Autonomic Control of the Heart

To see how the motor neurons of the sympathetic and parasympathetic divisions exert their actions on target cells, it will be useful to examine a particular example in detail. The example we will explore is the neural control of the heart. The heart is made up of muscle cells, which are in some ways similar to the skeletal muscle cells we learned about in Chapter 10. However, there are some important differences, which we must understand before we can examine the effects that the sympathetic and parasympathetic neurons have on the heart. Thus, we will first discuss the electrical and mechanical properties of the heart muscle, and then return to the modulation of those properties by norepinephrine and ACh, which are the neurotransmitters released by the sympathetic and parasympathetic inputs to the heart, respectively.

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