My professor's lecture notes say that " The basal rate of firing is called “sympathetic tone” and 'parasympathetic tone" , but a table I found on the internet says that the parasympthetic system has no tonic activity.

Does saying the ANS has tonic activity mean that it sends impulses continuously and at a low rate to effectors? How is the ANS considered rapid then?

On Euroform Healthcare It is written that without the sympathetic and parasympathetic tones, we would not be able to regulate the activity of organs or bring it up and down, I don't understand why that's the case ?

I'm very new to this whole topic (ANS) so please go lightly on me.

  • $\begingroup$ Thanks for the edit! We do still need more context... are we talking about tonic activity in cardiac muscle? Peripheral blood vessels? Urethral sphincters? Without seeing more context my guess is that your professor and the articles / pictures you're running across are talking about totally different physiological systems which accounts for the difference. $\endgroup$ – rotaredom Apr 10 at 22:31
  • $\begingroup$ The thing is, I am so naive when it comes to this topic so I can't be sure but, my professor's notes seem to give a general idea on the topic but the topic's name in the book is " The Autonomic Nervous System and the Adrenal Medulla" If that helps. Regarding the table and the website, no specifications are made , I just want understand the general concept $\endgroup$ – Jaja bae Apr 10 at 22:40

Short answer
Parasympathetic tone is not necessarily mediated by tonic firing.

Nice question! I think part of the confusion stems from terminology. Let's start with some definitions first.

  • 'Tone' in sympathetic tone can be translated as mean activity level (Hayano & Yuda, 2019).
  • 'Tonic' firing by neurons may be translated as a sustained response, which activates during the course of the stimulus (Wang et al., 2014), although some neurons have intrinsic tonic activity as well, like thalamocortical neurons. This opposes to phasic firing neurons.
  • 'Phasic firing' refers to a transient response with one or few action potentials at the onset of stimulus followed by accommodation (Wang et al., 2014).

In your post you seem to assume that parasympathetic tone equals tonic firing activity. I'm not so sure about this. For example, I found a catching paper on the parasympathetic regulation of lung function in guinea pigs (which lacks sympathetic innervation altogether). The paper nicely illustrates (Fig. 1) that parasympathetic regulation of the bronchi in guinea pigs is mediated by both tonic and phasic (burst) stimulation (Myers, 2000):

[P]hasic neurons in guinea pig bronchial parasympathetic ganglia respond to a prolonged suprathreshold stimulation with a high‐frequency burst of action potentials ..., whereas tonic neurons are nonaccommodating and will respond with relatively lower frequency action potentials...

enter image description here
Fig. 1. Phasic and tonic neurons in guinea pig bronchial parasympathetic ganglia. source: (Myers, 2000)

- Hayano & Yuda, J Physiol Anthropol (2019); 38(3) (2019)
- Myers, JCN (2000); 419(417): 439-50
- Wang et al., Channels (2014); 8(4): 298–307

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