Audio-vestibular system Flashcards
what is the difference between a vestibular organ and a hearing organ?
vestibular organs capture low frequency motion (movements) whereas hearing organs capture high frequency motion (sound)
Where is the ear located?
petrous portion of temporal bone
What are the three sections of the ear?
outer, middle and inner (cochlea)
what are the functions of the outer ear?
To capture sound and focus it to the tympanic membrane. modest amplification of upper range of speech frequencies by resonance in the canal. To protect the ear from external threats
What is the function of the middle ear?
mechanical amplification
How many dB can mechanical amplification in the middle ear add?
20-30dB
what is the function of the cochlea?
transduce vibration into nervous impulses that captures the frequency and intensity of the sound
What are the three compartments of the cochlea?
scala vestibuli, scala tympani, scala media
Describe what makes up the scale vestibule and scale tympani
Boney structures containing perilymph
Describe the structure of the scala media
Membranous structure containing endolymph
What is the hearing organ called and where is it located?
Organ of Corti, located in the basilar membrane
What cations are found in high concentrations in the 3 compartments of the cochlea?
High Na+ found in the scala vestibuli and scala tympani. High K+ found in the scala media
Describe the structure of the organ of Corti
Contains 1000s of hair cells, inner and outer. The tectorial membrane above hair cells allow hair deflection which depolarises the cell
How are the inner hair cells in the organ of Corti arranged?
In one column
Are the IHC or OHC of the organ of Corti in constant contact with the tectorial membrane ?
Outer hair cells
Describe the arrangement of the outer hair cells of the organ of Corti
In 3 columns
What information if carried by the IHC of the organ of Corti?
Afferent information
What type of information is carried by the OHC of Corti?
Efferent information
What is the function of the IHC of Corti?
Transduction of sound into nerve impulses
What is the function of the OHC of Corti?
Modulation of sensitivity of response
What are the hairs on hair cells in the auditory system known as?
Sterocilia
Describe the process of transduction by hair cells in the organ of Corti (4 steps)
Deflection of sterocilia towards longest cilium opens K+ channels.
Ionic interchange depolarises cell and NT liberated.
Higher sound amplitudes i.e. louder sounds cause more deflection of stereocilia and K+ channel opening.
Hyperpolarisation closes K+ channel (deflection of hair cells the other way, in direction of shortest cilium)
Where do spiral ganglions from each cochlea project to and how?
Project to ipsilateral cochlear nuclei via auditory vestibular nerve (CN 8)
What word describes how hearing is organised?
Tonotopically
What happens to hearing acuity with age?
Decreases, particularly higher frequencies
What is frequency/ pitch?
Cycles per second, perceived tone
What is amplitude?
Sound pressure, subjective attribute correlated with physical strength
How is the basilar membrane arranged?
Tonotypically (same principle as a xylophone)
Where does auditory information decussate?
At the superior olive level, after this point all connections are bilateral
Describe the path information takes from the cochlea to the auditory cortex
Cochlea , cochlear nucleus and superior olive, inferior colliculusm medial geniculate body, auditory cortex
What is conductive hearing loss?
Problem located in outer or middle ear
What is sensorineural hearing loss?
Loss due to The sensory organ or the nerve damage
What timing is associated with sudden hearing loss?
Minutes to days
What timing is associated with progressive hearing loss?
Months to years
What is central hearing loss?
Originates in the brain and brainstem, very rare
What are the causes of conductive hearing loss in the outer ear?
Wax or a foreign body
What are the causes of conductive hearing loss in the middle ear?
Otitis and otosclerosis
What is otitis?
Infection of the middle ear that causes inflammation and a build up of fluid behind the eardrum
What is otosclerosis?
A condition where there’s abnormal bone growth inside the ear, a common cause of hearing loss in young adults
What are the causes of sensorineural hearing loss in the inner ear?
Noise, presbycusis, ototoxicity
What is presbycusis?
Age-related hearing loss, affects more than half of all adults by 75
What is ototoxicity?
When a person develops hearing or balance problems due to medicine
What are the causes of sensorineural hearing loss in nerves?
Acoustic neuroma
What is an acoustic neuroma?
Benign brain tumour - vestibular Schwannoma (unilateral)
What is pure tone audiometry?
Science of measuring hearing acuity for variations in sound intensity and frequency
What is an otoacoustic emissions test?
The normal cochlea produces low intensity sounds, this is tested in newborn hearing screening
How is hearing loss treated? 4 mechanisms
Treating the underlying cause, cochlear implants, hearing aids, brainstem implants
What is a tuning fork used to assess?
Used to establish presence or absence of a hearing loss with a conductive component
How is audiometry conducted?
Use audiometer to produce sound, plot audiogram using hearing thresholds to define if hearing loss, normal threshold between 0-20dB
What is the central processing assessment (audiometry)
Assessment of hearing abilities other than detection e.g sound localisation, filtered speech
What is tympanometry?
Tests the condition of the Middle ear and mobility of eardrum and conduction bones by creating variations of air pressure in ear canal
What is the input and output of the vestibular system?
Input = movement and gravity, output = ocular reflex and postural control
What type of sensors are otoliths?
Mechanical sensors
What are the two otolith organs in the vestibular system?
The Utricle and Saccule
Where are the otolith cells in the Utricle located?
On the maculae horizontally
Where are the otolith cells located in the Saccule?
On the maculae, vertically
What does the maculae of the Utricle and saccule contain?
The hair cells, a gelatinous matrix, with the otoliths on top. These otoliths are carbonate crystals that help the deflection of the hairs
The Utricle detects which type of movement?
Horizontal, the Saccule is vertical movement
How do the three semicircular canals of the vestibular system work to define the three planes (anterior, posterior and horizontal)
The anterior and posterior canals form a 90 degree angle, lateral canals are horizontal to the other canals, they work in pairs
Where are the hair cells of the semicircular canals located?
Ampulla, the rest of the canal only has a liquid high in potassium - endolymph
Describe the structure of the ampulla in semicircular canals
Has Crista where the hair cells are located, the cells are surrounded by the cupula which help hair cell movement
What two types of cilia do vestibular hair cells have?
Kinocilium (biggest) and sterocillia
How do the cilia of the vestibular system depolarise cells
Cilia allows the cells to depolarise the cells with movement if the endolymph generated by head movement
Hair cells in the vestibular system have a resting potential which has a ____________ to the nerve
Has a basal discharge
What affect does the hairs in the vestibular system moving towards to kinocilium have?
Generates depolarisation and an increase in nerve discharge
Where do primary afferent in the vestibular system end?
In the brainstem (pons)
What are the three main vestibular system functions?
To detect and inform movement about head movements, to keep images fixed in the retina during head movements, and balance
What are the two types of vestibular reflexes?
Vestibulo-ocular reflex (VOR) and vestibulo-spinal reflex (VSR)
What is the VOR?
Vestibulo-ocular reflex: keeps images fixed in the retina as eye movement occurs in the opposite direction to head movement at same velocity and amplitude
How does the VOR function?
Via a connection between vestibular nuclei and oculomotor nuclei
How are vestibular disorders categorised?
Acute AND unilateral or slow AND unilateral or any bilateral loss
What are the main complaints associated with and acute AND unilateral vestibular disorder?
Imbalance, dizziness, vertigo and nausea
What are the main complaints associated with slow AND unilateral/bilateral vestibular disorders?
Imbalance and nausea, NO vertigo
Peripheral vestibular disorders are due to an issue with which part of the vestibular system?
The vestibular organ and/or CN8
What are three examples of peripheral vestibular disorders?
Vestibular neuritis, Benign paroxysmal positional vertigo, Ménière’s disease
Central vestibular disorders are due to an issue with which part of the vestibular system?
CNS (brainstem or cerebellum)
What are three examples conditions caused by central vestibular disorders
Stroke, multiple sclerosis and tumours
What is the clinical approach for diagnosis of a vestibular disorder? (Differentials, exams, red flags)
Main diagnoses = BPPV, vestibular neuritis, vestibular migraine and cerebellar stroke.
Core exam = eyes, ears, legs
Red flags= headache, gait problem, hyper-acute onset, hearing loss, prolonged symptoms (>4 days)
What are the four categorisations of balance disorders based on timing (evolution)? Give examples of each
Acute = vestibular neuritis, stroke
intermittent = benign paroxysmal positional vertigo (BPPV)
recurring = migraine, Ménière’s disease
progressive = schwannoma vestibular (CN 8), degenerative conditions such as MS
What is a HINTS exam and when is it used?
Clinical exam in acute dizziness.
Head Impulse test (horizontal rotational VOR)
Nystagmus
Test of Skew deviation (vertical misalignment)
Outline the pathology of Benign paroxysmal positional vertigo
BPPV is a peripheral disorder where the otoliths (carbon crystals) from the utricle, detach from the maculae and float around the semi-circular canals. Otoliths are not supposed to be found in the canals and therefore when these are floating in the canals, will induce a bigger endolymph flow when the head moves (the crystals will carry more liquid) and therefore the movement of the head would be processed by the brain as bigger and faster than it is in reality. This will cause vertigo attacks every time the head moves quickly, especially when lying down or standing up. The attacks are short, because these will end when the endolymph settles (usually less than 1 min) but will be recurrent, happening every time the person changes the head position quickly
