Transcription
In this video, we will look at the anatomy of the ear.
The ears, in general, can be divided into three sections: the external ear, which goes to the eardrum; the middle ear, from the eardrum to the oval window; and the inner ear, which is basically your cochlea and your hair cells, this shell-looking structure.
Let us first look at the external ear. The external ear is composed of the outer auricle and the external acoustic meatus. The lateral one-third of the external acoustic meatus is surrounded by cartilage, and the inner two-thirds of the external acoustic meatus, more medial, is made up of bone.
Let us look at the middle ear, which contains our three bones called the auditory ossicles. Let us look more closely at what makes up our middle ear. The middle ear has boundaries: here is the bone and the eardrum. The top border is called the tegmental wall, which is made up of the temporal bone. The bottom of the middle ear is called the jugular wall or floor because this is where the jugular vein passes.
The lateral wall is called the membranous wall because this is where your eardrum is. The medial wall is the labyrinth wall because this is where the labyrinth of the inner ear is located. Then we have the anterior and the posterior walls, so the front and the back. The posterior wall is your mastoid bone, and the anterior wall is your carotid wall because your carotid passes through there.
Now, the content of the middle ear, as I mentioned earlier, are your auditory ossicles, which are made up of three bones. These are the smallest bones in your body: the malleus, incus, and stapes. The stapes bone interacts with the inner ear through the oval window.
Then you have muscles of the middle ear, which are your stapedius muscle, which, as the name suggests, interacts with the stapes bone. The second muscle is the tensor tympani muscle, which sort of interacts with the malleus and the tympanic membrane.
Okay, so that was a little bit about the middle ear. Let us talk about the inner ear. The inner ear receives mechanical signals, vibration signals, from the stapes bone through the oval window. The inner ear is made up of a shell-looking thing where we have three semicircular canals, the vestibule, which is important for balance, and then the cochlea, which contains the hair cells.
If you remember the physiology of hearing, it's the vibrations coming from the bones in the middle ear that vibrate the fluid within the cochlea, which will subsequently move the hair cells. This will then send the hearing signals to the brain.
But it's important to know that signals being received by the cochlea, vibrating the fluid, have to come out somehow to adjust the pressure, and it comes out through the round window of the cochlea.
Anyways, the movement of the hair cells causes signals, these hearing signals, to be sent to the brain through nerves. So here we can see nerves leaving the cochlea and the vestibule. These nerves are sensory nerves and form cranial nerve eight, also known as the vestibulocochlear nerve. Hence, where it's coming from: cranial nerve eight.
The vestibulocochlear nerve passes through a small opening in the bone here called the internal acoustic meatus, and the nerve goes towards the pons of the brain. The pons is part of the brainstem. Here is the brainstem, and you have the pons and the medulla oblongata.
Remember, the brainstem will continue to form your spinal cord. Of course, we have two vestibulocochlear nerves, one for each ear.
So, there's another cranial nerve that actually travels through, well, travels along together with the vestibulocochlear nerve through the internal acoustic meatus. This cranial nerve is cranial nerve number seven, also known as the facial nerve.
The facial nerve also originates in the pons next to the vestibulocochlear nerve and is responsible for muscles of facial expression, secretory glands, amongst many other things.
Anyways, I hope you enjoyed this video on the introduction to the anatomy of the ear. In the next video, we will go into a bit more detail. Thanks for watching.