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Year 2- Neuroscience > Vestibular Systems > Flashcards

Vestibular Systems Flashcards

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1
Q

Which structures in the body are responsible for angular (rotational) motion of the head?

A

Semi-circular canals

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2
Q

Which structures in the body sense the acceleration of the head and the strength of gravity?

A

Otolith organs

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3
Q

What are the two otolith organs?

A

Saccule

Utricle

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4
Q

What are the main functions of the vestibular system?

A

Subserve perception of motion in space and tilt (with respect to gravity).

Provide reflex balance reactions to sudden instability of gait/posture (vestibulo-spinal reflexes).

Stabilise the eyes on fixed targets during head movement, preserving acuity (vestibulo-ocular reflexes).

Assist in control of heart rate and blood pressure during rapid up-down tilts.

Assist synchronisation of respiration with body reorientations.

Provokes motion sickness

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5
Q

Define vertigo.

A

False perception of movement in space

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6
Q

Define vestibular ataxia

A

Instability of gait or posture

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7
Q

What happens to the ability of the brain to stabilise the eyes in unilateral vestibular lesions?

A

Vestibular nystagmus.

The eyes start moving in the direction of the lesion

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8
Q

What happens to the ability of the brain to stabilise the eyes in bilateral vestibular lesions?

A

Oscillopsia.

Everything appears to be shaking – the ability to stabilise the eyes is lost

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9
Q

What are some other consequences of vestibular loss?

A

Slight impairment of orthostatic control.

Severe nausea and vomiting.

Loss of coordination on directional reorientation, motion intolerance, oversensitivity to visual motion in the environment

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10
Q

What type of cell is involved in the detection of movement in the vestibular system?

A

Hair cells

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11
Q

Describe the cilia of these hair cells.

A

There is one kinocilium and the rest are stereocilia

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12
Q

What does the hair cell fibre synapse with and where does it project?

A

It synapses with a primary neurone dendrite (cell body in Scarpa’s ganglion).

They project to the vestibular nuclei in the brainstem

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13
Q

What stimulates hair cells?

A

In Otoliths: deflection by forces of inertial resistance to acceleration.

In Semi-circular Canals: endolymphatic fluid rotation

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14
Q

Describe how the hair cell receptor potential can be changed.

A

Depolarisation = movement towards the kinocilium.

Hyperpolarisation = movement away from the kinocilium

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15
Q

Describe how ganglion cell discharge from otolith organs can be changed.

A

Towards the kinocilium = increased firing frequency.

Away from the kinocilium = decreased firing frequency

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16
Q

Describe the orientation and sensitivities of the saccule.

A

Saccule is oriented vertically with the hair cells projecting normal to the plane.

They are sensitive in all combinations of vertical and antero-posterior directions

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17
Q

Describe the orientation and sensitivities of the utricle.

A

Utricle is oriented almost horizontally with the hair cells projecting vertically.

Directional sensitivities in all combinations of lateral and antero-posterior directions

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18
Q

How do the otolith organs give a signal of linear acceleration in all 3-dimensional directions?

A

Vector sum of utricular and saccular stimulation patterns gives signal of linear acceleration in all 3-dimensional directions

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19
Q

Describe the structure and function of the semi-circular canals.

A

Hair cells project from the ampulla in the wall of the canal and are uni-directionally oriented so that acceleration to a particular side stimulates the canals on that side

(e.g. rotation of the head to the right stimulates the right canal, rotation in the other direction inhibits the right canal activity).

When head rotation decelerates to a stop, the canal on the other side (left side) is stimulated

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20
Q

Describe the firing of the canals when the head is still.

A

Each canal has a tonic firing rate so that they equal out when the head is still

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21
Q

What are the effects of loss of canal function on one side? (Physiology)

A

There is unopposed signal coming from the intact side meaning that there is partial impairment of sensitivity to rotation in the ‘on’ direction of the defunct canal

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22
Q

Why would a unilateral canal lesion cause vertigo?

A

The unopposed tonus of the intact canal gives a signal as if the head is rotating to the intact side.

Patient may feel like they’re spinning even though they’re not.

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23
Q

Why would acute unilateral vestibular disorder cause vestibular nystagmus?

A

Unopposed tonus of the intact canal causes the eyes to be driven to the lesioned side – this is a vestibulo-ocular reflex (because it thinks that your head is rotating towards the intact side)

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24
Q

Where do superior and medial vestibular neurones project?

A

They project to the motor nuclei supplying extraocular muscles.

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25
Describe the path of medial vestibular neurones.
The axons of medial vestibular neurones cross the midline and project to the contralateral abducens (VI) nucleus to abduct the eye on the opposite side (in the opposite direction to head rotation). Axons from the abducens nucleus ascend in the MLF to the contralateral oculomotor nucleus (III) to adduct the other eye (in theopposite direction to head rotation)
26
Describe the path of superior vestibular neurones.
Project ipsilaterally to the oculomotor and trochlear nuclei to generate **VERTICAL** vestibulo-occular reflexes
27
What is oscillopsia?
Everything appears to be oscillating. This is due to marked loss of vestibular function impairing eye stabilisation during rapid head movements. The vestibulo-ocular reflex is lost.
28
How would you test if a patient has oscillopsia?
Tell the subject to look at a fixed target and then rapidly move their head. If they have bilateral loss of vestibular function then their eyes will be taken off target by the head swing.
29
What are the effects of bilateral vestibular disorder on gait?
Mild gait ataxia
30
What are the effects of unilateral vestibular disorder on gait?
Tendency for the body and head to **lean or fall to the lesioned side**
31
Describe the path and function of the lateral vestibulo-spinal tract.
Descends ipsilaterally in the **ventral funiculus** of the spinal cord. Axons terminate in lateral part of **ventral horn Influence motor neurones to limb muscles**
32
Describe the path and function of the vestibulospinal tract coming from the medial vestibular nucleus
Descend bilaterally in MLF to cervical and upper thoracic spinal cord. Axons terminate in medial part of ventral horn Influence motor neurones to back and neck muscles
33
State a common cause of vestibular vertigo that lasts: a. Seconds b. Minutes c. Hours d. Days e. Fluctuating/continuous f. Silent
a. Seconds -Benign Paroxysmal Positional Vertigo (BPPV) b. Minutes Vertebrobasilar insufficiency c. Hours- Meniere’s Syndrome d. Days- Vestibular neuritis e. Fluctuating/continuous- Uncompensated vestibular lesion f. Silent- Acoustic neuroma/schwannoma
34
What is BPPV ?
Benign paroxysmal positional vertigo- It is caused by otoconial debris in the canals and is provoked by head movement. the otolith carry more endolymph and hence generate a large false signal about head rotation Debris floating in the canal stimulates the ampulla and generates false signals of head rotation.
35
What does the vestibular system consist of? Give inputs and outputs. DRAW
Includes three main inputs: * visual * proprioceptive * vestibular information (detects gravity and rotation of head) - outputs are **mainly reflexes** to maintain a **stable posture** and **stable gaze** - CNS integrates this information and generates the responses
36
What is the location of the vestibular organ?
vestibular organ is in the **posterior area of the inner ear**
37
What is the structure of the vestibular organ?
- **utricule and saccule** are located in the vestibule and are joined by a **conduit** - saccule is also joined to the cochlea - **three semicircular canals on each ear**: anterior, posterior and lateral - semicircular canals have an ampulla on one side, and they are **connected to the utricle**
38
What is the significance of the location of the labyrinth?
- location of the vestibular organ **draws planes for anterior and posterior canals** - planes determine which structure will be stimulated with a **specific head movement** - head movements in different planes stimulate different parts of the vestibular organ - important for generating the correct response
39
What is the role of the hair cells in the vestibular system?
- vestibular hair cells have a **kinocilium** (the biggest cilium) and stereocilia - cilia allows depolarisation of the cells with movement of the endolymph generated by head movement - present **in all vestibular organs.**
40
Describe the **otolith organs**
- They are the utricle and saccule - Cells are located on **maculae** containing gelatinous matrix and hair cells - Cells are placed horizontally in the utricle and vertically in the saccule - these **hair have otoliths on top:** * carbonate crystals * weight of crystals helps deflection of hairs
41
Describe the structure and function of the semicircular canals
- NO otoliths here (pathology can arise here) - **hair cells in the canals are located in the ampulla** - rest of the canal only has a liquid high in potassium called endolymph - ampulla **has the crista, where the hair cells are located** - **cells are surrounded by the cupula** which helps the hair cell movement
42
Describe the planes of the semi circular canals
- orientation of the canals in the head defines three planes - anterior and posterior canals form a 90° angle - lateral canals are horizontal to the other canals
43
What are the projections of vestibular nuclei? Give name of specific tracts you can rememebr. DXraw if possible
- Primary afferents **end in vestibular nuclei** and in **the cerebellum** - vestibular nuclei have projections to: * spinal cord * nuclei of the extraocular muscles * cerebellum (feedback on coordination) * centres for cardiovascular + respiratory control * autonomic centre
44
Describe the vestibular pathways. Draw
- Hairs cells receive inputs, then there's afferents to vestibular nuclei. - superior + lateral \> ventroposterior nucleus \> vestibular cortex. - lateral + medial + inferior \> vestibulospinal - inferior \> vestibulocerebellar reflexes \> vestibulo-ocular reflex (VOR)
45
What is the vestibular cortex?
- **not one specific area** - since many inputs and integrators are involved, many cortical areas participate - main processing centre thought to be in the **parietal lobe**, in the **Parieto-Insular Vestibular Cortex (PIVC)**
46
Summarise vestibular physiology. Draw if possible
47
What are the functions of the vestibular system?
- detect and inform about head movements - keep **images fixed in the retina** during head movements - postural control
48
How do hair cell potentials change?
- Hair cells have a resting potential which has a basal discharge to the nerve \> when upright system should still be active to keep yourself straight. - Hairs moving **towards** the kinocilium generates **depolarization** and an **increase** in nerve discharge. - Hairs moving **away** from the kinocilium generates **hyperpolarization** and a **reduction** in nerve discharge
49
How do the otolith organs work?
Respond to linear acceleration and tilt: due to otolith movement Utricule: horizontal movement Saccule: vertical movement
50
How do the semicircular canals work? Describe in detail
- Respond to **angular acceleration** - **cupulla moves and displaces hair cells** - causes **either depolarisation or hyperpolarisation** - output signal on VIIIth (vestibulcochlear) nerve is velocity - info integrated in the brainstem - SCC work in **pairs according to the planes (both laterals)** - **anterior from one side** with **posterior of the opposite side**
51
What are the vestibular reflexes?
- Vestibulo-ocular reflexes: fastest reflex in the body - Vestibulo spinal reflexes
52
What is the vestibulo-ocular reflex?
- keeps images fixed in the retina - connection between **vestibular nuclei and oculomotor nuclei** - allows compensatory movement - eye movement in **opposite direction** to head movement, but **same velocity and amplitude**
53
What is the vestibulo spinal reflex
connection between **vestibular nuclei and spinal cord** - motor neurons to limb muscles (lateral tract) - motor neurons to neck and back muscles (medial tract) This leads to postural control, avoidance of falls and compensatory body movement according to the head position ◦
54
How is the vestibular system assessed?
Anamnesis (history) Posture and gait Cerebellar function Eye movements ***Vestibular tests***: 1. Caloric test- use heat in inner ear to generate nystagmus. it tests the caloric reflex (lateral semicircular canal only) 2. Video head impulse test, vHIT (easy test, but better for recovery) 3. Vestibular-evoked myogenic potential, VEMP (when absent **may not be abnorma**l) 4. Rotational test (needs bigger equipment) Imaging: CT scan, MRI Symptoms and impact assessment (eg. dancer)
55
What are the features of balance disorders?
Main symptom is **dizziness or vertigo** \> vertigo is the perception of rotation \> dizziness is more vague, eg blurred vision, nausea Can be categorised based on **location of the affected structure and evolution of signs and symptoms** - very common, **25% of ENT and neurological referrals**
56
Describe balance disorders based on location
**Peripheral vestibular disorders: labyrinth and/or VIII nerve (more common)** * eg. vestibular neuritis * Benign Paroxysmal Positional Vertigo (BPPV) - crystals in canals * Meniere's disease - hearing and balance * Unilateral and Bilateral vestibular hypofunction **Central vestibular disorders: CNS (brainstem/cerebellum)** * eg. stroke * MS * tumours
57
Describe balance disorders based on evolution (how the disease presents itself overtime)
**Acute** * Vestibular Neuritis ('labyrinthitis') * Stroke **Intermittent** * \> Benign Paroxysmal Positional Vertigo (BPPV) **Recurrent** * Meniere's Disease- one ear (vertigo) * Migraine **Progressive** * Schwannoma vestibular (VIIIth nerve) * Degenerative conditions (MS)
58
What is the issue with the symptom "dizziness"? Other differential diagnosis?
Could be any other disease that is not necessarily vestibular: * **H**eart disorders * **O**rthostatic hypotension * **P**resyncopal episodes * **A**naemia * **H**ypoglycaemia * **P**sychological * **G**ait disorders HOPAHPG
59
How do you treat BPPV
Cured by turning the head vigorously in the opposite direction to that which provokes the vertigo, through 360 degrees, flushing out the debris. Treatment name: particle repositioning manoeuvre * Epley manoeuvre - posterior canal BPPV * Semont manoeuvre- Right posterior canal
60
Why is BPPV intermittent and outline what makes the symptoms better is there any hearing loss with BPPV
endolymph settles down within 1 minute that is why it's intermittent keeping your head still makes the symptoms better lying down or standing up triggers symptoms No hearing loss associated; this is not a permanent disease
61
what is presbycusis
Normal age hearing loss

Year 2- Neuroscience (13 decks)

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