Lecture 29: Neuroanatomy of the Auditory and Vestibular Systems Flashcards
What are the functions of the vestibular system
Transduce and interpret head movements, maintain position of visual axes when head is moving, send motor commands to the trunk and limb muscles in order to maintain balance
What is the vestibulo-ocular reflex
Maintain positioning of the visual axes when the head is moving
What is the function of the auditory system
Transduce and interpret vibrations due to sound
What structure receives information from the organs of balance on head movement and information on muscle firing from the cerebellum
Vestibular nuclei in the brain stem
What is the pathway of information on the head and body movement
Utricle, saccule and ampulla—> scarpa’s ganglion—> CN VIII—> nuclei in brainstem
What is responsible for sending motor to antigravity muscles to maintain upright posture
Vestibulospinal tracts
What is the pathway of motor to extraocular nuclei to coordinate eye movements
Medial longitudinal fasciculus—> oculomotor, trochlear and abducens nuclei
What brain structure is responsible for receiving input on body position and movement from cortex, spinal cord and vestibular movement. Coordinates motor output through the cortical and vestibular pathways. Coordinates timing of movement
Cerebellum
What could be the result of a lesion to CN VII or the vestibular nuclei
Disruptions in stance, head posture, and balance. Damage that includes the vestibular nuclei can also lead to loss of extensor muscle tone
What structures are encased within the bony labyrinth
Organs of balance and hearing, contained with the petrous portion of the temporal bone
What is the flow from the air filled outer and middle ear cavities to fluid filled ear cavities
Sound energy (outer)—> through tympanic membrane—> auditory ossicles (malleus-incus-stapes in middle ear)—-> oval window (inner ear)
What are the vestibular organs
Semicircular ducts, utricle, saccule and vestibular nerve
What are the cochlear organs
Cochlear duct and cochlear nerve
What region contains endolymph
Membranous labyrinth
What region contains perilymph
Region between the membranous ducts and the bony labyrinth
What type of receptors are located in the vestibular and cochlear apparatus and what do they depend on
Mechanoreceptors that depend on the mechanical displacement of receptors by fluid
What structures are responsible for sensing rotation of head
Semicircular ducts and ampulla
What structures are responsible for sensing linear head movement in a horizontal plane
Utricle and macula
What structures are responsible for sensing linear head movement in vertical plane
Saccule and macula
What is the vestibular ganglion
Scarpa’s ganglion
What vestibular organs and how many of each are located on each side of head
3 semicircular ducts with 1 ampulla
1 utricle with one macula
1 saccule with one macula
1 vestibular ganglion/scarpa’s ganglion
What is the function of the saccule
To monitor and activate in response to linear acceleration of vertical movements (up and down) relative to gravity vector
What is the function of the utricle
To monitor and activate response to linear acceleration of horizontal movements (side to side, front to back) relative to the gravity vector
What is the function of the three semicircular ducts
Function to monitor and respond to angular acceleration (rotation) of head in all planes
What organs of the vestibular membranous labyrinth Transduce acceleration
Utricle, saccule and semicircular ducts
Where are the hair cells located within the semicircular ducts
Ampulla
Ampullary crest hair cells embed in the ___
Crista
Stereocilia embed in the ___
Gelatinous cupula
Moving ____ bends the cupula which tilt the ___ towards ____
Endolymph, sterocilia and kinocilium
Cilia are surrounded by ___
Endolymph
What is the concentration of K+ and Na+ in the endolymph
K+ (high)= 150mM and Na+ (low)=1mM
Cell bodies and dendrites of the hair cells are surrounded by ___
Perilymph
What is the concentration of K+ and Na+ in perilymph
Low K+ and high Na+
What happens when stereocilia move towards kinocilium
Hair cells depolarize and Ca2+ enters cell and increase firing rate
What happens when sterocilia are deflected away from kinocilium
Hair cells hyperpolarize and decrease firing rate
What makes up the internal structure of stereocilia and kinocilium
Actin
What are the otolith organs
Utricle and saccule
Otolith organs Transduce ___ acceleration
Linear acceleration
Utricle- detects horizontal displacement
Saccule- detects vertical displacement
Moving of the head allows displacement of ___ which moves and tilts sterocilia toward kinocilium
Gelatinous cap
Hair cells in macular organs have ___ orientation
Mirrored
What does the reversal line indicate and what is the functionality
Indicates where hair cell orientation changes. Functionally some hair cells are depolarizing while others are hyperpolarizing
What structure is responsible for summing the signal of the variation in stimulation from the reversal line
Vestibular nuclei
Hair cells are ___ polarized on right and left sides
Oppositely polarized
Hair cells will ___ on the side of the head toward which the person is turning meanwhile will ___ on the side from which the Person is turning
Depolarize (increase firing rate), hyperpolarize (decrease firing rate)
Vestibular nuclei compare firing rates from each side, magnitudes should ___ in a healthy individual
Match
What structure controls vestibuloocular relfex
Semicircular canals
Ex: head rotates to the right but eyes stay forward. What organ monitors head rotation? What muscles receive motor commands to keep eyes centered
Vestibular organs monitor head rotation
Motor commands are sent to contract the LEFT lateral rectus and RIGHT medial rectus
A lesion to CN VIII, vestibular apparatus or vestibular nuclei leads to an imbalance of ____ received by vestibular nuclei
Action potentials
What is the result of imbalanced action potentials received by vestibular nuclei
Perception that the head is constantly moving when its not
What structures provide mammals with an extended range of hearing compared to other vertebrates
The middle ear contains the malleus, incus, and stapes in mammalian anatomy whereas the anatomy in non-mammalian vertebrates only contains the stapes, therefore mammals have a greater ability to amplify sound
What animal can hear at the highest frequency
Bottlenose dolphin
What animal can hear at the lowest frequency
Elephant
Where is the cochlea located in relation to the semicircular ducts
Rostromedially
The footplate of the stapes transmits vibrations to the membrane of the ___ and ___ of the scala vestibuli
Oval window and perilymph
The mechanoelectrical mechanism is embedded in
Scala media
Fluid displacement from the oval window creates waves and displacements in membranes of the ____
Cochlea
What fluid fills the cochlear duct
Endolymph
What fluid fills the scala vestibuli and scala tympani
Perilymph
Stereocilia hair cells along the basilar membrane are embedded into the ____ membrane
Gelatinous tectorial membrane`
Displacements of the basilar membrane relative to the tectoral membrane displaces the stereocilia resulting in what
Causing mechanoelectrical transduction and depolarization
What membrane helps encode frequency
Basilar membrane
What frequency is best encoded closest to stapes and oval window
high frequencies
What frequency is best encoded farthest away from stapes and oval window
Low frequencies
How can animals determine where a sound came from
Interaural time/arrival difference and interaural level difference are used to compute location based on timing and sound level differences received between each side
