The dependence of the phasic response of the taste nerves on stimulus flow rate arises in the diffusion boundary layer region at the lingual surface: A convective-diffusion analysis

作者：DeSimone John A^*

来源：Chemical Engineering Science, 2017, 168: 289-308.

DOI：10.1016/j.ces.2017.04.034

• Taste nerve response
• Phasic response
• Stimulus transport
• Convective-diffusion
• Stagnation-point flow
• Diffusion boundary layer

The dynamics of the taste neural response are highly dependent on the velocity of the stimulus solution delivered to the taste receptor cells. In anesthetized rats, stimulus solution delivered at high stimulus flow rate (1 m1/s) to the taste receptor cells on the dorsal lingual surface by axisymmetric stagnation flow yields a neural response with a rapid transient increase above baseline to peak response. At flow cessation (after about 3 s) the neural response then rapidly declines exponentially to steady state or tonic response. This rapid transient or phasic response is not observed at low stimulus flow rate (e.g. 7.5 ml/min). In the latter case the neural response rises with a slow exponential decline ultimately attaining the same steady state value observed in the high flow rate case. Although the taste quality may be nominally the same in each case, the dynamics of the afferent response differ markedly. Therefore, the input to the brain, where a variety of sensory inputs related to food ingestion are combined to yield a food's flavor value, is not the same for each flow rate. Thus physical variables at work in the oral cavity, such as flow velocity and viscosity, play a role in determining the palatability of a meal through their effects on both taste and tactile receptors. I show here that stimulus flow rate controls the appearance of a phasic transient neural response by its effect on the thickness of the diffusion boundary layer in contact with the dorsal lingual surface. This is accomplished by solving the convective-diffusion equation with the normal component of the stimulus flow velocity determined by stagnation flow fluid dynamics. In so doing I derive useful approximate closed form solutions for both planar and axisymmetric stagnation flow. I propose a mathematical model of taste receptor function that depends on the surface concentration of the taste stimulus. I show that the surface stimulus concentration (and therefore the neural response) increases with fluid velocity and that the thickness of the diffusion boundary layer is inversely proportional to the square-root of stimulus fluid velocity. A phasic transient neural response emerges at high flow rates because the surface stimulus concentration initially rises rapidly and then subsequently declines as the system evolves through a succession of steady states of diminishing fluid velocity. The model also accounts for diminished taste responses observed with increased stimulus solution viscosity.

• 出版日期2017-8-31