Case 4 Flashcards
What is a name for the outer ear?
Auricle
where is the middle ear cavity located?
Petreous part of the temporal bone
What type of cartilage makes up the auricle?
Elastic
What arteries supply the auricle?
Posterior auricular and superficial temporal
What part of the s-shaped E.A.M is cartilagenous?
lateral 1/3 is cartilagenous
medial 2/3 is bony
What is another name for earwax?
Cerumen
What part of the E.A.M. secretes cerumen?
Lateral cartilaginous 1/3
What covers the tympanic membrane externally and internally?
Skin externally, and mucous membrane internally
What provides the auricle sensory innervation?
The auriculotemporal branch of the mandibular nerve (V3) and auricular branches of the vagus nerve
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 does the lateral process of the malleus form at the tympanic membrane?
Anterior and posterior malleolar folds
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 of the tympanic membrane?
Mostly the auriculartemporal branch of mandibular (V3), 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 is the roof of the middle ear called?
Tegmental?
What bone separates the roof of the middle ear and the M.C.F dura
Tegmen tympani
What are the two main parts of the cavity of the middle ear?
The tympanic and epitympanic cavities.
What is the area above the level of the tympanic membrane?
epitympanic recess (attic)
What is the floor of the middle ear called and what is below the floor?
Jugular floor, and the superior bulb of the internal jugular vein is below the floor.
What is the posterior wall of the middle ear called?
Mastoid
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 medial wall of the middle ear called?
Labyrinthe
What is the rounded bulge on the medial wall of the middle ear called? and what is associated with this bulge?
promotory, and the tympani plexus is associated with this bulge.
What is the lateral wall of the middle ear called?
Membranous
What is the anterior wall of the middle ear called?
Carotid
What is on the superior surface of the anterior wall of the middle cavity?
Opening for the pharyngotympanic tube.
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 to the 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.
Which of the muscles of the middle ear is larger - tensor tympani or stapedius?
The tensor tympani
What is the origin and insertion of the tensor tympani muscle?
It originates from the cartilaginous part of the eustation tube the greater wing of the sphenoid and it passes through its canal and ends at 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
what forms the medial border of the inner ear?
The internal acoustic meatus.
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 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 is the central column of bone of the cochlea?
The modiolus.
What is the lamina of bone that spans the length of the modiolus called?
lamina of modiolus or osseous spiral lamina
What does the osseous spiral lamina attach to?
Basilar membrane
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 oval window into the scala vestibuli.
How do the basilar fibres 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 fibres 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 fibres are present in the pars tensa part of the tympanic membrane?
circular and radial
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. This allows the high frequency waves to spread out 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, more hairs are stimulated at the point along the cochlear that responds to that frequency
What are the three methods the cochlea has to determine the loudness of a sound?
- greater rate of action potential firing
- 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
What do the hair cells project their stereocilia into?
The tectoral membrane.
Where are the hair cells located? Between the basilar membrane and ____________
reticular lamina
What is the name given to the parts that separate the inner and outer hair cells?
Rods of corti
What are the channels called in the stereocilia?
TPR1 channels
What is the normal resting potential of the hair cells?
-70mV
What makes the stereocilia rigid?
actin filaments
What is the phenomenon where outer hair cells control the frequency inner hair cells are sensitive to known as?
Tuning
What type of cells are the first order neurons?
bipolar cells
Where are the cell bodies of the first order neurones?
spiral ganglion
Where do the first order neurons synapse
The dorsal and ventral cochlear nuclei of the upper part of the medulla.
What information does the dorsal cochlear encode?
information about pitch
what cells are found in the ventral cochlear nuclei, and what information do they encode?
stellate - volume/intensity
bushy - timing
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?
- mask low frequency sounds in low environments allowing us to concentrate on frequencies where the bulk of our communication takes place.
- mask the sound of our own voices as collateral nerve fibres are activated at the same time as the voice mechanism.
In the auditory cortex where are high frequency sounds represented?
caudally and medially
In the auditory cortex where are low frequency sounds represented?
rostrally and laterally
Where do the scala vestibuli and scala tympani meet?
at the helicotrema
In the auditory cortex where are high frequency sounds represented?
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?
Ultricle
which sack is most important in determining the orientation of the head when a person is lying down?
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/otoliths 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?
heir weight distorts the stereocillia producing the electrical impulse.
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.
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 are the receptors in the semicircular ducts called?
ampullary crests/ crista smpullaris
What is the lateral wall of the cochlear duct called?
stria vascularis
What is the name of the gelatinous loose tissue mass that sits on top of the crista ampullaris?
The cupula
What are the three pairs of accessory nuclei found in the auditory pathway?
- superior olivary nucleus
- trapezoid body
- lateral lemniscus nucleus
What are otoacoustic emissions?
Inaudible sounds produced by the cochlea
What is the frequency range of normal conversation?
2000-5000Hz
What amplitude is discomfort produced?
120dB
What is the amplitude of normal conversation?
60dB
What is a pure tone sound?
A sound with a single frequency
What are the two senses of balance?
static and dynamic
What does static equilibrium detect?
Vertical or horizontal acceleration (linear acceleration)
What apparatus detect static equilibrium?
utricle and saccule
What does dynamic equilibrium detect?
spinning (rotational acceleration)
What apparatus detects dynamic equilibrium?
semicircular canals
How is rotation detected in the semicircular canals?
(1) SCC move as head turns
(2) Endolymph lags due to inertia
(3) cupula is pushed over and bends stereocilia
What happens if head rotation is maintained at a constant velocity??
Bending of the cupula is eliminated after 15-30 seconds
What is inertia
resistance of any physical object to any change in its state of motion
What happens when a semicircular canal is excited, to the corresponding canal on the opposite side of the head
Inhibited (opposite)
What is the striola?
A curved ridge that runs through the middle of the macula
In the utricle how are the kinocilia orientated?
towards the striola
In the saccule how are the kinocilia orietated
away from the striola
Where are the first-order neurones of the vestiblar pathway located?
Scarpa’s ganglion
What are the 4 vestibular nuclei?
Medial
lateral
Inferior
Superior
What is the lateral vestibulaspinal tract?
An ipsilateral descending tract from the vestibular nuclei to the sacral spinal cord
What is the medial vestibulaspinal tract?
A bilateral descending tract from the vestibular nuclei to the thoracic levels of the spinal cord.
What are the 4 places that the vestibular nuclei project to?
(1) spinal cord -to control head and body movement
(2) oculumotor nuclei - to control eye movements
(3) thalamus
(4) cerebellum
What is the vestibulo-ocular reflex?
Stabilizes the images on the retina during head movement
When does ear development begin?
22 days
What does the development of the ear begin with?
Thickening bilaterally on the rhomencephalon
Brief overview of development of the iner ear
(1) otic placodes
(2) otocyst
(3) utricle and saccular portions
(4) saccule - turns of cochlear completed 8th week
(5) Utricle - Semicircular flat outpocketing of 6 week, the centres of these disks later dissolve
What month does the mesenchyme dissolve from around the ossicles?
8th month
Where is the E.A.M derived from?
first pharyngeal cleft
Where is the auditory tube derived from?
first pharyngeal pouch
What bone/s derived from first pharyngeal arch?
malleus and incus
What bone/s derived from second pharyngeal arch?
stapes
What are the two types of hearing loss?
Conduction and sensioneural
What is central auditory dysfunction?
Caused by deficits in the pathway that does not cause hearing loss, but difficulty in locating or discriminating the sound
What is considered normal hearing?
when somebody can hear 25dB or lower
What is the range for mild deafness?
25-39
What is the range for moderate deafness?
40-69
What is the severe for moderate deafness?
70-94
What is the profound for moderate deafness?
95+
What are the clinical signs of damage to the auditory nerve?
Deafness or tinnitus
What is tinnitus?
The sensation of sound when there is no auditory stimulus
What is presbycusis?
Age-related hearing loss, due to deterioration of the organ of corti, or auditory pathways
What gene is associated with hearing loss, and responsible for 20% of childhood cases of deafness?
DFNB1B / GJB2 gene
Connexin 26
What is diplacusis
perception of a single auditory stimulus as two separate sounds which may differ in pitch or in time
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 would the results of a Webers test be for someone with conductive hearing loss?
Affected ear will block out ambient sound which will mean that the affected ear would hear it louder
What would the results of a Webers test be for someone with sensioneural hearing loss?
the unaffected ear would hear better
Where do you place the tuning fork in rinnes test?
mastoid process - behind ear
What is the magnifying lens strength of an otoscope
8 dioptres
what is another name for otitis media?
tympanitis
What is otitis media?
Middle ear inflammation
what is the most common cause of otitis media?
Dysfunction of the auditory tube
