List the sequence of structures through which sound passes to reach and be interpreted by brain?

Sound waves travel from the environment into the ear and to the brain through the following sequence of structures:

1. External Ear:

- The sound waves first enter the outer ear, also called the auricle or pinna.

- The auricle is shaped to collect and channel the sound waves toward the ear canal.

2. Ear Canal:

- The ear canal is a curved passageway that leads from the auricle to the middle ear.

- It amplifies the sound waves by resonating at specific frequencies.

3. Tympanic Membrane (Eardrum):

- The ear canal ends at the tympanic membrane (eardrum).

- The sound waves strike the eardrum, which vibrates in response to the sound.

4. Middle Ear:

- The middle ear is a small air-filled cavity behind the eardrum.

- The middle ear contains three tiny bones: the malleus (hammer), incus (anvil), and stapes (stirrup).

- These bones form a chain that transmits the vibrations of the eardrum to the inner ear.

5. Inner Ear:

- The inner ear is a complex, fluid-filled structure that contains the sensory receptors for hearing and balance.

- The cochlea is a spiral-shaped structure within the inner ear that is responsible for hearing.

- Inside the cochlea, there is a coiled tube called the cochlear duct, which is filled with fluid.

- The stapes bone (from the middle ear) connects to a membrane in the cochlea, called the oval window.

6. Basilar Membrane and Hair Cells:

- When the stapes vibrates, it creates pressure waves in the fluid of the cochlea.

- The waves travel along the cochlear duct and cause the basilar membrane inside the cochlea to vibrate.

- The basilar membrane is lined with hair cells, which are sensory cells that convert the mechanical vibrations into electrical signals.

- Different hair cells are tuned to respond to specific frequencies of sound.

7. Auditory Nerve:

- The electrical signals generated by the hair cells are transmitted to the auditory nerve, a bundle of nerve fibers that connects the inner ear to the brain.

8. Brainstem and Auditory Pathway:

- The auditory nerve carries the electrical signals to the brainstem, where some initial processing of the sound information occurs.

- The signals are then sent to the auditory cortex, located in the temporal lobes of the brain, through a series of relay stations.

9. Auditory Cortex:

- In the auditory cortex, the brain processes the sound information, including the pitch, loudness, and location of the sound.

- This allows us to perceive, interpret, and understand the sounds we hear.