Med-Surg - Nervous System, part 4: A&P Review - Eye and Ear
by Cathy Parkes October 27, 2021 Updated: December 29, 2021 4 min read
Hi, I'm Cathy, with Level Up RN. In this video, I am going to continue my anatomy and physiology review of the nervous system. This video will be focused on eye and ear anatomy and physiology because as part of our nervous system playlist, we will be talking about several vision and hearing disorders. At the end of this video, I will be giving you guys a little quiz to test your knowledge of some of the key points I'll be covering in this video. So definitely stay tuned for that. And if you have our Level Up RN medical-surgical nursing flashcards, definitely pull those out so you can follow along with me.
Here's an illustration of the basic anatomy of an eye, that you can find in our medical-surgical nursing flashcard deck.
So the eye is made up of three layers.
So this outer layer includes the sclera here, which is white fibrinous tissue.
At the front of the eye, in this third layer, we have the cornea, which is made of transparent tissue, which allows light to enter the eye there.
The middle layer includes the iris here, which is the colored portion of the eye and controls pupil size.
The middle layer also includes this ciliary body, which produces aqueous humor.
And then, we have the choroid here in red, which is the main source of blood supply to the retina.
And then, the inner layer includes the retina here, which kind of lines the back of the eye. The retina contains the rods and cones, and transmits impulses to the optic nerve here.
So let's trace the path of light waves. So light waves will come in here through the cornea, and then it will enter this aqueous humor, which fills both the anterior and posterior chambers of the eye. It will then go through the pupil, which is the opening at the center of the iris. It will then go through the lens, which helps to focus light on the retina. The light wave will then enter the vitreous body, or humor, which fills the vitreous chamber, and then the light waves will go to the retina, and then the retina will convert the light to an electrochemical impulse. And that impulse will be transmitted here to the optic nerve. And then it will be transmitted up to the brain, to the visual cortex in the occipital lobe of the brain.
So a couple of things to keep in mind as you look at this illustration later on.
In this video series, we are going to talk about cataracts, which causes proteins to clump up here on the lens, which creates a lens opacity.
We're also going to be talking about glaucoma.
So glaucoma occurs when we have an overproduction of aqueous humor, which is produced here by the ciliary body, or it can be caused by obstruction of outflow of that aqueous humor. And we'll talk more about that in that video.
And then, we're also going to later on talk about a retinal detachment.
So when we do talk about retinal detachment, this is caused by a build-up of vitreous humor, or vitreous body, that basically collects behind the retina and causes the retina to detach. So I just wanted you to kind of take a look at those things because when we talk about those disorders, it will make more sense having seen this illustration.
Moving on to the ear now. You can find this illustration in our medical-surgical nursing flashcard deck.
We have our external ear structures, which include the pinna as well as the external ear canal. A couple of things I want to point out here.
Cerumen, which is a fancy name for earwax, is an expected finding here in the external ear canal.
Also, when you hear the term otitis externa, that is referring to inflammation of this external ear canal. It's also called swimmer's ear.
The tympanic membrane is right here, and it separates the external ear from the middle ear.
In the middle ear, we have these bony ossicles, which include the malleus, incus, and stapes.
We also have the Eustachian tube here, which connects to the nasal pharynx, and it helps to equalize air pressure in the middle ear.
Now, when you hear the term otitis media, that means we have a middle ear infection. It's pretty common in children.
So with a respiratory infection, we end up with inflammation and congestion, which can lead to obstruction of the Eustachian tube, which causes the accumulation of fluid in the middle ear, leading to infection.
Okay. So the round and oval window separates the middle ear from the inner ear. In the inner ear, we have the cochlea here, which contains the nerve cells responsible for hearing.
And then we have our semicircular canals up here, which contain receptors for balance.
All right. So let's follow the pathway of sound waves. So sound waves will come in through the external ear canal. They will reach the tympanic membrane, causing it to vibrate. And then that vibration will be passed along to the bony ossicles here, through the oval window, and then reach the cochlea. Inside the cochlea, those hair cells, which are the nerve cells, translate those vibrations into electrical impulses, and those impulses are passed along to the auditory nerve, which is cranial nerve number eight, and then onto the brain into the auditory cortex in the temporal lobe.
All right. You guys ready for your quiz? I have three questions for you. First question. What portion of the eye contains rods and cones and transmits impulses to the optic nerve? The answer is the retina. Question number two. What part of the ear contains nerve cells responsible for hearing? The answer is the cochlea. Question number three, what structure in the ear is responsible for equalizing pressure in the middle ear? The answer is the Eustachian tube.
Okay. I hope this video has been helpful. Hope you're enjoying these quizzes as well. Take care and good luck with studying.
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