20.5 Vestibular Flashcards
What are the otoliths?
2 otolith organs (utricle and saccule) → sense linear acceleration and head position
What are the semi-circular canals?
3 semi-circular canals (anterior, posterior, horizontal) → sense rotational velocity/ angular acceleration.
What is the vestibular system?
A somatosensory portion of the nervous system that provides us with awareness of the spatial position of our head and body (proprioception) and self motion (kinesthesia)
Where is the vestibular system found?
deep in the temporal bone
Label the semi-circular canals and the otolith organs.
What is the name of the terminal end of each semi-circular canal?
Ampulla = opens into the vestibule
What are the clusters of hair cells in the utricle and saccule called?
Maculae (sensory epithelium)
Which cranial nerve innervates the semicircular canals and otolith organs?
Vestibular portion of the vestibularcochlear nerve (VIII) which originates from a different nuclei in the brain to the cochlear portion. It enters posterior cranial fossa and synapses with vestibular nuclei in the brainstem and cerebellum directly
What is the origin of the vesitubulocochlear nerve?
vestibular and cochlear nuclei in the brainstem which merge to form the vestibulocochlear trunk in the posterior cranial fossa in the petrous part of the temporal bone
Where does the vestibulocochlear nerve split?
When it reaches the inner ear (special somatic afferent as provides special sensory funciton of hearing and balance)
Where is the vestibular area?
Lateral corner of the rhomboid fossa of the brainstem
How are the vestibular ganglia formed?
Vestibular ganglia → formed from cell bodies which receive NTs from HCs + project to brainstem vestibular nuclei + cerebellum
4 at junction between pons + medulla:
medial/ lateral
superior/ inferior (aka descending)
How many vestibular nuclei are there? Where do they get their inputs?
Four nuclei (medial, lateral, superior and inferior)
Receive inputs from receptors of the utricle, saccule and semi-circular ducts
What are the vestibulo-spinal tracts?
*Lateral vestibulospinal tract
*Medial vestibulospinal tract
Which nuclei form the lateral column of the vestibular tract?
Inferior, lateral and superior nuclei
Describe the lateral vestibulospinal tract
From vestibular nuclei descends to lumbar regions to influence limb extensors involved in balance.
It adjusts the posture of the body and tone of extensors.
What is the vestibulospinal reflex mediated by?
lateral vestibulospinal tract
What is the vestibulospinal reflex?
Uses vestibular organs and skeletal muscles to maintain balance and posture in an environment with gravity to evoke a response from the muscular system below the neck
ENGAGES EXTENSOR MUSCLES
Inhibition of ispilteral flexors and facilitates contralateral flexors
Which nuclei form the medial vestibular tract?
Medial nuclei
Describe the medial vestibulospinal tract.
projects bilaterally to cervical spinal cord to mediate the vestibulocollic reflex
What is the vestibulocollic reflex?
a neural reflex that activates neck muscles when head motion is sensed by the vestibular organs in the inner ear
Where are the second order nuclei in the vestibular system found?
In the vestibular nuclei
Where do second order vestibular fibres project?
Oculomotor nuclei
Cerebellum (floculo-nodular lobe)
Reticular formation
Spinal cord to motor nuclei
Thalamus to cortex
What is the vestibulo-Ocular Reflex?
Maintaining gaze on fixed object/location during head movement (eye move to counter head movement).
Which part of the cerebellum receives inputs from vestibular nuclei and fibres?
Flocculonodular lobe for eye movements and posture
What is highlighted?
Vestibular ganglion (ganglion of Scarpa)
What does the superior and medial vestibular nuclei receive most their inputs from?
Cristae ampullaes of semi-circular canals
Which pathways do vestibular nerves take to enter the cerebellum?
Synapse directly as mossy fibres
Synapse with Vestibular nuclei –> flocculonodular lobe
Synapse with vestibular nuclei –> inferior olivary nucleus –> vermis and flocculonodular lobe
For balance
What is vertigo?
Vertigo is a condition in which a person has a false sensation that either him or surroundings are in motion . It can cause nausea, dizziness, sweating and vomiting.
What are the causes of vertigo?
-Benign paroxysmal positional vertigo (BPPV) = Pieces of otolithic membrane break off and fall into semicircular canal displacing fluid. Common in elderly.
-Vestibular neuritis (labyrinthitis),
-Meniere’s disease
-VIII nerve damage
What is motion sickness?
Motion sickness is a condition characterized by nausea and vomiting due to the travelling, it is most often seen in some people travelling by vehicle.
What causes motion sickness?
fluctuations in the maculae (otolith organs for linear acceleration)
What is nystagmus?
Alternating slow phase (compensatory) and quick phase (anti-compensatory) eye movements
Vestibular nystagmus is normal when a person is being rotated. It is pathological when the head is still.
