Flashcards in Lecture 27 RH Deck (58):
What is the eardrum?
What is the middle ear?
space between tympanic membrane and petrous part of temporal bone is called the middle ear.
What is the inner ear?
Space within petrous part of temporal bone is the inner ear
What is the outer ear?
Before the tympanic membrane is the outer ear.
How is loss of balance controlled?
In the petrous part of the temporal bone is a portion that allows us to control balance.
What are the components of the outer ear?
auricle: cartilaginous and collects sound. Tragus is the flap anterior to the ear canal.
How is sound able to reach the middle and inner ear?
Sound is transmitted through external auditory meatus to the tympanic membrane.
What is the structure of the external acoustic meatus?
External acoustic meatus is supported laterally (lateral 1/3) by cartilage and medially by the temporal bone. It is lined by hairy skin and cerumen glands.
What is the function of cerumen?
prevents maceration of skin with water.
What does "maceration" mean?
Maceration is defined as the softening and breaking down of skin resulting from prolonged exposure to moisture.
What nerves supply the external auditory meatus?
Nerve supply to external auditory meatus is done via several nerves:
posterior+inferior by vagus
anterior +superior by auriculotemporal nerve (from V3 of trigeminal nerve)
Where are other locations that pain of the ear could be referred to?
Pain of ear could be referred to other locations that the mandibular division of the trigeminal nerve innervates. (eg teeth)
*Pain from teeth could be referred to the ear.
What is the indentation on the tympanic membrane called?
Indentation on the tympanic membrane formed by the malleus of the inner ear.
What shape does the tympanic membrane have?
tympanic membrane is concave laterally.
What causes the concavity seen in the tympanic membrane?
Concavity depends on pressure within the middle ear relative to the outer ear.
What is the cone of light of the tympanic membrane?
Cone of light can be seen at the antero inferior quadrant. If that light is not visible then that means the pressure difference is indicating a problem with the middle ear.
What is the epitympanic recess? What is the problem with it?
Communicates with mastoid air cells and so infection of nasal cavity and auditory tube can go to mastoid air sinuses.
What are the cavities of the middle ear?
middle ear is split up into 2 compartments:
Tympanic cavity proper (immediately medial to tympanic membrane)
Epitympanic recess: superior to the tympanic cavity.
How does the nose/mouth connect to the ear's tympanic cavity?
Pharynx is connected to the tympanic cavity in the ear via the auditory tube (aka pharyngotympanic tube)
What is pharyngotympanic tube made of?
Primarily cartilaginous with the exception of the tympanic cavity which is embedded in bone.
What direction does the pharyngotympanic tube point?
anteriorly and inferiorly
What is a problem that arises with having the pharyngotympanic tube between the nasopharynx and the tympanic cavity?
because of the downwards opening infection could travel between cavities
What is the problem of inflammation on the ear?
Inflammation causes ossicles to be interrupted and pressure increase could push out the tympanic membrane and potentially damage it.
What are ossicles?
ossicles are the smallest bones in the body. 3 types of these bones:
These bones articulate with each other.
How is sound heard?
sound vibrates tympanic membrane and this causes vibration of ossicles in the inner ear and this is transmitted from stapes to another membrane in the inner ear which in turn activates sensory nerves.
What is the difference between the auditory tube in adults and in children and the infection rates?
in children the auditory tube is shorter smaller and more horizontal. For this reason infection transfers more often in children than it does in adults. (more middle ear infection in children)
What is a potential complication of middle ear infection in children?
Chronic ear infections in infants could negatively influence language development.
What kind of muscles can be found in the ear? What is their function?
Ossicles are associated with several muscles that are attached to the walls of the middle ear and attach onto some of the ossicles. They dampen the amplitude of vibration of the bones and so they decrease the perceived loudness of the sound.
How is it that when we hear very loud that they become less loud to us over time?
A reflex arc attaches to muscles in the ear to decrease loudness of sound when required.
What innervates stapedius?
stapedius is innervated by the seventh cranial nerve (the facial nerve)
What innervates tensory tympani?
5th cranial nerve (trigeminal nerve)
What happens to people with weakness in their trigeminal nerve?
cerebral palsy or weakness/damage to the trigeminal nerve causes less contraction in the ossicle/attached muscles thereby making them hear sounds louder and makes the reflex more difficult to stimulate.
Where are stapedius and the round window located?
stapedius sits over an opening on the medial wall of the middle ear.
round window is located below stapedius and is an opening to the inner ear.
What is the promontary of the ear?
Basal turn of the cochlear.
What is the chorda tympani? What path does it take?
Chorda tympani is a branch of the facial nerve and runs a tortuous path and goes to the anterior 2/3rds of the tongue to innervate the taste buds. It branches somewhere in the petrous part of the temporal bone from the facial nerve.
Path of the facial nerve to the anterior 2/3rds of the tongue as described by DrJason.
just before the facial nerve exits the stylomastoid foramen it says "oh shit i forgot to provide sensory innervation to the anterior 2/3rds of the tongue" and so gives off a branch (chorda tympani) which goes through middle ear, breaks through a fissure to the base of the skull just medial to ramus of the mandible (temporomandibular joint) realises it is a mile away from its destination and so it hitchhikes a ride with the branch of the trigeminal nerve (lingual branch of the third division of the trigeminal nerve) down towards the tongue with that.
Where does the facial nerve run relative to the ear?
facial nerve runs posterior to the middle ear through the temporal bone. Chorda tympani breaks off and goes through middle ear directly posteriorly
What openings are anterior to the middle ear?
tensor tympani muscle cavity
Where does the internal carotid artery run relative to the middle ear?
Internal carotid artery runs anteriorly to the middle ear right next to the tympanic membrane and the auditory tube.
Why can pulsation be heard during some infections of the ear?
fluid accumulation in the middle ear/infection/inflammation. Mechanical waves of the carotid artery's pulsations gets transmitted through the fluid and to the ossicles.
What is the inner ear?
inner ear is complex and consists of a system of fluid filled spaces and membranes embedded in spaces within the temporal lobe.
What is the inner ear composed of?
Bony labrynth of inner ear is filled with fluid called perilymph. Membranous labrynth is found within the bony labrynth and contains endolymph and all the sensory receptors for hearing and equilibrium.
How does vibrational energy that creates sound exit the inner ear?
If energy is passed into the inner ear it escapes through the round window which is a membrane covered window which communicates with middle ear (medial surface)
Where is the round window of the inner ear located?
posterior and inferior to the promontory
What is the inner ear in reality?
In reality the inner ear is a series of spaces within the temporal bone rather than a discrete structure.
Where exactly is the membranous labrynth located?
membranous labrynth is suspended within the bony labrynth
How does the inner ear allow sound to be perceived?
Membranous labrynth consists of a cochlea which is a snail-like shape which contains receptors and this is attached to a nerve known as the cochlear nerve via a membrane.
what cranial nerve innervates the inner ear?
The vestibulocochlear nerve (8th cranial nerve)
What kinds of semicircular ducts are there? How are they named?
anterior, horizontal, and posterior semicircle ducts.
These ducts are named based on the direction they point.
What is the function of the semicircular ducts of the inner ear?
They sense dynamic equillibrium (head movement).
Where are the sensory receptors of static equillibrium (head position) located?
They are located within the utricle and the saccule
Where are sensory receptors of the semicircular ducts located?
Within the ampulla
What nerve do the cochlear nerve and vestibular nerve come from?
vestibular nerve comes together with the cochlear nerve to form the 8th cranial nerve (vestibulocochlear nerve)
How does the vestibulocochlear nerve reach the temporal bone?
vestibulocochlear nerve goes through posteromedial aspect of the temporal bone.
How can frequency of sound be distinguished?
low frequencies are transmitted further than high frequency. This causes us to be able to distinguish between them.
Where are sound receptors located?
sound receptors are found along the inner membrane and form a structure known as the organ of corti
How is head movement sensed?
Endolymph moves in opposite direction to head movement and as it does that it produces variable activation at different receptors based on the coding it is relayed to the brain. (Threshold coding)