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
Equilibrium Pathway
- bending ________ of hair cell
- ________ or __________ the hair cell
- change the pattern of ______/_______ of peripheral axon of bipolar neuron in _________ ganglia
- exit petrous portion of temporal bone at ________ acoustic meatus
- enter brainstem at level of ______ and _________
- stereocilia
- depolarize or hyperpolarize
- excitation/inhibition, vestibular
- internal
- pons and medulla
After entering the brainstem at the pons and the medulla, the fibers from the semicircular canals, utricle, and saccule go to specific vestibular nuclei. What are they?
-semicircular canals- superior and medial vestibular nuclei
utricle maculae- lateral vestibular nucleus
-saccule maculae- lateral and inferior vestivular nuclei
- Angular equilibrium (semicircular canals) go to ___ and ___.
- Linear equilibrium (maculae and utricle) go to ___ and ___.
- SVN and MVN
- IVN and LVN
After the fibers from the semicircular canals, utricle, and saccule go to their specific nuclei they project to 5 main locations via the MLF, what are these locations?
- cerebellum flocculondular lobe = posture and balance
- medial vestibulospinal tract = head turning
- lateral vestibulospinal tract = cervical and lumbar spinal cord extensor muscles
- CN3,4,6 = EOM via MLF
- premotor and other regions of cerebral cortex = head proprioception
BASAL NUCLEUS (GANGLIA)
BASAL NUCLEUS (GANGLIA)
What does the basal nucleus do to the precentral gyrus to refine movement?
inhibits
What are the 8 parts of the basal ganglia and their function?
- ) caudate = emotion, cognitive learning
- ) putamen = regulate movements and influence learning
- ) striatum (neostriatum) = caudate + putamen
- ) ventral striatum = area where caudate joins putamen (contains nucleus accumbens), functions primarily in limbic
- ) globus pallidus (GP) internus and externus) = regulate voluntary movement
- ) lentiform = putamen + globus pallidus
- ) subthalamic nucleus
- ) substantia nigra (compacta and reticularis) = compacta-dopamine
What are the 2 overall functions of the basal ganglia (psychomotor)?
- behavior
- motor
What are the aspects of behavior related to the basal ganglia?
- goal directed behavior
- social behavior
- emotions
What are the motor aspects related to the basal ganglia?
- decision making = initiation
- judgement = fractionation of force
- prioritizing = multi-joint movements and sequencing
- emotional response
- learning
- eye movements
- spatial attention
The BG acts by reducing _________ input to the motor cortex ie it is __________.
- excitatory
- INHIBITORY
What are the 3 main afferent inputs to the BG? What is their NT? Excitatory or inhibitory?
- CEREBRAL CORTEX/glutamate/excitatory
- PEDUNCULOPONTINE NUCLEUS/glutamate and ACh/ excitatory
- RAPHE NUCLEUS/serotonin/inhibitory
Most afferent input to the BG is __________.
EXCITATORY
Efferent output from the BG = _____/inhibitory from GP internus to what 3 structures and why?
(S41)
-GABA
- VA and VL of thalamus =decrease precentral gyrus activity
- Pedunculopontine nucleus = increase activity of axial, postural muscles
- Tectum = decrease activity of stepping pattern generators (walking); affect reflex eye movements
What is different about the efferent output to the pedunculopontine nucleus from the BG?
acts to inhibit an inhibitor (DISINHIBITION)
What does inhibiting the basal ganglia ultimately do to motor activity of the axial and postural muscles when inhibiting the PPN (pedunculopontine nucleus)?
increase
The basal ganglia is broken down into 5 pathways, 3 are _________ loops and 2 are ______ loops.
- non-motor
- motor
What are the 3 non-motor loops?
- goal-directed behavior loop
- social behavior loop
- emotion loop
What is the pathway of the goal-directed behavior loop and its function?
- prefrontal cortex→caudate→ GPi→decrease activity VA thalamus
- decision making; goal directed behavior; planning; chooses action; learning
What is the pathway of the social behavior loop and its function?
- prefrontal cortex→ head/caudate nuc. + SN reticularis→ MD Thalamus
- recognize social cues; regulate self control; evaluates what information is relevant and irrelevant
What is the pathway of the emotion loop and its function?
prefrontal cortex→striatum→MD Thalamus
-link emotions to cognitive and motor systems; reward seeking; outcome predictions ie. emotions to facial expression
What are the 2 motor loops?
- oculomotor loop
- motor loop
What is the pathway of the oculomotor loop and its function?
frontal and supplementary eye fields→caudate nuc.→SN reticularis→decrease activity VA thalamus allow for reflexive prosaccades
-spatial attention; initiate fast eye movements toward an object=prosaccades
What are prosaccades?
rapid eye movement towards an object
The motor loop goes from the motor and premotor cortex to affect level of GABA inhibitory activity of ____.
GPi
The motor pathway goes to what 3 structures and for what?
- motor cortex- voluntary movement
- PPN- posture muscle control
- Midbrain tectum (superior colliculus)- eye movements and step generator = walking
What are the 3 pathways of the motor loop of the BG?
- hyper direct no go
- go
- no go
The hyper direct no go pathway uses the subthalamic nucleus which ________ GPi.
stimulates
Describe the pathway of the hyper direct no go pathway and how it affects the motor cortex, PPN, and tectum.
-cortex→subthalamic nuc→GPi (↑ activity of stimulator of GPi so activity GPi ↑) this results in:
- inhibits motor thalamus = precentral cortex
- inhibits PPN which ↑ activity of reticulospinal tract/ postural and girdle muscles by INHIBITING and INHIBITOR (DISINHIBITION)
- inhibits tectum (midbrain) locomotor/step pattern generator
The go pathway is a direct pathway which ________ activity of GPi.
decreases
Describe the pathway of the go pathway and how it affects the motor cortex, PPN, and tectum.
-cortex→putamen→ decrease activity GPi (stim. an inhib of GPi so activity GPi↓)
- disinhibits motor thalamus/cortex to increase precentral gyrus activity
- disinhibits PPN to inhibit reticulospinal/postural and girdle muscle activity
- disinhibits tectum (midbrain) locomotor/ step pattern generator
The no go pathway is an indirect pathway that works by inhibiting ____ which normally inhibits GPi which results in ________ activity of GPi.
- GPe
- increased
Describe the pathway of the go pathway and how it affects the motor cortex, PPN, and tectum.
-cortex→putamen→decrease activity GPe which was an inhibitor of GPi resulting in a ↑ GPi activity
- inhibit motor thalamus/cortex
- inhibit PPN/ ↑reticuluospinal/postural & girdle muscle activity
- inhibit Midbrain locomotor/step pattern generator
The substantia nigra modulates the _________ to modulate the GPi.
neostriatum
What are the 2 parts of the substantia nigra?
- substantia nigra reticularis
- substantia nigra compacta
The substantia nigra reticularis has input from where and output to where?
Input= GABA inhibitory from neostriatum
Output= GABA inhibitory to
- substantia nigra compacta
- midbrain tectum
- motor thalamus
The substantia nigra compacta has input from where and output to where?
Input= GABA inhibitory from substantia nigra reticularis
Output=
- Dopamine stimulation (D1 receptor) of neostriatum
- Dopamine inhibition (D2 receptor) of neostriatum
D1 receptors act to _______ the GO pathway.
stimulate
D2 receptors act to _______ the NO GO pathway.
inhibit
11
1
1
111
11
1
1
1
1
1
1
1
1
1
1
1
1
1
What are 2 disease states involving the basal ganglia and are they hypokinetic or hyperkinetic?
- Parkinson’s Disease= hypo
- Huntington’s Disease= hyper
Parkinson’s Disease
- due to loss of Dopamine from substantia nigra pars ________
- go pathway is no longer ________→↓thalamic motor activity
- no go pathway is no longer ________→↓thalamic motor activity
- compacta
- stimulated
- inhibited
Huntington’s Disease
- due to loss of GABA from neostriatum
- no go pathway no longer _________ thalamus→↑thalamic motor activity
inhibits
CEREBELLUM
CEREBELLUM
The cerebellum is divided into what 3 lobes? What are their function?
Anterior Lobe = Spinocerebellum
-controls axial muscles tone; degree of flexion/extension
Posterior Lobe = Cerebrocerebellum
-planning, organization, and coordination of motor activity
Flocculonodular Lobe = Vestibulocerebellum
-control of eyes and head position
The lateral anterior and posterior lobe control what?
efferent fine motor to limbs
The vermal/paravermal (medial anterior and posterior lobe) control what?
efferent axial muscles for head turning, posture, and tone
What are the 4 deep nuclei found bilaterally in the cerebellum?
- fastigial nucleus
- dentate nucleus
- globose nucleus
- emboliform nucleus
The fastigial nuclei relays efferent signals to _________ nuclei and _____________.
- vestibular
- reticular formation
The dentate nucleus relays efferent signals to the cortex via _____________.
superior colliculus
The interposed nucleus (globose and emboliform) relay efferent signals to the ___________.
red nucleus
What are the 3 peduncles of the cerebellum and what do they carry?
Inferior
-afferent from spinal cord/medulla (cuneocerebellar; rostrocerebellar; posterior spinocerebellar)
Middle
-afferent from cerebral cortex to cerebellum via pontine nucleus
Superior
-efferent from cerebellar nuclei to brain stem and cortex (anterior spinocerebellar)
The cerebellum and associated peduncles form the roof and sides of what?
4th ventricle
What are the openings for the CSF to enter the subarachnoid space?
- 2 lateral foramen of Luschka
- 1 median foramen of Magendie
Afferent input to the cerebellum comes from what 7 areas?
- spinal cord = body
- inferior olivary nucleus
- vestibular apparatus
- reticular formation
- cerebral cortex
- tectum
- mesencephalic trigeminal nucleus
The spinal cord input to the cerebellum goes to the vermis and perivermal cortex of the __________ and adjacent _________ lobes. What are the 4 inputs from the spinal cord and their function?
-anterior, posterior
- dorsal spinocerebellar- proprioception of leg
- ventral spinocerebellar- monitor ventral horn activity of leg spinal cord segments
- cuneocerebellar- proprioception of arm
- rostrocerebellar- monitor ventral horn activity of arm spinal cord segments
The inferior olivary nucleus relays information from the _________ and __________ to the anterior and posterior lobes of the cerebellar hemispheres.
- spinal cord (proprioception)
- sensory motor cerebral cortex to red nucleus to ION
The vestibular apparatus has a direct connection to the __________ lobe of the cerebellum.
flocculonodular
The reticular formation information is sent to the vermis and paravermis of the _________ and _________ lobes.
-anterior and posterior
The cerebral cortex sends information to the anterior and posterior cerebellum lobes through what 3 structures?
- red nucleus to ION
- deep pontine nuclei (motor cortex to cerebellum)
- reticular formation
The tectum sends information from the _______ and ___________ to anterior and posterior lobes of the cerebellar hemispheres.
inferior and superior colliculus
Afferent neurons from the input sources have what 2 types of fibers? What is the difference?
Mossy Fibers: Glutamate Excitatory Fibers
- from all areas of afferent input except inferior olivary nucleus that synapse with;
- deep cerebellar nuclei
- excitatory granule cells of cortex
- inhibitory golgi cells of cortex
Climbing Fibers: Glutamate Excitatory Fibers
- from the inferior olivary nucleus that synapse with;
- deep cerebellar nuclei
- purkinje cells of cortex making the refractile to granule cell stimulation
What are the 3 layers of the cerebellar cortex?
- granule cell layer (innermost layer)
- purkinje cell layer (middle layer)
- molecular layer (surface layer)
The granule layer is composed of what 2 cells?
- granule cells
- golgi cells
Granule cells are glutamate ________ cells with diverging collateral capable of exciting many Purkinje cells which does what?
- excitatory
- influence broad regions of body musculature simultaneously
Golgi cells are GABA _________ interneurons that inhibit ________ cells.
inhibitory
-granule
The granule cell turns itself off by activating a ______ cell.
golgi
Purkinje cells are _______ inhibitory cells which inhibit deep cerebellar nuclei and are stimualted by _______ cells. They provide a burst of inhibition to deep cerebellar nuclei.
- GABA
- granule cells
What are the 4 projections of purkinje cells?
- vermal Purkinje cells project to fastigial nuc.
- anterior and posterior lobe Purkinje cells project to dentate nucleus
- paravermal Purkinje cells project to interposed nuc.
- some anterior lobe Purkinje project to vestibular nuc.
Purkinje cell interconnections can be changed to facilitate ____________.
motor learning
The molecular layer contains what types of cells, what is their function?
basket cells- stimulated by granule cells to inhibit Purkinje cells adjacent to those stimulated by granule cells
Cerebellar cortex regulates the excitatory activity of _______________ nuclei
deep cerebellar nuclei
Efferents from the cerebellum are ________ and come from the deep cerebellar nuclei.
excitatory
