Lecture 9: Cerebellum & Vestibular Ocular Reflex (VOR) Flashcards
What does the cochlear portion of the inner ear detect?
sound
What does the vestibular portion of the inner ear detect?
movements
In humans the vestibular system has evolved to provide?
- Orientation
- Equilibrium
The vestibular system is responsible for sensing head motion via what two mechanisms?
- Maintaining postural control
- Stabilizing images on the fovea of the retina (gaze stability)
The vestibular system transmits information to the central vestibular pathways to control what?
Reflexes and perceptions
the vestibular system is part of a complex multisensory system- it never stands alone, and works w/ other systems
The peripheral vesitibular is a membranous labyrinth within what structure?
The temporal bone
What are the 5 neural structures of the peripheral vestibular and what do they respond to?
- 3 semicircular canals: respond to ANGULAR acceleration
- 2 otolith organs (utricle & saccule): respond to LINEAR acceleration, tilt, and gravity
the SSC are positioned in the orthogonal planes
What are the 2 otolith organs and they sense motion in what planes ?
- Utricle: senses motion in the HORIZONTAL plane (foward-back, left-right, or combination)
- Saccule: senses motion in the VERTICAL plane (up-down) and gravity
They work together. Utricle: braking in a car & Saccule: going up or down in an elevator
What 4 structures does each otolith organ have?
- Macula
- Hair cells = project into a gelatnious mass containing otoconia (calcium carbonate crystals)
- Gelatinous substance = embedded with otoconia
- Afferent nerve fibers
When the head moves, the otolith-gel mass (otoconia) drags on the hair cells causing what?
An excitatory or inhibitory response
The semicircular canal responds to what and where are the 3 canals positioned?
- Responds to angular acceleration and are positioned in the orthogonal planes.
- Each canal is sensitive to movement in its own planes
- Together, the 3 canals can code the direction and amplitude of any head roation
Each end of the semicircular canal is enlarged to form the sensory receptor called the _____.
ampulla
What are the semicircular canals filled with?
endolymph
Has a lot of potassium
What are the 3 structures within the ampulla of the SCC?
- Cupula (gelantinous mass): separates the SCC from vestibule
- Crista w/ hair cells: kinocilium (long stereocilia), 50-100 stereocilia
- Vestibular afferents
tonotopically organized
During ____ _____, endolymph inside the SCC lags behind movement of the SCC due to inertia
Causes deflection of the stereocilia
rotational acceleration
SCC are “coplanar mates” Explain this concept
Associated with respective SCC on opposite side. (Left Horizontal paired with Right Horizontal)
How do the SCCs work to respond to a given rotational head movement?
Pairs of SCC on opposite sides of the head respond in opposite ways to a given rotational head movement (excitatory for one, inhibitory for the other).
Disagreement between corresponding SCCs on the two sides of the head causes what?
due to pathology or trauma
- Vertigo
- Nausea
What are the two branches of CN VIII?
- Vestibular nerve
- Cochlear nerve
Primary vestibular neurons are bipolar neurons whose cell bodies form ____ in the internal auditory canal
Scarpa’s Ganglion
What are the 2 branches of the scarpa’s ganglia?
- Superior vestibular nerve
- Inferior vestibular nerve
What does the Superior Vestibular Nerve innervate?
- Horizontal canal
- Anterior (superior) canal
- Utricle
“sUp”=U for utricle
What does the Inferior Vestibular Nerve innervate?
- Posterior canal
- Saccule
Where do MOST vestibular nerve fibers terminate?
in the ipsilateral vestibular nucleus on the floor of the 4th ventricle
Where do some vestibular nerve fibers (mediating postural control) terminate?
Cerebellum
- Contributes to body movement, coordination & posture during static & dynamic activities
- Discriminate between movement of self & movement of the environment
What is the ascending pathway of the vestibular nerve tract?
Medial longitudinal fasciculus (MLF)
What are the descending pathways of the vestibular nerve tract (2)?
- Lateral Vestibulospinal Tract
- Medial Vestibulospinal Tract
What are the 3 classic vestibular reflex arcs and what are they responsible for?
- Vestibulospinal Reflex (VSR): Keeping you upright
- Vestibulocolic Reflex (VCR): Keeping your head upright/in a horizontal plane (to protect brain)
- Vestibular-Ocular Reflex (VOR): Allows eyes to be stable during head movements = gaze control
Example: Trip and catch yourself
The peripheral vestibular neurons that innervate the SCCs are connected to what muscles (3) that control the eyes?
- medial and lateral rectus
- superior and inferior rectus
- inferior and superior oblique
- The ears can tell eyes to move in diff directions and work together.
- One pair of muscles can be excited while the other is inhibited
What is the order of the pathway of signals of the VOR?
- SCC
- Vestibular nerve
- Vestibular nucleus
- Ocular nucleus (depends on which muscle)
- Ocular muscle
CN III = oculomotor
CN VI = abducens
VOR: When the head turns to the LEFT, which direction do the eyes turn to maintain frontal gaze?
To the RIGHT
VOR: When the head turns to the LEFT,
- Which SCC is Excited? Inhibited?
- Which muscles Contract? Relax?
HIGH yield
SCC
- Excitation: Left Horizontal
- Inhibition: Right Horizontal
Muscle
- Contraction: Left Medial Rectus & Right Lateral Rectus
- Relaxation: Left Lateral Rectus & Right Medial Rectus
VOR: When the head turns to the RIGHT, which direction do the eyes turn to maintain frontal gaze?
To the LEFT
VOR: When the head turns to the RIGHT,
- Which SCC is Excited? Inhibited?
- Which muscles Contract? Relax?
SCC
- Excitation: Right Horizontal
- Inhibition: Left Horizontal
Muscle
- Contraction: Right Medial Rectus & Left Lateral Rectus
- Relaxtion: Left Medial Rectus & Right Lateral Rectus
The cerebellum influences movements primarily by modifying the activity patterns of what?
upper motor neurons
What are the primary functions of the cerebellum?
- Detects differences between. “intended” movements and “actual” movements (motor “error”)
- Acts through its influences on upper motor neurons to correct the “error” during ongoing movements initiated elsewhere
- Incorporates motor learning and changes in synaptic strength to adjust movements
Cerebellum is a multisensory system that is ADAPTIVE
Note that it does sensory-motor coordination INDIRECTLY, it sends info back to sensory systems to do the functions mentioned
What are the 2 main gray matter structures of the cerebellum?
- laminated cortex
- clusters of cells in nuclei buried deep in the white matter
What are the 3 hemispheres of the cerebellum?
- Cerebrocerebellum (lateral hemispheres)
- Spinocerebellum (median & paramedian region)
- Vestibulocerebellum (caudal & inferior parts)
What structure does the cerebrocerebellum receive input from? What is its function (2)?
- Receives indirect input from areas of cerebral cortex.
1. Regulation of skilled movements
2. Planning and execution of complex spatial and temporal sequences
What structures do the vestibulocerebellum (caudal and inf) include (2)? What is its function (2)?
- Includes the flocculus and nodulus
1. Regulation of movements associated with posture and equilibrium/balance
2. Vestibular-Ocular Reflex (VOR)
What structure does the spinocerebellum (median and paramedian) receive input from? What is its function?
- Receives direct input from spinal cord
1. Paramedian part – movements of distal limbs
2. Median part (along vermis) – movements of proximal muscles and eyes
What structure is responsible for the major INPUTS of the fiber bundles of cerebellum?
Cerebellar peduncles (superior, middle, inferior)
Sensory information can enter/leave the cerebellum by BOTH the cerebellar peduncles and deep cerebellar nuclei.
Input pathways that reach the cerebellum from other brain regions project to which 2 structures?
- cerebellar cortex
- deep nuclei
What structure is responsible for the major OUTPUTS of the cerebellum (excitatory)?
Deep cerebellar nuclei (fastigial nucleus, interposed nucleus, dentate nucleus)
Sensory information can enter/leave the cerebellum by BOTH the cerebellar peduncles and deep cerebellar nuclei.
Major inputs to the cerebellum enter via ____ and ____ peduncles.
middle and inferior
- Not a direct pathway
- Input pathways that reach the cerebellum from other brain regions project to both the cerebellar cortex and deep nuclei
The output from the cerebellum comes mainly from what structure? What is the exception?
- deep cerebellar nuclei
- Exception: the inferior peduncle contains descending output(efferent) fibers from cerebellum
This is the cerebellum telling our body to make a correction think of the deep cerebellar nuclei as an intermediate before reaching the target organ
What are the 3 layers of the cerebellar cortex?
- Molecular
- Dendrites
- Axons
- Purkinje cell
- output cells of cerebellar cortex to deep cerebellar nuclei
- inhibit the excitatory neurons of the deep cerebellar nuclei
- granule cell
What is the destination of the afferent pathways before they reach the cerebellar cortex?
Purkinje cells
afferent n. fibers will lands on purkinje cell
What do Purkinje cells of the cerebellar cortex inhibit?
Inhibit the excitatory neurons of the deep cerebellar nuclei
Sensory information enters the cerebellum via the cerebellar peduncles. From there, input information synapses at the purkinje cells of the cerebellar hemispheres. They then send inhibitory signaling to the deep cerebellar nuclei (main output centers).
Signs associated with the cerebellar dysfunction
What is nystagmus?
oscillatory instability of ocular fixation
Signs associated with the cerebellar dysfunction
What is dysmetria?
inaccurate movements that are too large or small (over and under reaching)
Signs associated with the cerebellar dysfunction
What is dysdiadochikinesia?
duhs ·da· a· duh· kow· kuh·nee· zhuh
difficulty with rapid alternating movements
Signs associated with the cerebellar dysfunction
What is asynergia?
decomposition of movement (strategy to compensate for dysmetria)
Signs associated with the cerebellar dysfunction
What is a tremor?
during intended movement or at intentionally held position
Signs associated with the cerebellar dysfunction
What are errors of gait?
unsteadiness
The human vestibular system has evolved primarily to provide orientation and equilibrium as well as detect movement. Which of the following structures is responsible for sensing motion in the horizontal plane?
A. Utricle
B. Horizontal SCC
C. Saccule
D. Posterior SCC
Utricle
The anterior (superior) semicircular canal is innervated by which of the following nerves?
A. Inferior Vestibular
B. Superior Vestibular
C. Both Superior and Inferior Vestibular
D. Neither Superior nor Inferior Vestibular
Superior Vestibular
Which of the following cerebral hemispheres is primarily responsible for movement of the distal limbs, proximal muscles, and eyes?
A. Cerebrocerebellum
B. Vestibulocerebellum
C. Spinocerebellum
D. All of the above
Spinocerebellum
Major inputs to the cerebrocerebellum enter via the ____________ while its major outputs exit via the ____________.
A. Middle peduncle; Dentate nucleus
B. Inferior peduncle; Interposed nuclei
C. Inferior peduncle; Dentate nucleus
D. Superior peduncle; Interposed nuclei
Middle peduncle; Dentate nucleus
A 25-year-old male is admitted into the intensive care unit following a severe blow to the back of his head at a sporting event. During neurological examination, the patient is unable to produce accurate movements (i.e. over-reaching for objects placed directly in front of him). Which of the following is most likely the patients diagnosis?
A. Nystagmus
B. Dysdiadochokinesia
C. Tremor
D. Dysmetria
Dysmetria
