Neuro4 Flashcards
What is the structure that houses the auditory and vestibular sense organs called?
The bony labyrinth (petrous portion temporal bone)
Where is the membranous labyrinth of the Auditory System?
Inside the bony labyrinth
- of the petrous portion of the temporal bone
What type of fluid fills the inside of the membranous labyrinth?
Endolymph
What fluid lies between the bony and membranous labyrinths?
Perilymph
Is the perilymph inside the membranous labyrinth?
NO.
It is just outside the membranous portion.
What comprises the auditory apparatus within the labyrinth?
the Cochlea
What comprises the vestibular apparatus within the cochlea?
Three semicircular canals/ducts
as well as the utricle and saccule
How does sound enter the ear?
Via outer ear and external auditory meatus and Tympanic Membrane
What is the middle ear filled with?
Air and 3 small bones
What are the 3 ossicles of the middle ear called?
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Trace the structures involved through the inner ear beginning with the Tympanic Membrane:
Tympanic Membrane
Malleus
Incus
Stapes
(this makes up the connection between the inner and outer ear)
Is air pressure of the inner ear normally equal to atmospheric pressure?
Yes.
connected by the auditory (eustachian) tube
What connects the Stapes to the Cochlea?
The Oval Window
What are the 3 scalae (fluid filled compartments) of the inner ear?
Scala Vestibuli (superior) Scala Tympani (inferior) Scala Media (between)
Where do the scala vestibuli and the scala tympani meet?
Helicotrema
the end of the ducts
What are the scala vestibuli and scala tympani filled with?
Perilymph
What is the scala media filled with?
Endolymph
What windows open up on to the scala vestibuli and scala tympani
Scala vestibuli - Oval Window (stapes connection)
Scala tympani - Round Window
What structure houses the Organ of Corti (the sound sensing organ), and what fluid lines it?
Scala media (aka Cochlear duct) Endolymph
Trace the vibration through Cochlea, starting with stapes
Stapes > Oval window > scala vestibuli > scala tympani > Round window
What stimulates the (Basilar Membrane) hair cells of the organ of Corti?
oscillations in both the scala vestibuli and scala tympani
Why does the input to the Cochlea necessitate amplification through the ossicles?
(and amplification through concentration of sound from tympanic membrane to oval window - which is much smaller)
Fluid has a higher impedence than air
What is responsible for the transduction of mechanical vibrational energy to neural activity?
Hair cells in the cochlea
What happens when the basilar membrane moves?
Causes stereocilia to bend and change shape in relation to their FIXED tips (in tectorial membrane)
This mechanical deformation opens ion channels in the hair cells. Cation influx, generates receptor potential.
Hair cell then releases neurotransmitter > depolarizes CN VIII
Where are the cell bodies of CN VIII?
Where do their central processes synapse?
Spiral Ganglion
Cochlear nuclei
The organ of Corti lies between what two structures?
The inferior chamber (Scala Tympani) and the Scala Media
At the base of the cochlea, next to the Oval Window, the basilar membrane is ______, which optimizes sensing ______ sounds
Narrow
High frequency sounds
At the end of the cochlea, next to the helicotrema, the basilar membrane is _______, optimizing hair cells for ________ sounds.
Thick
Low Frequency
High frequency sounds (15000 Hz) have their peak amplitude near the ______, which low frequency sounds (100 Hz), have their peak amplitude near the ______.
Base
Apex
T/F
Not only is the basilar membrane thin and stiff near the oval window, but so are the ciliary hair cells (same with basilar membrane/ciliary cells being thicker/longer near the apex)
True
How many inner and outer rows of hair cells are there, and which one can alter its hair length?
1 inner 3 outer (alters - thought to selectively tune to important sounds)
Central Auditory Pathway, aka…
8CSLIMA
What does 8CSLIMA stand for?
8 - CN VIII
C - Cochlear nuclei
S - Superior Olivary nuclear complex
L - Lateral Lemniscus
I - Inferior colliculi
M - Medial geniculate
A - Primary auditory cortex (lateral temporal lobe)
How are dorsal and ventral cochlear nuclei organized, and where are they found?
Tonotopically
Medulla
Where does the central auditory pathway decussate?
Lower Pons
between the C & S in 8CSLIMA
What percentage of ascending fibers in the central auditory pathway cross at the pons and synapse on the superior olivary nucleus?
What % DON’T cross in the pons and synapse on the Reticular Formation?
about 80%
20%
What does the A in 8CSLIMA stand for, and where is it?
primary Auditory cortex
Superior Temporal Gyrus
Why would a unilateral lesion of the central auditory pathway cause more pronounced hearing loss to one side?
Which side?
The 80/20 split in the Pons, with majority crossing.
If lesion is above pons, more hearing loss opposite to lesion
If lesion below pons, more hearing loss same side of lesion
What is special about Brodmann’s areas 41 and 42
Site of the primary auditory cortex (Heschel’s gyri) in the transverse temporal lobe
Within the central auditory pathway, what are the functions of the:
Primary auditory cortex
Superior olivary nuc. and Inf. Colliculus
Reticular formation
?
Conscious hearing
Orientation/Localization of sound (Batman!)
CNS activation
What is the function of the descending efferent of CN VIII
descending auditory pathway
More inhibitory than excitatory
dampens extraneous noise - like crowd noise and background
What are the two middle ear muscles?
What is their innervation?
What is their function?
Tensor Tympani - CN V (inserts malleus)
Stapedius - CN VII (inserts stapes)
Both dampen vibration in response to loud noise (protective function)
What is Conductive Deafness, and what are 3 examples?
Interruption of sound passage
- Obstruction (foreign object)
- Otosclerosis (fixation of Stapes - excessive bone growth)
- Otitis Media (middle ear inflammation - common in children)
What is the most common cause of meningitis and the most common cause of brain abscesses?
Otitis Media
What structure and in what bone are the auditory and vestibular receptors located?
Inner ear
Temporal Bone
What is the term for nerve/perceptive deafness caused by diseases (Rubella, syphilis), drugs (aspirin, quinine), or toxins?
Sensorineural deafness
What is the degenerative hearing loss that occurs with ageing (involving degeneration at the base of the Organ of Corti), that disproportionally affects perception of high frequency sounds?
Presbycusis
What tumor, located where, can result in unilateral deafness and tinnitis?
Acoustic neuroma (aka “schwannoma”)
located at cerebellopontine angle
What causes Hyperacusis?
Damage to V or VII
- affecting Tensor Tympani or Stapedius
What is the general term (with multiple causes) for abnormal sounds of ringing, buzzing, etc.?
Tinnitus
What is the disease caused by an overproduction of endolymph (endolymphatic hydrops) or inability to absorb endolymph, resulting in tinnitus and vestibular disturbances?
(this is all caused by an increased pressure in the labyrinth)
Meniere’s Syndrome
Why won’t lesions in the 8CSLIMA pathway cause bilateral deafness?
The 80/20 cross at the pons
Do lesions of the Auditory cortex affect the ability to perceive sound frequency?
No.
Batman.
They disrupt the ability to localize the sound
T/F
Taste evolved to detect whether food is toxic/non-toxic.
True
What are the 5 main tastes, what is their primary stimuli and function?
Sweet - Sugar - (carbs=calories)
Sour - HCl or Citric acid - (acids/bacteria)
Bitter - caffeine/nicotine - (poisons)
Salty - NaCl - (water homeostasis)
Umami - L-glutamate - (peptides/proteins)
What are the 4 types of papillae?
Which ones have taste buds?
Circumvallate
Foliate
Fungiform
Filiform (most numerous - only one without taste buds)
How many types of gustatory receptor cells are there?
What are they responsive to?
I, II, III, IV
II - sweet, bitter, umami, possibly salty
III - sour
Taste receptor division of the tongue?
Ant 2/3 - VII
Post 1/3 - IX
Epiglottic - X
New terms:
Where are the 1st order sensory neurons for taste?
Geniculate Ganglion (VII - this isn't new) Petrosal Ganglion (IX) Nodose Ganglion (X)
Where is the 2nd order sensory neurons for taste? (where do they begin?)
Nucleus Solitarius - Medulla
What/where is the 3rd order sensory neurons for taste?
Ventral Posteromedial nucleus (VPM)
located in the Thalamus