By: Susan Barman and Michael Kenney (Clinical and Experimental Pharmacology and Physiology (2007) 34, 350–355)
The basis of biology relies heavily on the idea of rhythmicity. More specifically, the functions of every day life, such as a heart beat, breathing, flexion-extension, etc. The autonomic system is vital in a lot of these rhythm controls.
Three aspects of rhythm are discussed to be an important contributor. The first being the idea of synchronization. The second is the ability to predict repetitive events. Lastly, information encoded by frequency is more resistant to distortion by noise.
To quantify rhythmicity, one can perform a time domain analysis or a frequency domain analysis. Time domain will use time to detect periodicity by comparing a signal to a replica of itself. The lags in the signal will represent the peaks and valleys of the original signal. Fast Fourier transformation is an algorithms used to analysis the frequency of a signal. It matches the signal to sine waves over a range of frequencies. Frequency domain is more efficient to use, especially if a signal has multiple components. These analysis are also vital to assessing the correlation between two signals, or coherence. It defines the strength of the signal at each specific frequency. A value of 1.0 means the signal is undisturbed by noise.
Signals can vary depending on the physiological state of the animal, the type of nerve being recorded from, and what the species actually is. The characteristic of the signals also relate it to various events in the biological system, for instance, a heart beat or a respiratory cycle. These are called the cardiac-related rhythm and the respiratory-related rhythm. A range of frequencies will correspond to these events. The alteration of these physiological events will alter the signal. For example, smooth muscle can be induced at frequencies below 0.5 Hz, while arterial pressure in cats is controlled at a frequency of 10 Hz. One observation pointed out was that in an aperiodic setting, the signal was not as strong, but when signals were compared to each other, the coherence was high. This observation was crucial to validating the importance of synchronization of activities. The inputs that are driving each of these signals are strongly related. They also pointed out the prevalence in change when the body attempts to maintain homeostasis. For example, when acute heat or hypothermia is introduced, synchronization of sympathetic nerve discharged was gone.
The signals are vital to the responses in the biological system. It keeps processes in line and in sync with each other. When one thing is effected, the signaling changes, to address this change.
-Tsetse Fly
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