BB2 Revision6 Flashcards
Vestibular System Function
Name the 3 main functions of the vestibular system
- Detection and conscious perception of head perception and movement
- Compensatory eye movements during head movement in order to provide stabilisation of visual image and target fixation
- Compensatory postural adjustments of the trunk and limb muscles following head movement
Vestiublar system anatomy:
The vestibular system is connected with the spinal cord via which tracts? [2]
The vestibular system is connected with the cerebellum via the which lobe [1] and which nucleus [1]?
The vestibular system is connected to which CNs? [3]
The vestibular system is connected with the spinal cord via which medial and lateral vestibulospinal tracts
The vestibular system is connected with the cerebellum via the floccculonodular lobe and fastigial nucleus
The vestibular system is connected to CN III, IV & VI
Vestiublar system anatomy:
Name the parts of the vestibular apparatus (that lie within the inner ear)
- semi-circular canals
- utricle (which lies at the base of the semi-circular canals)
- saccule
Which of the following numbers depicted the vestibular tracts [1]
2c
Label A-F
A: (Macula of) utricle
B: (Macula of) saccule
C: cochlea
D: posterior semilunar canal
E: Stapes
F: Malleus and incus
Label
5 Cochlea
16 External acoustic meatus
17 Mastoid air cells
11 Posterior semicircular canal
(posterior canal)
Name and describe the function of the two types of solution found within the vesitubular apparatus.
Endolymph
* inside the semicircular canals and moves, and provides most of the signalling for the vestibular hair cells
Perilymph
* fills the scalae tympani and vestibuli.
What is the difference in ion concentration between endolymph and perilymph? [2]
Perilymph: has similar concentrations of ions to plasma; high sodium and low potassium
Endolymph: extremely low sodium and high potassium
Where in the vestibular system are vesitubular hair cells found? [3]
The ampulla, saccule and utricle is where vestibular hair cells are found.
Describe how the semicircular canals function to detect angular acceleration/deceleration of the head
There are three semicircular canals: anterior, posterior, and lateral. located in a different plane and each connect to an ampulla (widening of the canal) which conncects to the utricle
Within each ampulla there are hair cells and cristae with a gelatinous cupula above the hair cells * crista
Each canal is a continuous endolymph filled loop, when the head rotates endolymph displaces the gelitinous cupula and excites the hair cells causing depolarisation or hyperpolarisation
Movement towards the kinocilium causes the opening of channels and a subsequent depolarization of the cell. Movement away from the kinocilium causes the closure of channels leading to hyperpolarization of nerve fibers.
Describe the function of the utricle / saccle [1]
What is the macula of the utricle and saccle and what substance does it contain? [2]
Saccule and utricle is to keep the head vertically oriented with respect to gravity
Macula of utricle / saccle: cilia of hair cells embedded in a gelatinous mass.
Contains calcium carbonate crystals call otoliths
What is the difference in function betweenthe utricle and saccule? [2]
Describe how the saccule and utricle keep the head vertically oriented with respect to gravity [3]
Utricle: longitudinal acceleration,
Saccule: acceleration along the vertical axis
Mechanism:
* otoliths provide the inertia, so that when movement to one side occurs, the otolith-gel mass causes the hair cells to deviate
- The hair cells are excited, or inhibited, by bending of the stereocilia towards or away from the kinocilium, just as the hair cells in the semi-circular canals
- Linear acceleration of the head causes a shear force between the otolithic membrane and macula, causing displacement of the hair bundles.
Which direction are hair cells in the utrcile pushed during forward acceleration? [1]
Which direction are hair cells in the saccule pushed when a person descends?[1]
Utricle hairs pushed backwards during forward acceleration
Saccule hairs pushed upwards when person descends (gravitational force)
Describe the head-righting reflex.
If the head and body start to tilt, such as when a student falls asleep in a lecture, the vestibular nuclei will automatically compensate with the correct postural adjustments via activation of the VSTs
Describe the function of the vestibular-occular reflex
This reflex keeps the eyes fixed on a particular object when the rest of the body is in motion
Describe how the VOR works
Automatically sensing head rotations and elicits a compensatory adjustment in the opposite direction of the eyes
Causes innervation on the medial-lateral rectus muscles (adduction / abduction), the inferior rectus-superior oblique pair (depression and extorsion, elevation and intorsion) and the superior rectus-inferior oblique pair (elevation and intorsion, depression and extorsion via the ascending medial longitudinal fasciulus
The axonal connections between the vestibular and oculomotor nuclei that mediate the VOR travel in a tract called the []
The axonal connections between the vestibular and oculomotor nuclei that mediate the VOR travel in a tract called the medial longitudinal fasciculus (MLF)
Primary afferent fibres from the vestibular apparatus terminate mainly in the []
A small number of fibres project directly into the []
Primary afferent fibres from the vestibular apparatus terminate mainly in the vestibular nuclei (in the medulla and pons)
A small number of fibres project directly into the vestibulocerebellum (flocculo-nodual node & uvula)
Where do axons from the 4 vestibular subnuclei (LVN; MVN; SVN; DVN) project? [5]
- Vestibulocerebellum
- Thalamus and cortex
- Reticular formation
- Extraocular eye muscles
- Spinal cord motor neurones
Central pathways of the vestibular system
Where do the superior and medial vesibitular subnuclei recieve input from? [1]
Where do the lateral, inferior and medial vesibitular subnuclei receive inputs from? [1]
superior and medial: semi-circular canals
lateral, inferior and medial: saccule and utricle (together aka maculae)
Where does input from the: semi-circular canals to the superior and medial vestibular subnuclei project to? [4]
Where does input from the: saccule and utricle to the lateral, inferior and medial vesibitular subnucleii project to? [3]
Semi-circular goes to ocular nuclei and reticular formation, gaze centres and tectal nuclei
(double check which pathways these are sent via)
Saccule and utricle goes to spinal motor nuclei via the lateral and medial VSTs, which are involved in postural balance
The superior and lateral vestibular nuclei also interact with which structure in the brain [] ?
The superior and lateral vestibular nuclei also interact with the flocculo-nodular lobe of the cerebellum
Describe the neuronal connections that determine our conscious appreciation of equilibrium and head position.
Second order vestibular neurones project to the contralateral ventral posterior nucleus of the thalamus, and from there the somatosensory cortex and posterior parietal cortex.
What is the name given to the region of the cortex where there is convergence of the vestibular and proprioceptive signals?
What is important to rememver about this?
Parietal insular vestibular cortex
Remember that this is responsible for the contralateral side of the body/limb.
Describe the features of benign paroxysmal positional vertigo (BPPV) [1]
Describe the physiopathlogy behind BPPV? [1]
A brief, 60 second, intense sensation of vertigo that occurs because of a specific positional change of the head
Dislodged otolith from the utricle, which then gets stuck in the ampulla, making it sensitive to gravity.
In certain positions, the otolith can stimulate the cupula, causing abnormal sensations. These persist until the crystals relocate elsewhere or disperse
Describe the symptoms of Menieres disease [3]
Describe the pathophysiology of Menieres disease
Inner ear fluid balance disorder that causes episodes of vertigo, fluctuating hearing loss, tinnitus and the sensation of fullness in the ear
Caused by an imbalance between the production and reabsorption of endolymph, which eventually ruptures the membranes, causing changes in ion concentration of the solute, leading to depolarisation of the endolymph fluid, ultimately killing the hair cells.
Label A
Otoliths
What does this image depict?
benign paroxysmal positional vertigo (BPPV)
labyrinthitis
ménière’s disease
vestibular neuritis
perilymph fistula
What does this image depict?
benign paroxysmal positional vertigo (BPPV)
labyrinthitis
ménière’s disease
vestibular neuritis
perilymph fistula
What does this image depict?
benign paroxysmal positional vertigo (BPPV)
labyrinthitis
ménière’s disease
vestibular neuritis
perilymph fistula
What does this image depict?
benign paroxysmal positional vertigo (BPPV)
labyrinthitis
ménière’s disease
vestibular neuritis
perilymph fistula
What is the name for this test of vestibular function / dysfunction? [1]
Hallpike’s Manoeuvre:
Label A-C
A: ampullae
B: utricle
C: saccle
Label A-D
A: Ampulla
B: Cupulla
C: Crista
D: Vestibulocochlea nerve
Loss of NaV1.7 can lead to which disease? [1]
Congenital insensitivity to pain (CIP): Rare condition in which individual cannot feel pain so often have wounds, broken bones, health issues not detected.
Name a disease if NaV1.7 is overexpressed / gain of function occurs [1]
Inherited erythromelalgia (IE): A painful neuropathy involving severe chronic burning pain sensations in hands and feet.
Neuropathy pain (loss of sensory fibres)
Name a disease that is caused by insensitivty to pain from a deficit in nerve growth factor [1]
Which gene mutates to create this disease? [1]
Congenital insensitivity to pain with anhidrosis (CIPA)
- TRKA gene codes for TrKA receptor to create nerve growth factor (NGF)
- NGF is crucial for development of Adelta and C-fibres
Name an acquired neuropathy [1]
Diabetic neuropathy:
High blood glucose can damage nerve fibres, esp. legs and feet - loss of pain in peripheries
Different sensory neurons have distinct projections in the dorsal horn. State what they are
Lamina found within dorsal horn:
Lamina I to V
- Aβ: project deepest - lamina IV & V
- Aδ project middle: lamina I
- C fibres project into lamina I & II
Transmission
Describe the Aδ nociceptor pathway onto the dorsal horn [2]
Aδ nociceptor axon projects on to Lamina I via excitatory glutamate synapse on to either NMDA or AMPA receptors
Transmission
Describe the C-fibre nociceptor pathway [2]
C fibres activate lamina I cells via gluatmata onto excitatory interneurons in lamina II, which then excites lamina I dendrite with glutamate
Ischaemic stroke pathophysiolgoy
Describe the ischaemic stroke cascade at microscopic level [4]
Cellular ischaemia:
- Na / K+ pump failure
- Causes depolarisation
- Causes Ca2+ food in
- Cascade of enzymes that respond to ischaemia (like caspases)
- Causes cell death
Risk factors for stroke?
What are the key medical conditions that increase risk of stroke? [4]
Hypertension
Hypercholesteroamia
Diabetes
Cardiac - AF
TIA treatment?
