Vestibulocochlear System Flashcards
Vestibulocochlear System basics
- Sensory for hearing and balance
- Postural control with changing body positions
- CN VIII (Vestibulocochlear N); Functionally two seperate nerves that share a sheath
– Cochlear N: Auditory
– Vestibular N: Balance
Cochlear Pathway
- Begins in the cochlea (spiral) of the inner ear
- Primary neurons have cell bodies in the spiral ganglion
- Synapse within the cochlear nucleus at the pontomedullary junction
- Seconday neuron splits into three pathways:
– To the ipsilateral Superior Olivary Nucleus, synapse and travel to the inferior colliculus
– To the Contralateral Sueprior Olivary Nucleus, synapse and travel to the inferior colliculus
– Travel directly to the ipsilateral inferior colliculus - Inferior colliculi share commissural fibers
- Inferior colliculi send axons to bilateral medial geniculate nuclei
- Medial Geniculate Nuclei send axons on a unilateral path to the primary auditory cortex in the temporal lobe
Some axones from the ____ go to the ____ for reflexive activation of the stapedius muscle to dampen loud sounds
- ipsilateral olivary nucleus
- Facial Motor Nuclei
Why do we have a startle response from a loud noise?
Connections between the olivary nucleus to the reticular formation
The primary auditory cortex =
notice sound
Seconday Auditory Cortex =
interpret sound
Where and what is wernicke’s area?
- Superior temporal gyrus of the left hemisphere (90% of the population)
- Interprets the meaning of speech
Where and what is Broca’s Area?
- Specialized part of the inferior frontal gyrus and is part of the motor association area
- Creates spoken language
How does wernickes and brocas communicate?
Arcuate fasiculus
Lesions in the broca’s area will cause
expressive (or motor) aphasia
Lesions in wernicke’s area causes
Receptive aphasia
Recovery from broca or wernicke damage is good, why?
It can switch its function to the opposite side of the brain
Semicircular canals
- Fluid filled at 90 degrees
- Movement of fluid gives sensation of the position of the head
- Two semicircular canals, one on each side
Saccule
Hair cells that detect acceleration
Otoconia
- Crystals that move on the mass like jello
- Give acceleration and deceleration information
- If they break off and get into the smicircular canals can lead to vertigo and other vestibular problems
Vestibular Pathways basis
- Sensory for balance and motion (Eyes, head and neck position and postural control input)
- Primary neuron start in the semicircular canals
- Cell bodies in the vestibular ganglion
- 4 Vestibular Nuclei locate between Pons and Medulla; Assume as one
What are the 5 Vestibular Pathways
- Vestibulocerebellar
- Vestibulospinal
- Vestibuloocular
- Vestibulocortical
- Accessory
Vestibulocerebellar Pathway
- Feedback mechanism between cerbellum and Vestibular Nuclei
- Information concerning modifications to the motor planning for vestibular nucleus
- Vestibular to Cerebellum and back
Vestibulospinal Pathway
- Direct activation of the muscles for postural control and balance
- Medial Vestibulospinal tract: bilateral innervation (Modies head position; shorter)
- Lateral vestibulospinal tract: Unilateral (moderate postural control reponses, longer)
- Begins at the vestibular Nucleus at the pontomedullary junction
Vestibuloocular Pathway
- Coordinates eye and head movements, so eyes can remained fixed upon a subject even while the head moves (gaze stabilization)
- Secondary neurons from the Vestibular Nucleus ascend via Medial Longitudional Nucleus to the Paramedian Pontine Reticular Formation
- Fibers then sent out to the abducens, trochlear and oculomotor nuclei in pons and midbrain
What happens when vestibuloocular input from the two vestibular organs is different? How do we treat it?
- Signal comes in and one says something different than the other (ex: crystal got in one, changes the dynamic, results in change in sensory signal. Get nystagmus and dizziness. Mismatch of one side vs the other.
- Treat: Positioning technique for crystal; vitiation exercises (do things that gradually set off the system) these symptoms suck and is hard to get compliance. Brain will start to learn what the signals mean.
Vestibulocortical Pathway
- Perception of balance, movement and dizziness suggests connection between thalamus and cerebral cortex.
Accessory Pathway
- Indirect control of the postural muscles via cerebellum and reticular formation
- Vestibular Nuclei go to the Cerbellum via inferior cerebellar peduncle
- Fibers exit cerebellum via inferior cerebellar peduncle and travel to the reticular formation in the brainstem
- Fibers travel both crossed and uncrossed to the LMN in the spinal cord via Reticulospinal tract
What word describes vertigo?
Spinning
Often also have nystagmus
What does nystagmus look like? How do you know what side is effected?
- Result is a repetitive lateral movement of the eyes toward the effected side (side with vestibular problems) and then back to center.
