401 The Vestibular system

dizziness v. vertigo

dizziness: unsteadiness, feeling faint, feeling weak

vertigo: false sensation that the individual/environment is moving

Two main components of the balance system? What happens if there is a mismatch between their input/output?

• Sensory (visual, proprioceptive) - you can see and feel that you are on the ground.

• Motor - keeps feet moving

mismatch leads to balance problems

3 main body parts that are components of balance?

Eyes, feet, inner ear (vestibular system specfically)

What is the job of the vestibular system? (what kind of info does it provide to the CNS?)

• tells CNS what skeletal muscles to activate for postural adjustment

• stabilizes visual environment during movement (lets our eyes lock onto obj)

• gives CNS spatial info abt linear and angular acceleration.

3 primary structures of vestibular system? What directions of movement do they process?

3 Semicircular canals - angular acceleration

• yaw - spinning

• pitch - tilt forward/back

• roll - tilt side to side

utricle - linear acceleration (horizontal x & y axis)

• forward, backward, left, right

saccule - linear acceleration (vertical z axis)

• up, down

What 4 internal structures do the utricle and saccule have?

Macula - sensory epithelium. holds sensory hair cells

Otolith - the jelly surrounding hair cells. Toward their surface, they hold otoconia crystals.

Otoconia - heavy calcium carbonate crystals.

• Gives inertia to the jelly. The lag causes it to move in the opposite of the direction you move toward.

Stereocilia - the hair cells. They send off excitatory signals (when your head moves in the direction of the slope) or inhibitory signals (when your head moves in the opposite direction of the slope).

• Left ear: cilia positively sloped

• Right ear: cilia negatively sloped

What 5 internal structures do the Semicircular canals have?

Ampulla: The bulbous end of the SCCs. Holds the sensory epithelium.

Crista ampullaris: Sensory epithelium. holds hair cells, jelly, and endolymph fluid.

Cupula: the jelly surrounding the hair cells.

Endolymph: the fluid surrounding all structures inside the ampulla (think: cell’s cytoplasm around organelles.)

• Instead of otoconia (saccule/utricle), the endolymph pushes the jelly. Makes it move in the opposite direction you move in.

Stereocilia: the hair cells. They send off excitatory signals (when your head moves in the direction of the slope) or inhibitory signals (when your head moves in the opposite direction of the slope).

• Left ear: cilia positively sloped

• Right ear: cilia negatively sloped

Names (locations) of each semicircular canal? what designated movement direction each process?

RALP

• right anterior → left posterior

LARP

• left anterior → right posterior

Horizontal/lateral semicircular canal

• Left —> right side

In what pairs do the utricles/saccules work? How many are there on each side of the head? ****

The Utricle and Saccule work in pairs:

• Ipsilateral Utricle and Saccules work together

• Contralateral Utricles work together

• Contralateral Saccule’s work together

How many on each side?

• L: 1 utricle and 1 saccule, R: 1u + 1s

• Why?

  • To allow hair cells to process excitatory/inhibitory ipsilateral and contralateral information

How do the SSCs work to tell you what direction your head is moving in Yaw, Roll, and Pitch?

SCCs have excitatory/inhibitory relationship with its contralateral partner SCC.

• ie) Quick head movement to right excites right horizontal SCCs, inhibits left horizontal SCCs.

What structure connects the peripheral vestibular system (SCCs) to the extraocular eye muscles (EOM)?

Brainstem nuclei

• Sensory nerve fibers from SCC —> connect —> Motor neurons of EOMs

How many EOMs are there? What do they do?What do they connect to?

6 extraocular eye muscles.

Each muscle controls eye motion in a different direction. (Helps you lock onto a target while your head moves)

Each muscle pairs with specific SCCs.

What directions can the EOM move the eye?

Left, right

Roll left, Roll right

What happens during the vestibulo-ocular reflex (VOR)?

1. SCCs receive info about the direction your head is moving in

2. A motor signal is then sent to their paired EOMs to move in the opposite direction to stay/return on the target.

How do the horizontal SSCs work?

Left Horiz SCC

1. Head turn left

2. Endolymph flows to the right, toward one end of the SCC to its ampulla (Ampullopetal)

3. Along the way, fluid also pushes Cupula (structure inside ampulla) to the right toward utricle (Utriculopetal)

4. The left vestibule’s hair cell's (positively sloped) are pushed toward the right (with the direction of the slope), causing the L SCC to fire more.

Right Horiz SCC

1. Head turn right

2. Endolymph flows to the left, toward the SCC’s ampulla (Ampullofugal)

3. The fluid also pushes Cupula to the left toward the utricle (Utriculofugal)

4. The left vestibule’s hair cell's (negatively sloped) are pushed toward the left (working with the direction of the slope), causing the R SCC to fire more.

Nystagmus: What? Cause?

rapid, uncontrollable eye movements in one or both eyes

Cause: Peripheral vestibular system + EOMs not working together

Videonystagmography Testing? 3 Subtypes?

Oculomotor, Positional, or Caloric testing. Sees whether one has a vestibular, neurological, or ocular problem.

• Occulomotor: gaze, saccades, smooth eye movements, presence of nystagmus

• Positional: put hands on patient’s head and move their head quickly in unpredictable directions to see how quickly their eyes can lock back onto target (Dix-Hallpike). Could tilt you up and down, make you lay down/sit up, etc.

• Caloric: patient lies down with black out goggles on (to avoid fixation points). Cold/hot air or water is then put into ears to simulate inhibitory/excitatory reactions to movement