Ear Tour

– Hi, my name’s Olivia Feitshans. – And I’m Sean McClain. – And today we’re gonna be
doing a tour of the ear. First, we’ll start with
the anatomy of the pinna. (lighthearted instrumental music) At the bottom, we have the lobule. Then, we have the tragus, the antitragus, and the intertragal notch. Along the side and the top is the helix which ends at the crus of helix. This bump right here is the antihelix which divides into the
crural of the antihelix surrounding the fossa triangularis. Inside, we have the symba
concha and the cavum concha. This dip right here is the scaphoid fossa. This entryway right here is
the external auditory meatus. – Now, review the physiology of the pinna. First, the pinna aids in
the localization of sound. Second, the pinna enhances
high-frequency sound up to 3,000 hertz. It’s for this reason
that those with microtia will have difficulty hearing. – Now that we’ve discussed the anatomy and the physiology of the pinna, we can focus our attention on
the external auditory meatus, otherwise known as the
external auditory canal. There’s two main portions of the EAC, a lateral 1/3 cartilaginous portion, and a medial 2/3 osseous portion. The inside of the canal is
mostly epithelial tissue surrounded by temporal bone. Within it, there are sebaceous glands that create cerumen and hair. The EAC begins at the pinna and ends at the tympanic membrane. – Now, we’ll briefly
discuss the physiology of the external auditory canal, or EAC. Within the EAC, are sebaceous glands which create cerumen as well as hair that helps maintain the
cleanliness of the EAC. Also, the EAC helps to warm air before it reaches the tympanic membrane, so the tympanic membrane
can properly function. This is the tympanic membrane. Behind the tympanic
membrane are three ossicles, the malleus, the incus, and the stapes. The malleus attaches to
the tympanic membrane via the lateral process in the manubrium. The stapes attaches via the oval window. To simplify the middle
ear, we may visualize it as a six-sided cube. Each face has several
significant land markers. Superior wall houses the tegmen tympani. The posterior wall contains the aditus, the pyradimal eminence and
the chorda tympani nerve. The anterior wall houses
the tensor tympani muscle, the Eustachian tube, the carotid artery and the chorda tympani nerve. At the medial wall, we see the horizontal semicircular canal, the facial nerve canal, the oval window, the round window, the promontory and the tympanic nerve. I’m looking at the inferior wall. You see the jugular fossa. And finally, the lateral wall, which isn’t visible in this photo, contains the tympanic membrane. – Now, we’re going to discuss the physiology of the middle ear. Let’s just worry about the middle ear in that it acts as an
impedence matching system. The three ossicles use lever action to save about 30 decibles of sound between the tympanic
membrane and oval window. This helps to change acoustical energy into mechanical energy. – This is the inner ear. Behind the oval window is the vestibule, the cochlea and the semicircular canals. Behind the stapes and oval window is the vestibule, the
entrance to the cochlea. – OK, so the physiology of the cochlea is a bit complicated, so we
decided to break it down. I’m gonna use this photo to help explain what happens inside the cochlea in terms of fluids movements and pressure. It’s important to know that there are three main cavities within the cochlea, the scala vertibuli, the scala
media and the scala tympani. So the stapes presses
against the oval window via lever action from the middle ear. That movement then creates pressure and it pushes perilymph fluid
through the scala vestibuli all around the base and up to the apex. Once that paralymph
fluid reaches the apex, it then communicates
with the paralymph fluid of the scala tympani via the helicotrema. Once that communication occurs, the paralymph fluid then
moves down the scala tympani, down the apex around to the base, and pressure is release
through the round window. In between the scala vestibuli
and the scala tympani is the scala media. This houses endolymph fluid
and the organ of Corti. – If you were to cut the cochlea in half, you would be able to
view the organ of Corti, the modiolus and the spiral ganglia which leads out to the
vestibulocochlear nerve and the facial nerve. Now, we’ll discuss the
physiology of the organ of Corti which runs along the scala media. If you were to cut the cochlea, you would be able to
view all three canals, the scala vestibuli, the scala media and the scalar tympani. Between the scala
vestibuli and scala media is Reissner’s membrane. In between the scala
media and scala tympani is basilar membrane. Paralymph and endolymph fluid
stimulates both membranes causing the outer hair cells to shear in its tectorial membrane stimulating the inner hair cells which sends a signal to the brain
that a sound has been heard. – The vestibular system consists of three semicircular canals, the superior, horizontal and posterior. Each semicircular canal has an end organ known as the christae within the ampullae. The vestibular system uses fluids to help our bodies understand where we are in terms of space. – This aids in your posture, your balance, and your occular reflex. – So, just to do a quick review. We’ve gone over the outer ear which consists of the pinna and
the external auditory canal. The pinna aids in localizing sounds especially high-frequency
sounds up to 3,000 hertz. The external auditory canal warms air before it reaches the tympanic membrane and helps keep the ear clean. The tympanic membrane is
the end of the outer ear. It has three layers, the
lateral epithelial layer, the middle fibrous layer
and the medial mucosa layer. Behind the tympanic membrane are the six walls of the middle ear, and the three ossicles that are important for turning acoustical energy
into mechanical energy. The inner ear then consists of the cochlea and the vestibular system. All parts work together to send signals to the brain that a sound has been heard.

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