Lecture 20: Balance One Flashcards
Where is the first synapse of the auditory nerve?
- Cochlear nucleus. (all afferent fibres terminate here, nothing further)
Describe the cochlear nucleus first synapse;
- Obligatory synapse of all afferent auditory nerve fibres
- Some neural features to extra features of sound (e.g onset, offset, noise vs tones)
- Somatosensory influence. (tonotopic organisation) Important for cleaning the response and removing any biological noise i.e Heart and resp noise
How can the cochlear nucleus be divided?
In three;
- Dorsal cochlear nucleus
- Posteroventral cochlear nucleus
- Anteroventral cochlear nucleus
How do the cell types in the cochlear nucleus differ?
DCN; Fusiform cell types
PCN and ACN = bushy and stellate cell types
Whats the function of the DCN:
- Projects to midbrain
- More complex sound processing possibly important for speech detection
Whats the function of the vestibular system?
Balance and posture
What is balance?
- Maintenance of steady position
Essential for;
- coordination of motor responses, eye movement, posture
- Dynamic and static equilibrium
What is a key feature of balance?
Highly integrated system
what is integrated in balance?
Involves integration of;
- Vision
- Vestibular organs
- Proprioceptive inputs
What pathways are involved in balance?
Sensory input;
- Vision
- Vestibular organs
- Proprioceptive inputs
Integration of input;
- Cerebellum (posture,movement,balance co-ordination)
- Cerebral cortex (memory, higher think int)
- Brain stem (sensory int)
Motor Output:
- Vestibulo-occular reflex
- Motor impulses (to control eye movement)
- Motor impulses (to control posture)
What is the role of cognition in balance?
- Self motion perception
- Bodily self consciousness
- Spatial navigation
- Spatial learning
- Spatial memory and object recognition
Describe hippocampal connections, spatial memory and vestibular system interplay
- Hippocampal atrophy with bilateral vestibular lesion (i.e vestibular system contributes to spatial memory)
- Spatial representation in hippocampus influenced by vestibular organ
- contribute to navigational deficits in people with abnormal vestibular function
What does the vestibular system sense?
- Sense dynamic and static position of the head.
- Detect linear and angular acceleration of the head.
- Conscious awareness of head position and reflex control of eye movements.
Describe the sensitivity of the vestibular system;
Vestibular system is exquisitely sensitive and finely balanced
Describe the impact of small derangement of the vestibular system:
Minor, acute derangement have catastrophic effects on balance causing VERTIGO (sense of losing balance, movement), disorientation and nausea
What may chronic or gradual loss of vestibular function lead to?
Chronic or gradual loss of vestibular function may have limited symptom with compensation at central nuclei
What is vertigo?
Perception of motion, person or environment (the room is spinning) where there is none
- Differes from light headedness or dizziness
- accompanied by visceral, autonomic symptoms e.g pallor, sweating, nausea, vomiting
What is motion sickness?
Conflict between vestibular ,visual, proprioceptive inputs with an expected internal mode.
Mismatch of inputs promotes the symptoms associated with vertigo and motion sickness
Whats the effect of microgravity on vestibular function?
- No/low gravity renders the vestibular system useless, thus leading to motion sickness
- Cant sense direction
What nerve projects from the vestibular system?
Sensory organs in the inner ear project via vestibular section of 8th cranial nerve to vestibular nuclei in brain stem
What are the outputs of the vestibular nuclei?
- Motor spinal cord
- Cerebellum
- ANS
- Cerebral cortex
- Nuclei 3,4,6 (that drive eye muscles, so cranial nerves)
What are the directions of movement of the head?
Translational (linear) = XYZ
Rotational (angular) = Yaw, Pitch, Roll
What structures from the vestibular system?
3 semicircular canals;
- Superior (Anterior)
- Posterior
- Lateral (horizontal)
Saccule
Utricle
What is a feature of all three semicircular canals?
- Ampullae of semicircular canals
- Contain cristae of ampullaris; detects angular acceleration (sensory cells)
What do the utricle and saccule contain?
Contain otolithic organs, the macula sacculis and utriculus that detect static head position and linear acceleration
Describe the anatomical route of the vestibular nerves;
Superior and inferior vestibular nerve with cell bodies in scarpas ganglion exits as part of vestibulocochlear nerve in internal auditory meatus
What does the superior portion of the vestibular nerve innervate?
- Utricle, anterior port of saccule, anterior and lateral semicircular canals
What does the inferior portion of the vestibular nerve innervate?
Posterior part of saccule and posterior semicircular canal
Whats an important feature of the canals?
Vestibular sensory organs operate bilaterally as pairs
VIP
How are the lateral canals paired?
The L and R canals are paired
How are the A and P canals paired?
The Anterior canal is paired with the posterior canal of the other ear.
Describe the sensory cells in the vestibular organs;
Similar to sensory cells in the cochlea, except there is LARGE kinocilium (polarises the cells)
Type One and Type Two, huge synapses
Describe the sensory cells in the vestibular organ;
Invaginates to form a dam in the tube, gelatinous structure sits atop of sensory cells, (Cupula) (same density)
Describe kinocelium placement on sensory cells;
Kinocelium sits same side across all sensory cells. (therefore depending on direction of movement = inhib or activate)
