Lecture 27 DA Flashcards
What is the outer ear?
The auricle.
What does the auricle do?
Collects sound.
What is the auricle supported by?
Supported by cartilage, aside from the lobule inferiorly.
What is the outermost ridge of the ear called?
Helix.
What is the ridge medial to the helix called?
Antihelix.
What is the ridge inferior to the antihelix and directly superior to the lobule called?
Antitragus.
What is the bump medial to the ear canal called?
Tragus.
What is the space between the ear canal and the antihelix called?
Concha.
Which portion of the entire ear is cartilaginous?
The outer lateral 1/3rd is cartilaginous, the rest is bony, from temporal bone.
What does the ear canal lead into?
External acoustic meatus.
What is the external acoustic meatus lined by, and what purpose does this serve?
Lined by hairy skin and cerumen glands, which produce cerumen/ear wax.
What is the purpose of ear wax?
Prevents maceration of skin with water.
What is the ear innervated by posteroinferiorly?
By vagus nerve.
What is the ear innervated by anterosuperiorly?
Auriculotemporal nerve.
Which division of the trigeminal nerve does the auriculotemporal nerve originate from?
V3/mandibular division of the trigeminal nerve.
Where does the auriculotemporal nerve orginate from?
Trigeminal nerve.
What innervates the external surface of the tympanic membrane?
Auriculotemporal nerve.
What effect does the malleus bone have on the tympanic membrane?
An indentation is formed.
What is the tympanic membrane?
Ear drum.
What shape is the tympanic membrane laterally, and what does it depend on?
It is concave laterally, and depends on pressure medially which can turn it convex.
How can a physician detect a problem with the ear using light?
By shining light into the ear and looking at the anteroinferior quadrant, if the position of the beam of light produced changes, then there is a problem with the middle ear.
Where is the tympanic cavity proper found?
Just medial to the tympanic membrane.
Where is the epitympanic recess found?
Just superior to the tympanic membrane.
What was a pre-modern technique used to treat middle ear infections?
Drilling into the mastoid bone to drain the ear.
Where is the auditory tube found relative to the tympanic membrane?
Inferior and medial.
What does the auditory tube connect the tympanic membrane to?
To the pharynx.
Is the pharynx bony or cartilaginous?
Cartilaginous.
What is the tympanic end of the auditory tube embedded in?
Bone.
Is the auditory tube difficult for bacteria to infect? Why?
Yes it is, as it is on a decline, so it can drain well, and is difficult for bacteria to migrate.
What happens when the auditory tube is infected?
Ossicle movement will decrease, reducing hearing. It will also increase pressure against the tympanic membrane, damaging it.
What are the three ossicles, and what do they look like?
Malleus - hammer
Incus - anvil
Stapes - Styrup
In what order to the three ossicles attach to each other and the tympanic membrane?
Tympanic membrane -> malleus -> incus -> stapes
what is the purpose of the ossicles?
When sound enters the meatus, it is transmitted through the ossicles to the sensory receptors.
What happens if the auditory tube or epitympanic recess is blocked?
Impacts hearing.
How can the auditory tube become infected?
From bacteria in the nose.
What is the age dimorphism in the auditory tube?
It is more vertical in adults and can drain well, infections are less common.
It is shorter and more horizontal in babies, so infections are more common.
Why are ear infections a problem for children?
It can impact language development as they need hearing to develop it normally.
What are the two muscles associated with the ossicles?
Tensor tympani (attaches to malleus) - cranial nerve V Stapedius (attaches to stapes) - cranial nerve VII
What is the purpose of the two muscles associated with the ossicles?
They act to dampen loud sounds to prevent damage and discomfort.
What is facial palsy, and what is it caused by?
When half the face droops, occurs when facial nerves are damaged. There is a reduced response to loud sounds and increased sensitivity to loud sounds.
Where is the round window found?
Found inferior to stapes/stapedius
Where is the oval window, and what structure passes through it?
It is superior to the round window, and the cordae tympani nerve runs through it.
Does the cordae tympani innervate the ear?
No.
Which bone does the trigeminal nerve run through?
Temporal bone.
Which nerve does the cordae tympani arise from?
The lingual branch of the facial nerve.
What does the cordae tympani innervate?
Anterior 2/3rds of the tongue.
Is the cordae tympani tortuous?
Yes, so it can weave between ossicles.
What is the significance of the internal carotid artery being close to the tympanic membrane (inferior and medial)?
If the membrane is infected, pulse of the carotid can transmit to the ossicles, and one can hear their own pulse.
How is the inner ear different to the outer ear?
It is fluid filled.
Which bone is the inner ear located in? What is characteristic of this bone?
The petrous temporal bone, medial to the outer ear. Very dense bone.
What is the bony labyrinth filled with?
Perilymph.
What does the membranous labyrinth attach to?
Nothing, it is suspended within the bony labyrinth.
Is the membranous labyrinth continuous?
Yes.
What is the membranous labyrinth filled with?
Endolymph.
Where are sound sensory receptors found, and how are they activated?
On the cochlea, and are activated by ossicle vibrations.
What is the purpose of the round window regarding energy escaping?
Energy from sound input exits through the round window, preventing build-up.
What is the cochlea?
Snail-like medial structure of the membranous labyrinth.
What membranous labyrinth structure is found lateral to the cochlea?
Vestibule.
Where are the three semicircular ducts found, and what are their names?
Medial to the cochlea.
They are called anterior, horizontal and posterior semicircular ducts, depending on their direction of projection.
What is found at the base of the anterior semicircular duct, and what does it do?
The ampulla, which is a swelling. Contains receptors for balance and head movement, which is dynamic equilibrium.
Where is the utricle found, and what does it do?
It is found inferior to the ampulla, and has receptors for head position, which is static equilibrium.
How many ampullae are there in the inner ear?
3, one for each semicircular duct.
To which nerve is information on static and dynamic equilibrium relayed to, and what relays it? What happens to this nerve?
It is relayed to the vestibular nerve, which then merges with the cochlear nerve, forming cranial nerve VIII, the vestibulocochlear nerve.
How is sound relayed to the brain?
It is transmitted to the inner ear, then relayed to the brain via the cochlear nerve.
Where are high frequency sound detected?
At the base of the cochlea (imagine it unwound into a straight tube).
Where are low frequency sound detected?
At the apex of the cochlea (imagine it unwound into a straight tube).
What is static and dynamic equilibria?
Static - head position
Dynamic - head movement
What detects static equilibrium?
Utricle and saccule.
What detects dynamic equilibrium?
Ampullae.
What is the organ of Corti?
The sensory receptors found all along the cochlea, which merge to become the cochlear nerve.
How is dynamic equilibrium detected? What does it involve?
Involves mainly the ampulla. When the head is turned, endolymph lags behind in the opposite direction, activating its sensory receptors.
How is static equilibrium detected? What does it involve?
Involves mainly the utricle and saccule. When the head moves, the endolymph displaces the membrane of the saccule and utricle, which have dense crystal-like structures on them which detect this.
What structure of the utricle and saccule allows them to detect membrane displacement?
Crystals of calcium carbonate called otoliths.
