Lecture 13- CN8 Auditory and Vestibular; Basal Nuc; Cerebellum Flashcards
ANATOMY OF THE AUDITORY SYSTEM
ANATOMY OF THE AUDITORY SYSTEM
The auditory system is split into what 4 main parts?
- External Ear
- Middle Ear
- Inner Ear (labryinth)
- Auditory Apparatus
What are the 3 parts of the external ear?
- auricle (pinna)
- external auditory canal
- ear drum (tympanic membrane)
What is the auricle?
outer ear structure
What does the external auditory canal connect?
connects auricle to ear drum
The ear drum (tympanic membrane) is a sheet across the external auditory canal composed of what 3 things?
What is the function of the ear drum (tympanic membrane)?
- epidermis
- epithelium
- connective tissue fibers (elastic)
-vibrates with the force of the sound wave strike and transmits the vibrations further in, to the bones of the middle ear
The middle ear is a cavity filled with what?
air
What are the 5 main structures of the middle ear?
- auditory ossicles (smallest bones in the body)
- oval window
- round window
- tensor tympani (CN V3) and stapedius (CN7) muscles
- opening to the auditory tube (eustachian tube)
What are the 3 smallest bones in the body in order from external to internal and what do they connect/do?
- malleus (hammer), incus (anvil), stapes (stirrup)
- The auditory ossicles transmit vibrations of the tympanic membrane through the middle ear to the oval window
What is the oval window and its function?
- membrane covered opening into perilymph of cochlea
- when stapes “taps” on the oval window, it will create fluid filled vibrations within the cochlea
What is the round window and its function?
- membrane covered opening into perilymph at the other end of cochlea
- prevents scattering of sound waves
What is the function of the tensor tympani and stapedius muscles?
contract to prevent damage to middle ear structures by loud noise
The opening to the auditory tube (eustachian tube) connects middle ear chamber to nasopharynx to _____________ in the middle ear.
equilibrate pressure
What are the 3 main parts of the inner ear (labyrinth)?
- bony labyrinth
- membranous labyrinth
- vestibulocochlear nerve (CN8)
The bony labyrinth is lined by _________ and contains _________.
- periosteum
- perilymph
What are the 3 main parts of the bony labryinth and their function?
- semicircular canals- contains sensory receptors (crista ampullaris) for equilibrium(angular) (lie at right angles to each other in 3 geometric planes)
- vestibule- contains sensory receptors (macula) for equilibrium (linear)
- cochlea- contains sensory receptors (spiral organ of corti) for hearing
The membranous labryinth is sacs and tubes inside bony labryinth. The membranous labryinth is filled with __________.
endolymph
What are the 4 parts of the membranous labryinth?
- utricle
- saccule
- membranous semicircular canals
- cochlear duct for hearing
The utricle and saccule are both membranous sacs in the ________ therefore they contain _________, but what is the difference between them?
- vestibule
- endolymph
- utricle is connected to semicircular canals, saccule is connected to utricle
The receptors for the organ of hearing are contained in the _________ duct, while those for the organ of balance are contained in the _______, ________, and the three semicircular ducts.
- cochlear
- utricle, saccule (both in outer bony vestibule)
CN8 has special sensory innervation of the _________ and ____________ canal organs to function in equilibrium and the _________ organ to function in hearing.
- vestibular and semicircular
- cochlear
CN8 is split into what 2 branches? What are their ganglion?
- vestibular branch- superior and inferior vestibular ganglion
- cochlear branch- spiral ganglion
Auditory apparatus = ____________ = sensory/receptor for hearing
-Spiral organ of Corti
Hair cell stereocilia for hearing is embedded in ______ membrane which is __________.
- tectoral
- stationary
The base of hair cells are attached to ________ membranes which is the floor of the cochlear duct seperating endolymph from perilymph in the cochlea bony labyrinth.
basilar
Basilir membrane/hair cells move in response to ________. Higher frequencies go to the ______ of the basilar membrane while lower frequencies go to the ______.
- sound
- base
- apex
The auditory apparatus also has _________ cells.
support
In short, Spiral organ of Corti consists of hair cell layer on the basilar membrane arranged around the spiral core of the cochlear bony labyrinth (modiolus); hair cell stereo cilia are embedded in a matrix=_________ membrane which does not move.
tectoral
HEARING
HEARING
- Sounds alternating high and low pressure regions (______) in air that originate from a vibrating object.
- Pitch is the ________ of sound waves.
- Size of the wave is equal to intensity or __________ of sound which is loudness.
- waves
- frequency
- amplitude
What produces tone?
pitch + amplitude
Hearing Pathway
- Sound waves from a vibrating object directed to eardrum by _______and _________ auditory canal
- sound waves cause ear drum to vibrate
- Vibration is amplified and transmitted to oval window by auditory ossicles in what order?
- Pressure then transmits from mechanical to fluid vibration in the ________ and ___________.
- This vibration causes the basilar membrane to move and the stereocilia to ______ while the __________ membrane remains stationary.
- auricle, external
- ear drum → malleus→incus→stapes→oval window
- peri and endolymph
- bend, tectoral
- If the stereocilia are bent laterally, this results in ________ which releases chemical messengers (glutamate) to stimulate auditory sensory neuron.
- Bending the stereocilia medially results in what?
- depolarization
- hyperpolarization
High pitch = ______ of basilar membrane
Low pitch = _______ of basilar membrane
- base
- apex
Auditory Nerve Pathway
- signal on bipolar neuron in ________ ganglia (located in center, modiolus, of cochlea)
- signal travels on the ________ nerve
- cochlear n. travels through petreus portion of temporal bone exiting ________ auditory meatus
- enters brain stem at junction of pons and medulla synapse with dorsal and ventral ________ nuclei in _________ manner
- fibers from cochlear nuclei synapse ascend to the inferior colliculus resulting in _________ indirect connections and _________ direct connections.
-spiral ganglia
-cochlear
internal
-cochlear, tonotopic
-contralateral, bilateral
- Contralateral indirect connections of the auditory nerve pathway go where?
- Bilateral direct connections of the auditory nerve pathway go where?
- superior olivary complex, reticular formation, trapezoid body provides cross over
- inferior colliculus via lateral lemniscus
After the auditory nerve pathway splits and goes bilaterally to the inferior colliculus, what are the 2 structures it goes to?
- medial geniculate body of thalamus -> auditory cortex (superior medial temporal lobe) (CONSCIOUS)
- tectospinal head turning reflex
- IPSILATERAL ONLY GOES TO MEDIAL GENICULATE
- CONTRALATERAL GOES TO BOTH
In summary most fibers from the cochlear nucleus cross to the contralateral side, although some stay ipsilateral, _________ projection to the cortex allows discrimination of sound differences in each ear.
bilateral
VESTIBULAR SYSTEM
VESTIBULAR SYSTEM
Equilibrium can be defined as both ________ and _________ acceleration. What is the difference?
- linear- change in velocity when traveling in one direction
- angular- change in velocity when rotating
What 2 structures make up the Vestibular Apparatus organ of equilibrium?
- vestibule (linear)
- semicircular canals (angular)
What 2 structures are located within the vestibule?
- utricle (endolymph)
- saccule (endolymph)
What is the sensory receptor for linear acceleration and where is it located?
- macula
- in the walls of the utricle and saccule
The vestibular apparatus also has _______ cells.
support
The macula has hair cells that contain _________.
What is the difference between the macula hair cells in the utricle and saccule?
-stereocilia
- utricle stereocilia are on the floor and point up (horizontal linear)
- saccule stereocilia are on the back wall and point forward (vertical linear)
Above the hair cells we have the ________ membrane which is a gelatinous material that has calcium carbonate crystals called ________.
- otolithic
- otoliths
What are the stereocilia embedded in?
otolithic membrane
The macula of the utricle and saccule are arranged at _________ to each other.
right angles
Body movement causes the __________ to move and bend the stereocilia resulting in:
- membrane _________ to generate an action potential in CN8
- membrane ____________ to inhibit action potentials
- otolithic membrane
- depolarization
- hyperpolarization
What is the sensory receptor for angular acceleration and where is it located?
- cristae ampularis
- in the lumen of semicircular canals
The crista ampularis, like the macula has _____ and ____ cells.
-support and hair
The cristae ampulla, like the macula, has a matrix in which the hair cells are embedded. What is it called in the cristae ampulla?
cupula
Rotational movement of the head bends the stereocilia of the hair cells resulting in;
- membrane ___________ to generate an action potential in the vestibular nerve on one side
- membrane ____________ to inhibit signaling of vestibular n. on the other side.
- depolarization
- hyperpolarization