Auditory and Vestibule Pathways Flashcards
CN VIII enters the brain as 2 roots where?
At the junction of the pons and medulla
Pontomedullary junction
Medial root = vestibular root
Lateral root = auditory root
CN VIII exits the _______ cranial fossa and enters the _________ portion of the temporal bone via the _________.
Posterior Cranial Fossa
Petrous
Internal acoustic meatus
Schwannoma typically occur at which root of CN VIII
Vestibular part
What is in the petrous portion of the temporal lobe?
Labyrinth
Special organs of hearing and balance
CN VIII has 3 sensory ganglia containing bipolar neurons. What are they?
Spiral ganglion: bipolar neurons for hearing (in cochlea)
Inferior nad superior vestibular ganglia - bipolar nuerons that carry information from the vestibular portion
1st order neurons
The bipolar cells from the 2 vestibular ganglion project to?
Cerebllum (only sensory nerve in which it recieves direct afferents) and 4th vestibular nuclei (2nd order nueron)
The vestibular ganglion projections go to which two parts of the cerebellum?
- Flocculonodular lobe - oldest part of the cerebellum/balance and eye movement
- Vermis - central part of the cerebellum
What are the 4 vestibular nuclei?
- Lateral
- Medial
- Superior
- Inferior (descending)
Located in the rostral medulla/caudal pons (floor of the 4th ventricle around pontomedullary junction)
The Superior Vestibular nucleus is part of which tract?
Ipsilateral acending MLF
MLF interconnects the motor nuclei that control eye movement
The Medial Vestibular nucleus is part of which tract?
MLF and medial vestibulospinal tract
The medial vestibulospinal tract is a descending tract that controls movements for extension of the neck and head movement
The lateral vestibular nucleus is part of which tract?
Lateral Vestibulospinal tract
This a descending tract, contol excitation of antigravity muscles (what causes extension of our paraspinal muscles and limbs
Identify the nuclei in this image
Red: Superior Vestibular nucleus
Orange: Medial Vestibular nucleus
Green: lateral vestibular nucleus
Image slice form caudal pons
What are the vestibular outputs that essential control balance/gaze and posture?
- Extraocular motor nuclei via MLF (CN 3, 4, and 6)
- Cerebellum (reciprocal connection): recieve direct afferent and also second order input from vestibular nuclei
- Ventral posterior nucleus of thalamus - where the second order nuerons terminate (to post central gyrus )
- Reticular formation - forms the core of the medulla, pons, and the brain. Meshwork of connections
- Spinal Cord - spinal pathways
The extraocular motor nuclei via the MLF are involved in? Which two nuclei are involved?
Involved in horizantal gaze, lateral movements, and nystagmus
Medial vestibular nucleus and superior vestibular nucleus are involved
In this brainstem cut which cranial nerve is projecting to the MLF?
This is a image of the pons. CN VI is projecting to the MLF
In this brainstem cut which cranial nerve is projecting to the MLF?
This is a image of the midbrain
CN III is projecting to the MLF
Explain the VEstibulo-Ocular Reflex
Two neuron in the abducens nucleus. One is a motor that go to lateral rectus. There are a bunch of interneurons that receive the same input as the motor neurons. Interneurons will project to the oculomotor through the medial longitudinal fasciculus pathways
When the motor neurons of lateral rectus get engaged the motor neurons sitting right next door get excited and they project to the opposite side. The contralateral motor nucleus (MLF). So motor neuron controlling medial rectus get the same excitatory input.
This will cause the eyes to both look into the same direction (lateral gaze)
What are the steps involved in the Vestibulo-Ocular Reflex (VOR)?
- Endolymph flow stimulates hair cells (right)
- Increase nerve firing rate
- Simulates vestibular nuclei (projections to VI and III nuclei)
- Both eyes look left
Nystagmus (fast movement of the eye) occurs after the body realizes that the eyes are no longer looking forward.
When you turn your head to the left what happenes to the activity in the left vestibular nucleus?
It decreases
(eyes move in the opposite direction of increased activity)
Correction of eye gaze (Nystagmus) is done by what?
The cortex
What is Caloric Stimulation?
This test is performed on patients who are in coma to test their state of consciousness.
Warm Water (Right ear)
Increase firing in Right vestibular nucleus -> eyes look to the leff (opposite of stimulus) -> Nystagmus in the same direction of stimulus
Cold Water (Right Ear)
Decrease firising of Right Vestibular nucleas -> eyes move to the right (same direction as stimulus) -> Nystagmus to to the left (opposite of stimulus)
Lesion in the vestibular nuclei?
This is the same as having decrease firing of nucleus. Nystagmus will occur in the oppostie direction of the lesion
What is the purpose of the caloris test (Vestibulo-ocular reflex)?
To assess the degree of coma, warm or cold water is injected into an ear, stimulating the semicircular canals.
Normally, nystagmus (rhythmic beating of the eyes) is evoked. Failure to produce nystagmus is a poor sign indicating severe brain injury.
Outputs of the vestibular nuclei to the spinal cord involve which two tracts?
Medial Vestibulospinal tract (descending MLF)
and
Lateral Vestibulospinal tract
Medial Vestibulspinal tract
Continuation of the MLF caudal to the abducnes nucleus. Pathway goes all the way to the neck (cervical) muscles
a. medial vestibular nucleus (origin)
b. bilateral (via descending MLF)
c. extension of neck when excited (axial musculature)
d. vestibulo-cervical reflexes
e. terminates medially in the ventral horn of cervical regions (axial musculature/RExed Lamina 9)
Lateral Vestibulospinal tract
Extends the length of the spinal cord
a. lateral vestibular nucleus (origin)
b. ipsilateral
c. antigravity muscles (balance, shoulder and elbow)/excitatory
d. vestibulo-spinal reflexes
e. terminates in the intermediate, ventral horn
Overaction of the lateral vestibulospinal tract can lead to?
Decorticate and Decerebrate Rigidity
What is Decerebrate Rigidty?
Mal-formed Posture, if you cut away descending motor input to the vestibular nuclei or over activation of the lateral vestibular nucleus and the medial vestibular nucleus
Notice that his neck is in extension. Upper limb and lower limb is ridged in extension. Rigidity occurs because the cortex provides inhibition to the vestibular nuclei. So when you remove cortex the nuclei don’t have inhibition so they become over active
The first auditory neurons are located where?
At the spiral ganglion
(located in the middle of the cochlea
Central Auditory Pathways
- the auditory pathways are tonotopically organized from the cochlea to the cortex
- there are multiple, parallel auditory pathways to the cortex
Lesion at CN VII or the auditory nuclei can cause what?
Deafness
brainstem or cortical lesions after the cochlear nuclei will NOT produce monaural deafness
How many neurons are involved in the Auditory pathways for Pattern Recognition?
4
Describe the Auditory Pathway for Recognition
Identify the parts of the pathway
A. Dorsal cochlear nucleus
B. CN VIII
C. Trapezoid body: decussation
D. LAteral lemniscus
E. Inferior colliculus
F. Transverse gyrus of Heshl (Area 41 and 42)
G. Medial Geniculate
The auditory nerve axons synapse __________ on secondary neurons that are found in two cochlear nuclei.
Ipsilateral
What are the two cochlear nuclei and where are they found?
Dorsal and Ventral nuclei located at the pontomedullary junction.
Supplied by AICA
Ischemic stroke of the left Anterior inferior cerebral cortex causes whats?
Mono-deafness
Dorsal and Ventral nuclei lose their blood supply
What is the funciton of the dorsal cochlear nucleus?
Pattern Recognition of sound
Project mostly contralaterally
This nucleus projects bilaterally and if lesioned you will NOT have a lost of hearing.
Ventral Cochlear Nucleus
What is circled in this image?
Trapezoid body
bundle of crossing fibers from the cohlear nuclei
Identify the stuctures tages in this image
Red - Lateral Lemniscus
Yellow - Spinothalamic tract
White - medial lemniscus
Identify the structures in this image
Inferior colliculus
White arrow is pointing at the lateral lemniscus
Identify the structures in the image
Red circle - medial geniculate nucleus
Top yellow arrow = brachium of the inferior colliculus
Bottom yellow arrow = inferior colliculus
Identify the structures in this image
A. Superior Colliculus
B. Inferior Colliculus
C. Brachium of the inferior Colliculus
D. LAteral Geniculate nucleus
E. Medial geniculate nucleus
Identify the structure in the red circle
Medial Geniculate nucleus
Area 41 and 42 represent what?
Primary Auditory Cortex
What are the functional characterisitc of the Primary Auditory Cortex?
- Tonotopic organization but frequency selectivity is wide
- Localization, including a few in the median plane
- Some cells fire only when there is an auditory and visual
stimulus with the same receptive fields
- Some neurons fire only to tones, others only to noise
- Some fire only to a sound complex (patterning of auditory
stimuli)
•Some cells sensitive to frequency modulation (changes in the
frequency of a sound), and some only to ascending, others only
to descending changes, and others only to the rate of frequency
modulation.
SLide 38
SLide 38
What is the Planum Temporale?
Secondary Auditory Cortex located behind the transverse Gyrus
1. Larger on the left
2. Language (Wernicke’s )
3. Music (Perfect Pitch)
4. Sound localization
The localization of sound is mapped where?
In the brainstem
1) Low frequencies (<3 kHz): interaural time differences
2) High frequencies (>3 kHz): interaural intensities differences
Low Frequencies
detected in the anteroventral cochlea -> medial s. olivary (lateral-ipsi, medial cortex), coincidence detectors
High frequencies
Detected in the anteroventral cochlea -> lateral s. olivary and medial trap. nucleus
Sound localization mainly occurs where?
In the Ventral cochlear nucleus
(dorsal is more for oattern recognition)
What are the inputs and outputs of the superior olivary nucleus?
Inputs: bilateral - ventral cochlear n.
outputs: inferior colliculus
Function:
Sends bilateral inhibitory efferents to cochlea
form olivocochlear fibers (to hair cells)
reduces background noise
What is auditory Evoked Potential?
EEG: electrical activity/brain waves in response to activity
Characteristic potential of where auditory information is passing. Each beep represents another part of the auditory pathway
If there is a distance difference in the Auditory Evokes potential chart, what does that indicate?
Demylination of an axon
If there is a decrease in amplitude in Auditory Evoked potential, what does that indicate?
Nucleus or track lesion
