CRANIAL NERVE VIII

CN VIII:

• Axon type: SSA

• CNS termination: cochlea nuclei

• PNS origin:

CN VIII:

• Axon type: SSA

• CNS termination: cochlea nuclei

• PNS origin: organ of corti

CN VIII:

• Axon type: SSA

• CNS termination: vestibular nuclei

• PNS origin:

CN VIII:

• Axon type: SSA

• CNS termination: vestibular nuclei

• PNS origin:

  • Cristae of semicircular ducts

  • Maculae of utricle and saccule

Hearing and balance: different senses ___ but ___ sensing is similar

Hearing and balance: different senses FUNCTIONALLY but PERIPHERAL sensing is similar

Cranial nerve VIII has two divisions:

• ___: sound

• ___: head position and movement

Cranial nerve VIII has two divisions:

• COCHLEAR: sound

• VESTIBULAR: head position and movement

Both divisions of CN VIII innervate highly specialized organs with ___ called hair cells that sense different ___ stimuli.

Both divisions of CN VIII innervate highly specialized organs with MECHANORECEPTORS called hair cells that sense different MECHANICAL stimuli.

Hair cells —> mechanoreceptors —> sense mechanical stimuli

Auditory and vestibular receptors:

• Located in the walls of the ___ inner ear structure

• Embedded in ___ bone

Auditory and vestibular receptors:

• Located in the walls of the MEMBRANOUS inner ear structure

• Embedded in TEMPORAL bone

Bony labyrinth:

Three major structures:

• ___: coiled structure that enlarges and attaches to vestibule

• ___

• ___ ___ (3): attached to vestibule

Bony labyrinth:

Three major structures:

• COCHLEA: coiled structure that enlarges and attaches to vestibule

• VESTIBULE

• SEMICIRCULAR CANALS (3): attached to vestibule

Membranous labyrinth: a tube that is suspended and follows the contours of the ___ ___

• ___ duct (within cochlea)

• ___ duct (within semicircular canal)

• Vestibule contains 2 enlargements of membranous labyrinth:

  • ___ (semicircular ducts attached)

  • ___ (connected to cochlear duct and utricle)

Membranous labyrinth: a tube that is suspended and follows the contours of the BONY LABYRINTH

• COCHLEAR duct (within cochlea)

• SEMICIRCULAR duct (within semicircular canal)

• Vestibule contains 2 enlargements of membranous labyrinth:

  • UTRICLE (semicircular ducts attached)

  • SACCULE (connected to cochlear duct and utricle)

Perilymph:

• Fills ___ labyrinth

• Similar to ___ in composition

• Continuous with the ___ space through the cochlear aqueduct

Perilymph:

• Fills BONY labyrinth

• Similar to CSF in composition

• Continuous with the SUBARACHNOID space through the cochlear aqueduct

Endolymph:

• Fills ___ labyrinth

• Similar in composition to ___ fluid

• Closed off from outside, but all parts of ___ labyrinth communicate with each other

Endolymph:

• Fills MEMBRANOUS labyrinth

• Similar in composition to INTRACELLULAR fluid

• Closed off from outside, but all parts of MEMBRANOUS labyrinth communicate with each other

The bony labyrinth and membranous labyrinth are not ___ with each other.

The bony labyrinth and membranous labyrinth are not COMMUNICATING with each other.

Perilymph and endolymph are separated from each other by ___ ___ in hair cells. This establishes the ___ and ___ gradients needed for impulse transduction.

Perilymph and endolymph are separated from each other by TIGHT JUNCTIONS in hair cells. This establishes the VOLTAGE and CONCENTRATION gradients needed for impulse transduction.

Endolymph:

• Produced continuously by specialized cells in ___ (and elsewhere) and circulates

• Resorbed in ___ sac

• Obstruction of flow results in swelling of ___ labyrinth

  • ___ disease: transient attacks of vertigo, nausea, hearing loss, and tinnitus (ear ringing)

Endolymph:

• Produced continuously by specialized cells in COCHLEA (and elsewhere) and circulates

• Resorbed in ENDOLYMPHATIC sac

• Obstruction of flow results in swelling of MEMBRANOUS labyrinth

  • MENIERE’S disease: transient attacks of vertigo, nausea, hearing loss, and tinnitus (ear ringing)

Hair cells:

• ___ and ___ receptor cells

• Named for specialized ___ that project into the endolymph at one end of the cell

• Other end of the cell has processes of CN ___

Hair cells:

• AUDITORY and VESTIBULAR receptor cells

• Named for specialized MICROVILLI that project into the endolymph at one end of the cell

• Other end of the cell has processes of CN VIII

Hair cell features:

• Hair cell microvilli known as ___ are arranged in graduated rows with the ___ toward one side

• ___ near tallest stereocilia in semicircular ducts, utricle, and saccule

• Cochlear hair cells lack ___

Hair cell features:

• Hair cell microvilli known as STEREOCILIA are arranged in graduated rows with the TALLEST toward one side

• KINOCILIUM near tallest stereocilia in semicircular ducts, utricle, and saccule

• Cochlear hair cells lack KINOCILIA

Hair cells are ___.

Hair cells are MECHANOSENSITIVE.

Hair cells are mechanosensitive:

• Deflection towards tallest stereocilia ___ hair cell

• Deflection away from tallest stereocilia ___ hair cell

• Deflection in ___ plane has no effect

  • No receptor potential results

Hair cells are mechanosensitive:

• Deflection towards tallest stereocilia DEPOLARIZES hair cell

• Deflection away from tallest stereocilia HYPERPOLARIZES hair cell

• Deflection in PERPENDICULAR plane has no effect

  • No receptor potential results

All hair cells use the same basic transduction mechanism —> deflection of stereocilia initiated by a ___ mass

• It is the make up of the ___ masses that allows some hair cells to respond to sound or head movement/position

All hair cells use the same basic transduction mechanism —> deflection of stereocilia initiated by a GELATINOUS mass

• It is the makeup of the GELATINOUS masses that allows some hair cells to respond to sound or head movement/position

Location: organ of corti

Labyrinth part: cochlea

Gelatinous material: ___ membrane

Stimulus transduced: ___

Location: organ of corti

Labyrinth part: cochlea

Gelatinous material: TECTORIAL membrane

Stimulus transduced: SOUND

Location: cristae

Labyrinth part: semicircular ducts (3)

Gelatinous material: ___

Stimulus transduced: ___ acceleration

Location: cristae

Labyrinth part: semicircular ducts (3)

Gelatinous material: CUPULA

Stimulus transduced: ANGULAR acceleration

Location: maculae

Labyrinth part: utricle, saccule

Gelatinous material: ___ membrane

Stimulus transduced: ___ acceleration

Location: maculae

Labyrinth part: utricle, saccule

Gelatinous material: OTOLITHIC membrane

Stimulus transduced: LINEAR acceleration

Tips of ___ and ___ stereocilia are embedded in specialized mass of gelatinous material.

Tips of KINOCILIUM and TALLEST stereocilia are embedded in specialized mass of gelatinous material.

Movement of gelatinous mass relative to hair cells causes deflection of stereocilia and a ___ ___ is transduced.

Movement of gelatinous mass relative to hair cells causes deflection of stereocilia and a RECEPTOR POTENTIAL is transduced.

___ fills the bony labyrinth.

PERILYMPH fills the bony labyrinth.

___ is similar to CSF in composition.

PERILYMPH is similar to CSF in composition.

___ is similar to intracellular fluid in composition.

ENDOLYMPH is similar to intracellular fluid in composition.

Deflection ___ tallest stereocilia depolarizes hair cell.

Deflection TOWARDS tallest stereocilia depolarizes hair cell.

CN VIII Cochlear Division:

Transmission of sound:

• ___ and ___ ears convert airborne sound vibrations to fluid-filled inner ear

• ___ moves perilymph

CN VIII Cochlear Division:

Transmission of sound:

• OUTER and MIDDLE ears convert airborne sound vibrations to fluid-filled inner ear

• STAPES moves perilymph

CN VIII Cochlear Division:

Middle ear muscles stiffen the ___ ___.

Middle ear muscles stiffen the OSSICULAR CHAIN.

CN VIII Cochlear Division:

Middle ear muscles:

• ___ ___: pulls the malleus in toward the middle ear

• ___: pulls stapes away from oval window of the cochlea

CN VIII Cochlear Division:

Middle ear muscles:

• TENSOR TYMPANI: pulls the malleus in toward the middle ear

• STAPEDIUS: pulls stapes away from oval window of the cochlea

CN VIII Cochlear Division:

Tensor tympani:

• Blocks ___ sound

• Can anticipate ___ sounds

• Can spasm causing ___ at low frequency

• Innervated by CN ___

CN VIII Cochlear Division:

Tensor tympani:

• Blocks CHEWING sound

• Can anticipate LOUD sounds

• Can spasm causing TINNITUS at low frequency

• Innervated by CN V

CN VIII Cochlear Division:

Stapedius:

• Blocks sound of own ___

• Spasm can cause ___ sound when speaking

• Innervated by CN ___

CN VIII Cochlear Division:

Stapedius:

• Blocks sound of own VOICE

• Spasm can cause CLICKING sound when speaking

• Innervated by CN VII

CN VIII Cochlear Division:

Cochlea in cross section:

• ___ ___:

  • Perilymphatic space

  • Continuous with vestibule

• ___ ___ (aka ___ ___):

  • Contains endolymph

• ___ ___:

  • Perilymphatic space

  • Ends blindly at the round window

CN VIII Cochlear Division:

• SCALA VESTIBULI:

  • Perilymphatic space

  • Continuous with vestibule

• SCALA MEDIA (aka COCHLEAR DUCT):

  • Contains endolymph

• SCALA TYMPANI:

  • Perilymphatic space

  • Ends blindly at the round window

CN VIII Cochlear Division:

___: spongy bone at core

• Houses spiral ganglion and cell bodies of primary afferent fibers

• Primary afferent fibers collect and form cochlear division of VIII

CN VIII Cochlear Division:

MODIOLUS: spongy bone at core

• Houses spiral ganglion and cell bodies of primary afferent fibers

• Primary afferent fibers collect and form cochlear division of VIII

CN VIII Cochlear Division:

Organ of corti features:

• A strip of cells that rests on the ___ membrane

• 2 groups:

  • ___ hair cells

  • ___ hair cells

CN VIII Cochlear Division:

Organ of corti features:

• A strip of cells that rests on the BASILAR membrane

• 2 groups:

  • INNER hair cells

  • OUTER hair cells

CN VIII Cochlear Division:

Organ of corti features:

• Inner hair cells:

  • Not attached to ___ ___ membrane

  • Stimulated by ___ movement across the stereocilia

• Outer hair cells:

  • ___ inserted into tectorial membrane

  • Vibrations in ___ membrane causes ___ in membrane potential of hair cells

CN VIII Cochlear Division:

Organ of corti features:

• Inner hair cells:

  • Not attached to GELATINOUS TECTORIAL membrane

  • Stimulated by ENDOLYMPH movement across the stereocilia

• Outer hair cells:

  • STEREOCILIA inserted into tectorial membrane

  • Vibrations in BASILAR membrane causes OSCILLATIONS in membrane potential of hair cells

CN VIII Cochlear Division: cochlear duct

Vibrations are transmitted to ___ in vestibule and energy in transmitted to ___ ___, deforming the ___ ___ slightly and stimulating receptors within.

CN VIII Cochlear Division: cochlear duct

Vibrations are transmitted to PERILYMPH in vestibule and energy is transmitted to SCALA TYMPANI, deforming the COCHLEAR DUCT slightly and stimulating receptors within.

CN VIII Cochlear Division:

Organ of corti:

• ___ movement causes a pressure pulse in scala vestibule that leads to a traveling wave of ___ in the basilar membrane

• ___ properties of basilar membrane differ along its length, so a traveling wave reaches peak amplitude at a location that depends on ___ ___

• “___ ___” of basilar membrane is the beginning of tonotopic organization of auditory system

• ___ are mapped to specific locations of relay nuclei and cortex

CN VIII Cochlear Division:

Organ of corti:

• STAPES movement causes a pressure pulse in scala vestibule that leads to a traveling wave of DEFORMATION in the basilar membrane

• MECHANICAL properties of basilar membrane differ along its length, so a traveling wave reaching peak amplitude at a location that depends on STIMULUS FREQUENCY

• “MECHANICAL TUNING” of basilar membrane is the beginning of tonotopic organization of auditory system

• FREQUENCIES are mapped to specific locations of relay nuclei and cortex

CN VIII Cochlear Division:

CNS auditory processing:

• Analyzes sound ___ and ___

• ___ ___ is the primary ascending auditory pathway

  • Carries info from both ears

• Mostly consists of fibers from ___ ___ nucleus

CN VIII Cochlear Division:

CNS auditory processing:

• Analyzes sound FREQUENCY and INTENSITY

• LATERAL LEMNISCUS is the primary ascending auditory pathway

  • Carries info from both ears

• Mostly consists of fibers from DORSAL COCHLEAR nucleus

CN VIII Cochlear Division:

Auditory sensory processing:

1. ___ division of CN VIII

2. ___ nuclei (predominantly dorsal)

3. ___ ___ nuclei to lateral lemniscus or directly to ___ ___

4. ___ colliculus

5. Inferior ___

6. ___ of thalamus

7. ___ auditory cortex

CN VIII Cochlear Division:

Auditory sensory processing:

1. COCHLEAR division of CN VIII

2. COCHLEAR nuclei (predominantly dorsal)

3. SUPERIOR OLIVARY nuclei to lateral lemniscus or directly to LATERAL LEMNISCUS

4. INFERIOR colliculus

5. Inferior BRACHIUM

6. MGN of thalamus

7. PRIMARY auditory cortex

CN VIII Cochlear Division:

Primary auditory cortex:

• Located in ___ temporal gyri of Heschl

• On ___ surface of temporal lobe

CN VIII Cochlear Division:

Primary auditory cortex:

• Located in TRANSVERSE temporal gyri of Heschl

• On SUPERIOR surface of temporal lobe

CN VIII Cochlear Division:

CNS auditory localization:

• Sound coming from ___ reaches left ear before right ear and it is more intense in ___ ear

• ___ ___ nucleus important in sound localization

CN VIII Cochlear Division:

CNS auditory localization:

• Sound coming from LEFT reaches left ear before right ear and it is more intense in LEFT ear

• SUPERIOR OLIVARY nucleus important in sound localization

CN VIII Cochlear Division:

CNS auditory localization:

• Superior olivary nucleus: important in sound localization

  • Receives fibers from ___ cochlear nuclei

    • Fibers cross midline through ___ body

  • Two subnuclei:

    • Medial

    • Lateral

CN VIII Cochlear Division:

CNS auditory localization:

• Superior olivary nucleus: important in sound localization

  • Receives fibers from BILATERAL cochlear nuclei

    • Fibers cross midline through TRAPEZOID body

  • Two subnuclei:

    • Medial

    • Lateral

Lateral lemniscus conveys information from ___ ears.

Lateral lemniscus conveys information from BOTH ears.

Damage to auditory pathway rostral to cochlear nuclei does not cause deafness in either ear.

Cochlear nuclei project ___.

Cochlear nuclei project BILATERALLY.

Damage to auditory pathway rostral to cochlear nuclei does not cause deafness in either ear.

Superior olivary nuclei receive ___ input.

Superior olivary nuclei receive BILATERAL input.

Damage to auditory pathway rostral to cochlear nuclei does not cause deafness in either ear.

CN VIII Vestibular Division:

• Detects ___ and ___ acceleration

• Regulates ___ and coordinates ___ and ___ movements

  • Maintains orientation in response to movements

• Semicircular ducts, utricle, and saccule are suspended in ___ labyrinth

CN VIII Vestibular Division:

• Detects LINEAR and ANGULAR acceleration

• Regulates POSTURE and coordinates EYE and HEAD movements

  • Maintains orientation in response to movements

• Semicircular ducts, utricle, and saccule are suspended in BONY labyrinth

CN VIII Vestibular Division:

Receptors:

• Receptors in semicircular ducts detect ___ acceleration of the head

• Each semicircular duct communicates at both ends with the ___

• One end of each duct has an ___ (contains crista)

CN VIII Vestibular Division:

Receptors:

• Receptors in semicircular ducts detect ANGULAR acceleration of the head

• Each semicircular duct communicates at both ends with the UTRICLE

• One end of each duct has an AMPULLA (contains crista)

CN VIII Vestibular Division:

Semicircular ducts:

• ___: transversely oriented ridge with hair cells

• ___: in gelatinous mass (cupula)

• ___: covers crista and extends across ampulla

• All hair cells are aligned and face in same direction

• Deflection of cupula in one direction leads to ___ firing in afferent fibers

CN VIII Vestibular Division:

Semicircular ducts:

• CRISTA: transversely oriented ridge with hair cells

• STEREOCILIA: in gelatinous mass (cupula)

• CUPULA: covers crista and extends across ampulla

• All hair cells are aligned and face in same direction

• Deflection of cupula in one direction leads to INCREASED firing in afferent fibers

CN VIII Vestibular Division:

Deflection of the cupula: deflection of cupula in one direction leads to increased firing in afferent fibers

• Rotate semicircular duct in an axis ___ to it

• As rotation begins, ___ lags due to inertia and deflects cupula stimulating hair cells

• If rotation is maintained, ___ will catch up

• Rotation stops, ___ still moving

CN VIII Vestibular Division:

Deflection of the cupula: deflection of cupula in one direction leads to increased firing in afferent fibers

• Rotate semicircular duct in an axis PERPENDICULAR to it

• As rotation begins, ENDOLYMPH lags due to inertia and deflects cupula stimulating hair cells

• If rotation is maintained, ENDOLYMPH will catch up

• Rotation stops, ENDOLYMPH still moving

CN VIII Vestibular Division:

___ acceleration: each semicircular canal responds best to changes in speed of rotation in each plane

CN VIII Vestibular Division:

ANGULAR acceleration: each semicircular canal responds best to changes in speed of rotation in each plane

CN VIII Vestibular Division:

Utricle and saccule receptors: detect ___ acceleration of head

• Each contain a ___ (___)

CN VIII Vestibular Division:

Utricle and saccule receptors: detect LINEAR acceleration of head

• Each contain a PATCH (MACULA)

CN VIII Vestibular Division:

Utricle: macula is ___ when head is upright

• Stereocilia face ___

• Detects forward-backward and ___-___-___

CN VIII Vestibular Division:

Utricle: macula is HORIZONTAL when head is upright

• Sterocilia face UP

• Detect forward-backward and SIDE-TO-SIDE

CN VIII Vestibular Division:

Saccule: macula is ___ when head is upright

• Stereocilia face ___

• Detects forward-backward and ___-___

CN VIII Vestibular Division:

Saccule: macula is VERTICAL when head is upright

• Stereocilia face LATERALLY

• Detect forward-backward and UP-DOWN

CN VIII Vestibular Division:

Otolithic membrane:

• Gelatinous membrane of ___

• Contain ___ carbonate crystals, ___, and ___

• Makes membrane ___ than endolymph

CN VIII Vestibular Division:

Otolithic membrane:

• Gelatinous membrane of MACULA

• Contain CALCIUM carbonate crystals, OTOCONIA, and OTOLITHS

• Makes membrane DENSER than endolymph

CN VIII Vestibular Division:

Vestibular ganglion:

• ___ ___ cell bodies: vestibular (Scarpa’s) ganglion in internal auditory canal

  • ___ process: synaptic ending on hair cells

  • ___ process:

    • Most to vestibular nuclei of rostral medulla, caudal pons

    • Some to cerebellum and end in nodulus

CN VIII Vestibular Division:

Vestibular ganglion:

• PRIMARY AFFERENT cell bodies: vestibular (Scarpa’s) ganglion in internal auditory canal

  • PERIPHERAL process: synaptic ending on hair cells

  • CENTRAL process:

    • Most to vestibular nuclei of rostral medulla, caudal pons

    • Some to cerebellum and end in nodulus

CN VIII Vestibular Division:

Vestibular inputs:

• Four ___ nuclei:

  • Inferior

  • Medial

  • Lateral

  • Superior

• Each ___ duct and ___ has its own pattern of termination in these nuclei and connections

• ___ (flocculonodular lobe), spinal cord, and ___ vestibular nuclei also provide input

CN VIII Vestibular Division:

Vestibular inputs:

• Four VESTIBULAR nuclei:

  • Inferior

  • Medial

  • Lateral

  • Superior

• Each SEMICIRCULAR duct and MACULA has its own pattern of termination in these nuclei and connections

• CEREBELLUM (flocculonodular lobe), spinal cord, and CONTRALATERAL vestibular nuclei also provide input

CN VIII Vestibular Division:

Vestibular projections: regulate ___ and coordinate ___ and ___ movements

Project to:

• Spinal cord, nuclei of ___, ___, and ___, and cerebellum

• ___ vestibular nuclei

• ___ (VPL) to ___ cortex (parietal lobe, insula)

  • Conscious awareness of movement in space

• ___ nuclei of brainstem

  • Adjust cardiovascular system for lying down-standing up

  • Seasickness

CN VIII Vestibular Division:

Vestibular projections: regulate POSTURE and coordinate HEAD and EYE movements

Project to:

• Spinal cord, nuclei of III, IV, and VI, and cerebellum

• CONTRALATERAL vestibular nuclei

• THALAMUS (VPL) to CEREBRAL cortex (parietal lobe, insula)

  • Conscious awareness of movement in space

• VISCERAL nuclei of brainstem

  • Adjust cardiovascular system for lying down-standing up

  • Seasickness

CN VIII Vestibular Division:

Vestibulospinal fibers: lateral vestibulospinal tract

• Travels in the ___ vestibulospinal tract

• Arises from ___ nucleus down ___ funiculus

• Excitatory projections to ___ antigravity muscles

• Mediates ___ changes to accommodate tilts in body

  • Increases activity in ___

CN VIII Vestibular Division:

Vestibulospinal fibers: lateral vestibulospinal tract

• Travels in the LATERAL vestibulospinal tract

• Arises from LATERAL nucleus down LATERAL funiculus

• Excitatory projections to IPSILATERAL antigravity muscles

• Mediates POSTURAL changes to accommodate tilts in body

  • Increase activity in LVST

CN VIII Vestibular Division:

Vestibulospinal fibers: medial vestibulospinal tract

• Travels in the ___ vestibulospinal tract

• Arises from ___ nucleus

• Extends to ___ cord via MLF

• ___ head movement as we walk

• Coordinates head and eye movements

CN VIII Vestibular Division:

Vestibulospinal fibers: medial vestibulospinal tract

• Travels in the MEDIAL vestibulospinal tract

• Arises from MEDIAL nucleus

• Extends to CERVICAL cord via MLF

• STABILIZES head movement as we walk

• Coordinates head and eye movements

Cranial nerve nuclei III, IV, and VI receive vestibular projections via the ___.

Cranial nerve nuclei III, IV, and VI receive vestibular projections via the MLF.

The ___ vestibulospinal tract descends in the MLF.

The MEDIAL vestibulospinal tract descends in the MLF.

The vestibular nuclei on the ___ project to the corresponding nuclei on the right.

The vestibular nuclei on the LEFT project to the corresponding nuclei on the right.

CN VIII Vestibular Division:

Vestibuloocular reflex:

• Goal: maintain eyes on a target when moving your head

• If you turn your head to the left:

  • ___ semicircular duct excited

  • ___ semicircular duct hyperpolarized

  • ___ lateral rectus and ___ medial rectus muscles contract

  • ___ lateral rectus and ___ medial rectus inhibited

CN VIII Vestibular Division:

Vestibuloocular reflex:

• Goal: maintain eyes on a target when moving your head

• If you turn your head to the left:

  • LEFT semicircular duct excited

  • RIGHT semicircular duct hyperpolarized

  • RIGHT lateral rectus and LEFT medial rectus muscles contact

  • LEFT lateral rectus and RIGHT medial rectus inhibited

CN VIII Vestibular Division:

Nystagmus:

• If vestibuloocular reflex can’t compensate for head movements, it is interrupted by very ___ eye movements in the ___ direction

• Back and forth eye movements with a ___ phase in one direction and a ___ phase in the other

• Can be normal or pathologic

CN VIII Vestibular Division:

Nystagmus:

• If vestibuloocular reflex can’t compensate for head movements, it is interrupted by very RAPID eye movements in the OPPOSITE direction

• Back and forth eye movements with a RAPID phase in one direction and a SLOW phase in the other

• Can be normal or pathologic

CN VIII Vestibular Division:

Position sense:

• Mediated by ___, ___, and ___ systems all working together to produce a sense of orientation and movement

• If one is defective the other ___ can compensate

• Test by asking patient to ___ their eyes and may sway or lose balance

  • Known as ___ sign

CN VIII Vestibular Division:

Position sense:

• Mediated by VESTIBULAR, PROPRIOCEPTIVE, and VISUAL systems all working together to produce a sense of orientation and movement

• If one is defective the other TWO can compensate

• Test by asking patient to CLOSE their eyes and may sway or lose balance

  • Known as ROMBERG’S sign