The process of making sensory hair cells is called "hair cell regeneration." Although mammals, including humans, cannot regenerate sensory hair cells, this ability exists in other vertebrates like fish and amphibians. Here is a general overview of the process:

Progenitor Cells:

Hearing-related sensory hair cells arise from a specific group of progenitor cells called "hair cell progenitors" located in the inner ear. After birth or around the time of hatching in animals like fish and amphibians, these progenitors are responsible for generating new sensory hair cells.

Cell Division and Differentiation:

The hair cell progenitors divide symmetrically to increase their numbers. At a certain point, these progenitors undergo asymmetric cell division, giving rise to two unequal daughter cells. One daughter cell remains as a progenitor, while the other differentiates into a sensory hair cell.

Morphological Changes:

As the hair cell differentiates, it goes through distinct morphological changes. The cell elongates and develops a characteristic hair bundle, which is a bundle of actin filaments topped by sensory stereocilia. The stereocilia are arranged in a specific pattern and function as mechanical sensors.

Synapse Formation:

Once the hair cell reaches maturity, it forms synaptic connections with the auditory or vestibular neurons. These neurons transmit signals from the hair cells to the brain, carrying information about sound or movement.

It's important to note that the molecular mechanisms underlying hair cell regeneration may vary across species and are still an active area of research. In mammals, although mature hair cells cannot be regenerated, there are ongoing efforts to stimulate the regeneration of these cells as potential treatments for hearing loss.

The ability of non-mammalian vertebrates to regenerate hair cells is essential for maintaining their hearing and balance. Some animals can even repair damaged hair cells throughout their lives, while others have a limited capacity for regeneration. Understanding the mechanisms of hair cell regeneration in these species could provide valuable insights into potential therapeutic approaches for human hearing loss.