N18- Auditory and Vestibular systems Flashcards
What are the frequencies of the audible range?
20Hz to 20kHz
where is the cochlear found?
Imbedded deeply in petrous temporal bone
where are organs of hearing and balance found?
Inner ear
Name the 3 auditory ossicles of the middle ear.
- malleus
- incus
- stapes
what happens when a tuning fork rings next to the ear?
Vibrations vibrate tympanic membrane which is transferred to auditory ossciles to the open window
what happens to the vibrations at the open window?
concentrated not amplified
what nerve is associated with hearing?
CN VIII: cochlear nerve
what material is in each of the external, middle and inner ear and what happens in each of these parts of the ear?
External ear: air, collection of sound
Middle ear: bone, concentration of vibrations
Inner ear: fluid, detection (transduction) of sounds
what are the names of the 3 Scala tubes?
- scala vestibuli
- scala tympani
- scala media
what fluid is the Scala vestibuli and tympani filled with?
Perilymph
what fluid is the Scala media (cochlear duct)?
Endolymph
what are the 2 membranes that surrounds the cochlear duct?
- basilar membrane
- Vestibular membrane
what is perilymph fluid similar to and why?
mimics ECF- high in sodium, low in pottasium
what is endolymph fluid similar to and why?
mimics ICF- low in sodium and high In pottasium
what is the significance of the difference of ion concentrations in endolymph and perilymph?
Allows cells between the two different fluids to have a very high resting potential
what membrane gets longer as you go up the spiral in the cochlea?
basilar membrane
how do the frequencies change in the cochlea?
High frequency as base of cochlea, low frequency sounds at the top of the cochlea
where does the organ of corti sit and what is its function?
- sits in basilar membrane
- changes vibrations to sound
how does the organ of corti change vibrations to sound?
Hairs of the organ of corti move against the tectorial membrane after vibrating causing sound which releases neurotransmitter to produce action potentials that allows you to hear
what ganglion is involved in signals travelling to the brainstem via CN VIII?
spiral ganglion
why is input above the cochlear nuclei bilateral?
Superior to the cochlear nuclei some fibres are crossed and some are not
how do we know if there is NOT a brain stem lesion?
loss of hearing in one ear
For fibres that cross, where do they ascend and where do they synapse?
- ascend in lateral meniscus
- synpase in inferior colliculus
what is the superior olivary nucleus (and nucleus of the lateral lemniscus ) important in?
sound localization and also acts as relay for stapedial and tensor tympani reflexes
what are the 2 cochlear nuclei?
ventral and dorsal
what is lemniscus?
band of white matter
Describe the tonotopic organisation of the auditory cortex?
- Fibres carrying information regarding low frequency sound end in the anterolateral part of the auditory cortex
- Fibres carrying information regarding high frequency sound end in the posteromedial part of the auditory cortex
what is a results of broca’s area?
Patient’s have difficulty in producing language, often using few words and only saying the most important words in a sentence. They do not usually have difficulty comprehending language
-motor or expressive aphasia
what is the result of damage to Wernicke’s area?
Patient’s have difficulty comprehending language. These patients can manifest defects ranging from words out of order to meaningless words
- sensory or receptive aphasia
In the vestibular system, what does maintenance of equilibrium use information from?
- vision
- proprioception
- the vestibular apparatus (labyrinth)
what do nerve cell bodies sit as in the vestibular system?
Nerve cell bodies sit as swellings in vestibular portion
How many semicircular canals are found in the inner ear?
3
what does detecting position and motion depend on?
receptive hair cells
where are receptive hair cells found that detect head position?
utricle and saccule
where are receptive hair cells found that detect movement?
semicircular canals
what is the swelling called that is found in each semicircular canal?
ampulla
what is the ampulla?
sensory organ called the crista ampullaris
what does the ampulla consist of?
. It consists of a core of connective tissue bulging into the luman with a covering of epithelium containing hair cells with stereocilia. The stereocilia are embedded in a dome of gelatinous material called the cupola
what happens when the head turns?
The movement of the fluid bows the cupola, and this in turn bends the stereocilia. This changes the amount of transmitter released by these cells. They have a resting output, so bending them one way increases output, while bending them the other way decreases it
what are the utricle and saccule lined with?
lined by simple cuboidal epithelium everywhere except a small patch of sensory epithelium in each called the macula
what is the otoconia?
The stereocilia of the hair cells are embedded in a gelatinous layer which in turn has crystals of calcium carbonate and protein
what makes up the vestibular apparatus ?
two swellins- utricle and saccule - in the vestibule
how is head movement sensed?
Straight-line acceleration of the head produces relevant movement in the otoconia/gelatinous mass and bends the stereocilia
how is information about the position of the head when it is static sensed?
the otoconia are denser than the endolymph fluid around them, they are affected by gravity
where does the CN VIII enter the brain?
pontomedullary border
which if the vestibular and cochlear nuclei is larger?
Vestibular nuclei is much bigger than the cochlear nucleus
where is most of the vestibular nuclei found?
medial to the inferior cerebellar peduncle
what cranial nerves have a huge vestibular input?
CN III, IV, VI
how does the vestibular ganglion project down the spina cord?
as vestibulospinal tract
where is the termination of lateral vestibulospinal pathway ?
mostly to extensor “anti-gravity” muscles
where Is the termination of the medial vestibulospinal pathway?
Principally: neck, sternocleidomastoid , trapezius
what does the medial vestibulospinal tract innervate?
Medial VST innervates upper spinal cord and motor neurons to spinal accessory nerve to promote movement of head to help maintain balance and fixation of gaze
what areas of the cortex have vestibular information been found to converge?
- An area of the parietal cortex just posterior to the area of the postcentral gyrus that represents the hand and mouth.
- An area just rostral to the primary auditory cortex
