Auditory and vestibular systems Flashcards
What kind of motion do vestibular organs capture?
LOW FREQUENCY motion (movements)
What kind of motion do hearing organs capture?
HIGH FREQUENCY motion (sound).
Describe the three functions of the outer ear
-To capture sound and focus it to the tympanic membrane (eardrum).
-Modest amplification
-To protect the ear
What is the main function of the middle ear?
Mechanical amplification
What is the hearing part of the ear called?
The cochlea
What is the function of the cochlea?
To transduce vibration into nervous impulses
What are the three compartments of the cochlea (from top to bottom)
-scala vestibuli
-scala media
-scala tympani
What are the scala vestibuli and tympani, and what do they contain
They are bone structures in the cochlea and contain PERILYMPH which is high in sodium.
What kind of structure is the scala media and what does it contain?
It is a MEMBRANOUS structure, contains ENDOLYMPH which is high in potassium.
What is located in the scala media giving the proper name aswell.
The hearing organ (Organ of corti).
What exists in the hearing organ/ organ of corti
Hair cells
What is the structure where the organ of corti lies called?
Basilar membrane
How can the arrangement of the basilar membrane where the organ of corti lies, be described as?
Arranged tonotopically, (like a xylophone)
What types of hair cells does the organ of corti contain
-Inner hair cells
-Outer hair cells
Describe the differences in the arrangement of the inner and outer hair cells.
Inner hair cells arranged in 1 line whereas outer hair cells arranged in 3s.
What lies above the hair cells and what does this allow?
A TECTORAL MEMBRANE lies above the hair cells which allows hair deflection.
What does the hair deflection cause?
Depolarisation of the hair cells.
Shat is the difference between afferent and efferent
AFFERENT coming TOWARDS
EFFERENT going AWAY
Which hair cell type carries the majority of the afferent information of the auditory nerve.
Inner hair cells.
What is the function of the inner hair cells (IHC)?
Transduction of the sound into nerve impulses.
Which hair cell type carries the majority of the efferent signals of the auditory nerve?
Outer hair cells
What is the function of the luter hair cells?
To modulate the sensitivity of the response.
What are the hair cells actually called and what is the name for the longest hair cell?
Sterocilia, the longest is called the kinocilium.
Describe how the potassium ion channels are opened in transduction.
The deflection of the stereocilia towards the longest cilium (kinocilium) opens the K+ channels.
Describe how the excitatory signal is produced once the K+ ions have entered.
The entry of K+ depolarises the cell which allows Ca+ to enter and cause the release of glutamate towards the afferent nerve.
How does louder sound affect stereocilia?
Higher amplitudes of sound will cause greater deflection of stereocilia and K+ channel opening.
Describe how the movement of the tectoral membrane leads to the depolarisation and hyper-polarisation of the auditory nerves.
Depolarisation is caused by the movement of the tectoral membrane which moves the stereocilia towards the kinocilia to open the K+ ion channels.
Hyper-polarisation is caused by the tectoral membrane moving back and pushing the stereocilia in the opposite direction and closing the K+ channels.
What do the stereocilia sit on?
The basilar membrane.
What nerve does the auditory nerve combine with.
The vestibular nerve
Where does the auditory part of nerve from the cochlea go to and where does this happen?
It goes to the cochlea nucleus in the pons of the brainstem.
Which nuclei emerge in the midbrain
-The oculomotor nerve (III)
-The trochlear nerve (IV)
Which cranial nerves emerge from the pons?
-Trigeminal (5)
-Abducens (6)
-Facial (7)
-Vestibulocochlea (8)
Which cranial nerves emerge from the medulla?
-Glossopharyngeal (9)
-Vagus (10)
-Spinal accessory (11)
-Hypoglossal (12)
Why does brain damage very rarely lead to hearing loss in both sides?
It is bilaterally inervated at a very early stage before entering the brain.
Where does the vestibulocochlea nerve eventually reach?
The MEDIAL GENICULATE BODY in the thalamus.
Auditory cortex in temporal lobe.
Where does auditory information cross
At the superior olive level.
What are the three anatomical types of hearing loss
CONDUCTIVE hearing loss: problem located in the outer or middle ear
SENSORINEURAL hearing loss: The sensory organ (cochlear) or nerve (auditory nerve) most common
CENTRAL hearing loss: originates in brain and brainstem, very rare.
Causes of conductive hearing loss in outer ear
Wax and foreign bodies
Causes of conductive hearing loss in the middle ear
Otitis and otosclerosis
What is otitis and otosclerosis
Otitis- middle ear infection
Otosclerosis- abnormal bone growth inside ear
Causes of sensorineural hearing loss in the inner ear
-Noise
-Prebycusis
-Ototoxicity
What is prebycusis and Ototoxicity?
Prebycusis: progressive hearing loss due to age.
Ototoxicity: damage to the ear caused by certain medications or chemicals.
What are causes of sensorineural hearing loss affecting the Nerves
Acoustic neuroma (vestibular shwannoma).
Unilateral
How would you clincaly assess hearing loss?
Whisper in ipsilateral ear whilst rubbing fingers in contralateral ear.
What are two tests you can do with a tool to test hearing loss an describe how they work.
The WEBER test and RINNE test.
Useing a tuning fork.
Assess gross hearing loss.
What is it called when hearing thresholds are plotted to define if there is a hearing loss or not?
Audiogram
What is a normal hearing threshold
Between 0-20db
What can you use to distinguish between conductive hearing loss and sensorineural hearing loss
Audiometry
What are the two important outputs related to the vestibular system?
Ocular reflex and Postural control
What is the input of detection for the vestibular system?
Movement and gravity
What are the outputs of the vestibular system
Perception and reflexes maintaining posture and gaze.
What are the three semicircular canals of the vestibular organ connected to?
The UTRICLE.
What are the utricle and saccule called and where do there cells lie?
OTOLITH ORGANS, their cells are located on the MACULAE.
What is the orientation of the way the cells are placed in the utricle and saccule?
Cells are placed HORIZONTALLY in the UTRICLE
and VERTICALLY in the SACCULE
Where do the primary afferents of the vestibular nerves end?
In the vestibular nuclei in the pons.
What is vertigo?
Sensation of spinning or moving when you are actually stationary.
When will a person experience vertigo with a vestibular disorder, include the timing and laterality.
When it is acute AND unilateral.
When will a person not experience vertigo with a vestibular disorder.
In slow AND unilateral or any bilateral loss.
What is peripheral vestibular disorders used to describe.
Disorders of the vestibular organ or the VIII nerve (vestibulocochlea)
What are central vestibular disorders used to describe.
Disorders of the CNS (brainstem/cerebellum).
What are the clinical exams you do with acute diziness.
-Head Impulse test
-Nystagmus
-Test of Skew deviation
HINTS
Describe the head impulse test.
A patient is sat down and a doctor moves his head to test wether eyes remain fixated in an object.
What is nystagmus
Jerky movements of the eyes.
Describe the test of skew deviation.
Covering one eye and seeing if the gaze corrects itself in each eye.
