Autonomic Nervous System and the Heart

Autonomic Nervous System and the Heart

• The heart receives both sympathetic and parasympathetic innervation.
• The sympathetic nervous system increases heart rate, force of contraction, and the conduction of action potentials.
• The parasympathetic nervous system reduces heart rate and conduction through the AV node.
• At rest, both systems are active, but the parasympathetic system dominates.
• Respiration affects the heart rate.
• An isolated heart beats at 100 beats per minute.
• Adding sympathetic activity increases the rate to 120 beats per minute.
• Adding parasympathetic activity decreases the rate to 70 beats per minute.
• The heart, at rest, receives both sympathetic and parasympathetic activity, but parasympathetic is dominant.

Innervation of Heart and Vessels

• The table shows sympathetic and parasympathetic innervation of different parts of the heart and arteries.
• (Note: the table content of sympathetic/parasynthetic innervation is provided from the image)

Cardiac Dive Response

• Heart rate is recorded using a pressure transducer.
• The subject takes a deep breath and submerges their face in ice-cold water.
• The subject holds the position for as long as possible (usually about 20 seconds).
• Heart rate is recorded throughout the dive.
• The heart rate decreases during the dive, for example: from 88 (before) to 68 (during the dive) beats per minute.

Respiratory Sinus Arrhythmia

• During respiratory sinus arrhythmia, the heart rate increases or decreases during inspiration.
• This is due to changes in vagal tone and sympathetic activity.
• Consequences of RSA affect gaseous exchange in the lungs.
• Changes in heart rate are due to mechanisms like the Bainbridge reflex (aka atrial reflex)

Variations in Heart Rate: Questions

• Approximately what is the normal heart rate at rest in a human?
• At what rate does an isolated human heart beat at normal body temperature(NB. An isolated heart has no functional nerves running to it.)?
• At rest, is there sympathetic nerve activity or parasympathetic nerve activity?
• During the dive, which nervous system is activated?
• Which neurotransmitters and cardiac receptors are involved in the decreased heart rate during the dive response?
• What possible advantages does this parasympathetic reflex provide to diving animals?

Summary of the Autonomic Nervous System

• Heart receives sympathetic and parasympathetic innervation.
• Sympathetic nerves increase heart rate, conduction & contraction.
• Parasympathetic nerves decrease heart rate, conduction & contraction.
• Active at rest but Parasympathetic dominates.
• Respiration affects heart rate.
• Denervated heart (transplant) - any ANS control?
  • Denervated heart shows increased sensitivity to adrenaline.
  • Denervation increases the number of beta receptors.

Normal Heart Rate

• Normal heart rate at rest is roughly 70-80 beats per minute in humans.