Lecture 19/ Human circulation

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c. Atrioventricular node
The wave of depolarization is transmitted from the atria to ventricles through the atrioventricular (AV) node.

d. Transmission through ventricles
Special conducting fibers known as the bundle of Hisand Purkinje fibers transmit the signal throughout the ventricles.

e. Speed of transmision
Relative speeds of transmission are:

through atria
along atrioventricular node throughout ventricle

0.8 m/s 0.05 m/s 5 m/s

Q. What are the results of these differences?
- slow transmission through AV node creates a 0.1 sec delay - fast transmission throughout ventricles causes an explosive contraction

2. Extrinsic control
Although the heart beats spontaneously, both the heart rateand the stroke volumecan be altered by outside influences.

a. Peripheral nervous system
i. parasympathetic (acetylcholine)
- slows rate of K+ channel closing The intrinsic rhythm generated by the SA node would produce a HR of ~100 bpm; this is slowed to a resting rate of ~70 bpm by the action of the parasympathetic nervous system.

As with a neuron, the resting potential of heart muscle cells is generated by the action of both the Na+/K+ pump and K+ channels that allow some of the K+ to leak out. In the SA node cells, the K+ channels gradually close, causing the membrane potential to rise to threshold.

Acetlycholine released by the parasympathetic nervous system binds to receptors on cardiac muscle cells and causes K+ channels to remain open longer.

Q. What effect will this have and why?
- increases time to reach threshold, because slows depolarizationof cell


		c. Atrioventricular node The wave of depolarization is transmitted from the atria to ventricles through the atrioventricular (AV) node. d. Transmission through ventricles Special conducting fibers known as the bundle of Hisand Purkinje fibers transmit the signal throughout the ventricles. e. Speed of transmision Relative speeds of transmission are:
		through atria along atrioventricular node throughout ventricle		0.8 m/s 0.05 m/s 5 m/s
		Q. What are the results of these differences? - slow transmission through AV node creates a 0.1 sec delay - fast transmission throughout ventricles causes an explosive contraction 2. Extrinsic control Although the heart beats spontaneously, both the heart rateand the stroke volumecan be altered by outside influences. a. Peripheral nervous system i. parasympathetic (acetylcholine) - slows rate of K+ channel closing The intrinsic rhythm generated by the SA node would produce a HR of ~100 bpm; this is slowed to a resting rate of ~70 bpm by the action of the parasympathetic nervous system. As with a neuron, the resting potential of heart muscle cells is generated by the action of both the Na+/K+ pump and K+ channels that allow some of the K+ to leak out. In the SA node cells, the K+ channels gradually close, causing the membrane potential to rise to threshold. Acetlycholine released by the parasympathetic nervous system binds to receptors on cardiac muscle cells and causes K+ channels to remain open longer. Q. What effect will this have and why? - increases time to reach threshold, because slows depolarizationof cell