of Heart Rate





Body Temperature



Heart Rate

Persistant rate changes

Tachycardia - abnormally fast heart rate (> 100 bpm)

Bradycardia - abnormally slow heart rate (< 60 bpm)


Measurement of Electrical Conduction in the Heart

De- and Re-polarization are electrical events and can be recorded by an electrocardiogram (EKG or ECG)

Three deflection waves which represent atrial depolarization and ventricular depolarization and repolarization

P wave

QRS complex

T wave



Atrial contraction appears as a "P" wave on the EKG

movement of impulses from SA node through atria

Movement of impulse through the AV node results in a pause on the EKG



QRS wave results from ventricular depolarization

movement of impulse through the Bundle of His, Bundle branches and Purkinje fibers

T wave is caused by ventricular repolarization

no physical response from the ventricles