Final answer:
It is largely True that hair cells in the spiral organ of the ear are never replaced. Damage or loss of these cells, responsible for converting sound into neural signals, can cause permanent hearing loss, as they do not regenerate in humans.
Step-by-step explanation:
The statement that hair cells in the spiral organ of the ear are never replaced is largely True. In humans, the inner and outer hair cells within the organ of Corti (spiral organ) do not regenerate if they are damaged or lost, which can result in hearing loss. These cells play a critical role in converting mechanical vibrations from sound waves into neural signals that the brain interprets as sound.
The inner hair cells are the primary auditory receptors and number about 3,500, whereas the outer hair cells, which number approximately 12,000, are crucial for enhancing the precision of sound transduction. Both types of hair cells contain stereocilia that bend in response to sound waves, leading to the depolarization of the hair cell membrane and the initiation of a signal to the cochlear nerve.
The process of sound transduction is highly sensitive and relies on the proper functioning of these hair cells. Unfortunately, once hair cells are damaged, due to factors such as excessive noise exposure or ageing, the human body lacks the capacity to replace them, resulting in permanent hearing impairments.