Vestibular Lecture Flashcards
Vestibular system has 3 components:
- peripheral apparatus (the peripheral sensory apparatus-laberynthe, organs in the middle ear)
- the central nervous system processer (Sensory input comes in, areas in the cortex areas of the brain process it and lead to motor output)
- Mechanism for motor output (info comes in, is processed centrally and there is a motor output)
Peripheral sensory apparatus:
—–Motion sensors in inner ear send info to CNS
—–Head Angular Velocity and Linear acceleration
how fast head is going at different angles, side to side, up and down, forward to back
—–Motion sending to CNS on:
- Head angular velocity and linear acceleration
- Position of spine relative to head
- Spatial orientation WRAT gravity (special orientation of body relative to gravity, if I am upright or flat)
- Sense of motion
b. CNS Processor: 3 distinct areas
- Vestibular Nucleus complex (pons)
- Cerebellum (regulate movement, vestibulocerebellum)
Information that comes in combines with other sensory information to estimate head and body orientation
- Vestibular Cortex Monitored by cortical processes (“Vestibular Cortex”)-right perisylvian area (doesn’t have anatomical boundries); responding to and acting on input from vestibular apparatus
Mechanism for Motor Output:
movement causes motor output, so it is a type of reflex (but not a monosynaptic reflex): ocular muscles, spinal cord
- OCULAR MUSCLES and
- SPINAL CORD
3 reflexes—(not monosynaptic reflexes but they are movements that result in a specific motor output)[importance: VOR→VSR→VCR]
- vestibulo-ocular reflex (VOR):
- Vestibulocolic reflex (VCR):
- Vestibulospinal reflex (VSR):
vestibulo-ocular reflex (VOR):
eye stability with head movement
turn head quickly one way so eye movement equal and opposite to body and/or head movement
in this way we can keep our eyes focused on something even when we are moving
Vestibulocolic reflex (VCR):
Stabilization of head on the neck
If eyes fail can substitute with the VCR, if VOR fails can also substitute with VOR
Vestibulospinal reflex (VSR):
Compensatory body movements to prevent falls
If someone pushes me left the movement that brings my head back on my body is the VSR
Not only these reflexes but other factors such as proprioception and light touch that help too, but VSR is the main thing that stabilizes the head on the body
Peripheral Sensory Apparatus:
Labyrinth:
Motion sensors that are where? do what? send where?
- Combination: of Vestibular input, vision, and proprioceptive input in response to balance tasks (also attention, motor control)
- Balance is emergent: depending on the task, different balance apparatuses come in to act on the task
made up of Otoliths and Semicircular Canals
Labyrinth = “maze” in inner ear
Oto = ear
Lith = stones
—Motion sensors that are in the inner ear
—detect motion in specific ways
— send information to vestibular nuclei, cerebellum, and the vestibular cortex
Combination: of Vestibular input, vision, and proprioceptive input in response to balance tasks (also attention, motor control)
Balance is emergent: depending on the task, different balance apparatuses come in to act on the task
Balance is emergent:
Balance is emergent: depending on the task, different balance apparatuses come in to act on the task
Peripheral Sensory Apparatus: The Labyrinth:
What it is:
lies within the inner ear
bony labyrinth—protection and shape
membranous labyrinth
hair cells—lie within the membranous labyrinth
Bony Labyrinth: protection and shape
It has 3 semicircular canals
cochlea – hearing
vestibule—central chamber
perilimph—fluid
Membranous Labyrinth:
organ
1. Suspended in the bony labyrinth by perilymph and some connective tissue
- 5 sensory organs on each side (so that is 10 total): direct link to the CNS through the vestibular nerve
- —membranous portion of semicircular canals (3 semicurcular canals)
—-otolith organs: utricle and saccule (2 otolith organs)
- ampullae: (a sac) widening of the semicircular canals connecting to otolith organs
- There is a direct path from the semicircular canals , utricle, and saculae to the CNS through the vestibular nerve (movement picked up by these organs and goes via vestibular nerve to CNS)
ampullae:
what is it
(a sac) widening of the semicircular canals connecting to otolith organs
otolith organs:
utricle and saccule (2 otolith organs)
5 sensory organs on each side
5 sensory organs on each side (so that is 10 total): direct link to the CNS through the vestibular nerve
—-membranous portion of semicircular canals (3 semicurcular canals)
—-otolith organs: utricle and saccule (2 otolith organs)
Hair Cells
where
role
- Located in each ampullae and otolith organs
- Role: convert displacement of head motion into neural firing—head moves, hair cells move, hair cells have connection to VESTIBULAR NERVE and so the movement of the hair cells gets transduced into energy, the energy is sent through the vestibular nerve to CNS
- Innervated by afferent neurons located in Scarpas ganglion
- when hair cells are bent towards or away from the longest process in the Hair cell, the firing will either increase or decrease
ampullae:
how hair cells work here
(a sac) widening of the semicircular canals connecting to otolith organs
Hair cells lie within the CUPULA in the AMPULLAE,
endolymphatic flow across the cupula causes the hair cells to bend, stimulating the hair cells.
otolith organs (utricle and sacule):
how hair cells work here
Head movements cause the otoconia (calcium carbonate crystals) to deflect the hair cells of the otoliths (maculae). Otolithes are gravity sensitive !!!
Cupula:
where is it
how hair cells work
n the ampulla of each semircular canal
1. Located within the ampulla of each of the semicircular canals
- As fluid rushes by the cupula, hair cells within it sense motion, and transmit the corresponding signal to the brain through the VESTIBULAAR CHOCHLEAR NERVE (CN VIII)
- HEAD move left, PERILYMPH move right, hair cells deflected by fluid, send the info to sensory nerve
3 Semicircular Canals:
angular movement
- 2 sets of: (3 on each side = 6 total)
superior, posterior and horizontal
*oriented at 90 degrees to each other - respond selectively to head motion along with otoliths (otiliths for linear): ANGULAR VELOCITY, VOR for eye motion, clear vision if head movement
- Behave in coplanar pairs (left and right horizontal, left superior and right posterior, left posterior and right superior)
- —-Stimulation on one side/inhibition on the other side: when angular head motion occurs in the same plane, endolymph in pairs are displaced in equal and opposite directions = excitation on one side
Semicircular Canals respond selectively to head motion along with otoliths (otiliths for linear)
- responds to angular velocity, provides input about head angular velocity
- enables VOR to generate eye movement that matches head movement
- allows for clear vision during head motion
Semicircular Canals behave in coplanar pairs (left and right horizontal, left superior and right posterior, left posterior and right superior)
- They are close to planes of extra-ocular muscles—almost direct relationship of stimulation of hair cells in semicircular canals with corresponding eye motions
- Stimulation on one side/inhibition on the other side: when angular head motion occurs in the same plane, endolymph in pairs are displaced in equal and opposite directions—excitation on one side, inhibition on other side
- each semicircular canal corresponds to a specific type of motion of the head (ie yaw vs roll vs pitch), can have a pathology in a semicircular canal that will cause a specific issue, this will enable us to localize it
Otoliths:
linear movements
1. Utricle and sacculae
Register forces related to linear motion and acceleration
- Linear motion
- —-Vertical motion (up and down head tilts and acceleration) – sacculae
- —-horizontal motion – utricle - Respond to both linear head movement and static tilt
What does labyrinth interpret and how
Labyrinth: interprets the orientation of your head: the brain interprets head orientation by comparing these inputs to each other and to other input from the eyes and stretch receptors in the neck, thereby detecting whether only the head is tilted or the entire body is tipping
Symptoms of vestibular pathology:
any of these sx makes us need to question vestibular
- Vertigo
- Nystagmus
- Oscillopsia
- Dizziness—vague
- Disequilibrium
- Motion sickness –if it goes away when you close your eyes it is a hint it is vestibular, it is not due to motion, it is due to inability to keep stable eye position
- Nausea and vomiting
Oscillopsia—
jumping vision – feels like words jumping on page, even though not in a car (ie malfunctioning VOR)
Disequilibrium
—sense of imbalance
Motion sickness
–if it goes away when you close your eyes it is a hint it is vestibular, it is not due to motion, it is due to inability to keep stable eye position
Vertigo
what is it
if a patient has vertigo then the patient must have vestibular involvement (but if have vestibular involvement don’t have to have vertigo)
- only unambiguous symptom of vestibular damage***means vestibular going on
Differentiate from dizziness
Can occur with many other symptoms
Vertigo: can occur with movements that are:
- Vertical
- Horizontal
- Angular
- Rotary
- Sense of self motion
- environmental movement
- hallucination of motion: sense of movement occurring when movement is not occurring
Vertigo is not:
- –*Dizziness:
- –Lightheadedness, syncope, *orthostatic hypotension:
- –Disequilibrium: non-specific balance loss
- –Motion sickness:
Vertigo: can occur with movements that are:
- Vertical
- Horizontal
- Angular
- Rotary
- Sense of self motion
- environmental movement
- hallucination of motion: sense of movement occurring when movement is not occurring
Vertigo is not:
a. *Dizziness: this is not specific, not the unbalanced feeling
b. Lightheadedness, syncope, *orthostatic hypotension: check the medications, hypotension (do you feel lightheaded when stand up quickly, does it feel like the room is moving)
c. Disequilibrium: non-specific balance loss
d. Motion sickness: visual and vestibular mismatch
a. Rule these out
b. Do you get dizzy when stand up
c. Is the room spinning
If a patient has vertigo then the patient
if a patient has vertigo then the patient must have VESTIBULAR involvement (but if have vestibular involvement don’t have to have vertigo)
if have vestibular involvement do you have to have to have vertigo?
if have vestibular involvement don’t have to have vertigo
Nystagmus:
named what phase
what is it
does it have to be an abnormality
b. Nystagmus: named for the fast phase
- What it is:
- Involuntary eye movement
- Can be physiologic or pathologic
- Can be stimulated by pushing someone too hard, does not mean abnormality - Phases of Nystagmus:
- Slow phase: smooth pursuit phase
- Fast phase: saccadic phase
- Named for fast phase : ie slow to right and fast to the left named as a left beating nystagmus (or fast clockwise and slow counterclockwise) - Characteristics of Nystagmus: behavior of nystagmus can help diagnose type of vestibular pathology
- Direction can be vertical, horizontal, angular, rotary, mixed—direction can help us figure out where the lesion or pathology is
-Sustained or unsustained
Similar to clonus that can be sustained or unsustained (and we can thing of the rhythmic beating like spasticity)
-Nystagmus occurs with or without vertigo (we can trigger it in most people if push their VOR) without vertigo is a sign of CNS phenomenon
what is Nystagmus
- Involuntary eye movement
- Can be physiologic or pathologic
- Can be stimulated by pushing someone too hard, does not mean abnormality
Phases of Nystagmus:
- Slow phase: smooth pursuit phase
- Fast phase: saccadic phase
- Named for fast phase : ie slow to right and fast to the left named as a left beating nystagmus (or fast clockwise and slow counterclockwise)