Oscillation myogenic

Fig. 12.2 (a) Experimental recording of the proximal tubular pressure in a single nephron of a normotensive rat. The power spectrum (b) clearly shows the TGF-mediated oscillations at fsiow(t) 0.034 Hz and the myogenic oscillations at ffasi(t) 0.16 Hz. The spectrum also displays harmonics and subharmonics of the TGF-oscillations. A plot... 

Figure 12.2b shows such a power spectrum for the tubular pressure variations depicted in Fig. 12.2a. This spectrum demonstrates the existence of two main and clearly separated peaks a slow oscillation with a frequency fsiow 0.034 Hz that we identify with the TGF-mediated oscillations, and a significantly faster component at ffasl 0.16 Hz representing the myogenic oscillations of the afferent arteriole. Both components play an essential role in the description of the physiological control system. The power spectrum also shows a number of minor peaks on either side of the TGF peak. Some of these peaks may be harmonics (/ 0.07 Hz) and subharmonics (/ 0.017 Hz) of the TGF peak, illustrating the nonlinear character of the limit cycle oscillations.

Fig. 12.8 Phase plot illustrating the oscillation in the variables associated with the afferent arteriole. The dynamics is interpreted as a 2 8 synchronization between the slowTGF-mediated mode and the fast myogenic mode. T = 16 s and a = 24.2. This is the same solution that we referred to as a period-2 solution in connection with Fig. 12.5.

As demonstrated by the power spectra in Figs. 12.2a and 12.3b, regulation of the blood flow to the individual nephron involves several oscillatory modes. The two dominating time scales are associated with the period Tsiow 30—40 s of the slow TGF-mediated oscillations and the somewhat shorter time scale Tjast 5—10 s defined by the myogenic oscillations of the afferent arteriolar diameter. The two modes interact because they both involve activation of smooth muscle cells in the arteriolar wall. Our model describes these mechanisms and the coupling between the two modes, and it also reproduces the observed multi-mode dynamics. We can, therefore, use the model to examine some of the phenomena that can be expected to arise from the interaction between the two modes. 

Fig. 12.11 Two-mode oscillatory behavior in the single nephron model. Black colored regions correspond to a chaotic solution. The figure shows different regions in which 1 4, 1 5 and 1 6 synchronization occurs in the interaction between the fast myogenic oscillations...

Note the 1 5 synchronization between the slowTGF-mediated oscillations and the myogenic oscillations. The 1 5 synchronization can be considered to arise from a 1 1 synchronization between the fifth harmonic of the TGF oscillations and the myogenic oscillations. 

In the distal stomach, small intestine, and colon, there are intermittent bursts of rapid electrical oscillations, called the electrical response activity (ERA) or spike bursts. The ERA occurs during the depolarization plateaus of the EGA if a cholinergic stimulus is present and it is associated with muscular contractions (Figure 6.3). Thus, neural and chemical control systems determine whether contractions wiQ occur or not, but when contractions are occurring, the myogenic control system (Figure 6.4) determines the spatial and temporal patterns of contractions. 

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