Auditory and Vestibular Systems Flashcards
Term: Sense of sound
Audition
Describe the stimulus for the auditory system
Pressurized sound waves of varying frequencies
Structure: From the pinna to the tympanic membrane
Outer ear
Structure: From the tympanic membrane through the stapes
Middle ear
Structure: Past the stapes and containng the cochlea
Inner ear
3 Middle ear bones
- Malleus
- Incus
- Stapes
Describe the movement of sound waves through the auditory system
Pinna collects sound wave
Sound funneled through external auditory canal
Vibrates tympanic membrane, inner ear bones, oval window
Vibrates fluid in cochlea
Fluid moves and stimulates hair cells
Responses picked up by cochlear nerve
Travels to the cortex
Structure: Contains receptors that recieve sound
Organ of Corti
Describe the function of the partition between the perilymph and enodlymph of the cochlea
The parition forces fluid to move in one direction allowing for continuous sound reception
Describe the structure of the organ of corti
3 outter hair cells are attached to the inner hair cells. The outer hair cells fine tune the inner hair cell which transmits sound
Describe the function of the tectorial membrane
The tectorial membrane is pushed down by the fluid in the cochlea to stimulate the hair cells within the organ of corti
Describe how a hair cell is depolarized
Hair cells have cilia attached by tipplings. The direction of cilia movement determines if the signal is inhibitory or excitatory. As the cilia move/vibrate the tipplings are pulled opening K+ channels. Opening of the K+ channels depolarizes the hair cells letting Ca+ rush in. Neurotransmitters in vesicles then move to the membrane and are released stimulating the postsynaptic cell
Describe the arrangement of sound reception within the cochlea
Tonotopic arrangement
- higher frequencies at the base
- lower frequencies at the apex
ALL frequencies DO NOT stimulate every single hair cells.
3 functions of the auditory system in the CNS
- Activating effect of sound (will wake you up)
- Orienting effect (will move head and eyes to sound)
- Recognition of sound
Pathway: Connection to auditory system increases awareness
Reticular formation
Pathway: Connection to auditory system processes information from both ears allows you to determine where the sound is coming from
Inferior colliculus
Pathway: Connection to the auditory system moves your head and eyes toward sound
Superior colliculus
Pathway: Connection to the auditory system that relays information to the primary auditory cortex
Medial geniculate body
Cortical area: Comprehension of sound
Wernicke’s area
Condition: middle ear bones don’t move well, would NOT benefit from a cochlear implant
Otosclerosis
Condition: Common in children, middle ear infection
Otitis media
Condition: Hearing sound without stimulus to the auditory system
Tinnitus
Condition: Loss of hearing due to pressure on the nerves, may be due to a benign tumor
Acoustic Neruoma
How would you discriminate between and inner ear condition and a cochlear condition?
Use of tuning fork and place it on the mastoid process
Can hear = middle ear problem
Can’t hear = cochlear problem
Describe the cause of age related hearing loss
There is a loss of hair cells/receptors
Acronymn: BPPV
Benign Paroxysmal Positional Vertigo
Top 3 complains to PCP
- Chest pain
- Fatigue
- Dizziness
3 Systems that work together for Balance
- Vestibular
- Vision
- Somatosensory
Location: Vestibular
- Peripheral sensory appartatus
- Central processing system
- Motor system
- Inner ear
- Vestibular nuclei in brainstem
- Ocular/Skeletal muscle
Structure: Provides sensory input about both agnulgar and linear acceleration
(Vestibular) peripheral sensory apparatus
Structure: Oreitns the head with respect to gravity
(Vestibular) peripheral sensory apparatus
Structure: Somatosensory and visual cues with connections to the reticular formation, cortex, and direction connections to the cerebellum
(Vestibular) Central processing system
Describe the structure of the vestibular peripheral sensory apparatus
Consists of 3 semi-circular canals containing fluid and lined with hair cells. Stimulation of this system gives you information about the position of your head
2 Vestibular peripheral sensory apparatus structures that detect linear movement/acceleration and gravity
Utricle and Saccule
3 Vestibular peripheral sensory apparatus structures that detect angular movement (yaw, pitch, roll)
Anterior, Posterior, Lateral Semi-Circular Canal
Describe the push pull system within the vestibular peripheral sensory apparatus
Relates to the peripheral sensory apparatus working in tandem to make the system more sensitive
Ex. When you turn your head to the right, the right horizontal canal is stimulated and the left horizontal canal is inhibited
Ex. Bending down right anterior is stimulated and left posterior is inhibited. The same is turn for the left anterior/right posterior relationship
Describe how hair cells in the vestibular peripheral sensory apparatus are
- Stimulated
- Inhibitied
- Fluid moves toward the hair cell
- Fluid moves away from the hair cell
Term: Rotation
Yaw
Term: Up and down
Pitch
Term: Side bend
Roll
Describe how the horizontal canal is oriented
It sits at 30 degrees
Structure: Biological sensor which converts head motion to neural firing present in the ampulla and otolith organs
Hair cell
Describe the “window” into the vestibular system
The eyes, each canal has its own unique eye movement
2 Otolith organs and their orientation
- Utricle - horizontal plane (stimulated with sideways motion)
- Saccule - vertical plane (stimulated with up/down movement)
Purpuse of the information from otolith organs
Balance control
Describe the macula and the purpose of otoconia
Hair cells covered by a gelatinous substance with otoconia on top
The otoconia are senstive to gravity, get sheared along the gel with movement and that information is transferred to the hair cells
in BPPV the otoconia are disloged and moved to the semicircular canals disrupting the flow of fluid
2 Structures that provide information to postural muscles
Utricle and saccule
Structures for maintaining a stable gaze
Semicircular canals
2 Functions of the Vestibular system
- Maintain steady gaze
- Postural balance
Describe the firing rate of the central processing system at rest and with movement
There is a baseline firing rate that is symmetrical at rest
With movement the stimulated side increases its firing rate while the inhibited side decreases its firing rate resulting in balanced input to the CNS
Central Vestibular System: Describe the function of the following structures
- Flocculondular lob of cerebellum
- Inferior/Superior Vestibular Nuclei
- Vestibulospinal tracts
- Vestibulocolic pathways
- Vestibuloautonomic pathways
- move eye amount needed to maintain gaze
- MLF, CN III, IV, VI
- UE/head position
- Innervate the trap/SCM, turn/right the head
- Sweat/throw up
Defn: Vestibulo-ocular reflex
Stabilizes eyes when head moves
Defn: Vestibulo-spinal reflex
Balance control
Tract: Connection between vestibular system and stability muscles of the torso and LE (below neck)
Lateral vestibulospinal tract
Tract: Head position
Medial vestibulospinal tract
Reflex: Large perceptive field, slower to activate
Otokinetic reflex
Condition: Results from a deficit in the vestibulo-ocular relfex causing unmaintained gaze while walking/running/etc.
Oscillopsia
Defn: VOR Gain
As the head moves in one direction the eyes moves in the opposite direction with equal velocity
VOR Gain = Eye velocity/head velocity
1 is normal
Describe the system responsible for maintaining gaze stability at > 60 deg/sec
Vestibular
Describe the system responsible for maintaining gaze stability at < 60 deg/sec
CNS - smooth pursuit
Condition: Difference between sides in the tonic firing rate within the vestibular nuclei
Nystagmus
Term: More than 1 or 2 movements to look from point A to point B
Saccades
Describe how a disruption in th vestibular system manifests via eye movement
The eye movement that would indicate a vestibular problem would be saccades
Describe the direction of the saccade in relationship to the affected side
Nystagmus is named for the direction of the eye movement
The slow phase is driven by the ears while the fast phase is driven by the CNS
If the the lesion is defict causing, the nystamus will beat to the opposite side or AWAY from the lesion
If the lesion is irritative the nystamus will beat to the same side or TOWARD the lesion
7 Non-vestibular causes of dizziness
- Disuse equilibrium
- Orthostatic hypotension
- TIA
- Panic attacks
- Migraines
- Diabetes
- Concussions
Condition:
- Usually unilateral
- Sx with change of head position
- Debris in inner ear
BPPV
Disrupted canal that matches the following nystagmus
- Horizontal
- Upbeats with torsion
- Lateral semi-circular canal
- Posterior semi-circular canal
Condition: Acute inflammation of the vestibular nerve
Vestibular neuritis
Condition: Bacterial infection of the labrinth causing hearing loss
Vestibular labyrinthitis
Condition: Separation of the middle ear from the inne ear typically as a result of head trauma, penetrating injury, or vigorous straining
Perilymphatic fistula
Condition
- 40-60 yo
- Malabsorption of endolymph
- Hearing loss and vertigo
- Attack resolves in 48-72 hours
Meniere’s Disease
Condition: Severe balance loss without accompanying dizziness due to ototoxicity
Bilateral vestibular loss
Describe the appearance of central nystagmus
Unlike peripheral nystagmus which will have a consistent direction/beat, central nystagmus will have no pattern/keep changing directions
Condition: The sensation you’re still moving after spending extended time on a boat
Mal de Debarquement Syndrome
Describe the catch 22 with vertigo medications
Most suppress the vestibular system with can affect your balance while helping your dizziness