Vestibular system Flashcards
What organs / parts compromise the inner ear
Semi-circular canals for balance
Cochlea for hearing
What compromises the auditory vestibular system?
Semi-circular canals which link to the vestibular cochlear nerve and vestibular nuclei.
What is vertigo?
Can be with or without hearing loss, caused by blockage of a hollow organ or blood vessel(occlusion) - without hearing loss: anterior vestibular artery blocked - with hearing loss: internal auditory artery and common cochlear artery
What is the purpose of the vestibular system?
If you rotate your head in one direction the cilia bind in the opposite direction –> depolarisation
What is the vestibulo-ocular reflex?
The movement of the eyes elicited by vesitibular stimulation, in order to keep the retinal image stable and prevent degradation of visual processing.
- Important for when the head is moving
- If head turns lead, semi-circular canals keep eye position constant.
How are the semi-circular canals linked to the eyes?
Vestibular nuclei joins the semi-circular canals to eye muscles
Information travels from semi-ciruclar canal through the intermediatory vestibular nucleus to the eye muscles
How does the vestibulo-ocular reflex work?
When the head turns to one side, that side increases firing frequency of the vestibular nerve.
- Both sides are always active to allow for direction in both directions.
What are the affects of an injury on the vestibulo occular reflex?
Tonic firing stops due to inflammation or a lack of blood- any difference in nerve firing rate is still interepretted as movement.
What is vestibular compensation?
The vestibular nucleus can compensate for injuries affecting the vestibulo-occular reflex, by generating its own Na+/K+ channels which allow the production of action potentials.
- only happens after a period of time.
- two sides still unlikely to be balanced –> continous eye movement
What is the role of the cerebellum?
Important for fine motor control, balance and muscle tone.
Where do deficitis commonly occur in the cerebellum
Common in the vermis but can occur anywhere
How could you simplying explain the circuitry of the cerebellum
A molecular layer with many synapses, a purkinje cell layer, home to the purkjene cell which inhibits the vestibular nucleus. One climbing fibre to ever purkinje cell.
What paths in the cerebellum are used to operate the vestibular ocular reflex?
Direct and In-direct path
Describe the direct path from cerebellum to operate the vestibulo-ocular reflex?
Semi-circular canal –> vestibular nuclei –> eye muscles
Describe the indirect path from cerebellum to operate the vestibular ocular reflex:
Semi-circular canal –> mossy fibres –> granule cells - synapse –> purkinje cells
Purkinje cells can inhibit the vestibular nucleus
Feedback mechanism:
Eye muscle –> inferior olive –> climbing fibres –> purkinje cell
What are the 4 types of cerebellum deficit
1 side - cerebellar hemisphere syndrome
1 half- rostral vermis syndrome
Middle- caudal vermis syndrome
Whole - Pan cerebellar syndrom
What are the affects of cerebellum deficits?
All four syndromes lead to dystaxia which can have a wide variety of affects including nystagmus
What is nystagmus?
Involuntary movement that is part of the vestibulo-ocular reflex.
- Characterised by smooth movement in one direction and quick movement in the other
- Direction of nystagmus determined by the quick movement not the slow one
- There are many different types of nystagmus
What are the different types of nystagmus
Peripheral- result of normal or diseased functional states of vestibular system
Central- result of normal or abnormal processes not related to the vestibular organ e.g. lesions of cerebellum or midbrain
Spontaneous- randomly occuring
Positional- specific position triggers nystagmus
Gaze induced- occurs or exacerbated by change of gaze.
Post rotational- due to rapid shaking or rotation.
What is benign paroxysmal positional vertigo?
Debris collects in part of the inner ear so when the head moves –> debris movement –> false signals
Horizontal debris –> horizontal directional nystagmus
Posterior canal debris –> rotatory up-beating nystagmus
Anterior canal debris –> down beating positional
