The provided code models the biomechanics of the cochlea, specifically the basilar membrane (BM) dynamics in the gerbil cochlea. It focuses on the interaction between fluid movements within the cochlea and the mechanical properties of the cochlear partition, including the basilar membrane. Here are the key biological concepts embedded in the model:
The cochlea is a spiral-shaped organ in the inner ear responsible for sound transduction. It is composed of three main fluid-filled chambers or scalae: scala vestibuli, scala media, and scala tympani. The model represents the fluid volume velocity across these chambers, as well as the resulting pressure differences that drive the basilar membrane movements.
The basilar membrane plays a critical role in sound frequency discrimination. In the code, the BM's volume velocity and mechanical impedance are calculated. The code highlights that the BM width (Wbm) and organ of Corti thickness (y) are spatially invariant parameters, reflecting the constant morphological characteristics of these structures along the cochlear length for this model.
The frequency-place map determines the resonant frequency at different points along the cochlea. The code uses the Greenwood function parameters to map different frequencies to specific cochlear locations. This reflects the tonotopic organization of the cochlea, where high frequencies are detected at the base and low frequencies at the apex.
The impedance calculations (Zp) model the cochlear partition's resistance to fluid movement, incorporating mass, compliance, and resistance parameters of the cochlear structures. These are crucial for understanding how sound-induced fluid motion affects BM displacement.
The helicotrema is effectively modeled as an impedance boundary condition, representing its role in allowing fluid movement between the scala vestibuli and tympani. This passage acts as a pressure relief and is considered in the apex boundary conditions.
The code incorporates viscous resistance (Rbm) and compliance (Cbm), which are essential for modeling how the cochlear partition responds to fluid motion. These parameters highlight the mechanical dampening effects and elasticity of the cochlear tissues.
The input frequency (f) represents the sound stimulus being investigated, and the quality factor (Q) models the sharpness of the resonant peak, important for understanding frequency selectivity in the cochlea.
The resulting pressure difference, basilar membrane velocity, and cochlear partition impedance at various points along the cochlea's length are calculated. This highlights how sound is transformed into mechanical motion, causing a traveling wave along the basilar membrane that is crucial for auditory perception.
In summary, the code models the biomechanical processes within the cochlea that facilitate sound frequency discrimination, focusing on how sound pressure waves are transformed into mechanical signals through the dynamic properties of cochlear structures in the gerbil.