Vestibular Proprioception

Vestibular proprioception

the sense of where the head is in space and is generated by the vestibular apparatus in the inner ear

What are the three main functions of output from the vestibular nuclei?

• maintain steady visual field in the event of head movement

• control neck muscles so the head is held in a good position

• modify posture to compensate for head movements that shift the center of gravity

Peripheral Vestibular Structures

vestibular apparatus in the petrous temporal bone and the vestibular nerve and ganglia

Central Vestibular Structures

vestibular nuclei in the medulla and their projections

True or False: a peripheral vestibular problem will not produce somatosensory proprioceptive deficits or UMN signs in the limbs

TRUE

How is maintenance of the visual field achieved?

vestibular nucleus projections (MLF) to the CN nuclei (CNIII, CN IV, CNVI)

What is the vestibuloocualar reflex?

When the head turns horizontally, the eyes move slowly together in the opposite direction until they are reset to a forward-looking position

• physiologic nystagmus

What muscles does CNIII control?

Dorsal rectus, medial rectus, ventral rectus, ventral oblique

What mscles does CN IV control?

dorsal oblique

what muscles does CNVI control?

lateral rectus

When head is still and balanced, the tonic activity from left and right is _____

equal

Slow phase of nystagmus

when eyes move together to the right as head turns left and vice versa

Fast Phase of Nystagmus

resetting of eyes to natural position

True or False: The slow phase of nystagmus is used to classify nystagmus

FALSE

The fast phase is controlled by the _____

pons

How are nystagmus classified?

direction of the fast phase

If the head turns to the left ___ vestibular apparatus is stimulated and the _____ vestibular apparatus is inhibited.

stimulated; inhibited

Pathway if the head turns left.

Left vestibular nerve → left vestibular nuclei → contralateral abducent nucleus -? lateral rectus m contraction (on right) → across midline again to oculomotor nucleus on left → medial rectus contraction on left

The fast phase of nystagmus is always toward the side with more ______ vestibular system.

active

Pathological nystagmus

when damage occurs unilaterally to the vestibular apparatus, vestibular nerve, or vestibular nuclei

The fast phase is _____ the side of the lesion when the lesion is in peripheral structures.

away from

True or False: Rotary nystagmus can only occurs in peripheral lesions

FALSE - both peripheral or central

A patient presents with vertical nystagmus. Where is the lesion?

brainstem

Most of the time the vestibular input to the cervical spinal cord _____ contractions of epaxial cervical muscles

enhances

What is needed to keep the top of the head parallel with the ground?

left and right cervical epaxial muscles to contract equally

Describe the pathway of the vestibulo-collic reflex.

vestibular nerve → ipsilateral vestibular nuclei → descending arm of ipsilateral descending medial longitudinal fasciculus (vestibulospinal tract) → ipsilateral cervical spinal gray matter → excitation/inhibition of LMNs to epaxial cervical muscles

A head tilt due to a unilateral lesion result from a lesion on the ________ side

ipsilateral/less active

Why does a head tilt toward the same side as the lesion?

The muscles are not being innervated as much as they should be from the lesion

True or False: The head will tilt towards the affected lesion side with central OR peripheral damage.

TRUE

What determines an animal’s center of gravity?

where its head is

What induces changes in posture with the changes in head position?

Vestibulospinal reflex

How does the vestibulospinal reflex apthay work?

vestibular nerve → ipsilateral vestibular nuclei → ipsilateral spinal cord ventral funiculus as the vestibulospinal tract → ipsilateral spinal grey matter → LMNs axial muscles and ipsilateral limb extensor muscles compensate

For an upright stance, activity of CNVIII increases on the side moving _______ and decreases on the _______.

toward; opposite

If looking right, there will be ____ extensor tone on the right than the left.

more

When the vestibular system is damaged unilaterally, the extensor muscles on the _____ side will lose vestibulospinal input

same

Why do animal’s lean or circle toward the lesioned side (center of gravity changes)?

will have normal/enhanced extensor thrust on the normal side and diminished on the affected

For central vestibular lesions, look for postural deficits on the ______ side.

ipsilateral

True or False: A strictly peripheral vestibular problem will not produce somatosensory proprioceptive deficits or UMN signs in the limbs.

TRUE

What is the only peripheral sensory axons that have access to the cerebellum?

Vestibular nerve CNVIII

Paradoxical Vestibular Syndrome

unilateral cerebellar lesions with the flocconodular lobe which causes loss of Purkinje cell output on the damaged side resulting in more active ipsilateral vestibular nuclei → OPPOSITE of unilateral lesions

In paradoxical vestibular syndrome the ______ is less active

normal

In Vestibular nuclei disorders, vestibular signs and proprioceptive deficits will involve the _____ side of the body

same

In paradoxical vestibular syndrome, vestibular signs are on _____ sides of the body.

both - lesion on one side and deficits show the other side

The side of the lesion is always on the side showing ____________ in the limbs.

proprioceptive/UMN deficits

• medulla and cerebellum always associated with same side

A patient comes in with vestibular signs but normal reflexes, muscle strength, and postural reactions. Where is the lesion (central/peripheral)?

Peripheral