Lecture 43 - Vestibular Flashcards
Describe the Vestibular System and areas involved
inner ear reports information about head and body position/movement along cranial nerve 8 to areas of the brain stem (vestibular nuclei), cerebellum, and somatosensory cortex (vestibular cortex)
What is the function of the Vestibular System
Convert mechanical energy into sensory information about head and body position and movement that allows rapid compensatory movements in response to both self-induced and externally generated forces to maintain balance
Vestibular system is a key component of (2)
postural reflexes and eye movements
The vestibul-oculo reflex is a
Gaze stabilizing reflex
Describe the vestibulo-ocular reflex
Sensory signals of head movements are transformed into motor commands that generate compensatory eye movements in the opposite direction of the head movement, thus ensuring stable vision
Vestibular Dysfunction and Sensory Conflict Theory often leads to:
dizziness due to a sensory mismatch: what our vision, proprioception, and vestibular systems are telling our brain do not align or our brain is unable to interpret the information.
For example, if the VOR isn’t working properly, we’d observe clients unable to maintain stable gaze with head movement, and clients would experience blurred vision, dizziness, and sometimes nausea/headaches.
What is Vestibular Hypofunction
Weakness of the inner ear, nerves, and/or vestibular areas of the brain steam, cerebellum, cerebrum, caused by trauma or illness (e.g., traumatic brain injury, vestibular neuritis). May be unilateral or bilateral in presentation. Patients likely to report dizziness with changes in positions that last more than a minute.
What is Benign Paroxysmal Positional Vertigo (BPPV) and it’s symptoms (2)
Inner ear disorder caused when otoconia (tiny crystals of calcium carbonate) come loose from the utricle or saccule and move about in the semicircular canals. On observation, we’d note nystagmus with the Dix-Hallpike test. Patients likely to report vertigo with rolling over in bed or transitions from sitting to lying.
Vertigo
false sense that you or your surroundings are spinning or moving. Typically occurs if there’s an issue with inner ear (infection or trauma), but could also occur with brain tumour or stroke. Vertigo is a type of dizziness (they are not interchangeable terms).
Dizziness
Term to describe range of sensation, such as feeling faint, woozy, weak, or lightheaded; unsteadiness, disequilibrium; imbalance, off balance, or loss of balance
Imbalance
loss of balance or unsteadiness (e.g., while standing or walking).
Diagram of anatomy of vestibular system
The vestibular labyrinth contains the
semicircular canals
The semicircular canals detect (3)
Head movements:
-Tilting head side to side
-Nodding head up and down
-Looking left to right
The semicircular canals are filled with a fluid called
endolymph
How are neurotransmitters released in the vestibular system
Endolymph moves into ampulla and bends stereocilia which triggers the hair cells to send neurotransmitters to the brain
How are the otolith organs and its parts triggered
Otoconia (crystals of calcium carbonate) cause displacement of hair cells in response to movement/gravity sending signals to brain
Bipolar sensory neuron cell bodies are located in the
Scarpa’s Ganglion
Vestibular afferents synapse on what 4 vestibular nuclei in the brain stem and function
- Lateral and Inferior nuclei which receive information from the otolith organs
- Medial and Superior nuclei which receive information from the semicircular canals
Vestibular nuclei connect to what 4 pathways and the functions
- Cerebellum: to coordinate movement
- Vestibulospinal tracts: Serve as descending/motor output
- Ocular Motor and abducens nuclei: to coordinate movement of eyes (CN 3,4,6)
- Thalamocortical pathways: To mediate conscious sense of head movement and position
Lateral Vestibulospinal tract is involved in
postural reactions of the body
Pathway of lateral vestibulospinal tract
- Axons from otolith organs project to lateral vestibular nucleus
- Tracts run ipsilaterally (uncrossed)
- Facilitates extensor muscles in ipsilateral limbs to maintain equilibrium
Medial Vestibulospinal tracts is involved in
Head movements and facilitates vestibulo-ocular reflex
Describe the VOR in response to left head rotation (7 steps)
- causes excitatory impulse to be sent to left vestibular nucleus
- Excitatory impulse sent to right abducens (CNVI)
- Right lateral rectus muscle is activated
- Excitatory impulse is sent to left oculomotor nucleus (CNIII)
- Left medial rectus muscle is activated
- Excitatory impulse is sent from left vestibular nucleus to left oculomotor nucleus (redundancy)
- Inhibitory impulse from left vestibular nucleus is sent to left abducens nucleus to inhibit left lateral rectus and right medial rectus muscles
