Regulation of heart rate
Intracelluler regulation
Bowditch phenomena: increasing of HR causes increasing of force of cardiac muscle contraction
Intracardiac reflexes
If during diastole volume of the blood is very high there is overstretching of the cardiomyocites. It causes excitation of Cholinergic efferent neurons and inhibition of cardiac activity by Acetilcholine.
If during diastole volume of the blood is not very high, the stretching of the cardiomyocites is not very high too. It causes excitation of Adrenergic efferent neurons and increase of cardiac activity by Adrenaline.
Autonomic regulation of the heart
Autonomic regulation of the heart occurs by the sympathetic and parasympathetic nerve fibers
Parasympathetic tone reduces the typical resting heart rate to approximately 70 beats/min, and parasympathetic stimulation reduces the heart rate further (produces a negative chronotropic effect). Parasympathetic nerves release acetylcholine, which acts via the muscarinic receptors on the nodal cells. Acetylcholine increases the membrane permeability to K+.
Sympathetic nerve stimulation or circulating catecholamines increase the heart rate (produce a positive chronotropic effect). Sympathetic nerves release norepinephrine, acting on the β1-adrenergic receptors. Norepinephrine increases the membrane permeability to Ca+.
Activation of the sympathetic nervous system occurs in response to stress.
Examples of intrinsic activation of the sympathetic nervous system include pain, fear, anxiety, or hypotension; examples of extrinsic activation include the use of drugs such as caffeine, cocaine, methamphetamines, or ephedrine.
Nerve centers of heart rate regulation:
Medulla oblongata and Spinal cord centers
Heart rate is regulated by vegetative nucleuses of sympathetic and parasympathetic parts of autonomic nervous system in lateral horns of the spinal cord or in the Medulla oblongata.
These centers change Heart rate according the “fight and flight” or “rest and digest” states.
Hypothalamus
Hypothalamus changes Heart rate according the functional state of the body (rest, sleep, physical exercises, hot or cold weather and so on)
Cortex
Cortex changes Heart rate according the emotional activity and reflectively
