Lecture 18 - Vestibular influences on occulomotor control and posture Flashcards
Where does the output of the vestibular labyrinths project to?
The vestibular nuclei
What is the role for vestibulo-ocular reflexes?
To keep images on the eyes still when the head moves
What is the role for the vestibulospinal relfexes?
To enable the skeletomotor system to compensate for head movements
What signals how fast the head is rotating?
The vestibular apparatus
The occulomotor system uses information from the vestibular apparatus to do what?
Stabilise the eyes to keep images in the retina
What are the three different types of VOR? [3]
- Rotational vestibular-ocular reflex
- Translational vestibular-ocular reflex
- Ocular counter-rolling response
What does Rotational vestibular-ocular reflexes compensate for?
- Head rotation
- Recieves inputs from the semicircular canals
What does the Translational vestibular-ocular reflex compensate for?
Linear head movements
What does the Ocular counter-rolling response compensate for?
Head tilt in the vertical plane
How does the rotational vestibular-ocular reflex control the eyes?
They cause them to slowly rotate in the opposite direction to any rotational head movement
The coordination of head and eye movements to direct the fovea is called?
Gaze
What do small gaze movements cause?
Saccades
What happens when gaze movements are larger?
- Head and eyes move simultaneously
- VOR is supressed
What are two problems with the VOR?
- It habituates
- The canals do not response well to very slow head movements
How can the problems with the VOR be componsated for?
The optokinetic system provides the central vestibular system with visual information
What properties are shared between the VOR and the optokinetic reflex?
- Builds up slowly
- Responds to very slow visual image motion
What is circular vection?
When the whole scene is moving it messes up the vestibular stabilisation
What does vestibular stabilsation do?
Allows one to tell which items are moving and which are stationary
Vestibular nuceli respond identically to what?
- Head mvoements
- Movement of an image on the retina
How do we know we are falling?
- Visual
- The head moves
What is the major factor in the maintainance of posture?
Signals from the vestibular nuceli to the spinal cord
What are the four different vestibular nuclei? [4]
- Medial
- Lateral
- Superior
- Descending
Where does the superior and medial nuclei recieve inputs from?
The semicircular canals
Where do the superior and medial nuclei send outputs to?
- Occulomotor centres
- Spinal cord
The nuerons on the medial nuclei are?
Excitatory
The neurons in the superior nuclei are?
Inhibitory
What are the superior and medial nuclei responsible for?
Reflexes that control gaze
Where does the lateral nucleus recieve inputs from?
- Semicircular canals
- Otolith organs
Where does the lateral nucleus send ouputs to?
Lateral vestibularspinal tract
What is the lateral nucleus responsible for?
Postural reflexes
Where does the descending nucleus recieve inputs from?
Otolith organs
Where does the descending nucleus send ouputs to?
- Cerebellum
- Reticular formation
- Contralateral vestibular nuclei
- Spinal cord
What is the descedning nucleus responsible for?
Intergrating vestibular signals and central motor signals
What does posture refer to?
The relative postiiton of the body parts of the body with respect to one another and the environment
What is static equilibrium?
When all the forces acting on the body are balanced so the body is at rest
What is dynamic equilibrium?
Intended movement without losing balance
What is the main force our body must oppose?
Gravity
How does an individual remain balanced after moving one leg and standing on the other?
A counterbalancing movement that shifts the centre of gravity over to the other leg must be done
What does anticipatory response for postrual control depend on?
- Feedforward control
- Adjustments to unexpected disturbances uses feedback control
What suggest that the cerebellum is important for motor learning?
Patients with cerebellar lesions were unable to make adaptive changes in postural control
What organ plays an important role in balance when walking?
Vestibular labryinth
