cranial nerve Vlll (8) - vestibular

Functions of Vestibular System

•Coordinates Eye Movements

•Maintains Equilibrium

•Maintains Head Position

•Gives us a “sense” of Head Position

the vestibular/ hearing system is asscoited with ______

hair cells

Endolymph

fluid filling the inner ear's membranous labyrinth

• essential for hearing and balance

wets hair cells

Meniere’s Disease

acculination of fluid

• too much firing of vestibular aid

symptoms

• tenitius

• hearing loss

• dizziness

Maximum Velocity of the Slow Phase (MVSP)

measures the fastest speed of the eye's slow, tracking movement during nystagmus

• Focuses on neck musculature for head stability

Lateral vestibulospinal tract

control posture, balance, and muscle tone

• by exciting extensor (antigravity) muscles and inhibiting flexors

Crista ampullaris

bending of the cilia

• allowing for the detection of rotational motion and maintaining dynamic equilibrium

essential for stabilizing gaze during movement, acting similarly to a camera stabilizer

Maculae (otolith organs)-crystals

when the head moves or tilts, gravity causes the heavy otoconia to shift, creating a shearing motion that bends the hair cells, triggering nerve signals

• vital for balance, posture, and spatial orientation

Nystagmus

happens when artificially stimulated by rotation

ex:

• right (fast phase)

• left (slow phase)

right “beating” nystagmus

The eyes move slowly to the left and fast to the right

Rotary nystagmus

slow eye movement opposite direction of rotation

• occurs during rotation

• direction of nystagmus is the same direction of rotation

• not esily detected

can always be inhited by fixating

Post-rotary nystagmus (PRN)

Rapid eye movement opposite the direction of rotation

• Occurs after rotation has ended

• easily detected

otoconia

calcium carbonate crystals in the inner ear's utricle and saccule

• detect gravity and linear acceleration to maintain balance

Macula

specialized sensory organs within the inner ear's vestibule

• detect linear acceleration

• head tilt

Hairs bent away from kinocilium

Inhibition of hair cells

• causes hyperpolarization of the hair cell by closing mechanically-gated ion channels

Hairs bent towards kinocilium

Excitation of hair cells

• ion channels open

• cell depolarization

• an increased rate of nerve impulses

Maintains equilibrium

Via lateral vestibulospinal pathways to extensor
   muscle LMNs

medial vestibulospinal tract

regulating neck and upper back muscles

• stabilize the head during movement

Caloric Testing

Identifies Labyrinthine Weakness

• Determines if one ear has a, or reduced, response (unilateral weakness)

L beating nystagmus (COWS)

Cold air or water into R ear

L beating nystagmus (COWS)

Warm air or water into L ear

Testing of Semi-Circular Canals

test for vestibular hyper function

Risk factors of Vestibular Dysfunction

alcoholism, and TBI, especially concussion

Benign Paroxysmal Positional Vertigo (BPPV)

common inner ear disorder causing brief

• triggered by head movements like rolling over in bed

• youve been in a postion for a long time