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)
