Case 4 Flashcards
What are the three parts of the ear?
external middle and internal
What is the other name for the outer ear?
the auricle
What divides the outer and middle ear?
The tympanic membrane
The middle ear is a cavity located where?
The petrous part of the temporal bone
What connects the middle ear to the pharynx?
The pharyngotympanic tube.
what forms the medial border of the inner ear?
The internal acoustic meatus.
Describe the functions of the outer middle and inner ear respectively?
the outer captures sound and transfers it, the middle ear converts the sound into a mechanical signal and the inner ear takes this mechanical signal and converts it to an electrical signal.
What is the external acoustic meatus?
The canal of the outer ear that leads to the tympanic membrane.
What is the one part of the auricle not supported by cartilage?
The lobule
What is the outer rim of the auricle called?
the helix
What is the hollow area of the auricle called?
The concha
What are the three extrinsic auricular muscles?
The anterior superior and inferior.
what provides the auricle sensory innervation?
The auriculotemporal branch of the mandibular nerve (V3) and auricular branches of the vagus nerve
What is cerumen?
earwax
Which bone attaches to the tympanic membrane what is the concavity caused by this attachment called?
The malleus (by its handle) the concavity produced is called the umbo.
What is the eardrum attached to?
The tympanic part of the temporal bone by a periphery of a fibrocartillaginous ring.
What are the areas above and below the anterior and posterior malleolar folds respectively?
The pars flaccid and the pars tensa
What provides innervation to the outer surface o fhte tympanic membrane?
Mostly the trigemnal (V) but also the facial (VII) and Vagus (X) nerves
What provides sensory innervation to the inside of the tympanic membrane?
The glossopharyngeal nerve (IX)
What are the two main parts of the cavity of the middle ear?
The tympanic and epitympanic cavities.
What are the three bones of the middle ear? give them in order of outermost to innermost
The malleus, the incus and the stapes
What does the incus attach to?
The incus laterally and the oval window medially.
What is the other name for the pharyngotympanic tube?
eustachian tube.
What is just posterior to the epitympanic recess of the middle ear?
The auditus leading to the mastoid antrum
Why can infections of the middle ear easily spread to the mastoid area?
Because the mucous membrane of the mastoid is continuous with that of the middle ear.
What is the role of the eustation tube?
To equalize the pressure either side of the tympanic membrane.
What is the eustation tube surrounded by?
The third closest to the middle ear is surrounded by bone the two thirds closest to the nasopharynx by cartilage.
Where does the eustation tube enter the nasopharynx?
just posterior tot he inferior meatus of the nasal cavity.
What provides arterial supply of the eustation tube?
The ascending pharyngeal artery ( a branch of the external carotid) the middle meningeal artery and the artery of the pterygoid canal (branches of the maxillary artery)
What provides venous drainage for the pharyngotympanic tube?
The pterygoid plexus off the veins in the infratemporal fossa.
The do the three bones of the middle ear form?
The osseous chain
where is the enlarged body of the incus found?
in the epitympanic recess.
What are the two muscles of the middle ear?
The tensor tympani and the stapedius
Which of the muscles of the inner ear is larger?
The tensor tympani
What is the origin course and insertion of the tensor tympani muscle?
It originates from the cartillagious part of the eustation tube the grater wing of the sphenoid and its own taill it passes through its canal and ends in a rounded tendon that inserts into the upper part of the handle of malleus.
What innervates the tensor tympani muscle?
The mandibular branch of the trigemnal nerve (V)
What effect does contraction of the tensor tympani have on the ear what function does this serve?
Contraction of the tensor tympani pulls the head of the malleus medially making the tympanic membrane tenser reducing the force from vibrations in loud noices this protects the ear from damage as a result of loud noises.
Where does the stapedius muscle originate from? where does it insert?
it originates from the pyramidal eminence ( a small projection on the mastoid wall) and inserts into the posterior surface of the neck of the stapes.
What innervates the stapedius muscle?
a branch of the facial nerve (VII)
What is the effect of the contraction of the stapedius muscle what purpose does this serve?
It pulls the stapes posteriorly preventing excessive oscillation protecting the ear from damage caused by loud noises
What is the bony labyrinth what is contained within it?
The bony labyrinth is the series of bony cavities contained in the inner ear within these is the are a group of membranous ducts and sac known as the membranous labyrinth
Where are the labyrinths of the inner ear located?
In the petrous part of the temporal bone.
What are the three parts of the bony labyrinth what lines them and what fluid are they filled with?
The vestibule, the three semicircular canals and the cochlea. They are lined with periosteum and contain a clear fluid called perilymph.
What are the three parts of the membranous labyrinth? What are these membranous spaces filled with?
The semicircular ducts, the cochlear duct and the two sacs the utricle and the saccule. they are filled with endolymph
What part of the ear is the organ for hearing?
The cochlear
What are the organs for balance in the ear?
The utricle and the saccule
What nerve is responsible for the functions of hearing and balance?
The vestibulocochlear nerve (VIII)
what does the vestibulocochlear nerve (VIII) split into before entering the internal acoustic meatus?
vestibular and cochlea parts.
What is the central column of bone of the cochlea?
The modiolus.
Branches of what enter the cochlea at its wide base?
the cochlear part of the vestibulocoochlear nerve (VIII)
What are the three tubes of the cochlear coiled side by side one another in the cochlea?
The scala vestibuli, the scala media and the scala tympani
What separates the scala vestibuli and media?
the reissner’s membrane/ vestibular membrane
Why might the scala vestibuli and media be considered a single chamber?
The reissner’s/vestibular membrane is so thin and easily moved it does not obstruct the passage of sound.
What separates the scala media and the scala tympani?
The basilar membrane.
What lies on the basilar membrane?
The organ of corti.
What are the electromechanically sensitive cells within the organ of corti?
hair cells.
Where do sound vibrations enter the cochlea what chamber are they passed into?
They pass through the round window into the scala vestibuli.
How do the basilar fibers vary as you move further away from the oval window how does this effect their stiffness?
They vary from being about 0.04mm to .5mm in length and as the length increases their diameter decreases this results in their overall stiffness decreasing 100 fold.
Which basiliar fibers are best for what frequencies?
The short thick fibers near the oval window are best for high frequencies and the long flexible fibers are best for low frequencies.
What causes a fluid wave in the scala vestibuli
As the foot of the stapes moves inward against the oval window the round window bulges inside as this occurs the elastic basilar fibers’ elasticity initiates a fluid wave.
The fluid waves traveling the through scala vestibuli starts off weak when does it become stronger?
It flows as a weak wave till it reaches the portion of the basilar membrane it has a natural frequency equal to it.
What happens when a fluid wave flowing through the scala vestibuli reaches the portion of the basilar membrane it has a natural frequency to?
The basilar membrane vibrates back and forth dissipating the wave.
How far do sound waves of different frequencies travel along the scala vestibuli?
high frequency waves travel a very short distance low frequency waves travel a long distance.
What happens to the speed of the sound waves as they pass through the cochlea? How does this help distinguish certain frequencies?
The speed of the sound waves decreases as they pass through the cochlea. The high speed they enter the cochlea allows the high frequency waves to spread out separating themselves from one another meaning they can be distinguished from one another.
What is the primary method by which different frequencies of sound are distinguished from one another
different frequencies are distinguished from one another by the point on the organ of corti where the maximum nerve stimulation occurs.
What is spacial summation what quality of a sound does it help determine?
As the volume of a sound increases the more hairs at the periphery of the resonant point of the sounds frequency are stimulated the body can process this information to determine how loud a sound is.
What are the three methods the cochlea haas to determine the loudness of a sound?
The loud a sound the greater the amplitude of the vibration of the basilar membrane and the hair cells causing the nerve ending in the cochlea to be excited at a greater rate, spacial summation, whether or not the outer hair cells have been stimulated.
What are the outer hair cells what quality do they help determine?
Outer hair cells are hair cells of the organ of corti that are only stimulated when a sound is particularly loud helping to determine volume.
What are the two ways the ears can work to determine the direction of a sound?
The time difference between the stimulation of one hair cell and its corresponding hair cell in the other ear and the relative intensity of the signals received from each ear.
How many stereocilia does each hair cell have?
about 100
How do the stereocilia of hair cells vary as you approach the modiolus?
They get progressively longer.
What do the hair cells project their stereocilia into?
The tectoral membrane.
How are the sterocilia attached to one another?
The shorted hair fibers are attached to the longer ones via filaments that insert into their backsides.
What happens when the stereocilia are pulled out of the surface of the hair cell?
200-300 cation channels are opened allowing positive potassium channels to move into the stereocilia depolarizing the membrane. (mechanical transduction)
What happens when the stereocilia are bent towards and away from and away from the scala vestibuli respectively what does this result in when they are shaken by a sound wave what does this stimulate?
the cell is depolarized and hyperpolarised thus creating an alternating hair cell receptor potential stimulating cochlea nerve endings.
What is the phenomenon where outer hair cells control the frequency inner hair cells are sensitive to known as?
Tuning
Where do efferent fibers from the cochlea synapse?
The dorsal and ventral cochlear nuclei of the upper part of the medulla.
Where do the second order neurons of the auditory pathway travel to from the dorsal and ventral cochlear nuclei? what side do the fibers from each side travel on?
They travel to the superior olivary nucleus most of the neurons decussate but some travel ipsilaterally.
Where do fibers from the auditory pathway travel to after the superior olivary nucleus.
The third order neurons travel upward through the medial lemniscus pathway some of the fibers terminate at this point but others travel onwards to the inferior colliculus and on to the medial geniculate nucleus where the fibers synapse.
What does information from the cochlea travel from the medial geniculate nucleus to the auditory cortex via?
The auditory radiation.
Where is the auditory cortex located?
The superior gyrus of the temporal lobe.
Where do the collateral third order nerve fibers travel what purpose does this serve?
They travel to the reticular activating system of the brain stem which is capable of activating the whole nervous system in response to loud sounds.
As well as protecting the cochlea and other structure from damage from loud sounds what are the other two functions of the tensor tympani and stapedius?
They can mask low frequency sounds in low environments allowing us to concentrate on frequencies where the bulk of our communication takes place. It also helps to mask the sound of our own voices as collateral nerve fibers are activated at the same time as the voice mechanism.
What is the balance organ what is it composed of?
the vestibular apparatus composed of the 3 semocircular ducts and the two sacs (utricle and the saccule)
What are the sensitive areas of the ultricle and saccule called?
Macullae.
Which sac is most important in determining the orientation of the head when it’s upright?
the ultricle.
which sack is most important in determining the orientation of the head when a person is lying down?
the saccule.
What is each macula covered with what are embedded in each?
each macula is covered in a gelatinous layer in which many small calcium carbonate crystals called statoconia are embedded in.
How many stereocillia does each macula of the ultricle and saccule have?
50-70
What is the function of the gelatinous layer and statoconia of the macullae of the saccule and ultricle?
Their weight distorts the stereocillia (most importantly the kinocillium) producing the electrical impulse.
What is the large cillium on each saccule and ultricule macular hair cell called?
the kinocilium
What happens when the stereocilium of the hair cells of the saccule and ultricule are bent one way and the other?
depending on the direction the hairs are bent either receptor membrane depolarization or hyperpolarisation occurs.
under resting conditions what frequency of impulses do hair cells give off how is this effected by the distortion caused by the movement of the stereocilia?
on rest they give off roughly 100 pulses/s bit this canincrease to several hundred if depolarized or 0 in hyperpolarized.
What nerve fibers transmit information from the saccule and ultricle maculae?
macular nerve fibers.
One they have received information from the macular nerve fibers where might signals from the vestibular, cerebellar and reticular systems send information to?
The postural muscles?
Do the maculae detect linear velocity or initial acceleration how might this effect a runners posture?
they only detect initial acceleration so a runner would have to lean forward when accelerating but once he is running a regular speed can stand upright.
What are the three semicircular canals?
The anterior, posterior and lateral.
What are the enlargements at the end of each semicircular duct called? What are they filled with?
the ampulla, they’re filled with endolymph.
What is the crest within each ampulla called?
the crista ampullaris.
What is the name of the gelatinous loose tissue mass that sits on top of the crista ampullaris?
The cupula.
What is the name for the persistant suppurantive perforation of the tympanic membrane?
chronic ottitis media
name some risk factors for chronic ottis media
acute ottitis media, blockage of the eustation tube or craniofacial abnormalities such as cleft palate.
What can exacerbate chronic ottitis media?
an upper respiratory tract infection, the entrance of water through the perforation in the tympanic membrane during swimming bathing etc
What are some of the destructive changes that can occur in persistent ottitis media?
necrosis of the long process of the incus and aural polyps possibly indicating a cholesteatoma.
What is the treatment for chronic ottitis medi?
antibiotic drops if granulation tissue is present then it is removed using microinstruments or cauterisation.
What is the name of the hearing test that consists of activating a tuning fork and placing it on a patients forehead?
Weber’s test
What are the two types of hearing loss?
Conductive and sensorineural loss
Which ear would a person with conductive hearing loss ear the noise from a Webbers test louder in why is this?
the affected ear as the conductive loss will block out ambient sound which will interfere with th sound of the tuning fork.
Which ear would a person with sensorineural loss hear the noise from a webbers test louder in?
the uneffected ear
If a patient heard the bone conduction of a rinne test louder than the air conduction what kind of hearing loss might they have?
conductive hearing loss
What type of conduction would someone with a sensorineural loss hear better in a rinne test? why is this?
Bone conduction as the sound would transmit through the skull and be heard by the other cochlea.
