Inner and outer hair cells, both located in the cochlea of the human ear, play crucial roles in our hearing process. However, they differ significantly in terms of their functions, innervations, and anatomical characteristics. Let's delve deeper into understanding these differences.
Primarily, inner hair cells are responsible for transforming sound vibrations from the cochlear fluid into electrical signals. These signals are then transmitted to the brain via auditory nerves. Conversely, outer hair cells work to amplify low-level sounds, mechanically guiding them into the cochlear fluids.
In the mammalian cochlea, there are two distinct types of hair cells - inner hair cells and outer hair cells. Each type has unique functional and anatomical attributes.
A Closer Look at Inner Hair Cells
The cochlea contains a single row of inner hair cells, contrasted by three rows of outer hair cells.
Inner hair cells are the primary sensory receptors. Approximately 95% of auditory nerve fibers originate from these cells and connect to the brain.
These cells convert vibrations in cochlear fluids into electrical signals, which are then transmitted through the auditory brainstem to the auditory cortex.
Examining Outer Hair Cells
Outer hair cells amplify low-level sounds, directing them mechanically towards the cochlea.
The amplification process is facilitated by the movement of hair bundles.
The terminals of these hair cells mostly arise from efferent axons, which originate from cells in the brain.
Comparing Inner and Outer Hair Cells
The table below provides a comprehensive comparison between inner and outer hair cells.
Inner Hair Cells
Outer Hair Cells
What is their function?
Inner hair cells are receptive cells in the cochlea that convert sound waves into nerve signals.
Outer hair cells in the cochlea mechanically amplify low-level sound through the movement of hair bundles.
How are they innervated?
Inner hair cells are predominantly innervated by afferent nerves.
Outer hair cells are mainly innervated by efferent nerves.
How many are present at birth?
Approximately 3500 inner hair cells are present in the human cochlea at birth.
Around 12000 outer hair cells are present in the human cochlea at birth.
How are they organized?
Inner hair cells are organized in a single row.
Outer hair cells are organized in three rows.
Where are they located?
Inner hair cells are located at the terminals of the inner hair cells.
Outer hair cells are located at the terminals of the outer hair cells.
Is prestin expressed?
No, inner hair cells do not express prestin.
Yes, outer hair cells do express prestin.
What is their primary role?
Inner hair cells convert sound vibrations into electrical signals.
The main function of inner hair cells is to transform the vibrations in the cochlear fluids into electrical signals. These signals are then relayed through the auditory brainstem and then to the auditory cortex.
What is the role of outer hair cells?
Outer hair cells amplify the low-level sounds mechanically, which are directed towards the cochlea. This amplification is governed by the movement of the hair bundles.
What is the difference between the innervations of inner and outer hair cells?
Inner hair cells are innervated by more afferent nerves compared to efferent nerves, while outer hair cells are innervated by more efferent nerves compared to afferent nerves.