PBL 4 Flashcards
(39 cards)
Name the two perilymph chambers present within the cochlea, and how they are both separated from the cochlear duct, as well as which window they are connected to.
Scala vestibuli - connected to the oval window, separated from the cochlear duct by reissners membrane
Scala tympani - connected to the round window, separated from the cochlear duct by the basilar membrane
What is the tip of the cochlear spiral known as where the two scala chambers are interconnected?
Helicotrema
Name the two structural properties of the basilar membrane that determine its response to sound
Width - wider at the apex and narrow at base
Flexibility - more stiff at base and flexible at apex
What is the difference between outer and inner hair cells in the organ of corti?
Outer hair cells - tips end in the tectorial membrane
Inner hair cells - tips end just below the tectorial membrane
What is the decibal level at which sound becomes harmful
80Db
What differences are there in high and low frequencies on their impact on the basilar membrane?
High frequency sound - shorter wavelength, vibrates the basilar membrane nearer to the oval window (base/stiff part)
Low frequency sound - longer wavelength, vibrates the basilar membrane nearer to the round window (apex/flexible part)
What differences are there in loud and quiet sounds on their impact on the basilar membrane?
Loud sounds - distort the basilar membrane more
Quiet sounds - distort the basilar membrane less
How does the movement of hair cell receptors in the organ corti allow sound transduction in the spiral ganglion cells
TRPA1 channels are opened when hair cells bend, allowing an influx of Na+ and K+
Entry of K+ causes the hair cells to become depolarised, which activates Ca2+ channels
Entry of Ca2+ triggers release of glutamate, which then activates spiral ganglion fibres lying post synaptic to the hair cell
Desribe the auditory pathway to the cortex?
- Information is carried from hair cells by CN VIII
- CN VIII synapses at the cochlear nucleus on the ipsilateral medulla oblongata
- medulla oblongata sends axons to the contralateral inferior colliculi in midbrain
- inferior colliculi mediate reflex responses
- inferior colliculi send axons to medial geniculate nucleus of thalamus
- medial geniculate nucleus of thalamus projects information to auditory cortex in temporal lobe
What is the difference in the ventral and dorsal cochlear nucleus and how they communicate with the inferior colliculi?
Ventral cochlear nuclei cells - send axons to superior olive, which then communicates with inferior colliculi at each side
Dorsal cochlear nuclei - send axons directly to contralateral inferior colliculi
Which are the muscles involved in the auditory reflex and what nerves are they innervated by?
How does contraction of these muscles help to diminish sound conduction?
Tensor tympani - mandibular nerve (V3)
Stapedius - facial nerve (VII)
Diminishes sound conduction by causing the ossicles of the middle ear to become more rigid
What is the name of the sensory receptors of the vestibular complex?
Maculae
What are the different forms of acceleration that the otoliths organs detect?
Saccule - vertical acceleration
Utricle - horizontal acceleration
What are the different types of plane that your semicircular canals are sensitive to?
Superior/Anterior - pitch (looking up and down)
Posterior - roll (tilting head side to side)
Lateral - yaw (looking side to side)
Regarding hair cells in the semicircular ducts, what is a cupula?
A gelatinous structure that extends the full width of the ampulla (the area above the hair cells, which is pushed to one side during endolymph movement)
What are the different types of cilium present on a hair cell?
Stereocolia (80-100)
Kinocilium (one large one at the end)
How does the direction of endolymph within a semicircular canal result in the firing or inhibition of the vestibular nerve?
Endolymph pushing fluid towards the kinocilium - increases firing
Endolymph pushing fluid away from the kinocilium - decreases firing
Where are the cell bodies for the vestibular nerve located?
Scarpa’s ganglion
How are acceleration sensations detected by the macula of the oolith organs?
- during acceleration, the statoconia ‘lag behind’ the gelatinous material, distorting the hair cells below
- hair cells are depolarised and a signal is sent through the vestibular nerve
Where are the vestibular nuclei located on the brainstem?
Between the pons and medulla oblongata
How does the rotational VOR cause your eyes to rotate right, when your head rotates to the left?
- left horizontal semicircular canal senses rotation towards the left sending a signal to left vestibular nucleus
- excitatory fibres to right abducens nuclei (excite lateral rectus of right eye)
- excitatory fibres to left occulomotor nuceli (excite medial rectus of left eye)
How does alcohol effect the VOR?
Alcohol has an effect on the cerebellum, which is essential in controlling the VOR. Therefore the VOR tends to breakdown with alcohol consumption
What is nystagmus?
- Where the vestibular system thinks the head is moving, when it actually isn’t.
- Slow and fast phase of VOR are triggered
- Trouble controlling eye movements
What are the two phases of the VOR?
Slow phase - eyes slowly rotate in opposite direction
Fast phase - eyes rapidly reset to centre of vision
