Which correctly describes a step in auditory signal transduction ?

Options

A. Displacement of the basilar membrane with respect to the tectorial membrane stimulates stereocilia on the hair cells.
B. Pressure waves on the oval window cause vibrations of the melleus, which are transferred via the stapes to the round window.
C. Movement of the stapes causes oscillations in the tympanic membrane, which is in contract with the endolymph
D. Oscillations of the stapes against the oval window set up pressure waves in the semicircular canals.

Explanation

### Step-by-Step Solution:

1. **Understanding Auditory Signal Transduction**:
- Auditory signal transduction refers to the process by which sound waves are converted into electrical signals that can be interpreted by the brain. This process primarily occurs in the cochlea of the inner ear.

2. **Components of the Cochlea**:
- The cochlea is a spiral-shaped organ filled with fluid (endolymph) and contains structures such as the basilar membrane, tectorial membrane, and hair cells (stereocilia). The basilar membrane vibrates in response to sound waves.

3. **Mechanism of Signal Transduction**:
- When sound waves enter the cochlea, they create pressure changes that cause the basilar membrane to move. This movement occurs relative to the tectorial membrane, which is situated above the hair cells.

4. **Activation of Hair Cells**:
- The displacement of the basilar membrane relative to the tectorial membrane causes the stereocilia on the hair cells to bend. This bending opens ion channels, leading to depolarization of the hair cells and the generation of action potentials.

5. **Transmission of Signals**:
- The action potentials generated by the hair cells are transmitted to the auditory nerve, which carries the signals to the brain for interpretation.

6. **Evaluating the Options**:
- **Option 1**: "Displacement of the basal membrane with respect to the tectorial membrane stimulates stereocilia on the hair cells." This accurately describes a step in auditory signal transduction.
- **Option 2**: Incorrect, as it misrepresents the role of the ossicles and their connection to the oval window.
- **Option 3**: Incorrect, as it suggests a relationship between the tympanic membrane and endolymph that does not exist.
- **Option 4**: Incorrect, as it mischaracterizes the function of the steps and their interaction with the semicircular canals.

7. **Conclusion**:
- The correct answer is **Option 1** because it accurately describes the process of auditory signal transduction.