Vestibular System

Question 1

describe the vestibular system (2)

Answer 1

1. special proprioception
2. determines balance/equilibrium by assessing head position, controlling eye position in relation to the head, and controlling the trunk and limbs in relation to the head, and also by controlling orientation in the face of linear and rotatory acceleration and deceleration

Question 2

what makes up the peripheral vestibular system? (2)

Answer 2

1. receptors in the inner ear within the petrosal portion of the temporal bone
2. CN 8 (but CN 7 and sympathetics also run close to the peripheral vestibular system in the inner ear)

Question 3

what are and where are the receptors of the inner ear of the peripheral vestibular system located?

Answer 3

1. bony semicircular canals contain membranous semicircular ducts which containt cristae ampullaris receptors
2. the bony vestibule contains membranous utricle and saccule which each contain a maculae receptors

Question 4

how do the receptors of the inner ear work?

Answer 4

they are tiny hair cells that contain tiny stereocilium around a larger kinocilium; bending toward or away from the kinocilium inhibits or stimulates the tonic neuronal activity hair cells;
these hair cells in the crista ampularis have a cupula of mucus that sits on top of the hair cells and provides inertia for these hair cells, meaning that they don’t have to be constantly moving for motion perception (this is why you still feel like you’re moving after you spin around a bunch)

(the maculae have an otolithic membrane that functions like the cupula and also contains crystals that help detect gravity)

crista ampularis: detects rotary and angular movements
maculae: detect linear movements

Question 5

how are the semicircular ducts and their crista ampullaris connected across each side of the body?

Answer 5

have 3 pairs; each pair is innervated by a branch of CN 8, which has a tonic firing rate; the movement of the hair cells alters that firing rate and is picked up by CN 8 which sends that info to the medulla to tell the brain which way the body is moving

Question 6

list the components of the anatomy of the peripheral vestibular system (5)

Answer 6

1. receptors (inner ear)
2. CN 8
3. external ear canal
4. osseus bulla (houses membranous structures)
5. cochlea

Question 7

what are the 2 components of the central vestibular system?

Answer 7

1. rostal medulla (4 nuclei: caudal, lateral, medial, rostral)
2. cerebellum

Question 8

what are 5 signs of vestibular system dysfunction?

Answer 8

1. heat TILT (one ear below the other) toward the side of the lesion
2. vestibular ataxia (to one side: falling, rolling, listing, veering, leaning, stumbling)
3. circling to one side
4. abnormal nystagmus
5. body posture: concavity toward the side of the lesion; animals will prefer to lay with lesion side down

Question 9

how is vestibular input to the eyes accomplished?

Answer 9

the medial longitudinal fasciculus links the nuclei of 8 with 3, 4, and 6 so that vestibular input can tell the eyes which direction they should move and is why you will see abnormal nystagmus with vestibular dysfunction because 8 is no longer doing its job

Question 10

what are the 2 flavors of nystagmus?

Answer 10

1. physiological: normal, doll’s eye, will even be present in blind patients because doesn’t involve vision (CN2)
2. abnormal: spontaneous/resting or inducible/position

Question 11

how do we describe nystagmus?

Answer 11

by the direction of the fast phase (where the eye is darting to), could be horizontal (L or R), rotatory, or vertical

Question 12

describe vestibular strabismus

Answer 12

1. occurs when the head is elevated
2. will see ventral deviation of the eye on ipsilateral side of lesion because no vestibular system to tell brain that head was elevated so 8 doesn’t tell 3, 4, or 6 to move eye dorsal
3. differentiate from LMN strabismus of 3, 4, 6 that would always be present no matter how move the head; this is only present when elevate the head

Question 13

GENERALLY, how do you differentiate central versus peripheral vestibular dysfunction?

Answer 13

look for other neurological signs that would indicate that the medulla is also affected to indicate central lesion (mentation, postural reactions, cranial nerves)

Question 14

what does abnormal mentation indicate?

Answer 14

central (either intracranial or ARAS/brainstem)

Question 15

what does NORMAL vestibular input to the spinal cord do? contrast to vestibular input to the spinal cord with a lesion

Answer 15

1. facilitate ipsilateral extensors
2. inhibit contralateral extensors

with a lesion, will reverse:
1. will increase contralateral extensor tone
2. decrease ipsilateral extensor tone

Question 16

contrast nystagmus for peripheral versus central vestibular dysfunction

Answer 16

PVD: horizontal or rotatory; fast phase AWAY from head tilt
CVD: vertical or toward head tilt

Question 17

what 3 other groups of cranial nerves are also involved with vestibular dysfunction and what region do they indicate?

Answer 17

1. 7, 8, horner (sympathetic): indicate middle ear (peripheral)
2. 5, 7, 8: pons/medulla junction (central)
3. any combination of CN 5-12 could indicate central

Question 18

describe bilateral peripheral vestibular disease (6)

Answer 18

1. may not have head tilt
2. wide head excursions
3. lack of abnormal nystagmus
4. lack of physiologic nystagmus
5. bilateral vestibular ataxia
6. curling (curl paws under body when lowered to ground face first instead of reaching like normal)

Question 19

where can you place a lesion and cause paradoxical vestibular disease? (4, but really only memorize the 1st)

Answer 19

1. cerebellum
2. caudal cerebellar peduncle
3. floculonodular lobe
4. fastigal nuclei

Question 20

describe paradoxical vestibular disease (3)

Answer 20

1. a form of ventral vestibular dysfunction
2. signs of vestibular disease are OPPOSITE the side of the lesion
3. postural reactions define the side of the lesion still!! the side of the lesion IS THE SIDE OF THE POSTURAL REACTION DEFICIT (right head tilt but left posture rxn deficit = lesion on left side of brain)

Question 21

compare and contrast PVD versus CVD (4)

Answer 21

1. both will have a head tilt and vestibular ataxia
2. PVD nystagmus is fast phase AWAY from lesion; CVD is fast phase toward head tilt
3. with PVD can also see horner and facial paralysis, with CVD can also see CN 5-12 deficits and facial paralysis
4. no abnormal postural reactions with PVD, but CVD will have abnormal postural reactions on the side of the lesion!